In April 2024, the White House launched a challenge to scientists: establish a lunar time standard in view of a growing international presence on the Moon and potential human bases as part of NASA’s Artemis initiative. However, the real question is not simply “What time is it?”, but rather “How quickly does time pass?”.
The time displayed on a clock can be set by any timekeeper, but physics determines how quickly time flows.
In the early 20th century, Albert Einstein demonstrated that two observers would not agree on the duration of an hour if they were not moving at the same speed and in the same direction. This disagreement is also present between a person on Earth and one on the Moon.
Relativity Effects on the Moon
“If we were on the Moon, clocks would tick differently compared to those on Earth,” explained Bijunath Patla, theoretical physicist at the National Institute of Standards and Technology (NIST) in Boulder, Colorado. The Moon’s movement relative to Earth causes lunar clocks to slow down compared to terrestrial ones, but the lesser lunar gravity accelerates them. “These two opposing effects result in a net drift of 56 microseconds per day“, said Patla.
Patla and his colleague Neil Ashby used Einstein’s general relativity theory to calculate this difference, improving previous analyses. Their results were published in the Astronomical Journal.
Implications for Lunar Missions
Although a difference of 56 microseconds may seem negligible by human standards, it is crucial for missions requiring millimeter precision or communications between Earth and the Moon. “The safety of navigation in a future lunar ecosystem depends on precise clock synchronization“, stated Cheryl Gramling, system engineer at NASA’s Goddard Space Flight Center. A 56-microsecond error per day could cause navigation inaccuracies up to 17 kilometers per day, an unacceptable problem for Artemis missions, which will require knowing the exact position of every rover, lander, and astronaut within a 10-meter margin.
A fundamental principle of relativity theory is that there is no absolute time. A clock on the Earth’s surface ticks more slowly than one in orbit due to gravitational effects, which is why GPS satellites must account for relativity. Establishing time on the Moon is further complicated by its orbit around Earth and Earth’s rotation, which influence time perception.
Ashby and Patla recognized that the Earth-Moon system is in free fall under solar gravity’s influence, allowing them to consider complex contributions such as celestial body rotation, tidal forces, and deviations from perfect spheres. They also calculated gravitationally stable positions between Earth and the Moon, known as Lagrange points, useful for communication relay satellites.
Towards a Standard Lunar Time Future
Other scientists, such as Sergei Kopeikin from the University of Missouri and George Kaplan from the US Naval Observatory, have also calculated a 56-microsecond time shift between Earth and the Moon. They also considered small periodic fluctuations due to variations in tidal force caused by the Sun and Jupiter.
“The scientific community has done a great service by publishing this work,” said Gramling. “Now we can propose a standardized model for lunar time to the entire international timekeeping community.”
Although it will take many years or decades before the Moon hosts enough humans and robots to necessitate precise timekeeping, scientists and engineers recognize the importance of establishing a standard much earlier than expected. They have already taken the first, difficult step towards determining time on the Moon.
The moon is often called the night luminary because it is associated with the dark hours of the day. However, you’ve probably seen it during the day too!
Generally, people with limited knowledge of our planetary system think that the Moon and the Sun oppose each other in the sky. They believe that during the day, the Sun is visible but not the Moon, and at night, the Moon is visible but not the Sun. However, this is yet another myth.
In reality, the Moon is directly opposite the Sun only once a month—during a full moon. At this time, you won’t see it in the daytime sky. Additionally, during a new moon, it’s also impossible to spot because the Moon is too close to the Sun and facing us with its unlit side. However, during other phases, you can see it.
The window for observing the Moon in daylight is about six hours a day, 25 days a month. It is best seen during the first and last quarters.
If Earth didn’t have an atmosphere, the Moon could be observed for 12 hours every day continuously. However, particles of nitrogen and oxygen in the air scatter sunlight with short wavelengths, such as blue and violet. This gives the sky its blue color and complicates the observation of celestial bodies.
Wherever we look, we see scattered sunlight in the atmosphere—it literally overshadows the radiation from other objects. This is why we can’t see stars and other planets during the day.
The Moon is an exception because it is very close to us, and the sunlight it reflects is bright enough to overcome even the lit daytime atmosphere. Therefore, it can be seen with the naked eye, though it will appear much paler than at night.
You’ve likely seen the movie Moonfall, read science fiction disaster novels, or simply gazed at the night sky, pondering eternity. Have you ever wondered: Why doesn’t the Moon fall to Earth? Let’s explore this together.
The theory of gravity, formulated by Isaac Newton in the 17th century, describes the orbit of celestial bodies, including the Moon’s movement around the Earth. According to this theory, the gravitational force between two objects is proportional to their masses and inversely proportional to the square of the distance between them.
In other words, Earth pulls the Moon with its gravitational force, and the Moon does the same. This interaction is due to the masses of both objects and the distance between them.
If the Moon were hanging motionless in a vacuum, Earth’s gravity would pull it much more strongly, and the satellite would fall onto our planet—a rather unfortunate outcome.
But luckily, the Moon moves around the Earth and at a significant speed—1.023 km/s. This speed provides the necessary inertia, which is an object’s tendency to maintain its state of motion unless acted upon by other forces.
If the Moon were moving more slowly, Earth’s gravity would overpower its motion, and it would fall onto the Earth. On the other hand, if the Moon were moving faster, it would break free from its orbit and fly off into space.
Where does the Moon get such inertia, allowing it to orbit Earth for billions of years? To answer this, we need to recall how our satellite was formed.
According to modern understanding (the giant impact hypothesis), the Moon was formed when a large object, roughly the size of Mars, collided with Earth about 4.5 billion years ago. As a result, Earth and the colliding celestial body (a planet named Theia) merged into the planet we live on today.
The impact was so intense that the ejected debris didn’t fall back to Earth but instead gathered in orbit, eventually forming the Moon. You can watch an animation prepared by NASA to better understand what this looked like. In reality, scientists believe the process took only a few hours.
Fortunately, there was no life on Earth at the time (life had not yet emerged), so these cosmic-scale events occurred without us. We now witness only the result of this collision—the moon.
According to the law of conservation of momentum, if no external forces act on an object, its momentum (the product of its mass and velocity) remains constant. Since space has little resistance or friction, the Moon continues to move by inertia, orbiting the Earth.
In fact, the Moon isn’t falling toward Earth; rather, it’s gradually drifting away into space. Earth’s strong gravitational pull slows the Moon’s rotation on its axis, a phenomenon called tidal interaction. Because of this, the Moon is moving away from Earth at a rate of about 3.8 cm per year. In billions of years, our satellite will likely drift off completely, but by that time, Earth will be uninhabitable due to the increasing heat from the sun.
So, don’t worry—the moon definitely won’t fall on us.
The mission was by no means perfect; after all, the Japanese lunar lander SLIM was off-balance from the start. But at least the probe from the Japanese space agency JAXA accomplished something that only four other nations had achieved before: a (somewhat) gentle landing on the Moon.
Although the lander did not stand upright on the Earth’s satellite as planned and suffered from energy shortages, it survived several lunar nights and was later able to re-establish contact with the ground station on Earth. However, the project has now definitively ended: JAXA has declared the SLIM mission over after nearly eight months.
No More Communication
Communication with the probe has not been possible since last week, the agency announced on Monday on the online service X. “We have concluded that there is no prospect of successfully restoring communication with SLIM.
SLIM stands for “Smart Lander for Investigating Moon.” With the landing of the 2.40-meter by 1.70-meter probe on the Earth’s satellite, Japan became the fifth nation to land on the Moon, following the USA, the Soviet Union, China, and India, in early January. Two earlier Japanese lunar missions in 2022 and April 2023 had failed.
[Press Release] Conclusion of Lunar Activities of the Smart Lander for Investigating Moon (SLIM)#JAXAhttps://t.co/eO9xtP1zis
— JAXA(Japan Aerospace Exploration Agency) (@JAXA_en) August 26, 2024
Longer Than Expected
“SLIM continued to transmit information on its status and the surrounding environment for a much longer period than expected,” explained the space agency JAXA. The probe had landed on its side during its Moon landing, causing its solar panels to face west instead of upwards as planned. As a result, the device initially received only a little sunlight and consequently little power. Nevertheless, SLIM managed to transmit images of the lunar surface back to Earth.
The mission’s goal was to reach rock at the lander’s site in the Shioli crater that is usually buried deep beneath the lunar surface. This rock could provide clues about potential water occurrences on the Moon.
It shines in the night sky and causes high and low tides. The Moon is a natural part of everyday life on Earth. But what would happen if the Earth did not have a satellite? What would our planet look like then? Would terrestrial life have arisen at all?
The Moon seems quite normal to us, but in the solar system it is the great exception. Because no other planet has a relatively large satellite, and no other moon was formed in such a catastrophic way. Moon has had a decisive impact on the history of our planet and many of its fundamental features. This raises the question of what Earth would look like without its companion.
Why the Moon is an exception in the solar system
The collision of the young Earth with a Mars-sized protoplanet created Earth’s moon. Credit: NASA/JPL-Caltech
Even if it seems natural and normal to us, Our Moon is unusual in many respects. Both its size and its formation make it special in the solar system.
But how does a moon come into being? For a long time, there were only two possible explanations. According to the first one, a moon can be formed in the early time of its planet from leftover dust and gas remains of the primordial cloud – similar to the rings of large gas planets. As this material orbits around the planet, the particles cluster together into ever larger chunks. This process of moon formation can be observed at Saturn, for example.
The second variant is the capture: Many moons in the solar system are minor planets or asteroids that have been steered out of their old orbits by their planet’s gravity and held in place. These include most small, irregular moons, but also large satellites such as Triton, the largest moon of Neptune.
But our Moon does not fit into either of these categories. Because it owes its formation to a catastrophic accident about 4.5 billion years ago. The Mars-sized protoplanet Theia collided with the young Earth and was destroyed. Also, the Earth could have evaporated to a large part thereby. From the debris cloud, the two-man team of Earth and the Moon were formed.
Exception among its neighbors
Jupiter and its four largest moons – even they are small in relation to their planet. Credit: Kevin M. Gill/CC-BY-SA 2.0
In the inner solar system, the Earth is thus an exception. Because among the terrestrial planets moons are rather scarce. Mercury and Venus have no satellites at all, and Mars is orbited by only two comparatively tiny moons: Phobos, which is only 20 kilometers across, and Daimos, which is not even 15 kilometers across. Therefore, planetary scientists assume that the Martian moons are probably either captured asteroids or perhaps remnants of a former ring.
It becomes clearly more luxuriant with the moons only further outside in the solar system. There the large gas planets Saturn and Jupiter compete for the largest court. After Jupiter had been in the lead for a long time with 79 moons, astronomers discovered twelve additional moons around Saturn in October 2019, making it the “king of the moons” with 82 satellites. In September 2020, however, the ringed planet had to cede this title again: Further moon discoveries on Jupiter suggested that the gas giant might even have hundreds of satellites.
What makes a satellite a Moon?
This raises the question: What makes a moon a Moon? And what distinguishes it from asteroids orbiting a planet? Surprisingly, there is no official definition of a moon yet. It is only specified that such a satellite must orbit a planet. But there is no minimum size, which some astronomers criticize: “At some point, you end up with mere ring particles, so a clear lower limit would be very useful,” says Edward Ashton of the University of British Columbia.
In theory, therefore, any chunk, no matter how small, can be declared a moon at the moment. Only then does it not get a name. The International Astronomical Union (IAU) only officially gives moon names to satellites with a diameter of more than one kilometer. So far, 240 such moons are known in the solar system. However, only 19 moons in the solar system are large enough to have assumed a uniformly round shape due to their own gravity. Moon is the fifth largest among them, with a diameter of 3,476 kilometers.
No other pair is so similar
The real special feature of our Moon, however, is not its absolute size but its size in relation to its planet. The Earth is only 3.7 times larger than its satellite; no other planet in the solar system is as large. Planetary scientists have determined by means of simulations that even in collisions similar to those of the early Earth, only in every 12th case does a Moon arise that large in relation to its planet.
Yet this is precisely what has decisively influenced the evolution of our planet.
When the lunar tides are absent
Credit: NASA
If it had not been for the primeval collision with the protoplanet Theia, the Earth probably would not have a Moon today. But what would be the consequences? It seems clear that there would be hardly any tides on many coasts. But this would have much more far-reaching consequences than only on ebb and flood.
Ebb and flow in everything
The Moon’s gravity exerts a tangible influence on our planet: Not only does it cause the water in the oceans to move in time with the tides, but ice masses, rocks, and even the atmosphere resonate with this rhythm. For example, the Earth’s crust rises and falls by up to 35 centimeters, and earthquakes also follow the tidal rhythm. The influence of the Moon’s gravitational pull on atmospheric pressure is even more subtle: because it rises slightly during a full Moon, the probability of raindrops is around one percent.
A few years ago, researchers also discovered that even a large inland glacier in Antarctica flows in time with the ebb and flow of the tide. “We have never seen anything like this before,” explained Hilmar Gudmundsson of the British Antarctic Survey. “The discovery that the cycle of spring and neap tides has such a strong influence on an ice flow dozens of kilometers away from the sea is a complete surprise.”
Without Moon, heat transport suffers
Without the Moon, all these movements wouldn’t exist – though we’d hardly notice most of them. Only at the sea would we be able to see it directly: “There would still be high and low tides, because the sun also has a tidal effect,” explains Kaare Aksnes of the University of Oslo. But the tidal range would only be about a third of what it is today.
Much more noticeable, however, would be the effect of the missing Moon on the climate. That’s because the tidal mountains that migrate around the Earth not only cause high and low tides – they also contribute to heat distribution on our planet. “The tidal currents of the oceans help transport heat from the equator to the poles,” explains Bruce Bills of NASA’s Jet Propulsion Laboratory.
True, the main work for this is done by the thermohaline circulation, which is driven by salinity and water temperature. But at least in some regions, the absence of tidal currents could lead to climate changes. Specifically, the gradient of temperatures and air pressure between the poles and the equator could increase. That, in turn, could lead to stronger winds and more extreme climate swings.
Every year, the Moon furthers its distance from Earth by around 1.5 inches (3.8 cm).
The day would be only half as long
But there is one consequence of the missing Moon that no one could overlook: Without the Moon, our days would be much shorter. Instead of 24 hours, a day would only last a good twelve hours—for us and for nature, this would be life in fast motion. The reason for this is the influence of the Moon on the rotation of our planet. When the young Earth was formed, it was still rotating much faster. But the Moon’s gravity and the tidal forces it generates exert a creeping but persistent braking effect. “We’re not talking about full braking here; this braking effect only accounts for about two seconds per 100,000 years,” Aksnes explains.
But it adds up: As recently as the time of the dinosaurs, about 70 million years ago, days were about 30 minutes shorter than they are today. And the slowing effect of the Moon on the Earth’s rotation continues: Current measurements show that day length is currently increasing by an average of 1.78 milliseconds per century. Without compensating effects, the Moon would even slow down the Earth by 2.03 milliseconds per century.
But what would be the consequences of a faster Earth rotation? For life on Earth, it would probably not be very dramatic if the Earth’s days were only half as long. This is because the internal clock of organisms adapts to such external timers. Our metabolism, our hormones, and our day-wake rhythm would also oscillate in a shorter rhythm on an Earth without a Moon.
Less benign, however, would be the effect of the faster rotation on the weather: if the Earth spins faster, then the possible wind speeds also increase. Thus, an Earth with shorter days could also be significantly stormier.
But there are lunar influences that are even more long-term and profound.
Wobbling axis
The layered ice of the Martian poles, here the North Pole, testifies to strong climate changes. Credit: ESA, DLR/FU Berlin, NASA MGS MOLA Science Team.
Without the Moon, our planet would be nowhere near as conducive to life. For it was the presence of the great satellite that stabilized Earth’s axis and thus its climate. The lunar magnetic field also protected the young Earth from the worst solar storms. If the Moon did not exist, the first cells and organisms could possibly have developed much later or even never.
What consequences a missing Moon has on the stability of a planet is demonstrated by Mars with its almost negligible mini-moons. The rotation axis of our neighboring planet changes its inclination much more strongly than that of the Earth, both in the short and long term. On the one hand, the Martian axis wobbles by about ten degrees over the course of several 100,000 years. The axis thus wobbles as if in serpentine lines around its mean inclination of 25 degrees against the ecliptic.
This relatively strong fluctuation has consequences for the Martian climate: Because the angle of the sun’s incidence changes periodically, the climate zones shift. On the ice caps of the Martian poles, these periodic fluctuations can be seen in the alternating views of ice and dust. They reflect warmer and cooler periods on the respective Martian hemispheres.
On Earth, the precession varies much less, by 1.5 degrees, because the gravitational pull of the large Moon dampens the wobbling of the Earth’s axis. Terje Wahl of the Norwegian Space Center compares this stabilizing effect to that of the hammer in a hammer thrower: “As long as he holds the hammer, he can rotate almost on a point,” Wahl said. “But as soon as he lets it go, he loses his balance and has to take several compensating steps to keep from falling.”
Mars, however, experienced even more drastic changes. It has been shown that the tilt of the rotation axis can flip from zero to 60 degrees in less than 50 million years. Without the Moon, Earth’s obliquity would also undergo such large and chaotic fluctuations, and that would have a strong influence on planetary climate. As a result, seasons and climate zones could shift dramatically, and at some times even regions at the equator would be icy.
Double protection by the lunar magnetic field
In its early days, the moon had a bipolar magnetic field similar to Earth. Credit: NASA
In the early days of the solar system, another positive effect of the Moon came into play: its magnetic field formed a protective shield for the young Earth. As researchers led by James Green of NASA recently discovered, the Earth’s satellite probably had a strong magnetic field until about 3.5 billion years ago. This was connected with that of the Earth, because the Moon was only one-third as far away from the Earth at that time as it is today.
For the young Earth this could have been crucial. Because the magnetic field of the Moon lent it additional protection against the violent eruptions of the still-young sun. “The Moon formed a substantial protective barrier for the Earth against the solar wind, and so may have been instrumental in helping the young Earth retain its atmosphere at that time,” Green explains. Without the atmosphere, life would likely never have evolved on Earth.
Did lunar tides make life possible in the first place?
In order for the DNA to be copied, the strands must separate. (Image: Kornilov17, Depositphotos)
To this day, it remains a mystery how the first life once arose on our planet. There are also many hypotheses about where the first building blocks of life and cells came together, but no evidence. The range of possible cradles of life extends from the hydrothermal vents of the deep sea to hot pools to pores in solid rock.
All these “candidates” have one thing in common: they must offer conditions under which the hereditary molecules RNA or DNA come together from precursor molecules and do not immediately disintegrate again. This only happens if the concentration of the necessary building blocks—nucleic acids, phosphates, and sugars—is high enough. The open sea is therefore ruled out as a primordial soup, according to most researchers. More favorable are confined spaces where the building blocks accumulate and environmental conditions promote synthesis.
But there is a second hurdle: Probably no enzymes existed at the beginning of life that managed the copying and multiplication of the hereditary molecules. The RNA or DNA must therefore have been replicated without their help—but how? In the case of RNA, the solution could be so-called ribozymes, a variant of RNA molecules that can take over the functions of enzymes. That’s why some scientists think it’s likely that the first life forms encoded their genetic material with RNA rather than DNA.
But recent research suggests that DNA may also have been at the beginning of life – because there was the Moon and its tides. Only through them could both the linking of the four nucleic acids and the replication of the finished DNA strands have proceeded without the help of enzymes.
Lunar way out of the dead end
“Normally, non-enzymatic copying of DNA strands is a dead end,” explains Richard Lathe of the University of Edinburgh. This is because a second strand is formed by the addition of complementary bases to the first. Once this second strand is ready, however, it remains attached, blocking the space for another copy. If there are no external forces to separate the two DNA strands again, the process stops and so does replication.
At this point, the Moon comes into play: Because it was still far closer to the young Earth and it was spinning faster, the tides were stronger and faster than they are today. “As a result, tidal zones extended several hundred kilometers into the land,” Lathe explains. In these zones, water cover, salinity, and temperatures changed every few hours in rhythm with the ebb and flow of the tide. There were countless tidal pools that overflowed and washed out at high tide, but at low tide, they formed small, isolated basins in which salts and chemical molecules could accumulate.
Alternation of concentration and dilution
Tide pools, such as here, may have provided ideal conditions for the formation and replication of genetic molecules. (Credit: Back Yard Biology)
These tidal pools, Lathe believes, may have provided the ideal conditions for the replication of the first DNA molecules. When the intertidal zone went dry and the water in the pools became warmer and saltier, this promoted the attachment of new nucleic acids to the single-stranded DNA, which was copied. “With increased salt concentration, the repulsive charges of phosphates are neutralized and hydrogen bonds between strands are favored,” the biochemist explains.
Then, when the tide came in, it diluted the water in the ponds. As a result, the salt content dropped, which in turn destabilized the bonds between the two complementary strands. The DNA broke down into two individual strands and was thus ready for a new copying cycle.
But regardless of whether RNA or DNA were at the beginning of life and how exactly they came about: Other scientists also think it likely that the first building blocks of life formed under changing conditions. And the most ubiquitous and reliable changes are produced by the tides caused by the Moon.
Conversely, this means that if the Earth did not have a Moon, this path to life would have been blocked, or at least much less likely.
Because then all those celestial bodies would be the most promising candidates, since they are under the influence of tidal forces. This could be an exoplanet with a large satellite, but also a moon that is regularly “rolled through” by its much larger planet. One example is Jupiter’s moon Europa, which owes its subglacial ocean to Jupiter’s tidal forces.
Titan is the only moon in the solar system with a dense atmosphere—and the only one with lakes, clouds, and even Earth-like material cycles. But does that mean there is life on Saturn’s moon? Titan was considered an early candidate for extraterrestrial life. However, anyone who wants to live here must be able to tolerate extremes. Hydrocarbon methane serves as water on this moon because the temperature is well below zero. Nevertheless, Titan has turned out to be astonishingly Earth-like, especially in recent years. It has mountains and volcanoes, lakes and seas, and even tropical storms that race across its surface. Whether life exists on Titan, however, remains an open question.
Titan at a Glance
Discovery: March 25, 1655, by Dutch scientist Christiaan Huygens.
Distance from Earth: 746 million miles (1.2 billion km).
Mean distance from Saturn: 759,222 mi (1,221,850 km)
Orbital period around Saturn: Just under 16 days
Mean diameter: 3,200 mi (5,150 km)
Radius: 1600 mi (2,575 km)
Mass: 35 x 1023 kg
Atmosphere: 94 percent nitrogen, 6 percent methane, and argon, traces of other organic compounds
Wind speeds: 270 mi (430 km) per hour at 75 mi (120 km) altitude, a few feet per second on the ground
The temperature on the surface: -288 °F (-178 °C)
Atmospheric pressure on the surface: 1,5 bar
Highest mountain range: Mithrim Montes, about 10,950 ft (3,340 m high).
NASA’s Dragonfly Mission
NASA’s Dragonfly spacecraft designed for Titan. (Credit: NASA)
The Johns Hopkins Applied Physics Laboratory created and will oversee the Dragonfly mission, which will launch in June 2027. As New Frontiers 4, it consists of a big RTG-powered drone designed to travel through Titan’s atmosphere. Its tools will investigate how far prebiotic chemistry may have come. The target date for the mission’s arrival on Titan is 2034.
Titan Raises Many Questions
Hyperion, Iapetos, Phoebe, Rhea, Tethys, Atlas, Prometheus, and Titan: These are not only all gods from the lineage of the Titans in Greek mythology, but they are also the names of some of Saturn’s moons. One of these many satellites has fascinated scientists ever since its discovery by Dutch astronomer and naturalist Christiaan Huygens on March 25, 1665: Titan.
Opaque Atmosphere
View of the surface of Titan with an impact crater in the center and a mountain range in the southeast. (Credit: NASA/JPL/University of Arizona)
What makes it so special is not only its enormous dimensions—it has a diameter of 3,200 miles (5,150 km) that is even larger than the planet Mercury—but it is also the only moon in our solar system with a dense atmosphere. Like a gigantic, orange-colored veil, it envelops Titan and protects it from intrusive glances of any kind. Titan’s atmosphere is impenetrable not only to the human eye but also to most telescopes on Earth and in space.
Even the Voyager 1 and Voyager 2 probes, which visited the “Lord of the Rings” for the first time about 25 years ago, were unable to dispel the myth of mystery. They delivered the first meaningful images of Saturn and its moons, and they also carried out numerous measurements. However, even they were unable to get a look at Titan’s surface. Voyager 1 and 2, however, at least clarified the composition of its atmosphere.
Striking Resemblance to Primordial Earth
How Voyager saw Titan. (Credit: NASA/JPL)
According to the results, the gas envelope consists of about 94 percent nitrogen and about 6 percent methane and argon, as well as about a dozen other organic compounds.
This makes Titan’s atmosphere strikingly similar to the shell of the primordial Earth more than four billion years ago when the first primitive organisms were formed. However, the air pressure on Titan, which is about 1.5 bars, is half that on the primordial Earth.
On the other hand, this is roughly ten times the atmospheric pressure at sea level on Earth and the gas envelope is also five times denser near the ground.
But what does the surface of Titan look like? Are there huge methane oceans, as scientists suspected, or is it a solid ice world? Does Titan, despite its icy cold of -178 °C, offer conditions as favorable for the emergence of life as our planet did in its early days? These are just some of the questions that planetary scientists ask themselves.
Landing on the Moon of Saturn
The Cassini-Huygens mission, which NASA, ESA, and the Italian space agency ASI sent to Saturn in 1997, gave the first glimpses under Titan’s veils. The goal of the two probes, the orbiter Cassini and the piggybacking Titan lander Huygens, was to gather new information about the ringed planet and moons like Titan. The scientists also hoped to find an answer to the question of the origin of the solar system.
On July 1, 2004, the time had come: Cassini and Huygens had reached the ringed planet and its moons. The landing of Huygens on Titan was an adventure not only for the many astronomy freaks worldwide but also for the scientists involved in the mission. What made it a real challenge was not so much the fact that it was the first time a spacecraft was to touch down on a celestial body in the outer solar system.
Residual Risk During Landing
The maneuver was risky primarily because the descent and landing had to be completely automatic. Earth is around 760,000 miles away from Titan. Radio signals to control the probe would have taken more than an hour to cover this distance. For this reason, the course of the action was precisely calculated and planned in advance, including a residual risk that could not be measured.
Radar view of Titan’s tallest mountains. (Credit: JPL)
To the great relief of the scientists, however, everything went like clockwork: from separation from the Cassini spacecraft on December 25, 2004, Huygens’ entry into the atmosphere, the two-hour descent and waking of the instruments on board, to impact on Titan at 1:45 p.m. Central European Time (CET) on January 14, 2005.
However, deafening cheers erupted at ESA’s control center in Darmstadt as early as 11:25 a.
m.: The Green Bank telescope in the U.S. state of West Virginia had received the first clear radio signal from the probe—Huygens was alive. The probe was already diligently collecting data on the structure of the atmosphere during its descent, recording sounds, and, above all, taking the first images of Titan’s surface.
Images of a Strange World
But that was not enough. What the scientists had hardly dared to hope for also happened: Huygens survived the landing on Titan, apparently completely unscathed, and continued to send data to Cassini for well over an hour. There, the data was saved several times and then forwarded to Earth, just like the measurement results and images recorded by the mother ship itself. Around 500 megabytes in the form of images, measurement results, and other data arrived on Earth within the next few hours.
The scientists immediately began sifting through and analyzing the material, and after just a few days, they had their first impression of the distant moon in the outer solar system.
The images they finally presented to the public showed a strange world that, despite everything, bears a remarkable resemblance to Earth. “In fact, Titan looks more like Earth than any other celestial body in the solar system – despite the vast differences in temperature and other environmental conditions,” explains Rosaly Lopes of NASA’s Jet Propulsion Laboratory (JPL) in Pasadena.
There are towering mountains, dunes, lakes, and canyons deeply carved by erosion on Titan. As on Earth, erosion over time has leveled most meteorite craters and caused them to nearly disappear. Gullies and river-like formations lead from a higher-elevation area to a lower, flat terrain, where they end in depressions. These are bordered by a kind of coastline and are dotted with islands and sandbanks.
Lakes and Oceans – From Methane
Long before the Cassini mission, planetary researchers had speculated whether there might be liquid methane on Titan. This hydrocarbon is also found as a gas in the atmosphere. It could therefore have risen by evaporation from liquid reservoirs (lakes or even seas) in a similar way to water vapor on Earth.
But when the lander Huygens touched down near the equator of Titan in January 2004, the data were initially disappointing: no trace of liquid hydrocarbons. The early images of the Cassini probe also showed extensive depressions with shore-like boundaries. But these were dry; liquid methane was not found in them.
In 2016, Cassini discovered a network of deep, steep-sided canyons draining into Ligeia Mare, marking the first evidence of fluid-filled passageways on Titan.
On July 22, 2006, however, the turning point came: Cassini sent new radar images to Earth that clearly showed numerous well-defined, very dark areas in Titan’s north polar region. In the radar image, however, these areas appear extremely smooth—like the surface of a stagnant liquid, for example. “This is a big deal,” comments NASA researcher Steve Wall. “We’ve now discovered for the first time a place outside Earth where lakes exist.”
Nearly a hundred such lakes of varying sizes are now known to exist. Some are completely filled with liquid, while others appear to be half-dry or even empty. Most of them are concentrated near Titan’s north pole. This is also the location of the largest lake known so far, Kraken Mare. This liquid hydrocarbon-filled sinkhole is probably as large as the Caspian Sea on Earth.
“Titan’s northern lake landscape is one of the most Earth-like and fascinating in the entire solar system,” states NASA planetary scientist Linda Spilker. It is possible that these lakes of methane even change with the seasons. Because photographs from Cassini had shown bright areas around some of these lakes, they could arise, for example, from the evaporation of methane and the deposition of residues from larger chemical molecules. In addition, the reflectivity of the lakes varies unusually: Sometimes they appear dark and smooth, then brighter again.
Gas Bubbles Make Methane Ice Float
Jason Hofgartner from Cornell University in Ithaca and his colleagues proposed an explanation for this in early 2013. Using a model, they show that ice on the surface of the lakes could be responsible for the differences in albedo. Normally, solid methane is denser than liquid methane and would therefore sink. But under certain conditions, even this hydrocarbon ice can float if it contains gas bubbles that lower its density.
This happens when the temperature is just below the freezing point for methane, at 90.4 degrees Kelvin. Then small bubbles of nitrogen become trapped in the forming methane ice. They make up only about five percent of the ice mass, but that is enough to make the ice float. If, on the other hand, temperatures drop just a few degrees lower, too few bubbles form, and the ice sinks. “We now know that there may well be thin ice floes on the Titan lakes, similar to the new sea ice in the Arctic at the beginning of winter,” Hofgartner explains.
The researchers suspect that these ice floes made of hydrocarbons are similarly transparent to water ice. But because of the reddish-brown atmosphere and thus also slightly colored gas bubbles, they could also have a slightly reddish tint.
Another aspect that could make the ice on the Titan lakes exciting is that on Earth, many organisms live in the channels and margins of sea ice. Therefore, the boundary layer between ice and liquid hydrocarbons could also provide a habitat for possible life on Titan.
A Turbulent Atmosphere Characterizes Titan’s Surface
It has lakes and seas, an atmosphere, and ice. If water were involved in all these phenomena, Titan would not only be extremely Earth-like, but it would also provide important conditions for life. But on Titan, the defining element is not water but a hydrocarbon, methane. The clouds in the moon’s ice-cold, dense atmosphere therefore also consist not of water droplets but of methane. Initial measurements by the Cassini spacecraft already showed that Titan’s atmosphere consists of two layers of very thin, barely visible veil clouds separated by a distinct gap.
Eternal Rain
The upper layer consisted of ice clouds, while the lower layer contained methane and nitrogen in liquid form. The hydrocarbon rains down from there onto Titan’s surface. “The rain on Titan is just a light drizzle, but it rains all the time. “Day in and day out,” explains Christopher MacKay of NASA Ames Research Center. To be sure, the amount of rain on Titan is not excessive at two inches (five cm) per year; it’s about the same as what falls in Death Valley in the United States. “The difference is that the rain on Titan falls evenly throughout the year.” The liquid methane makes the ground wet and muddy.
Even storms can occur on Titan, as was shown in April 2008. Researchers at NASA’s Infrared Telescope Facility (IRTF) on Mauna Kea in Hawaii registered a telltale increase in the thermal radiation Titan was emitting at the time. Astronomers quickly turned to their colleagues at the neighboring Gemini North Telescope, a 26 feet (eight-meter) dish, and asked them to take high-resolution snapshots of Titan. The unique feature of this telescope is a special adaptive optics system that compensates for atmospheric disturbances, allowing it to achieve resolutions comparable to those of space-based telescopes.
Sure enough, the high-resolution infrared images revealed a massive storm that covered more than 1,1 million square miles (3 million square km) of Titan’s atmosphere—roughly the area of the entire Indian subcontinent. Since Titan is less than half the size of Earth, this was not only the largest storm detected on it but also the first to lie over the tropics of the Moon.
Methane Cycle Replenishes Lakes
At least 75 methane lakes with islands at Titan’s North Pole. (Credit: NASA/JPL/USGS)
Astronomers believe storms like this one could well explain why deep canyons and valleys exist even at the Moon’s equator, as they typically do from the erosion of large bodies of water. Heavy methane rain from such storm clouds probably causes rip tides of liquid methane to race through the valleys for a short time. For several weeks, the researchers estimate, such a storm can affect the entire weather patterns of Titan.
The discovery of these phenomena made it clear that, on Titan, the surface and the atmosphere form part of a large cycle—the methane cycle. Liquid methane continuously evaporates from lakes and seas and also from temporarily filled canyons and valleys. The rising gas in turn ensures that the methane content in Titan’s atmosphere remains stable. At the same time, some of this methane gas falls to the surface as rain, which in turn replenishes the lakes there.
How Did Titan’s Mountain Ranges Form?
As early as 2005, radar images from the Cassini spacecraft revealed that the highest mountain peaks on Titan rise some 10,950 feet (3,340 m) into the air. Titan’s Himalayas, a massif in the moon’s southern hemisphere, are about 90 miles (150 km) long, 19 miles (30 km) wide, and around 1 mile (more than 1,500 m) high. The peaks and higher elevations are covered with a sugary coating of shiny white material that is probably methane snow.
Rock-Hard Mountains of Ice
These massive mountain ranges remind us of the Sierra Nevada. These mountains are probably as hard as stone, but they are made of an ice-like material and are covered by various layers of organic compounds. At the time, Brown and his colleagues initially suspected that these mountains might have formed in much the same way as mid-ocean ridges on Earth—through plate tectonics.
According to this theory, large amounts of material—probably water, methane, and ammonia—rose from Titan’s warmer interior through convection currents and then filled the gaps created when crustal plates moved apart. There, they cooled down and piled up over time to form today’s visible mountain range. The heat necessary for the convection currents could have come from the decay of radioactive minerals or from so-called tidal forces from the parent planet, the scientists say.
Mountain Ranges by Shrinking Crust
In the meantime, however, something speaks against this scenario. So far, the Cassini data have provided no evidence for tectonic processes. Mapping of Titan has also shown that most of the mountain chains near the equator run in an east-west direction; for planetary researchers, this is a possible indication of the common origin of these chains.
In 2010, a team of NASA researchers used the probe data to develop a computer model that they used to recreate possible geologic processes on Titan. Based on the known geological and physical conditions on Titan, the researchers modified their model until they succeeded in growing mountain chains similar to the existing ones.
It turned out that Titan’s Himalayas and other mountain formations were most likely to form when the model called for the shrinking and contracting of the moon’s ice crust.
A Liquid Ocean Beneath Titan’s Crust
An ice shell separates Titan’s liquid ocean and organic-rich surface. The components for the development of life may be waiting in the ocean below if the organic matter can find a way to break through that shell. (Image credit: A. D. Fortes/UCL/STFC)
But this scenario has a catch: the moon’s crust can only shrink so much if there is a liquid layer beneath it—an ocean. In fact, researchers had already discovered circumstantial evidence for the existence of such an ocean of ammonia and water with the help of Cassini data in 2008. For their study, they compared the positions of 50 conspicuous landmarks in images from the probe’s first and most recent surveys.
Moving Mountains and Lakes
The results showed that the mountains, lakes, and canyons were no longer in the same place. Up to 15 miles (25 km) of offset resulted from the data comparisons. According to Ralph Lorenz of Johns Hopkins University in Baltimore and his colleagues, such a systematic shift can only be explained if one assumes a decoupling of the crust from the core of the celestial body—for example, by a huge ocean beneath the crust.
NASA researchers made the assumption that a very thick layer of high-density water ice surrounds the moon’s inner core when creating their model of how to build mountains. The ocean, which is a liquid layer of water and ammonium, follows this. Above this lies the crust of ice, which is about 50 miles (80 km) thick.
Because Titan has been gradually cooling since its formation about four billion years ago, all the layers are contracting slightly. This ultimately causes the entire moon to shrink very slightly; scientists estimate that Titan has lost about 4 miles (7 km) in radius and about one percent of its volume since its formation.
This shrinking compresses the outer ice crust and causes faults to form, which, among other things, lift the mountain ranges out of the landscape like shrinkage seams. A similar mechanism—shrinkage and collapse of a limited area of Earth’s solid rock crust—is responsible on our planet for the formation of the Zagros Mountains in Iran.
Unusually Tilted Axis of Rotation
Another study using Cassini data in 2011 provided additional proof that there is a liquid ocean beneath Titan’s crust. Gravity and radar measurements reveal that Titan’s rotation and orbit are very similar to those of our Earth’s moon but with one important difference: the rotation axis of Titan is tilted by 0.3 degrees, which, according to the researchers, is unusual for such celestial bodies.
Such a tilted axis usually occurs when there is at least one liquid layer inside the object. When the researchers fed a model with different variants of the internal structure of Titan, the variant with an ocean under the crust gave the best agreement with the moon’s rotation and inertia data. But even that was only a theoretical model, not real evidence.
Tides Provide Missing Evidence
NASA researchers then came closer to this in 2012 with another observation: the moon, which orbits Saturn once every 16 days, has pronounced tides.
Its surface rises and falls by 100 feet (30 m) depending on its orbital position, Cassini’s measurements revealed. “The tides on Titan are not huge compared to those on some of Jupiter’s moons,” says Sami Asmar of NASA’s Jet Propulsion Laboratory. “But these data tell us quite a bit about Titan’s possible internal structure.”
That’s because if Titan were solid throughout, its surface would only fluctuate by about 10 feet (3 m). But it does so ten times more. But this leads scientists to the almost inevitable conclusion that Titan must have an ocean beneath its crust.
How deep this ocean lies and how thick the liquid layer is are something about which planetary researchers can only speculate. However, to cause the observed tidal effects, a relatively narrow layer between the outer, deformable ice crust and the solid mantle would be sufficient. Such an ocean could also explain another phenomenon Cassini revealed on Titan: ice volcanoes.
Titan’s Volcanoes with Lava Made of Ice
Ganesa Macula, a mountain on Saturn’s moon Titan. Scientists think that this mountain is really an “ice volcano” that occasionally belches “lava” consisting of liquid water. (Credit: Michael Carroll)
There are towering mountain peaks and entire mountain ranges on Titan. But are there also fire mountains on it—volcanoes that transport material from the interior to the surface? As long as Titan lay hidden under its dense veil, this question was unanswered. But the first images taken by the Cassini spacecraft in 2005 already showed the first signs of volcanism. At that time, researchers identified a 19-mile (30 km) snail shell structure near Titan’s equator that rose several hundred feet above the surrounding area like a dome.
Frozen Water Instead of Hot Magma
Scientists have not seen anything similar on any other icy moon in the solar system. The preferred interpretation is that methane is leaking out of this mountain from underground onto the surface and escaping into Titan’s atmosphere. Scientists refer to this phenomenon as “ice volcanism” because it involves frozen water or methane rather than hot magma being transported upward.
New infrared images from a Cassini flyby on Oct. 25, 2006, appeared to confirm this type of volcanism on Titan, showing a fan-shaped structure that strongly resembled lava flows. The Cassini radar had already photographed this phenomenon and a circular structure on the surface from which this flow appears to emanate during an earlier flyby, but not in such good quality.
“The likelihood is increasing that this ring-shaped structure is indeed a volcano,” explained Rosaly Lopes of the Cassini radar team at NASA’s Jet Propulsion Laboratory. “Just from the radar data, we identified it as a possible volcano, but the combination of radar and infrared makes it much more definite.”
Do Volcanoes Light Up or Darken the Surface?
Then in 2008, another flyover by the probe revealed telltale changes in brightness and reflectivity in two specific regions of Titan. “The Cassini data suggest that Titan’s surface may be active,” said Jonathan Lunine of the University of Arizona’s Lunar and Planetary Laboratory in Tucson. “This is based on evidence of changes that have occurred on Titan’s surface between Cassini flybys.
In some regions, the radar images indicate some kind of volcanism.”
In one of the two regions, the albedo rose steeply and remained higher than expected. In the second, it also rose but then dropped again. Albedo is the ability of a surface to reflect solar radiation. The higher the albedo, the more reflective the surface.
Cassini also detected frozen ammonia in both areas. “Ammonia is thought to be present only beneath Titan’s surface,” explains Robert M. Nelson of NASA’s Jet Propulsion Laboratory. “The fact that we’ve detected it at times where the surface has brightened the most suggests that material from within Titan has been transported to its surface.” The existence of methane-spewing volcanoes would also explain why the atmosphere of Titan didn’t dissipate long ago.
Ground Fog or Mudflows
Other researchers, however, interpreted these data much differently at the time: they argued that the identification of the ammonia was not certain and that the changes in brightness could also be due to ground fog from ethane droplets—and thus to atmospheric rather than geophysical processes. Nelson, however, thought this rather unlikely. “There remains the possibility that this effect is caused by local fog, but if it were, we would expect it to change in magnitude over time due to wind. That’s not what we’re seeing, though.”
Researchers at NASA Ames Research Center postulated another alternative: “Similar to Jupiter’s moon Callisto, Titan may have formed as a relatively cold body and thus never received enough tidal heat to allow volcanism,” speculated NASA planetary geologist Jeffrey Moore. “The surface structures resembling rivers might also be ice debris that methane rains liquefied and then carried downhill like mudflows.”
Proof of Cryovolcanoes
Anezina Solomonidou’s team at the Observatoire de Paris provided conclusive evidence of active cryovolcanism on Titan in September 2013. For their study, they analyzed data collected by the Cassini spacecraft’s Visual and Infrared Mapping Spectrometer (VIMS) from three potentially ice-covered volcanic regions: Tui Regio, Hotei Regio, and Sotra Patera. “Thanks to the VIMS, we were able to penetrate Titan’s atmosphere and observe changes in the surface over time,” Solomonidou explains.
In the process, they noticed telltale changes. “Interestingly, the albedo actually changed over time for two of the three areas,” the researcher reports.
If there is active cryovolcanism on Titan, freshly spewed water or methane should freeze and then become visible as bright deposits on the darker, older surface. Elsewhere, freshly rupturing vents could perhaps also be seen briefly as darker patches. As the researchers report, Tui Regio actually grew darker from 2005 to 2009, and Sotra Patera—the top candidate for ice volcanoes on Titan—brightened significantly from 2005 to 2006.
This would fit with previous observations that landscapes strongly resembling terrestrial volcanoes, calderas, and lava flows exist, especially in these areas. According to the scientists, these observations, together with the new data, suggest that Saturn’s largest moon may have ice volcanoes associated with the liquid water reservoir beneath its crust. “These results also have great significance for Titan’s potential to sustain life,” Solomonidou states. “This is because the cryovolcanic regions could provide environmental conditions in which life could arise.”
They have long existed in science fiction: life-friendly moons around alien planets. And theory also predicts their existence. But reality has lagged behind so far. Only in recent years have astronomers discovered a few candidates for extrasolar moons. This raises the question: where are all the exomoons? And what makes them so difficult to observe?
After all, astronomers have now tracked down two exomoon candidates – massive satellites around large gas giants. But given the thousands of exoplanets and more than 200 moons in our solar system, there should be many more such extrasolar moons. How they form, when they remain stable in their orbits, and when they might be habitable are questions that astronomers have been increasingly investigating recently – with some exciting results…
The location of the countless exomoons in space
In our own solar system, there is no shortage of moons: More than 200 moons orbit the planets of the Sun – only the two innermost planets Mercury and Venus are moonless. Especially the two big gas planets Jupiter and Saturn have a considerable number of moons, which are constantly growing due to new discoveries. Jupiter has 79 moons, and Saturn 82 moons.
There are more than 200 moons in our solar system, here some of the largest satellites. (Credit: NASA)
The variety of solar moons is also astonishingly large: Although the Earth’s satellite is today a cold, hull-less world, its presence could have contributed decisively to the development of the Earth and the emergence of life on our planet. In contrast, moons of other solar planets remain fascinatingly complex and dynamic to this day. Jupiter’s moon Io, rolled by the powerful tidal forces of its planet, is the most volcanically active celestial body in the entire solar system, while its nearest neighbor Europa has a liquid ocean beneath its ice crust and is considered the most promising candidate for extraterrestrial life in the solar system.
There are also some dynamic worlds among the moons of the ringed planet Saturn. Enceladus also has a liquid ocean under its crust, and Saturn’s largest moon Titan is even surprisingly Earth-like despite its cold: it has lakes, rivers, dunes and mountains, and its weather knows storms, rain and snow. However, on Titan, icy hydrocarbons rain down from the haze-shrouded sky, and liquid methane and ethane also flow in the waters.
From science fiction to reality
No wonder that this variety of satellites made science fiction authors dream of moons around extrasolar planets decades ago. In their stories, these exo-moons are often life-friendly worlds orbiting super-earths or large gas planets and offering a home to intelligent inhabitants – whether the moon Endor from “Star Wars,” Pandora from the movie “Avatar” or Andoria from the series “Star Trek.”
But it is also considered almost certain among astronomers that many extrasolar planets have satellites. “Given the large number of moons in our solar system, it’s natural to assume that there are also exomoons around some exoplanets – we just need to find them,” says David Kipping of Columbia University in New York. The U.S. astronomer and his team are among the most active exomoon searchers in the world.
So far, however, the yield has been modest: Although thousands of extrasolar planets are already known, astronomers so far know of less than a handful of potential exomoon candidates. But why? What makes the search for exomoons so difficult?
How to find an exomoon?
When it comes to searching for extrasolar celestial bodies, a simple telescope is not enough – most exoplanets, let alone their moons, are too small, too distant, and heavily outshone by their stars to be directly visible. Astronomers must therefore resort to indirect search methods.
One method is to search for tiny wobbles caused by the gravity of a planet or moon at the central star. These wobbles of the star cause slight shifts in the spectrum of its light, which can be detected with high-resolution spectrographs. Using this analysis of radial velocity, astronomers discovered the first exoplanet in 1995, and the three planets around our nearest neighbor star Proxima Centauri were also detected in this way.
The problem, however, is that the smaller and lighter a planet or moon is, and the farther it is from its star, the smaller is its gravitational influence – and the weaker are the changes in radial velocity. Even planets the size of the Earth are difficult to detect with this method. It is much more difficult with the even more subtle signal of an exomoon. Its effect is so weak that it is lost in the general “noise” of the spectral signal.
Shadows in the light curve
When an exoplanet passes in front of its star together with a satellite, the light curve of the transit can reveal this by a second smaller dent. (Credit: W. Commons)
A second search tool is the transit method. In it, astronomers look for the faint dimming of starlight caused by the passage of an orbiting planet directly in front of its star. This transit shows up in a characteristic, periodically recurring dip in the light curve. If this exoplanet has a moon, it will also leave a trace in the light curve.
If the exomoon orbits relatively far from its planet, it ideally appears well before or after its planet in front of the star. This creates a flatter, shorter dent in the light curve that is right next to the larger planetary dent. In 2018, this feature led to the discovery of the first known exomoon, a satellite orbiting a gas giant about 8,000 light-years away.
For their search, U.S. astronomers Aley Teachey and David Kipping tracked the 19-hour transit of the exoplanet Kepler-1625b with the Hubble Space Telescope. They had previously encountered anomalies with this planet in the transit observation data from the Kepler space telescope. “We saw small deviations and fluctuations in the light curve that caught our attention,” Kipping reports.
A first tracking success
The Hubble data confirmed it: There was a small “second dent” in the light curve that occurred 3.5 hours after the shadowing caused by the planet. “This is consistent with a moon that follows its planet like a dog on a leash,” Kipping said. And there was a second indication in the Hubble light curve: Kepler 1625b began its transit nearly 78 minutes earlier than would be expected based on its orbit.
Such so-called Transit Timing Variations (TTV) are also among the signs by which exomoons can be discovered.
That’s because they occur because the moon’s gravity pulls on the planet, slowing it down slightly or accelerating it, depending on the moon’s position. “If an extraterrestrial civilization were to observe the transit of the Earth and Moon in front of the Sun, they would see similar anomalies in the Earth’s transit times,” Kipping explains. At Kepler-1625b, the planet began its transit 1.25 hours earlier than it should – another indication of a satellite.
In January 2022, Kipping and his colleagues made their second find: After targeted re-analysis of Kepler data, they came across eleven potential exomoon candidates, one of which proved particularly persistent: “It’s a very robust signal – we put it through its paces, but it didn’t go away,” Kipping says. Dubbed Kepler-1708b-i, the exomoon is the satellite of an exoplanet some 5,500 light-years away.
How is an exomoon formed?
It is probably no coincidence that the second exomoon candidate, Kepler-1708b-i, also orbits a large planet far from the star. (Credit: Columbia University)
Which planets are the most likely hosts of one or more moons? And how are exomoons formed? Already in our solar system there is no simple answer to this question. Because their formation histories are as diverse as the moons themselves.
Nevertheless, they can tell us something about where exomoons are most likely to be found.
Grown from dust and gas
In our solar system, the planets with the most moons are the large gas giants beyond the asteroid belt. Jupiter and Saturn are massive enough to bind whole courts of moons to themselves by their gravitational pull. According to common theory, these moons were formed from dust and rock fragments that orbited these planets in the early days of the solar system and then slowly grew into larger celestial bodies. In the case of Saturn small new moons could develop in the rings even today.
For this to be possible, the protoplanetary disk around the parent star in this region must already be dense enough to contain enough material for one or more moons in addition to the planet. Because massive stars tend to be able to attract more matter, the chance for exomoons around red dwarfs should be lower than around sunlike or even heavier stars. In addition, moons around more massive planets are more likely than around very small ones because they can pull more of these protoplanetary remnants into their orbits.
In fact, astronomers discovered a possible nursery of exomoons for the first time a few years ago. It lies around one of the two young planets of the star PDC-70, about 400 light-years away, a star slightly lighter than the Sun and still surrounded by its protoplanetary dust disk. Images from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile revealed that the outer planet PDS-70c is surrounded by an extended and massive circumplanetary dust disk. This could contain enough material to form three Earth’s Moon-sized satellites.
Captured and held
Neptune’s moon Triton, pictured here by the Voyager 2 spacecraft, is an example of a captured moon. (Credit: NASA)
The second way a planet can acquire a moon is by capture. For example, Saturn’s moon Phoebe and Mars’ moon Phobos may once have been asteroids held in place by the gravity of their planets. The largest example of such a captured moon, however, is Neptune’s moon Triton. Its retrograde, inclined orbit and its resemblance to the icy chunks of the Kuiper belt suggest that this moon was once one of the transneptunian objects and then captured by Neptune.
Astronomers assume similar for the exomoon Kepler-1625b-i. Accordingly, this Neptune-sized giant moon may have originally been the core of a nascent protoplanet in the system around its star. However, the gravity of its larger neighbor Kelper-1625b pulled this planetary seed toward itself, making it a satellite before it had a chance to pull gas toward itself and become a gas giant itself. “The radius and mass of this exomoon are consistent with the characteristics of the planetary core of a gas giant,” explains Bradley Hansen of the University of California at Los Angeles.
Formed from collision debris
And there is a third scenario. Our Earth’s moon owes its existence to it. It was formed when the Mars-sized protoplanet Theia collided with the young Earth, nearly destroying both. A part of the evaporated rock was attracted by the still intact earth core and regenerated our planet, the rest condensed out and formed first a debris ring and the earth, then from this the moon was formed.
Also formed from collision debris is probably Saturn’s moon Hippocamp, which is only 34 kilometers small. This orbits so close to the large inner moon Proteus that it was probably formed from debris from a huge impact on this neighboring moon. Astronomers suspect that this collision ejected large amounts of rock debris, providing raw material for little Hippocamp.
But no matter how a moon was formed, whether it will last depends on another condition.
What makes an exomoon stable?
The only two halfway confirmed exomoon candidates have one thing in common: Not only do they both orbit large gas giants and are themselves quite heavyweights – their planets are also at a relatively large distance from their star. And this is probably no coincidence. For a moon to remain stable in its orbit, it must move between two tightly defined boundaries. And where these lie depends on both the planet’s mass and its proximity to the star.
Keeping distance is advisable
The first limit is set by the planet: its gravity keeps the moon firmly in its orbit as long as planetary gravitational attraction and the centrifugal force of the orbiting moon balance each other out. If the moon orbits too far out, it can easily be flung away by external perturbations; if, on the other hand, it orbits too far in, it is threatened with destruction. This is because the so-called Roche limit marks the range above which the tidal forces caused by the planet are so great that they begin to tear the moon apart.
A moon close to this limit could be the Martian moon Phobos: In its spirally narrowing orbit, it has already approached the Red Planet to such an extent that Martian gravity is gradually attacking its structural integrity. Astronomers assume that the already rather loose and porous Martian moon could break apart at some point – but this will probably not be the case for several million years. The orbit of Neptune’s moon Triton is also unstable and could bring the icy moon close to the Roche limit in the distant future.
A three-body problem
The second limit is the so-called Hill sphere. It describes the range up to which a planet’s arresting gravity outweighs the gravity of its star. If a moon moves at the outer boundary of this sphere, or even beyond it, it can very easily be thrown out of its orbit and flung away. Where the boundary of this Hill sphere lies depends on the mass and distance of the planet and star.
There is hardly any danger with the Earth’s moon: Its orbit, at 380,000 kilometers from the Earth, lies well within the Earth’s Hill sphere, which extends up to 1.5 million kilometers into space. However, the situation is different for the innermost planet in the solar system: Mercury has a Hill sphere of only 200,000 kilometers – there is not much room for a moon between the Roche limit and the Hill radius.
In addition, planets close to the star usually move in bound rotation around their star – they rotate slowly and always turn the same side to the star. This, however, also slows down the motion of moons in their orbit. The gravitational interactions cause a moon to slow down and sink lower and lower around such slowly rotating planets. As a result, sooner or later a moon crashes into its planet or is torn apart at the Roche limit by its tidal forces.
More chances with outer planets
But what does this mean for the search for extrasolar moons? Astronomers investigated this in 2020 using the example of a good 4,000 exoplanets known so far. To do this, they determined the Hill sphere based on planetary and stellar mass as well as the distance between the planet and the star, and then used a model to simulate whether and how long a moon would remain in orbit around such an exoplanet.
It appears that the most important factor in the persistence of an exomoon is the orbit of its planet. For most exoplanets with orbital periods of less than ten days, there is no stable lunar orbit. Then, in the range of ten to 300 days, the survival rate slowly increases from zero to about 70 percent. In other words: If we’re looking for exomoons, we should be targeting mostly massive, far-out orbiting planets – like Kepler-1626b or Kepler-1708b.
Difficult search
The problem, however, is that such planets, which are farther away from their stars, are difficult to observe with conventional methods and even more difficult to examine for moons. This is because the long orbital periods of such planets make transits very rare – catching them is almost a matter of luck. Moreover, these exoplanets are so far away from their star that they make their star “wobble” only very weakly. Measuring the effect of their moons via radial velocity is nearly impossible.
It is therefore no coincidence that the first exomoon candidates are massive giants of several times Earth’s mass: Only their effect was strong enough to be detected by our telescopes. “So the first discoveries are the odd ones out – such giants are the ones that are easiest for us to find,” says U.S. astronomer David Kipping.
That, however, could change with NASA’s new James Webb Space Telescope. That’s because its spectroscopes are so high-resolution that they could detect the signal of even smaller exomoons. “It’s a no-brainer for Webb,” Kipping explains. “It can find extrasolar moons smaller than Jupiter’s moon Europa.”
How life-friendly can an exomoon be?
Tidal forces of Jupiter generate enough heat to create an ocean of liquid water beneath the icy crust of the moon Europa. (Credit: NASA/ JPL-Caltech / SETI Institute)
In science fiction, exomoons are often life-friendly, water-rich worlds. But what about in reality? In the solar system, most moons are too far from the Sun and cold to be habitable. And if satellites do indeed form more frequently around gas giants orbiting far out, this could hardly be different in other planetary systems – or could it?
More chances than with an exoplanet
In fact, the chances of habitability are even better for an exomoon than for an exoplanet, as model simulations suggest. Because such a moon is under the influence of both its planet and the star, more factors interact. Such synergistic effects mean that an exomoon can still be warm enough for water and life even outside the habitable zone of its planetary system – because the planet provides the necessary heat.
“Exomoons are more complicated than exoplanets – but that also brings more chances to be life-friendly,” explains Rory Barnes of the University of Washington. A few years ago, the astrobiologist investigated what an exomoon has to bring along to become a life-friendly world – and which factors influence this.
Tidal forces as a heat source
An example of such combined effects: If an exomoon orbits around a gas giant with an orbit similar to Jupiter or Saturn, it would normally be too cold for liquid water – too little radiative heat arrives from the star. But just looking at Jupiter’s moons shows that this need not be an obstacle: The moon Europa has a thick ice crust, but underneath there is a warm, liquid ocean. The source of this warmth is Jupiter’s strong tidal forces, which churn and warm the interior of the moon.
Similarly, tidal forces from exoplanets can also heat their moons, creating their own habitable lunar zone. Scientists can imagine some scenarios where an exomoon becomes habitable just from this tidal heat. However, there is also the flip side: If a planet-moon pair is already orbiting in the star’s habitable zone or at its inner edge, then tidal heating can push the exomoon across that boundary: It then becomes too hot and too volcanic for liquid water and life-like Jupiter’s moon Io.
Not only that, but if tidal forces provide enough heat to keep the exomoon’s interior hot and liquid, they can also give it a magnetic field and plate tectonics. Both occur when there are flows of liquid metal or hot magma inside a celestial body – as is the case with our Earth. Both are also factors that increase the life-friendliness of a celestial body.
Light and shadow from the planet
Besides the tidal effect, an exomoon can also receive additional light and thermal radiation from its planet. This is because, depending on its orbit, the satellite passes through areas where starlight reflected from the planet’s surface falls on it. Such satellites can therefore receive more irradiation than their planets. This also extends the habitable zone for exomoons outward.
Conversely, an exomoon can also be protected and cooled by its planet. This is the case, for example, when it regularly passes through the shadow of a large, nearby planet. This lunar eclipse can significantly affect the climate on the exomoon, astronomers explain. At the same time, this alternation of planetary light and starlight can cause a kind of seasons on the exomoon: Depending on whether there is only one light source in the sky, both, or none, it is winter, summer, or something in between on the lunar surface.
Orbit and size of the satellite are crucial
As astronomers noted, this combination of factors determines the inner limit of the habitable zone of exomoons. If they cross it, tidal forces and irradiation cause the moons to overheat and there is a self-reinforcing greenhouse effect. Outwardly, there is no sharp limit to the distance from the planet. As long as the Hill radius is not exceeded, an exomoon can be habitable far from its planet if the planet orbits in the habitable zone of its star.
Why then, one may ask, do none of the moons around Saturn or Jupiter bear any resemblance to Pandora or Endor? According to astronomers, this could be due to their size: More massive exomoons have a larger habitable zone around their planets than lower-mass ones. For one thing, the inner limit beyond which a moon becomes too warm and unstable is further inward for larger celestial bodies. For another, such moons have enough gravity to hold an atmosphere and thus water vapor and liquid water.
According to the calculations, an exomoon around an extrasolar gas giant would have to be at least the size and mass of the planet Mars to be life-friendly in the longer term. Such a moon would also be massive enough to retain its water as its parent planet migrates inward from the ice-rich outer reaches of its planetary system. An icy moon could then become a water-covered satellite.
Late this night, at about 1:47 a.m. ET, the Artemis-1 mission lifted off; it is now on its way to the Moon. The 320-foot-tall (nearly 100-meter) Space Launch System, the most powerful launch vehicle ever built, and the Orion space capsule, which was partially built in Europe, will orbit the Moon and then return. The still-unmanned lunar mission serves as a dress rehearsal for the manned return to the Moon, with only three dummies on board this time.
50 years after the last Apollo mission, the Earth’s satellite has once again become the target of manned space flight. With the Artemis program, the USA and Europe want to land humans on the Moon once again by 2025. This time, a space station in lunar orbit and later a lunar base are intended to enable the long-term presence of astronauts on the Moon. But other nations, including China in particular, also have their eyes on the Moon and are preparing a manned return to the Earth’s satellite.
The Launch is Finally Successful
Structure of the SLS launch vehicle with the Orion module. (Credit: NASA)
Artemis-1 launched to the Moon from Cape Canaveral on November 16, 2022, at 6:47 a.m. UTC. The countdown and launch were broadcast live by both ESA and NASA. For the first time, the Space Launch System (SLS) launch vehicle developed by NASA specifically for lunar missions and the Orion capsule designed and built in Europe will now fly together to the Moon, orbit it, and return to Earth.
But the development of the SLS in particular had its difficulties: its completion was delayed by years, and in 2022 there were repeated problems with refueling; the launch of Artemis-1 had to be postponed several times.
The excitement with which the launch of the giant was followed around the world was correspondingly great. Powered by four engines fed with liquid hydrogen and oxygen and two solid rockets, this 321-foot-tall vehicle is the most powerful launch vehicle ever built. It surpasses even the legendary Saturn V of the Apollo missions.
Aboard the Artemis-1 mission, there is a crew of a truly special kind. Three dummies are taking part in the first lunar flight of the Artemis program and, with the help of numerous sensors and measuring instruments, recording the stresses to which human astronauts will be exposed. The pilot dummy, named “Moonikin,” will test not only sensors for radiation, vibration, and pressure forces but also the space suit that the astronauts will later wear during critical mission phases.
The ‘crew’ of the Artemis I mission to the Moon. (Credit: NASA/Lockheed Martin/DLR)
The two passengers, “Helga” and “Zohar,” are torso dummies whose materials are modeled on those of the female body, because the next Artemis flights will be the first time female astronauts fly to the Moon. Zohar wears a special radiation protection vest, while Helga does not. Several thousand radiation sensors determine the level of cosmic radiation to which the dummies are exposed during the flight.
Flight to the Moon
The SLS launch vehicle is designed to accelerate the Orion module to a good 22,350 miles (36,000 kilometers) per hour. After about eight minutes, the solid rocket boosters and the four engines of the first rocket stage burn out and are jettisoned. Artemis-1 first reached orbit around Earth and the Orion capsule deployed its two solar sails.
Next, to give the spacecraft the thrust it needs to leave Earth’s orbit and fly to the Moon, the rocket’s upper stage, called the Cryogenic Propulsion Stage (ICPS), kicks in. Its engine, also fed by liquid hydrogen and oxygen, puts the Orion spacecraft on a lunar course. About two hours after launch, the Orion capsule separates from the ICPS burn stage. The Orion capsule now receives enough thrust to continue on its own to the Moon.
Meanwhile, the ICPS releases ten mini-satellites, known as CubeSats. These carry various small measuring instruments and sensors with which they investigate, among other things, the lunar surface and the radiation, particles, and magnetic fields between the Earth and the Moon. One CubeSat is also designed to land on the Moon, and another will fly to a near-Earth asteroid using a light sail.
Around the Moon and Back
Artemis 1 mission flight plan. (Credit: NASA)
The Orion capsule needs several days to reach the Moon. On the sixth day after launch, it is expected to pass the closest point to the Moon on its trajectory. It will fly over the lunar surface at an altitude of around 60 miles (100 kilometers).
The space capsule will then ignite its propulsion jets to enter an elliptical orbit around the Moon. This takes Orion around 40,000 miles (64,000 kilometers) above the Moon. It will then be about 280,000 miles (450,000 kilometers) from Earth—further than any spacecraft designed for manned missions before it.
To bring the spacecraft back out of lunar orbit and on course for Earth, the engines of the Orion service module will be fired again about a week later. 26 days after launch, Orion will reach Earth again and enter the Earth’s atmosphere. This marks the beginning of the crucial test for the Orion module’s newly developed heat shield.
Re-entry and Landing
Because the capsule will enter Earth’s atmosphere at nearly 25,000 miles (40,000 kilometers) per hour during its return to Earth, it will heat up to nearly 5,000 degrees Fahrenheit (2,800°C)—far more than it would if it were returning from the International Space Station in low Earth orbit.
The Orion heat shield, like the Apollo lunar missions, therefore uses a material that is consumed by the heat but allows little of it to pass through to the capsule. An additional layer of insulation and cooling systems in the walls of the spacecraft ensure that the Orion capsule is not damaged.
After the heat shield and the friction of the atmosphere have slowed the space capsule from about 25,000 miles to 300 miles (40,000 to 480 km) per hour, the first pair of special parachutes are triggered at an altitude of about 25,000 feet (7,600 meters). A short time later, the three large main parachutes take over and allow the capsule to glide gently down to the sea. The landing site is not far from the California coast in the Pacific Ocean.
Next Steps in the Artemis Program
If the flight of Artemis-1 is successful, the next manned steps in the Artemis program will follow. The follow-up mission, Artemis-2, is expected to take place in 2024.
For the first time, four humans will then fly to the Moon in the Orion capsule and orbit it on a similar trajectory to Artemis-1. Unlike Artemis-1, however, this mission will probably not enter a lunar orbit but will fly an eight-shaped loop in which the spacecraft is deflected by lunar gravity alone and returned to Earth’s course.
Artemis-3—probably in 2025 or 2026—will be the first time humans set foot on the Moon. On this mission, two astronauts will fly down to the lunar surface with a landing module and land. The remaining two astronauts will remain in lunar orbit. Whether all this will happen, however, depends crucially on how the dress rehearsal for the Artemis-1 mission goes.
One of the main issues throughout the Cold War was the race to the Moon, which the Soviets and Americans clashed in a race that led one of them to the Moon in July 1969. From 1957 through 1969, the Cold War’s focus was mostly on the race to conquer space. It’s where the US and the USSR squared off in a heated technical duel, with both sides looking to prove their mettle. After the launch of Sputnik-1, the first artificial satellite, in 1957, the focus shifted to human missions and the goal of landing a man on the Moon.
Before the 1950s, interstellar travel was more science fiction than reality. The notion of transporting an item or a man beyond the atmosphere was not a priority for the Russian or American governments, even if Wernher von Braun collaborated with Walt Disney in the United States to publicize and propagate his ideas of space conquest. However, military engineers on both sides, particularly those specializing in ballistics, were giving this idea significant thought.
V2 missiles give the necessary boost
V2
During WWII, Nazi scientists created a brand-new kind of missile known as the V2. They were employed to bomb London towards the conclusion of the war, and their rocket propulsion made them particularly effective. This revolutionary technique allowed for the destruction of the enemy at a great distance (350 kilometers), at high speed (Mach 3.5), and without the need for airplanes.
The Cold War’s armaments competition prompted massive expenditures in research, including this promising new area. The V2s did get attention from both the East and the West. Wernher von Braun, the Nazi engineer who developed the V2, later joined the SS and the American army, and it was he who, together with Walt Disney, educated the American public about space.
The Sputnik 1 satellite, a world first
Despite some lag in the nuclear industry, it is the USSR that has made the greatest use of this innovation. In the 1950s, it began the development of an ICBM that could deliver an atomic weapon. The A-bomb is much larger than the H-bomb. They were dropped from an aircraft over Japan. That’s why it was such an ambitious project: to create a missile with an intercontinental range (a few thousand kilometers as opposed to the V2’s 350) and the ability to deliver a payload weighing several tons. The Ukrainian engineer Sergei Korolev, who was rescued from the gulag during World War II for his expertise in aeronautics, was given the task of leading the project.
He was granted permission to construct a tiny satellite and attempt to launch it into orbit after seeing the potential of such a rocket and sharing von Braun’s passion for space exploration. Korolev’s rocket design is a step in the right direction. While it had its share of problems during the first testing, it eventually worked well enough to launch Sputnik-1 into orbit on October 4, 1957. What started as a side project has become a significant technical and symbolic achievement, marking the crossing of a new boundary in the human environment. A little unit broadcasts a radio signal—just a beep—that anybody, anywhere may use to verify the Soviets’ claims.
The Sputnik 2 satellite and the dog Laika in space
This is a genuine embarrassment for the United States. This Soviet triumph has serious military implications, but it also severely undermines American faith in its technical dominance. The political power of the symbol is not to be underestimated, as the Soviet Union has always credited its success to the unique character of its own government. Therefore, in the United States, a crew has been assembled to be ready for the first launch. On the other hand, Sputnik-2 was launched by the Soviet Union on November 3, 1957. To further prove the Soviet Union’s progress, it carries a dog by the name of Laika. But unfortunately, the animal does not make it, and Russia is not quite ready to launch a human into orbit just yet.
Explorer-1, the first U.S. satellite
Despite the pressing need, the United States did not want to engage with former Nazi engineer Wernher von Braun, who was developing medium-range missiles, for obvious grounds of public perception. The official Vanguard project had initially failed, but on January 31, 1958, Braun’s crew was given the green light to attempt again with the Explorer-1 launch. It made the identification of the Van Allen radiation belt possible. Wernher von Braun, together with his rival Serguei Korolev, would thereafter play pivotal roles in the conquest of space. The USSR, on the other hand, decided to keep his identity a closely guarded state secret, so he would never get the same praise as his American counterpart.
The Luna to the Moon program
The U.S. eventually caught up and started investing in the long run. With this in mind, at the close of 1958, Eisenhower established NASA (the National Aeronautics and Space Administration). However, with the help of its Luna program, the Soviet Union goes on to become the undisputed leader in space exploration in the years that follow. Leaving Earth’s orbit and heading for the Moon, spacecraft Luna-1 took off on January 2, 1959. The Luna-2 spacecraft successfully landed on Earth’s satellite on September 13. After more than a month of searching, Luna-3 has finally revealed the Moon’s secret side to Earth.
It sends pictures with an uneven face superimposed on the real one. The Russians are encouraged by their accomplishments and decide to restart the Sputnik program, which aims to launch a man into space. Multiple launches occur, each time with a dog on board; unlike Laka, most of the dogs survive the trip back to Earth’s atmosphere. The United States is opposed to the Sputnik program and favors the Mercury program instead. Also in January 1961, thanks to these advancements, a chimpanzee named Ham was sent into space.
So the Americans go to the Russians and plot to get back at them by launching the first human into space. On April 12, 1961, however, the Soviet Union surpassed them with the launch of Yuri Gagarin on Vostok-1 from the Tyuratam spaceport. At an average height of 250 km, he flew in orbit around the Earth for 1 hour and 48 minutes. The Soviet Union continues to bolster its reputation for excellence in space exploration. As a response, on May 5, the Americans sent Alan Shepard into space, although at a far lower height and for a much shorter duration (15 minutes only).
The American Apollo program’s inception
This was the beginning of the Apollo project, which Kennedy first declared on May 25, 1961, when he said that an American would walk on the Moon by the end of the decade. The Gemini program ran concurrently, enabling a number of experiments in human spaceflight to be conducted in low Earth orbit. The Soviet Union kept working on the Luna project. In a nutshell, the race between the two nations to put a man on the Moon is the ultimate prize.
Therefore, all of 1960 was spent working towards this ultimate goal. There were as many phases to the programming as there were events. It took John Glenn about five hours and twenty minutes to complete three orbits of the Earth on February 20, 1962. In December of that year, thanks to the Mariner program, a U.S. satellite came within a few hundred miles of Venus. The Mariner-4 probe makes its way through Mars in July 1965. On March 18, 1965, the Soviet Union successfully completed its first spacewalk with Alexei Leonov. A few months later, in the context of the Gemini program, the Americans accomplished an identical feat.
The American Apollo program speeds things up significantly. There are three distinct stages of the curriculum. The first, which spanned 1960–1968, included equipment testing during pilotless flights. Since it was Wernher von Braun’s crew that created the Saturn V rocket, their contribution was crucial. During this time, Wernher von Braun oversaw the Mercury program, which allowed for piloted test flights.
Apollo 1 was the first mission of the second phase, but it was cut short on January 27, 1967, when a fire broke out during a mock launch, killing all seven men on board. Dramatically postponing the project, the mission’s failure adds more time to the process, since the capsule has to be redesigned. The first inhabited mission of the program, Apollo 7, did not take place until October 11, 1968. The testing lasted for 10 days, during which time the ship stayed in Earth’s orbit.
The Americans and the conquest of the Moon
When Apollo 8 successfully places a crew into lunar orbit in December 1968, the United States makes significant progress relative to the Soviet Union. Within the following six months, Apollo 9 and 10 successfully piloted mission scenarios for a potential lunar landing. On July 16, 1969, Apollo 11 lifts off from Cape Canaveral with astronauts Neil Armstrong, Michael Collins, and Edwin “Buzz” Aldrin on board, marking the beginning of the third phase.
His Eagle capsule touched down in the “Sea of Tranquility” on July 20. On July 21, 1969, Neil Armstrong and Edwin Aldrin made history by walking on the Moon for the first time. The astronaut would have subsequently made the now-famous statement, “That’s one small step for man, one giant leap for mankind,” after the successful landing. As a result, the United States now had the upper hand in its rivalry with the Soviet Union.
Moving toward Soviet-American collaboration
This was a decisive advantage, since Apollo 12 through 17 all accomplished the same thing (with the exception of Apollo 13, which was derailed by technical difficulties), but the Russians never stepped foot on the Moon. In addition, the setting of Détente (the thawing of relations between the superpowers) no longer justified such costly missions (the Apollo program cost the United States billions). They canceled the last four Apollo missions as a result of the economic crises in the 1970s. In truth, man’s historic moonwalk ended the Cold War-era rivalry between the United States and the Soviet Union in the race to space.
Everybody’s objectives were scaled down because of the new political reality and the high price tag that came with it. The Apollo-Soyuz collaboration represented détente despite the continued competition in unmanned exploration missions. This one began in 1972 and involved two spacecraft meeting in orbit around each other. In addition, human missions diminished in importance and were eventually confined to low-Earth orbit. The United States intended to enable frequent round trips, which was why new space shuttles had been built since 1976. The USSR, meanwhile, was placing its chances on orbital stations, as seen by Salyut, the world’s first permanently occupied space station, which was launched in 1971.
Space stations, from Mir to ISS
It was a Soviet space station that entered orbit in 1971. After their failed attempt to conquer the Moon, the Russians view this as an opportunity to reclaim space for themselves. They conduct a wide range of research and development, as well as military tests. Several space stations, including the MIR station, may be launched under the Salyut program and placed into orbit before 1986.
The Americans, not wanting to be outdone, developed Skylab. They employed parts from earlier Apollo flights to construct the station, but it suffered extensive damage when it was launched in 1973. It was inhabited for several years before facing unexpected solar activity. It decayed in the Earth’s atmosphere in 1979. In 1983, the United States planned to begin a new project; it would be the beginning of the International Space Station (ISS). In 1985, the Soviet Union launched the MIR station’s first module into space. Counting the optional ones, there would be seven. MIR was inhabited for twelve years. It was deorbited in 2001.
In the meantime, the International Space Station was launched in 1998. Countries like Russia and the United States, as well as many others, took turns working on the project. In 2011, work on the International Space Station was finally wrapped up. For their first space station, the Chinese picked this year, and they have given it the name Tiangong. For the time being, the International Space Station is still the biggest manmade object in Earth’s orbit. The facility is expected to remain operational until 2024.
Conquering Mars is the ultimate future project
The American space program has been a complete success. The American space program has not only caught up to the Soviet space program but has surpassed it. Numerous scientific and technical improvements have been made possible by the large human and financial resources used to transport men to the Moon. However, the lunar conquest was rapidly abandoned despite the economic gains and the impression this conquest had on the cultural imagination.
Although it made great strides in astronautics and expanded the bounds of possibility, the focus of the space conquest has shifted from the Moon to Mars. SpaceX fits this description; they are working on the Starship rocket to colonize Mars, but first, they want to conquer the Moon. Even though the United States hopes to train on the Moon before commencing its mission to transport humans to Mars, the details of the program are still quite hazy at this point.
Upcoming experiments: A lunar base
The Moon is currently of little interest to the world’s largest space missions. With the cancellation of the Constellation program in 2010 at Obama’s direction, even the United States has lost interest in the Moon. The main astronautical nations’ priorities have shifted in the wake of China’s successful landing of an autonomous probe on the far side of the Moon.
However, in order to be ready for a future Mars colony, the United States has planned a voyage to the Moon called “Moon to Mars,” which would enable the construction of a lunar facility in the year 2034. It is expected that the first lunar colony would be possible thanks to the Artemis program (scheduled to launch in 2022). So, after more than 50 years since the previous passage during the Apollo 17 mission, humanity might make its epic return to the Moon.
The industry of space travel is booming
A number of programs have been established since the turn of the millennium to make space flight possible for regular people without requiring them to undergo the rigorous training required of astronauts. The first flight was made in 2001 during the TM-32 mission aboard a Soyuz spacecraft.
Dennis Tito, an American multimillionaire, was the first space tourist. He paid a relatively modest $20 million to spend almost a week in Earth orbit. Many private enterprises have taken the lead in developing space tourism in recent years, and this has sparked a new race to the top. It seems that three firms have the necessary resources to take the crown.
First, Richard Branson’s Virgin Galactic (established in 2004) sells $250,000-per-person tickets for rides in space aircraft to an altitude of more than 80 kilometers. Then there’s Blue Origin, founded by Amazon’s founder Jeff Bezos, who takes things even farther by launching its New Shepard rocket over the Kármán line (100 km) for around 15 minutes.
Nonetheless, the price is substantially greater; $28 million was bid on the trip on July 20, 2021, with Jeff Bezos and his brother Mark. On September 15, 2021, tourists were finally able to ride SpaceX’s Falcon 9 rocket to the Crew Dragon spacecraft for the first time. Elon Musk, CEO and co-founder of SpaceX and Tesla, has made no secret of his fascination with space, as seen by his hopes for the colonization of Mars.
TIMELINE OF SPACE EXPLORATION
June 20th, 1944, and the V2 rockets had just been launched
In the Second World War, the Nazis developed the V2 rocket, marking the beginning of humankind’s conquest of space. It is possible to launch them over 100 km into the air.
On October 4, 1957, Sputnik was successfully launched
The first man-made satellite was launched into orbit by a Soviet R-7 rocket. Sputnik, whose name translates to “co-wayfarer” in Russian, is a 58-centimeter satellite that tips the scales at 83.6 kg. The satellite is then launched into a 900-kilometer orbit around the planet. We owe this technical achievement to Serguei Korolev, who is developing an ICBM. It’s based on the fact that the Germans were responsible for making V2 possible.
For the United States, this happened smack dab in the thick of the Cold War and was a direct provocation. There would be a “race to the stars” between the two superpowers, and it all started with the launch of the little spacecraft Sputnik 1. On January 4, 1958, Sputnik 1 disintegrated upon re-entry into Earth’s atmosphere.
On November 3rd, 1957, Sputnik 2 and the dog Laika were launched into space
Sputnik 2 was launched with Laika in a pressurized container one month after the first Sputnik satellite (Russian for “co-wayfarer”) was launched. The first live organism to be satellited is a little dog. Seven days later, the animal succumbs to oxygen deprivation.
First American satellite launched on January 31, 1958
It’s 10:48 p.m., and the Juno 1 rocket is finally ready to take off. The first American artificial satellite, Explorer I, weighing 14 kilograms, was launched into Earth orbit seven minutes later. America takes its turn in the conquest of space three months after the Soviet Union launched “Sputnik.”
On July 29, 1958, NASA was established
In order to beat the Soviet Union in the “space race,” President Eisenhower passed into law the creation of the National Aeronautics and Space Administration (NASA). NASA was in charge of coordinating the world’s aerospace and space exploration efforts. The United States was taken by surprise by the launch of Sputnik-1, and this organization was established in response. President Kennedy’s Moon program announcement in 1961 set the stage for NASA’s eventual success. In 1969, both parties honored the agreement to land a man on the Moon.
December 18, 1958, the world’s first communications satellite
This is the first experimental communications satellite launched by the United States, and the news came through a press release. The Atlas rocket launches the “SCORE” gadget into orbit for a 34-day test run. It sent seven transmissions to Earth, including a speech from President Eisenhower. In 1962, the first American television programs were sent via satellite to televisions throughout Europe.
The first space probe was launched on January 2, 1959
The Soviets are the first to successfully remove an artificial object from the pull of Earth’s gravity, after multiple failed efforts on both the Russian and American sides. The Lunik 1 spacecraft came within 6,000 kilometers of the Moon, but it ended up too far away from the Moon and instead entered a Sun-orbiting track a few months later. Even so, it sometimes broadcasted its scientific information. The American probe Pioneer made the same trip two months later.
A Soviet probe lands on the Moon on September 13, 1959
While the United States was still playing catch-up, the Soviets sent Luna II (or Lunik), the first lunar probe, to the Moon). This last one hits the Moon and leaves behind a Soviet flag shaped like a football. With this probe, scientists were also able to prove that solar winds do, in fact, exist.
October 7, 1959: First photos of the far side of the Moon
The first images of the far side of the Moon that cannot be seen from Earth were captured and sent back to Earth by the Soviet spacecraft Luna-3. Later, the world learned that it was far less uniform than the other side the Moon has always shown humans.
Yuri Gagarin launches into space for the first time on April 12, 1961
He was just 27 years old, yet his feat would live on in posterity. As the first human being to launch into space, Yuri Gagarin made history. He flew for 108 minutes on the rocket Vostok 1 (Orient in Russian), during which time he completed one orbit of the Earth. As a result, the Russians may rest certain that they are winning the space race against the United States.
May 5, 1961: Alan Shepard reaches space
Alan Shepard became the first American to circle the Earth a few weeks after Yuri Gagarin’s first voyage into space. This flight took just around 15 minutes and stayed at a low altitude (sub-orbital). John Glenn, on February 2, 1962, became the first true American astronaut.
On this day in 1961, man on the Moon by the end of the decade
The United States saw Yuri Gagarin’s orbital flight as a fresh insult; therefore, they made the strategic decision to strike back in the short term by achieving a goal that would demonstrate their technical dominance over the USSR. It was President Kennedy who made the public announcement that the Western powers wanted to put a man on the Moon by the end of the decade. Mankind would set foot on the Moon on July 21, 1969, proving that the Apollo program was successful and meeting its objectives.
September 12, 1961: Our destination is the Moon
In his now-famous “We chose to go to the Moon” address, President John F. Kennedy reaffirms the American goals first declared in May. As a result, the Apollo program is given more funding and attention at a time when its goals are most lofty. As the country that launched the first satellite and later the first man into space, the United States aims to beat the Soviet Union to this milestone.
February 20, 1962, John Glenn became the first American to orbit the Earth
The first American to take part in a human space voyage was astronaut John Herschel Glenn. It took him 4 hours and 56 minutes aboard the “Mercury Friendship 7” spacecraft to complete three orbits of Earth, covering a total distance of 129,000 kilometers. The ocean landing was successful 65 kilometers east of the Bahamas, close to the predicted target zone established by NASA scientists. Almost a year after Yuri Gagarin became the first man in space on April 12, 1961, the United States finally accomplished a human mission.
The satellite “Telstar” was launched on July 10, 1962
Florida’s Cape Canaveral was the site of the launch of the Telstar 1 communications satellite. It was created by the American telecom giant AT&T with the intention of keeping TV and phone lines open across the two continents. As a result of “Telstar,” the first transatlantic communications satellite, European viewers could tune in to a news conference held by President Kennedy, while American viewers could tune in to an entertainment show featuring Yves Montand.
Kennedy proposed space collaboration with the USSR on September 21, 1963
John F. Kennedy suggested to the United Nations that they organize a Soviet-American mission to the Moon as the United States and the Soviet Union entered a period of détente in the Cold War. The Soviet Union gave a neutral response. To the point where the Echo C satellite represents the culmination of their joint effort.
On March 18th, 1965, the first cosmonaut was launched into space
Alexei Leonov of Russia did a spacewalk for 15 minutes while still securely attached to his spaceship. The first human to ever float in space was him. On June 3, 1965, for around 20 minutes, American Edward White succeeded him.
The Space Race‘s first fatalities occurred on January 27th, 1967
Three astronauts perished in the burning capsule on Apollo 1, the first flight of the American space program. Spacemen Virgil Grissom, Edward White, and Roger Chaffee were all trapped aboard the burning spaceship on its first flight to Earth for preliminary ground testing. Initial plans called for launching the mission in February. According to the paper, the three astronauts died by breathing in a hazardous gas; however, the report did not specify what caused the fire. Before the Apollo program’s first human flight, several changes would be made.
October 18th, 1967: Venera 4’s mission was completed
Data on Venus’s atmospheric pressure and temperature are sent by the Russian space mission. There is a 94-minute window during which data is sent. The Soviet Union first sent a “Venera” probe to Venus in 1961. The first images of the surface of Venus were sent back by Venera 9 in 1975.
On December 24th, 1968, the first humans orbited the Moon
The Apollo 8 crew travels over the Moon three days after liftoff from Cape Canaveral. Frank Borman, James A. Lowell Jr., and William A. Anders make 10 times the turn of the star to conduct experiments for the future lunar landing, marking the first time that men have left Earth’s orbit to approach the Moon. On December 27th, after a successful six-day journey, they safely returned to Earth. The United States is getting ready to launch a mission to the Moon. For the first time, they made significant inroads against the Soviet Union.
Moon mission Apollo 11 lifted off on July 16, 1969
On July 16, 1969, on a mission to the Moon, astronauts Neil Armstrong, Edwin Aldrin, and Michael Collins took off. The Apollo 11 mission was a success on July 21, 1969, when astronauts Neil Armstrong and Buzz Aldrin became the first humans to set foot on the Moon.
The first human being landed on the Moon on July 20, 1969
At 02:56:15 GMT, Neil Armstrong stepped foot on the Moon at about 109 hours, 42 minutes after launch. He then said the thing that still remains engraved in our memories: “That’s one small step for man, one giant leap for mankind.” The world watched as Russia lost its space superiority in an event that was broadcasted across the globe.
Apollo 13’s “Houston, we have a problem” aired on April 13, 1970
When the Apollo 13 space shuttle is getting close to the Moon, an explosion occurs in the service module’s oxygen tank. The three astronauts on board are forced to immediately return to Earth once the program is terminated. During their rescue by the technical teams located in Houston, James Lovell, John Swigert, and Fred Haise took sanctuary in the LEM Aquarius. They make it to the South Pacific without any problems. Ron Howard’s 1995 film Apollo 13 dramatized the ill-fated mission of the crew of that spacecraft.
On April 17, 1970, the Apollo 13 crew successfully returned to Earth
Three American astronauts make it through the Apollo 13 mission unscathed, and they all touch down in the South Pacific without incident. Their dream journey into space was shattered four days before, 56 hours after departure, when an oxygen tank suddenly exploded at over 300,000 kilometers from Earth. The astronauts retreated to the Aquarius lunar module, which had dwindling supplies of oxygen and energy. There is a complete 180-degree turn from scientific goal failure to genuine human achievement.
On February 6, 1971, astronauts landed on the Moon and played golf
The first guy to play golf on the Moon was Alan Shepard. On January 31st, Shepard left the Apollo 14 spacecraft with Edgar D. Mitchell and Stuart A. Roosa and headed for the Moon. His “lunar walk” lasted 4 hours and 34 minutes, and he took Mitchell along for the ride. During his second walk (after 4 hours and 48 minutes), he indulges in his great enthusiasm for golf by hitting several balls near the Fra Mauro crater. In addition to Armstrong, Aldrin, Cernan, and Bean, Shepard is the fifth human to set foot on the Moon.
April 19, 1971: First manned space station
After failing to conquer the Moon, the USSR develops an orbiting station program and launches Salyut-1, the first station to host a human crew. In a pressurization disaster that occurred between June 7 and June 30, all three astronauts who inhabit the station perished. Humans occupied Salyut for a total of 813 days, and over 2,500 scientific experiments were conducted until the program was officially closed in 1986.
Mariner 9 went into orbit on November 14, 1971
After 167 days in space, the American spacecraft Mariner 9 was already in orbit around Mars. Its mission was to send back images of Earth’s surface and weather data. A catastrophic dust storm delayed the realization of photographs until January 1972, and the probe didn’t begin observing Mars’ satellites, Phobos and Deimos, until that month. Once the dusty mantle was removed, Mariner 9 would have until the end of its mission on October 27, 1972, to take over 7,000 photos. The spacecraft probably crashed into Mars’s atmosphere in 2022.
The United States sent its last lunar probe on December 11, 1972
Apollo 17 astronauts Gene Cernan and Harrison Schmitt, who set out on their mission on the 7th, finally landed on the Moon. A total of 74 hours, 59 minutes, and 30 seconds, or more than three days, were spent on the Moon by the crew. Apollo 17 was the final human trip to the Moon for the United States.
Pioneer 10 beginning its first orbit of Jupiter on December 3, 1973
The American Pioneer 10 probe was the first to provide data about Jupiter when it flew within 130,000 kilometers of the gas giant. The American interplanetary probe Pioneer 10 is the oldest of its kind, having been launched on March 3, 1973. In January of 1998, it vanished off the face of the Earth.
Apollo-Soyuz: a handshake in orbit, July 18, 1975
The United States and the Soviet Union hold hands in orbit to commemorate their historic first joint space mission. When the American Apollo and the Russian Soyuz spacecraft collide in orbit, astronaut Thomas Stafford and cosmonaut Alexis Leonov team up. In addition to the technological advancements, the actual revolution is political: after competing against one another for almost a decade in the race to space, the opposing forces finally came to an agreement. However, a more sophisticated level of collaboration between the United States and Russia can’t begin until the Mir orbital station is operational.
The Viking 2 probe set out toward Mars on September 9, 1975
NASA sent the Viking 2 spacecraft to Mars as part of an exploration initiative to take pictures of the Martian polar caps. The Viking 1 mission departed exactly one month before this one. The Viking project has returned hundreds of breathtaking images and other data about Mars and its moon Deimos. In 1978, the probes lost contact and were no longer transmitted.
On June 13, 1983, Pioneer 10 was launched into interplanetary space
The American probe “Pioneer 10” is the first terrestrial object to leave the solar system. Though it was only meant to operate for two years after its March 1972 launch, the probe was still sending out signals as late as January 2003. In 1973, it was the first to fly above the gas giant Jupiter; in 1983, it was the first to cross beyond Pluto’s orbit. The spacecraft was 82 times the distance from the Earth to the Sun away from us when it lost communication with us at a distance of 12.2 billion kilometers. The probe contains a gold plaque with a human description, Earth’s coordinates, and the mission’s launch date engraved on it.
February 7, 1984: Two astronauts spacewalk
To accomplish the first spacewalk without being tethered to a shuttle, two astronauts used the MMU (Manned Maneuvering Unit), essentially a rocket chair in 1984. For about five hours, astronauts Robert L. Stewart and Bruce McCandless floated in space roughly 100 meters from Challenger.
Voyager 2 passed by Uranus on January 24, 1986
The Voyager-II spacecraft stayed at a distance of 101,000 km (63,000 mi) from Uranus. Its studies shed light on the planet’s nine-ring system and its very diverse satellites, Miranda, Ariel, Umbriel, Titania, and Oberon. After leaving Earth in 1977, Voyager-II arrived at Saturn in August 1981 before continuing on to Uranus. They got to Neptune on August 25th, 1989. After that, it left the solar system and continued its orbit. As of now, communication is still going on.
The shuttle Challenger exploded on January 28th, 1986
The American space shuttle “Challenger” disintegrated into fragments 1 minute and 13 seconds after liftoff at 11:38 a.m. There were witnesses to the accident at Cape Canaveral, and millions more saw it on television. Sadly, the Challenger’s seven astronauts—including two women—were all killed in the blast. According to NASA’s study, the disaster was caused by the joint of one of the auxiliary thrusters breaking.
The Russian space station Mir was launched on February 20th, 1986
The core of the Russian space station Mir (which means “Peace”) was launched into orbit by a Proton rocket at a height of 350 kilometers. The 2.20-meter-diameter sphere weighed 21 tons. As of then, it was only waiting for modules to be connected to it. On March 13, 1986, humanity’s first mission to the “Mir” was launched. But the equipment obsolescence and the station’s prohibitive cost to maintain led to its demolition in 2001.
The planet Venus was discovered on May 4, 1989
The U.S. scientific exploration of Venus was assisted by the shuttle Atlantis, which propelled the American Magellan probe. Almost a year after it was sent into orbit, it was the first to provide a detailed map of Earth’s surface. After two years, it offered a map of 98% of the Earth using its radar to highlight the various volcanoes throughout the globe. Before it was destroyed in Venus’s atmosphere in 1994, the probe was used to explore the planet’s gravity. Learning about Venus’s geology and drawing parallels to our own planet was made possible by the Magellan expedition.
On April 24, 1990, the Hubble Space Telescope was sent into space
As a tribute to the late scientist Edwin Hubble, the space shuttle Discovery launched a telescope bearing his name into deep space. The first photographs that were sent to the scientists were a huge letdown. The primary mirror of the orbital telescope was flawed, resulting in very low picture quality.
In 1993, a crew of astronomers on the shuttle Endeavour were hopefully able to fix this flaw and make the system even better. There would be a series of subsequent missions to repair and upgrade this powerful orbiting observatory. Important findings made possible by these missions improve our understanding of how the cosmos works.
On August 28, 1993, Galileo discovered an asteroid with a moon orbiting it
On its approach to Jupiter, the American spacecraft Galileo found the first moon of an asteroid. A small satellite, just one kilometer in diameter, orbits the asteroid at a distance of around 100 kilometers from the surface. The asteroid measures 58 kilometers in length and 23 kilometers in width. Dactyl is a reference to a Greek god who ruled over Mount Ida.
On March 14, 1995, a Russian space shuttle carried an American astronaut
From Russia’s Baikonur spaceport first thing in the morning, astronaut Norman Earl Thagard takes off on the Soyuz TM-21 “Hurricane” rocket. For the first time ever, an American has flown on a Russian space mission. It is Thagart’s and his crewmates’ hope to make it to the Mir space station. Following 115 days in space, they have returned to Earth.
June 29, 1995: Assembly of Mir and Atlantis
Atlantis, a shuttle from the United States, arrived at the Russian space station Mir twenty years after Apollo and Soyuz first met. 395 kilometers above the ground, Vladimir Dezhurov and Robert Hoot Gibson did a handshake in a moment that went down in history. A total of ten astronauts share the spaceship until July 4 of the same year. The launch of international space cooperation and the building of a shared station called Alpha began with this gathering.
Incident at the Mir Space Station on June 25th, 1997
The Progress supply ship and the Russian space station Mir, whose core component was launched in February 1986, have been involved in a collision. Two Russians and an American astronaut work together to plug the leak and restore power. Due to the station’s many problems and the exorbitant expense of keeping it operational, the Russians made the decision to blow it up in March of 2001.
October 29, 1998: John Glenn returns to service
To begin a new mission aboard the shuttle Discovery, the 77-year-old man who was the first American in space in February 1962 prepared to lift off. He carried out experiments on the effects of ageing in space. After 9 days and 134 orbits around the Earth, John Glenn returned.
The Columbia space shuttle exploded on February 1, 2003
After 16 days in orbit, the shuttle Columbia was lost from NASA’s radar when it re-entered Earth’s atmosphere. Over Dallas, there are white streaks in the sky. There were seven fatalities; six Americans and an Israeli astronaut. A flaw in the heat shield has been discovered after extensive testing.
Launch of the Spitzer Space Telescope, 25 August 2003
NASA has launched its biggest infrared space telescope into orbit. The American astronomer who inspired its name is Albert Spitzer. Because of its superior sensitivity to infrared light, it can identify objects in the furthest reaches of the universe. Since infrared light cannot reach ground-based telescopes due to Earth’s atmosphere, it was crucial to launch such equipment into space.
The IRAS and ISO satellites were also able to examine star formation since they were launched before it. In fact, after stars are produced, they stay in a cloud state where they are completely hidden from view. Infrared radiation, however, may be used to pinpoint their location.
On October 15, 2003, China successfully launched its first cosmonaut
Yang Liwei, also known as a taikonaut, became the first Chinese cosmonaut after a 21-hour mission. After completing fourteen orbits of the planet, the Shenzhou V spacecraft returns to Earth and makes an emergency landing in a large Chinese plain. Forty years after the Soviet Union and the United States, China joins their ranks as the third nation with access to outer space.
July 1, 2004: Exploration of Saturn
Finally, the Cassini-Huygens spacecraft arrived at Saturn. Since its 1997 launch, it had traveled a long way to reach its current orbit, and during that time it had supplied some valuable data, especially on Jupiter. The probe’s objective was to learn more about Saturn and its surroundings by analyzing its rings, moons, and other features.
Cassini, which investigated Saturn and its moons, and Huygens, which examined Titan’s atmosphere, made up the spacecraft. Two modules broke apart in December 2004. On January 14, 2005, as scheduled, the Huygens module entered Titan’s atmosphere at a depth of 65,000 km as Cassini drew near. By the end of 2008, the mission was complete.
On July 4, 2005, the Deep Impact spacecraft collided with the Tempel 1 asteroid
A month after its launch in January, NASA’s Deep Impact space mission successfully impacted comet Tempel 1 at a speed of 37,000 kilometers per hour, as predicted. This results in a massive crater and a cloud of dust. The Deep Impact probe’s goal is to study the comet’s interior composition by analyzing the ejected debris, crater surface, and impact results. Researchers are hoping to fill in some gaps in their understanding of how our solar system came to be.
Titan was first seen by the Huygens spacecraft on January 14, 2005
In 1997, NASA launched the Cassini-Huygens spacecraft into space. The mission’s goal was to investigate Saturn and its moons. The Cassini orbiter has resumed its survey of Saturn’s moons while the Huygens probe has touched down on Titan. The mission, which had already been extended twice due to its overwhelming success, finally ended in 2017.
The last Space Shuttle launch occurred on July 8, 2011
The US’s Atlantis was the last space shuttle to launch to the ISS. Once the shuttles retired, conventional launchers were to take their place.
On November 12th, 2014, a probe touched down on the comet’s surface
Using the comet 67P/Churyumov-Gerasimenko as a target, the European space probe Rosetta deployed a miniature lander called Philae on the comet’s surface. It studied the comet’s structure and soil composition. The Ariane 5 rocket successfully launched Rosetta in 2004.
The New Horizons mission flew past Pluto on July 14, 2015
The American spacecraft New Horizons was launched in 2006 to investigate Pluto and its satellites. In 2015, it completed its mission and moved on to investigate other planets in our solar system.
The first lunar landing on the Moon’s dark side occurred on January 3, 2019
The Chinese spacecraft Chang’e 4, which was launched on December 7th, 2018, completed an orbit of the Moon on December 13th. The Chinese lander landed on the far side of the Moon on January 3, 2019. The Yutu 2 rover was dropped off to study this part of the Moon.
May 30, 2020: First manned space flight by a private company
Elon Musk’s SpaceX is the first private business to be contracted by NASA to transport humans to the International Space Station (ISS). Bob Behnken and Doug Hurley, the mission’s protagonists, used SpaceX’s Falcon 9 rocket to successfully lift off. The Dragon V2 (or Crew Dragon) capsule separated from the rocket’s first stage and continued on its way to the ISS. U.S. President Trump was there at the Kennedy Space Center in Florida to see the launch.
When oxygen was synthesized on Mars on April 20, 2021
As part of NASA’s Mars exploration program, the Perseverance rover successfully converted carbon dioxide into oxygen on April 20, 2021. This marks a first in the annals of space exploration: the creation of oxygen on a distant world.
The CO samples collected from Mars’s atmosphere, (which is 96% carbon dioxide) made this procedure feasible. Five grams of oxygen were produced during the reaction, which was enough for an average person to breathe for around ten minutes and make tiny amounts of rocket fuel.
The Ariane 5 rocket carrying the James Webb Space Telescope lifted off from Kourou. A space telescope of this magnitude has never been attempted before. It was a joint effort between NASA, the European Space Agency, and the Canadian Space Agency that resulted in the James Webb Space Telescope.
Was NASA on the Moon? Of course, most people — including myself — will respond in that manner. However, some critics question if Apollo 11 really landed on the Moon. We provide reasons why the “Moon hoax” idea is false. The theory of a “Moon landing conspiracy” has been popular since a 2001 documentary aired on the American television channel Fox TV. It claims that NASA manufactured the whole event for media impact in an effort to persuade the Russians and the rest of the world at the same time of their dominance in space. The photographs and video recordings made by the astronauts are allegedly full of proof of this fraud, according to skeptics supporting this hoax. But how credible is the whole argument?
Is the whole Moon landing just fake?
Even though the Moon landing remains one of the most impressive and successful feats in the history of human spaceflight, this very fact has been called into question more and more recently.
A “documentary” and its consequences
In a reenacted environment, Neil Armstrong and Buzz Aldrin practiced the lunar landing. Credit: NASA.
The program “Conspiracy Theory: Did We Land on the Moon” that was shown on February 15, 2001, by the American television network Fox-TV served as both the catalyst and the culmination of the campaign started by certain “skeptics.” In it, self-proclaimed experts attempt to demonstrate that the Moon landing could not have occurred and that all images and media stories are consequently faked based on supposed faults and hints in NASA photographs and interviews.
The creators of the idea claim that NASA simply lacked the technological capacity to carry out such a landing in the 1960s. The whole event was just fabricated in order to win the “race to the Moon”; Hollywood had plenty of acceptable backgrounds.
Contradictory evidence is abounding
View of the Eagle lander that has just been detached from the command module. Credit: NASA and KSC.
NASA and independent astronomers responded to the claims and categorically and unambiguously denied the purported “proof” before the episode ever aired. The majority of critics’ claims were just the result of poor research or ignorance of the lunar surface’s basic characteristics.
For instance, Bill Kaysing, one of the most persuasive proponents of a lunar landing conspiracy, said that NASA scientists had estimated the likelihood of a successful lunar landing at 0.017 percent, making it improbable that the project would really be implemented. However, even though these estimates could have been popular during the early stages of the Apollo program, various analyses carried out in the middle of the 1960s anticipated a success rate of at least 90%. Kaysing, of course, keeps this information private.
Persistent and long-lasting
Unmistakable evidence: The lowest portion of the Apollo 11 lander is still in place on the Moon. The Lunar Reconnaissance Orbiter spacecraft captured this in 2009. Credit: NASA
However, despite the evident ridiculousness of their claims, the “skeptics” were still able to unnerve at least some of the American public, which did not lessen the effectiveness of the “conspiracy theory.” The “Moon Hoax” theme persisted, especially in the USA, where more and more books and websites about it were produced.
These notions, which had long ago been disproven as illogical, were even spread in Europe, where they are genuinely taken seriously. The media businesses acquired the “documentary” from Fox and aired it on their networks many times, unmodified and often without any commentary.
The issue was ultimately brought up in court in the USA, where Bill Kaysing even charged NASA with purposefully causing the Apollo 1 catastrophe in an effort to silence any dissidents inside its own ranks. Jim Lovell, the commander of the Apollo 13 mission, was outraged by these ridiculous claims and referred to Kaysing as a maniac; Kaysing then filed a defamation suit against Lovell. But the presiding judge decided not to hear the case after the first hearing of the evidence.
Shadows and starry skies
The “indications” of a forgery put forward in the Fox documentary and the books of the “moon landing skeptics” can, in principle, be summarized as a handful of phenomena. Here, we’ve laid out the most important arguments for and against the Moon landing conspiracy theories.
The direction, duration, and form of the shadows in the NASA astronaut images are among the pillars of the doubters’ case. Kaysing argued that the pictures had to have been shot in a studio rather than on the Moon.
Shadow direction argument
These rock crystals have a crystal character that is easily discernible, however, this is not true of all of them. Credit: Ngsoft/pixabay
The shadows cast by various items and individuals on the surface of the Moon do not run parallel in the photos, and their lengths vary. The shadows of both astronauts seem to be leaning toward one another in the photo of Armstrong and Aldrin hoisting the American flag, and Aldrin’s shadow is also longer. Skeptics claim that this is a blatant indication that the “studio” employed various light sources.
Answer: This argument fails to take into account fundamental principles of perspective and vanishing point distortion. Every time parallel lines are shown in a picture, a photograph, or other two-dimensional media, they seem to converge on a three-dimensional surface. This idea may also be seen in action on Earth, such as while seeing a road heading in its direction.
The shadows of Aldrin and Armstrong are similarly distorted. The fact that the ground is not level but somewhat undulating accounts for the variations in the length of the shadows. A slope visually shortens a shadow on a sloping plane while optically lengthening it. There is a tiny drop between where Armstrong is standing and the modest elevation in front of him.
Each rise would have had numerous shadows if the photos had really been shot in a studio with various light sources; this effect may be seen, for instance, at a soccer stadium when a game is played under floodlights: Each player is encircled by four shadows.
Shadow depth argument
On the lunar surface, Buzz Aldrin exits the lunar lander. Credit: NASA and KSC
Why are the places that are under darkness still so brilliant if there is actually just one source of light, the sun, and no air to disperse the light? While Aldrin departs the LEM, for instance, why is he so easily visible when the ladder ought to be in deep shadow?
In response, this reasoning fails to take into account the fact that the lunar surface is extremely reflective due to its brightness and abundant microglass. As a result, it bounces the sunlight that strikes it back in its direction, illuminating the shadows.
Starry sky argument
This picture of the ISS space station also doesn’t show any stars. Credit: NASA
None of the NASA photos show any stars in the sky. But they ought to be present.
Answer: Although the skeptics’ main argument is the simplest to disprove, it is often raised. The photographic method is to blame for the alleged absence of stars: On the sun-lit, dazzling surface of the Moon, the astronauts recorded the happenings. They had to choose a short exposure time and a narrow aperture in order to make sure that these photographs weren’t overexposed. The stars, which were just extremely dim in comparison to the high-reflecting surface, were simply too faint for this exposure period.
Other conspiracy theories
Aldrin is seen next to the US flag. Credit: NASA and KSC
Waving flag argument
The American flag is another long-time favorite of conspiracy theorists: In certain TV scenes, the flag seems to be blown by a breeze or wind, and in photographs at least, it still exhibits unmistakable waves. However, because the Moon has no atmosphere, there is no wind.
Answer: If one carefully examines the TV records, they reveal that the flag only waves when a straight astronaut positions himself at its stalk. The vibrations produced by slamming the stem into the lunar surface are longer lasting than they would be on Earth because of the absence of an atmosphere.
The alleged ripples in the still photographs are not caused by the flag moving in waves, but rather by a setup error: The astronauts were unable to completely extend the pole that distributes the top of the flag widely, causing the flag fabric to hang down in folds rather than being taut. Later, NASA was so taken with the “natural” appearance of this folding that the crossbar was purposefully cut shorter on all following Apollo flights.
Moon dust argument
The time Aldrin spent on the surface was brief. Credit: NASA and KSC
Although the “Eagle’s” touchdown created dust, the landing module’s foot pads are absolutely dust-free.
Answer: Because the Moon lacks an atmosphere, there is also no drag, which on Earth causes the whirled-up dust to hover for a very long period until it ultimately settles. On the Moon, the dust does not go far before falling back to Earth in a ballistic arc. As a result, the landing’s dust was blown away from the module and did not physically rest on the lander’s feet.
Footprints argument
The lunar rovers’ tracks and the astronauts’ footprints are both very distinct and crisply detailed. But without water, dust is unable to leave these traces.
Yes, it is true. if the dust has very few grains. This is also conceivable with Moon dust, just as an impression is plainly discernible even in perfectly dry flour.
Backgrounds and crosshairs
Many different things can be argued about when it comes to photography techniques and hints of supposed retouching.
Crosshairs argument
In order to make it easier to determine the magnitude of the things being shot in the future, crosshairs were included in the cameras’ design. But how else can this be explained, if not by shoddy post-processing, since in some images the crosshairs are hidden by items in the frame?
On the one hand, cameras with crosshairs might have been utilized in research right away, thus, even a hoax wouldn’t have required a second application of such crosshairs.
Second, these occlusions seem to always occur when a crosshair is close to a starkly white or brilliant item. Printers and photographers are aware of the “bleeding” effect: The thin black line seems to vanish because the white region is brighter than the black area on the film material. Using a camera, one may easily recreate this phenomenon on Earth.
Identical backgrounds
The same background, the mountains, and their placement appear in two NASA footages that were supposedly filmed three days and a few miles apart. Was this scene perhaps staged using a studio background? Similar patterns may be seen in two photographs, where the landing module is sometimes visible in the foreground and other times it is not.
Answer: The first “argument” once again stems from the filmmakers’ shoddy research: They did not directly copy both segments from NASA, but rather from another documentary where it was wrongly claimed that they were both filmed three days apart. This error may have been resolved with a quick NASA study. The sequences were captured during a lunar outing at roughly the same location and three minutes apart, as the astronauts’ accompanying voice remarks further demonstrate.
On the other hand, physical effects are the reason the landing module seems to be “missing” in the pictures: Since the Moon lacks an atmosphere, it also lacks a feature that allows humans to estimate distances on Earth—the blurring of landforms or objects as they get closer to the viewer. Even if a shot is taken a few meters in front of the lander and another a few meters behind it, the mountains in the distance that seem to be so near are really kilometers distant and consequently scarcely alter.
Micrometeorites, radiation, and weak computers
Voyager 1 is now traveling across interstellar space after leaving our solar system. Credit: NASA/ESA, G. Bacon (STScI)
Was the Apollo mission technically possible?
The onboard computer of the Apollo lander module was incapable of controlling the lunar landing and had less processing capability than the microprocessor in a contemporary washing machine. Even the construction of such a compact but capable onboard computer was not possible in the 1960s due to the lack of computer technology.
Answer: While there were no current microprocessors in use in the 1960s, there were microchips that could do basic arithmetic calculations. Supercomputers on the ground handled a large portion of the intricate calculations required for navigation. A modest memory was adequate to temporarily retain the outcomes of the ground computations for the remainder of the navigation, leaving just a very small portion of the navigation to be handled by the onboard computer.
Radiation argument
Lunar landscape as seen via the lander Eagle’s window. Credit: NASA and KSC.
The Van Allen radiation band surrounding Earth, in particular, exposed the Apollo missions to lethal radiation without any safeguards. According to Kaysing, if the astronauts had really gone to the Moon, the radiation would have been so intense that they would have either died from radiation poisoning or suffered serious radiation damage.
The Apollo astronauts needed nearly an hour to get through the Van Allen belt, in response. The dosimeters indicate that they got a radiation dosage of roughly one SEM during the procedure.
Only at levels of 100 and more than 300 SEM may radiation illness or even death occurs.
However, if a solar storm had happened while the journey was in progress, the cosmic radiation would have considerably risen. But happily, for NASA and the crew, there were no significant radiation bursts or plasma ejections throughout the lunar trip since the sun stayed quiet.
Meteorites argument
Inadequate shielding prevented the spacecraft from withstanding the continual barrage of micrometeorites. Therefore, if the spacecraft had really been launched, thousands of holes would have been carried away.
Answer: Despite having a relatively little mass, micrometeorites are quite quick. Therefore, they may be stopped by even a small covering of metal. Such micrometeorite defense layers were included in both the spacecraft and the crew’s spacesuits.
Conclusion
The actions of the Moon landing deniers are terrifying in two ways: In addition to the space that such theories obtain in the media without response, numerous comparable Internet sites and book releases make pseudoscientific claims that mostly avoid debate.
Even while the documentary’s creators instruct the audience to “make up your own opinion based on all the facts” at the outset, the spectator regrettably does not obtain this precise information throughout the program. The purportedly damning images or video clips are often shown and discussed.
The arguments put forward by NASA or other objective astronomers, as outlined below, do not, however, find much room. When compared to the in-depth interviews with doubters, the remarks of NASA officials are at most brief, noncommittal, and dismissive, which must create the impression that NASA has nothing to really contradict or may even have something to conceal.
In reality, NASA doesn’t generally reply to many charges since it doesn’t have to because it doesn’t take the doubters seriously. Because the plethora of images, videos, and background information that the space agency has provided online, among other things, speaks a language that is really adequately clear and disproves many arguments on its own.
Dissemination without reflection
Nevertheless, people who see such material without a lot of background information might sometimes get confused. especially when it is broadcast on apparently legitimate TV channels. The viewers’ confidence is exploited to provide a platform to a loud but doubtful minority.
The Apollo astronauts were on the Moon, and the “Eagle” truly landed. Certainly, one may debate the wisdom or folly of human space flight, particularly the Moon landing, but at least this fact is undeniable among the worldwide scientific community.
50 years ago, in December 1968, mankind made history by going outside of Earth’s low orbit for the first time and reach an extraterrestrial body. The Apollo 8 crew became the first humans to orbit the Moon, allowing them to glimpse Earthrise over the lunar terrain and see the far side of our satellite for the first time. NASA began a historic and exceedingly risky mission on December 21, 1968. Astronauts left the protective confines of Earth’s orbit for the first time and explored the immensity of space. And the first Moon landing in July of 1969 was made possible by the Apollo 8 mission to the Moon.
Fifty years after its completion, the Apollo 8 mission remains a thrilling chapter in the human exploration of space.
Competition: Moon
Bankruptcies, bad luck, and unfortunate events
At first, NASA intended Apollo 8 to be a pretty routine test trip in Earth orbit, during which they would put the new lunar module through its paces. After all, this was the deciding factor in whether or not a lunar landing would be possible.
Accidents keep piling up
The Apollo lunar module during a test in Earth’s orbit – it was not ready in time for Apollo 8. Credit: NASA.
However, in the summer of 1968, everything changed. The Grumman Corporation’s design for NASA’s landing module was incomplete at first, and then problems started piling up: cables were connected improperly or caused short circuits, components were broken, and the nozzles that were meant to lift the module off the lunar surface didn’t work. In a short amount of time, it became apparent that the module would not be completed in time for the December launch of Apollo 8.
The Saturn V’s progress has been discouraging as well; it’s the only rocket capable of lifting the lunar module, the command capsule, and three astronauts into orbit. In April of 1968, during a second unmanned test, the rocket began vibrating so strongly that it ruptured several of the cables. Consequently, two of the rocket’s five engines go out prematurely, and the craft just barely reaches orbit. Then, the failure occurs during the third and final firing stage of the lunar mission. The signs for Saturn V’s human missions are not good.
Take on the Soviets in a race
U.S. space officials are also concerned that the Soviet Union is close to launching the country’s first human mission to the Moon. In September of 1968, the unmanned spacecraft Zond 5 completed its first orbit of the Moon. Soviet engineers have begun designing and testing a rocket designed for human trips called the Soyuz. There are hints that a cosmonaut may be doing a test journey toward the Moon soon.
NASA is now under significant time constraints. As far as we can tell, the Soviet Union is much ahead of the United States in the space race. They sent the first satellite into orbit with Sputnik, and cosmonaut Yuri Gargarin went into space before any American astronaut. This is a humiliating setback for the United States, which likes to see itself as the leader of the free world. Consequently, the race to the Moon must be won at whatever cost.
Is Kennedy’s programme tipping?
US President John F. Kennedy at Rice University Stadium in Houston during his famous “Moon Speech”.
It is also crucial to fulfilling John F. Kennedy’s pledge. In a speech delivered in Texas in September 1962, Kennedy said that a human would walk on the Moon before the end of the decade. “We choose to go to the Moon in this decade and do the other things, not because they are easy, but because they are hard.” Since then, NASA and its subcontractors have devoted massive resources to meeting this deadline, creating space capsules, docking methods, and rockets at breakneck speed and putting them through their paces in both human and unmanned trips around Earth.
However, by the summer of 1968, the whole Apollo program was in danger of being delayed. Despite all this, would the Soviets end up being ahead of the Americans?
How Apollo 8 became a lunar mission
Originally planned for Apollo 9, but then preferred to Apollo 8: James Lovell, William Anders and Frank Borman.
Time to make a decision
On this day in 1968, Apollo 9’s soon-to-be commander, Frank Borman, is in California running the ship’s Command Module through its last testing. This former Air Force pilot is no stranger to space travel; in 1965, he and James Lovell spent two weeks in a Gemini spacecraft orbiting the Earth. They plan to return to Earth orbit in early 1969 with a third guy, space rookie William Anders.
An insane scheme
The problem is that NASA officials in Houston have just canceled Borman’s scheduled trip, and he has no idea about it. Since the lunar module will not be completed in time for the December trip, a choice must be made. The Americans asked “Should we risk having the Soviets beat us to the Moon and missing Kennedy’s objective by delaying Apollo 8 and all following flights?” Or do you take an unusual risk even for the still young NASA?
As a NASA engineer, George Low has a seemingly insane plan: Apollo 8 should be launched without the landing module, bypassing Earth orbit entirely and heading straight for the Moon. The spaceship would next enter a lunar orbit and begin circling the Moon. The rationale for this is that while waiting for the lunar module, the crew could practice the required flying maneuvers. These are still simply conceptual at this point, existing solely on paper and in the thoughts of engineers. It’s also uncharted terrain for space travelers to establish contact with one another across such vast distances. A lunar orbit with Apollo 8 would offer the chance to test all this – and to beat the Soviets.
“Have you gone mad?”
Credit: NASA
But are astronauts and technology up to the task? Low keeps NASA Director James Webb in the dark about the Apollo team’s preparations for launch by having them surreptitiously figure out the required course adjustments and maneuvers and inspect the state of the rocket and space capsules. They conclude that by December 1968, the Apollo 8 spacecraft would have had advanced enough technology to make a trip to the Moon and even a spin into lunar orbit.
Now, all that remains is to persuade NASA’s upper management to go along with this strategy. As for Low’s relationship with Thomas Paine, the deputy director, there are no major issues. James Webb, who is now in Europe for a conference, may be an exception. Those that answer Paine’s appeal are less than enthusiastic. According to Andrew Chaikin’s “A Man on the Moon,” “Webb shouted down the transatlantic telephone line: ‘Have you gone mad?’”
To be fair, Webb is not completely incorrect. The strategy makes sense and is technically possible, but it’s also very dangerous. In the event of a problem with the command module, the astronauts would be stranded in space without the Lunar Module to rescue them. And not a single Apollo module had ever been crew-tested; suddenly they were all set to go for the Moon.
This makes it official
In spite of these worries, a middle ground was found: In a news conference held on August 19, 1968, NASA revealed that the Apollo 8 mission would proceed without the lunar module and with a new crew consisting of Borman, Lovell, and Anders. It seems highly probable that the two veteran Gemini astronauts will be able to complete this challenging first voyage.
Where the flight will go, however, NASA initially leaves in the dark. After all, the Soviet Union must not be given advance notice. The first human flight of an Apollo shuttle, Apollo 7, took place in October 1968, and it was then, the mission profile of Apollo 8 was finally decided. The test flight of Apollo 7 was a success, with the Saturn 1B rocket successfully lifting the command capsule into orbit and the propulsion nozzles on the capsule working as expected.
It’s finally time for Apollo 8, the first manned mission to the Moon.
First humans to orbit Moon
Goodbye, planet Earth
It’s the morning of the Apollo 8 launch, December 21, 1968. The Saturn V rocket, assembled on Launch Pad 39A at NASA’s Kennedy Space Center, soars into the sky. This 110-meter-tall monster is the most powerful rocket ever constructed. This, however, is the day when the Saturn V is put to the ultimate test, as astronauts will be placing their lives in the rocket’s hands for the first time.
The launch
Saturn V, Apollo 8 launch.
The Saturn V’s fuel tanks were refilled with liquid oxygen, kerosene, and liquid hydrogen for many hours the night before. Frank Borman, James Lovell, and William Anders, all astronauts, entered the spaceship at roughly five o’clock that morning. The astronauts must now put their faith in the rocket and the Apollo capsule’s onboard computer, both of which are quite rudimentary in comparison to what we have today.
The Saturn V’s engines start roaring to life at 7:51 a.m. local time. Even at a distance of 10 kilometers, the launch’s noise and vibrations are powerful enough to break the glass. The first combustion stage consumes 20 tons of fuel per second, or over two million liters, in only 2.5 minutes of operation as the rocket slowly, almost reluctantly, lifts off the ground.
However, the rocket’s force can only lift the space capsule 65 kilometers into the air. Then the five engines of the rocket’s second stage take over, followed by the third stage’s thrusters. The latter is what propels the Apollo spacecraft (composed of a command capsule and a service module) into low Earth orbit, at an altitude of around 190 kilometers.
Destination: the Moon
Since Apollo 7 and numerous Gemini flights have already reached Earth orbit, the three Apollo astronauts have not yet mapped out any new terrain. It takes Borman, Lovell, and Anders two orbits around the planet to double-check everything. The next step is to relight the third rocket stage, which will propel the spacecraft out of Earth’s orbit and onto the Moon.
It’s a critical time; if the burn stage’s ignition fails now, the lunar mission will be a failure, and the astronauts will stay in orbit. A mistimed or delayed ignition may throw a spaceship off track. But all goes according to plan, and two hours, 47 minutes, and 37 seconds after liftoff, the Apollo capsule is propelled by its engines and begins a steady, gradual acceleration away from the gravitational pull of Earth. The engines were turned off for the last time at 5 minutes and 18 seconds, putting Apollo 8 on a direct track to the Moon.
Approaching to the Moon
The historical moment
One of the first images of the Earth from outside the Earth’s orbit taken from Apollo 8.
It’s a big deal: Apollo astronauts Borman, Lovell, and Anders became the first people to ever gaze upon Earth from space. As their ship speeds away from the planet, Earth becomes a tiny blue dot on the command module’s display.
In one of the first space TV broadcasts, astronauts attempt to describe this incredible scene to viewers on Earth. The clouds that float above the Earth and are described by them as white bands and swirls also seem to be the color scheme they use to represent the planet itself. Jim Lovell told Anders, “Mike, here’s what I can’t stop imagining: I’m a lone space traveler from another planet, looking down at Earth for the first time. Whether or not I would assume there were people living there.”
Drawn to the Moon by its gravity
View over Mare Tranquillitatis, taken from Apollo 8.
A few times later, the astronauts pass another significant milestone as their spaceship exits the gravitational pull of Earth and enters the Moon’s gravitational field. It’s the first time that humans have made it this far. At this point, 326,400 km from Earth and 62,000 km from the Moon, the astronauts, and their spaceship are being drawn toward it. Therefore, Apollo 8’s speed in flight keeps increasing.
On their way to the Moon, the astronauts won’t be able to view it since the Moon would be right in front of them and the command module’s side windows are too tiny. Since they have no way of knowing whether or not the path is true or whether or not their flight is being tracked by the ground station, they have no choice but to trust on faith alone. The United States, Canada, Mexico, Australia, and a number of ships in the Indian and Pacific Oceans all contribute to this effort.
Here, on the Moon’s dark side
Apollo 8, Frank Borman, during an orbit around the Moon.
The Apollo 8 crew reached the Moon early on December 24, 1968. But now they must do a tricky maneuver: they must slow down Apollo’s trajectory and swing it into lunar orbit. To slow down enough, they run the engines in reverse for around four minutes.
The challenge is that this ignition has to occur on the far side of the Moon when radio communication with Earth is down. At this point, not even NASA’s ground personnel can assist the astronauts. As an added safety measure, the spacecraft stays on the dark side of Earth’s satellite until just before the last braking maneuver. As a result, the astronauts are essentially flying blind. However, everything goes well, and Apollo 8’s engines bring its speed to slightly under 6,000 kilometers per hour. With its current velocity, the spacecraft can be captured by the Moon’s gravity and guided into orbit.
After a long and perilous journey, the three Apollo astronauts arrived…
Borman, Lovell, and Anders’ primary focus now that they are in lunar orbit is to observe and photographically map the lunar surface. They are the first people to observe the Moon’s dark side and the closest humans have ever been to the Moon’s surface, at a distance of around 100 kilometers.
At first, Jim Lovell tries to relay his thoughts about the lunar surface to mission control: “Almost entirely devoid of hue, the Moon is a uniform gray. It resembles plaster or slightly grey beach sand. There is a great deal of specificity in view. All of the craters are circular in shape. Numerous examples exist, including some that occurred quite recently. It seems that meteorites or other projectiles may have damaged several of them, particularly the spherical ones.”
Unfortunately, Earth’s satellite is, on the whole, a very underwhelming sight. The landscape is flat and gloomy, with no striking landmarks such as mountains or canyons. Quite differently from how Stanley Kubrick’s soon-to-be-released film, “2001: A Space Odyssey,” portrayed it.
Making of a legendary photograph
Anders peered out the window during the third orbit and beheld a scene that has never been seen before: Earth rising over the drab lunar surface, bathed in blue light. “Oh my God, look at that sight, too!” he cries. Borman, who is busily rotating the Apollo spacecraft, gasps in surprise. The Earth is rising!” exclaims Anders.
Anders quickly swaps the black-and-white film in his camera for color so he may record the majesty of the Earth as it rises. Yes, it does work. Apollo 8’s “Earthrise” remains one of the world’s most iconic photographs. Anders later reflects, “It was the most gorgeous one I had ever seen — and absolutely unexpected.” While in lunar orbit, I had a revelation: “The most fascinating part of the voyage was viewing Earth from the Moon.”
Inspirational Christmas message
In the Christmas Eve live TV broadcast the astronauts transmit to Earth, Jim Lovell gives a similar account: “It’s terrible to be so far from civilization on the Moon’s surface. A sense of gratitude for Earth and everything we have here is sparked. From this vantage point, Earth seems like a magnificent paradise in the middle of empty space.” In the minutes that follow, the astronauts elaborate more on their first reactions to the lunar surface and the way that sunlight and shadows interact with the otherwise featureless landscape.
The three men on board the Apollo spacecraft then begin the ritualistic end to their live broadcast as they near the day-night limit of Earth’s satellite “The Moon dawn is rapidly coming. Finally, the Apollo 8 crew would want to relay a message to everyone back on Earth,” Anders says. Then he jumps into the opening of the biblical account of creation: “God created the universe and everything in it in the beginning. And all the land was barren and empty, and there was night over all the oceans. When God commanded, “Let there be light,” the Holy Spirit dove into the ocean. And finally, the Sun came out. Then God decided the light was good and built a barrier between it and the darkness.”
The reading from the account of creation is then continued by Lovell and Borman. And from the crew of Apollo 8: “We finish now with a good night, good luck, Merry Christmas, and God bless you all — all of you on the good Earth,” Borman says at the end of the 29-minute transmission. From the orbit of an extraterrestrial celestial body, a billion people across the planet may see and hear this Christmas greeting.
Let’s go down to Earth
Tension-filled seconds after the Moon
The crew of Apollo 8 gets ready to return to Earth while the rest of humanity sleeps in on Christmas Day, 1968. As the spacecraft completes its tenth and last lunar orbit, another critical maneuver—the spacecraft’s acceleration—is quickly approaching.
As we bid farewell to Earth’s satellite
View into the control center of the Apollo missions – here at Apollo 9.
This move must likewise be carried out on the far side of the Moon, away from Earth, leaving Borman, Lovell, and Anders to fend for themselves once again. Apollo 8’s engines fired just after midnight on December 25. After roughly three minutes, the spacecraft had gained enough speed to break free of the Moon’s gravitational influence.
Meanwhile, down at NASA’s Houston control center, everyone is on edge as they wait for Apollo’s first sign of life after the radio silence. In order for Apollo 8 to successfully return to Earth, radio contact must be established at the precise moment planned in advance.
After departing lunar orbit, the astronauts return to Earth’s protective zone eleven hours later. Their ship is suddenly being drawn to Earth at a frantic rate. The crew and spacecraft won’t face their next challenge until they re-enter Earth’s atmosphere.
The Apollo astronauts had already jettisoned the service module, at a distance of fewer than 3,000 kilometers from Earth’s surface, not long before. The control capsule is the only one still heading home. If the capsule malfunctions and crashes into Earth’s atmosphere, for example, all three astronauts would be killed. The oxygen and power in the capsule will run out just before the touchdown.
The Apollo spacecraft slows down as it hits the gas shell of Earth’s upper atmosphere at a height of 122 kilometers. When the capsule’s heat shield reaches 2,800 degrees Fahrenheit, it generates an ionized plasma. From outside, the astronauts notice a dazzling light that they initially think to be dawn.
Apollo 8 lands back on Earth
After landing on December 27, 1968: Apollo capsule aboard the USS Yorktown.
Forces of up to six grams are exerted on Borman, Lovell, and Anders as the Apollo spacecraft flies through the atmosphere, its bright heat shield illuminating the night sky. They say that after almost a week in zero gravity, they feel like an elephant is resting on their chest.
Fortunately, this stress doesn’t endure forever; the braking parachutes deploy and the capsule slows to subsonic speeds before long. Once the final few kilometers are reached, the Apollo spacecraft touches down on the ocean’s surface.
As of 5:51 a.m. EST on December 27 (13:51 GMT), the Apollo astronauts have safely returned to Earth. Their spacecraft crashes into the Pacific Ocean, but it is upside down when it first makes contact with the water. The three of them are being thrashed about by the powerful surf while hanging upside down in their harnesses. However, the capsule righted itself after a few minutes, and the hatch was opened by American combat swimmers. The three Moon explorers return to Earth and take their first deep breaths of sea air after a week of breathing “canned air.”
What Apollo 8 left behind
The Apollo 8 crew not only became the first humans to reach the Moon but also changed the course of space travel forever. Approximately six months after their mission, Apollo 11 successfully landed on the Moon for the first time. The path paved by Borman, Lovell, and Anders was eventually followed by Neil Armstrong, Buzz Aldrin, and Michael Collins. The three men on Apollo 8 captured the first photographs of the lunar surface from such a close range. Therefore, NASA was able to choose an appropriate landing location for Apollo 11.
Apollo 8 was an important stride for humanity since it was the first time humans ventured into deep space, even though it is generally eclipsed and replaced by Apollo 11 nowadays. In addition, the first lunar landing in July 1969 would not have been feasible without Apollo 8.
It’s been decades since humans last visited the Moon, but that could change soon. That’s because several space organizations have recently announced plans to send humans to the Moon, and unlike previous trips, they want to really settle there. The plan is to set up bases on the Moon’s surface and in orbit around it. However, what may these lunar outposts really resemble? Where will they acquire the supplies they need?
Apollo 11‘s first lunar landing was 50 years ago, marking a major milestone in human spaceflight. The next logical step would be to begin lunar colonization. Due to the fact that the Moon still contains valuable resources like helium-3 and rare metals, it also serves as a crucial staging area for missions to Mars and beyond.
Thus, there has been a resurgence in the Moon Race. This time around, material economic and geopolitical objectives are at the forefront, rather than political considerations. Major space powers and private enterprises are developing ideas and technology for future lunar orbits and surface stations.
The long-fictionalized “Moon Base Alpha” is therefore taking on more concrete shape, and may become a reality within the next 20 to 30 years.
Why do we want to go back to the Moon?
Eugene Cernan, Apollo 17 astronaut, with lunar rover – he and Harrison Schmitt were the last men on the Moon in 1972.
New beginnings on the Moon
Humans have only ever stepped foot on the Moon, yet it is the first and only extraterrestrial celestial body we have ever explored. When Apollo 11 landed on the Moon for the first time in July 1969, people all across the globe applauded in response. At the time, many people thought that we would soon have outposts on the Moon and possibly colonies on Mars.
The Moon takes a back seat
But the excitement didn’t last long, and in 1972 the United States government abruptly scrapped the Apollo program once again, after only six landings and a total of twelve astronauts. All three remaining missions were scrapped. After the United States and the Soviet Union won the historic and politically significant race to the Moon, many American leaders, including President Richard Nixon, decided that further space exploration was no longer a priority.
The Moon and its exploration have been put on the back burner since then. Few orbiter probes remain in Earth’s satellite orbit, but the information they provide from afar is invaluable. However, landings have not occurred for decades, not even with unmanned probes. That all changed in 2013 when the Chinese spacecraft Chang’e 3 and the lunar rover Hutu touched down on the Moon for the first time in four decades. The first two unmanned missions to the far side of the Moon—Chang’e 4 and Hutu 2—landed in January 2019. Even still, no one has set foot on the Moon since 1972.
Alluring raw materials
However, in the meanwhile, there is activity once again in terms of lunar missions, as many space agencies and commercial organizations have revealed plans to send people to the Moon in the near future. However, the current objective is a lengthier, and probably even permanent, human presence aboard Earth’s satellite, in contrast to the flying visits of the Apollo missions.
Another deviation from the Apollo period is that the stakes are now material, economic, and technological benefits rather than a race of political systems. One reason to go to the Moon is all the precious metals and minerals it contains, including iridium. Due mostly to meteorite impacts, they have collected in the lunar regolith. Desire may also be sparked by helium-3, an exceptionally uncommon isotope of the noble gas helium. We’ll need it for things like coolants, measuring devices, and potential fusion reactor coolants, and the Moon has just what we need. Several corporations have declared their future plans for “Moon mining.”
The significance of Moon
In addition, the Moon’s strategic value lies in the fact that it might be used as a launching pad for human trips to Mars and beyond due to the much reduced rocket fuel needs afforded by the Moon’s low gravity. Telescopes and other observatories might potentially help boost space exploration efforts from the Moon. This is because, in particular, the far side of the Moon provides complete protection from any terrestrial disturbance.
Finally, the potential for profit from well-heeled space travelers is exciting. Elon Musk, the creator of SpaceX, revealed his company’s first lunar tourist in 2018: Japanese tycoon Yusaku Maezawa, who paid millions of dollars for passage for himself and a large group of friends on SpaceX’s first voyage to the Moon in 2017. In 2023, we want to achieve lunar orbit.
Thus, the Moon is now again a very appealing vacation spot.
Moon Village and Lunar Gateway
The European Space Agency (ESA) is preparing to build a full-scale lunar village that will serve as a research and business hub. Image: ESA
New Moon missions are in the works
When will the world learn the truth about the space countries’ bold new Moon programs? It seemed to be getting serious after 10 years of lofty intentions that never materialized. The United States, the European Union, China, and Russia are all planning missions over the next several years to be ready for the eventual return of humans to the Moon and the eventual establishment of a lunar outpost.
Everyone living in their own “Moon Village”
Jan Wörner, the head of the European Space Agency, proposed the idea of a Moon Village in 2016. This would be a multi-national outpost on Earth’s satellite, available for any and all uses. Her goal is to set up shop on the Moon permanently. Science and fundamental research, economic operations like raw material extraction, and even tourism might all be conducted by participants at this permanent lunar outpost.
Robots and autonomous rovers might launch the first phases of construction for this lunar outpost, with human astronauts joining in later. One major benefit of this plan is that it may be launched with very few resources. A number of nations are currently making preparations to send modest land missions, so that’s where we can begin. Afterwards, bigger initiatives might be built upon that foundation and include worldwide collaboration. As such, the lunar town has the potential to serve as the ISS’s successor, although one that is located on the Moon rather than in Earth’s orbit.
America: We’re here to stay this time
In December 2017, the United States issued a directive making a trip back to the Moon and subsequent trips to Mars a top priority for the American space program. Rather than just leaving our mark this time, we want to lay the groundwork for future exploration of Mars and beyond.
We are taking cutting-edge technology and systems to the Moon in order to study previously inaccessible regions, said NASA Administrator Jim Bridenstine. We want to settle on the Moon this time, unlike Apollo. Our next giant step into space will be taken after that.
Lunar Gateway
In the 2020s, NASA hopes to realize its goal of constructing a lunar “gateway,” or space station in lunar orbit. Because of this gateway, we will be able to establish a strong foothold in cislunar space and more effectively investigate the Moon and its potential benefits. From there, we want to launch manned missions to the lunar surface.
In the same way that the ISS was built in increments, this next orbiting outpost will also be composed of modular components. The parts will be sent into orbit by NASA’s Space Launch System (SLS) and carried there aboard the Orion spacecraft. The core propulsion and supply portion of the station might be placed in lunar orbit really soon. In 2024, astronauts will have access to the first module that doubles as a home and lab. Once that happens, personnel may stay at the station for 30 or 60 days at a time to do their jobs.
Assisted landing by a private party
NASA is hoping to recruit commercial enterprises to help with the trip from the ISS to the Moon’s surface. Six businesses are competing in a tender announced at the end of 2018 under the NextSTEP initiative. The objective is to design a method that can transport, land, and return to the space station from the lunar surface.
In terms of requirements for future landing modules, durability and reusability are high on the list. In contrast to the Apollo lander modules, whose whole underpinnings were left on the Moon and are still there today, future landers will be entirely reusable. After that, they’ll be refueled either on the ground or in space. According to NASA Administrator Jim Bridenstine, we aim to return humans to the lunar surface within the next decade, but this time we want to do it sustainably.
How would a Moon base look like?
The European Space Agency’s (ESA) vision for a Moon base.
Lunar selters made of lava rock and regolith igloos
Those who choose to settle on the Moon in the future will be met with a harsh and perhaps lethal environment. As a matter of fact, the Moon is not exactly a warm and fuzzy location to spend some time. There is no magnetic field, no atmosphere to shield you from the elements, and no oxygen. Those who choose to remain on Earth’s surface are unprotected from the Sun’s radiation, the solar wind, and the meteorite showers. Simultaneously, there are dramatic shifts in temperature: If the Sun is out, everything will get to be around 120 degrees. Temperatures, on the other hand, dip to a chilly minus 170 degrees in the shadow and on starry evenings.
Therefore, the primary function of a lunar base is to offer shelter from these dangerous conditions. I mean, how? Obviously, an inflatable dome like the one seen in “The Martian,” a science fiction novel and film, would not be sufficient for a lunar outpost. A shield from radiation or meteors could not be created with this. Astronauts need sturdy walls in their lunar habitat if they are going to be able to stay there for an extended period of time.
Living and working in lunar lava caves
Lava caverns, which are found naturally on the Moon, might be used as a safe haven. Underground craters and tubes were formed by the Moon’s early volcanic activity. In 2017, scientists found a massive lava tunnel in the lunar Ocean of Storms (Oceanus Procellarum). It stretches for 31 miles (50 km) and is up to 3300 feet in height and width, providing enough room for an entire lunar metropolis. A hole with a diameter of around 165 feet (50 m) provides access to the surface.
Lava caverns near the Moon’s polar area, though, might be an even better fit. This is due to the presence of water ice, which may be used to provide both potable water and fuel for the astronauts. Philolaus crater, an impact crater of 44 miles (70 km) in size at 72 degrees north latitude, has been mapped and explored by scientists, and many spots inside it have been identified as promising candidates. Multiple shadowy crevices on the crater floor suggest the presence of lava caverns.
Moon bricks from the solar oven
We may also use Moon dust to construct the requisite defensive fortifications. DLR (German Aerospace Center) scientists in Cologne are already hard at work on a plan to fire regolith into a Moon block. They are focusing sunlight into a powerful beam using curved mirrors. The thin layer of volcanic grains used as a regolith mimic is heated to temperatures of over 1,000 degrees using this method.
Extreme heat causes the material to sinter, which means the granules adhere together and create a solid layer. Layer by layer, like a 3D printer, solid components may be created from regolith. Already, with today’s technology, we have access to a substance approximately as stable as gypsum. However, with more improvement, lunar regolith might be made into a construction material with the strength of concrete.
However, even with their solar 3D printer, it still takes the team around five hours to manufacture a single regolith building block. It would take around 10,000 of these bricks to create a protective shell around a lunar igloo. Months would pass before it could be accomplished. However, if many sintering plants were to be run in parallel on the lunar surface, the process may be sped up.
3D printing with regolith sludge
Together with the British firm Monolite, ESA researchers are researching an alternative method. First, a slurry is made by combining the regolith mimic with a magnesium oxide solution. This allows the document to be printed out. The business uses a binding salt to turn the substance into a stone-like solid, turning it from a liquid into “ink” for solid creations.
With this technique, the team can print and complete 6.5 feet (2 m) of material in an hour. If the next-generation design can achieve 11.5 feet (3.50 m) per hour, a whole skyscraper might be constructed in one week. Regolith material is used to make each block, which results in each one weighing 1.5 metric tons and featuring many holes throughout. It has not yet been determined, however, whether the building method would hold up in the lunar vacuum and dramatic temperature swings.
Catenary arch igloo design
A plan for the next ESA lunar outpost already exists, even though the building material has not been agreed upon. British superstar architect Norman Foster and his team designed it. The mathematical-physical theory of the catenary arch was adhered to in order to make the lunar dwellings as stable as possible. Arches are very stable because their shape, a parabola, takes the route of least energy.
In this way, the homes on the Moon seem more like igloos than like regular residences. They too are a hybrid of tube and dome shapes. The inflated inner shell serves as the structural base for these Moon igloos. This is the outline, which the robots are currently covering with regolith bricks from the outside. Each habitation module on the Moon will have enough room for four people and shield them from cosmic rays, meteorites, and temperature swings.
Water and oxygen
Both the Moon’s South Pole (left) and North Pole (right) have ice deposits (turquoise) in craters. Credit: NASA
Raw material sources: crater ice and regolith
Assuming the lunar base is complete and ready for its first residents. Then, at the very least, there’s the issue of getting fuel, water, oxygen, and food to the astronauts. It would be impractical and prohibitively costly to transport all of these materials from the Earth. Therefore, it is evident that a lunar colony, in order to exist, must make use of on-site resources.
Ice from the lunar craters
The most straightforward answer concerns the provision of water: if future lunar outposts are constructed in the polar regions of Earth’s satellite, sufficient water ice will be found there. In 2010, data from India’s Chandrayaan-1 lunar spacecraft indicated that there are ice layers a 3.2 ft (1 m) deep in the craters near the lunar north pole. Present evidence suggests there may be roughly 10 billion metric tons of water at each pole.
However, the exact amount and composition of the ice found in the lunar dust have not been determined. To this end, the possibility of obtaining potable water from ice remains open. In the next several years, this will be answered by a number of robotic lunar missions. To be fair, the needs of a lunar outpost wouldn’t be very high at first: NASA suggests that a crew of four may get by on just a few dozens of metric tons of water each year.
Water from the crater ice might be collected using solar energy. Using parabolic reflectors, the radiation may be focused and directed to evaporate the ice only in the parts that were shielded by the foil. In the event that this water vapor is dispersed and cooled once again, it condenses into potable water. Alternatively, robotic excavators may harvest ice, which could subsequently be melted or evaporated in stationary solar furnaces.
Regolith as a raw material supplier
Water could be retrieved from the regolith on the Moon even if there were no ice formations. This is because, as was recently discovered by spectrometer data from the Lunar Reconnaissance Orbiter, water is bonded to the rock as hydroxyl (OH) practically everywhere on the lunar surface. This trapped water is also located away from the lunar poles, making it a more accommodating site for a lunar outpost than the polar craters.
NASA’s Goddard Space Flight Center scientist William Farrell says that after being blasted by the solar wind, every rock on the Moon has the potential to generate water. According to the findings of his group, this bound water is produced by a chemical process in the regolith. Oxygen-containing minerals in lunar rock have their connections broken by the solar wind’s intense energy. Since reactive oxygen radicals are created, they may “grab” hydrogen from their surroundings to form hydroxyl.
Oxygen and water from the lunar soil
How, therefore, might this potentially hydrous rock be mined for potable water? Again, researchers showed that solar heat was crucial on a mock journey to Hawaii. At temperatures of around 900 degrees Fahrenheit, the regolith-like volcanic dust began to shine. Furthermore, passing hydrogen or methane across it causes it to react with the oxygen in the regolith to produce water. NASA estimates that 119 grams of water may be recovered from one kilogram of the most abundant lunar mineral, ilmenite (FeTiO3).
As a useful byproduct, the astronauts’ breathing air’s oxygen may be extracted from the regolith using this method. When water vapor is produced during heating, it must be separated back into its original hydrogen and oxygen components. One kilogram of ilmenite could provide enough oxygen for 106 grams of breathing space, at least in principle. However, studies are currently being conducted to ascertain which approach is most appropriate and how oxygen and water may be created using the fewest resources and the least amount of energy.
Electricity and fuel
The Moon’s 14 days long nights might hamper solar power generation. Credit: NASA’s Scientific Visualization Studio.
Generating power on the Moon
A lunar outpost needs its own power plant if its inhabitants are to survive. Electricity is essential for astronauts because it powers their heaters, lights, and other electronic gear. They should be able to use local resources to produce fuel for the landing shuttles and lunar vehicles.
Electricity from the Sun
Sunlight is a simple and effective way to get energy. Photovoltaic systems have a long history of usage in space exploration, and the Moon is a suitable location for them. The catch is, however: Since one lunar day is equivalent to 29 Earth days, the Moon is always in the dark for two weeks when the Sun isn’t available to provide energy. Aside from that, the Earth sometimes shuts out the Sun for a few hours during solar eclipses, which happen several times a year.
Scientists, however, have come up with answers for this as well: Aidan Cowley of the European Space Agency says that throughout the day, there is sufficient solar energy to split water into its component parts of hydrogen and oxygen. We could convert these gases back into water and use them to generate energy when the Moon was asleep. In theory, this might work by having fuel cells soak up sunlight throughout the day and then churn out power after the Sun goes down.
In a perfect world, hydrogen, oxygen, and the resultant water would all be recycled indefinitely inside this system, forming a closed cycle. The only other component needed is sunshine. According to David Bents of the Glenn Research Center, who studied these regenerative fuel cells for NASA a few years ago, if nothing breaks or wears out, this may operate indefinitely without having to be recharged.
Moon as a gas station
Among the many resources needed for space flight, fuel is one of the heaviest and most vital. As of now, it constitutes the vast majority of the total launch mass of a rocket, and thus, a significant proportion of the associated launch expenses. A lunar outpost would have to generate its own fuel to be cost-effective.
In addition, a lunar outpost is seen as crucial by space organizations as preparation for Mars and beyond. For this reason, NASA’s lunar orbiting station Lunar Gateway will, in the long run, serve as a refueling station for space trips. After all, space probes won’t have to struggle against Earth’s gravity to lift their entire fuel load into space if they only do it in lunar orbit. Concepts for such “refueling stations” in lunar orbit are already being developed by a number of academic organizations and businesses.
Even if these filling stations are built, the issue of where to get gasoline for them remains. Once again, the regolith of the Moon is being seen as the best option. It contains the ingredients for a standard rocket fuel, hydrogen, and oxygen, and can be extracted using the Sun’s heat. The upper burn stage of the Saturn V, the Atlas 5, and the engines of the space shuttles have all employed liquid oxygen and hydrogen. However, this fuel combination is also used by cutting-edge rockets like the European Ariane 5 rocket.
What is the source of the food on the Moon?
A Mars greenhouse is seen in this artist concept. Using a hydroponic method, plants are being grown with the aid of red, blue, and green LED light strips. Image credit: SAIC
Plants grown in the Moon
That remains the issue of sustenance for the lunar colonists of the future. For a long time, astronauts (including those living on the ISS) have needed to rely on supplies sent all the way from Earth. But the logistics and prices of a lunar colony would not allow for something that is currently difficult and costly in Earth orbit. Because of this, it is essential that the lunar station’s personnel generate as much as possible inside the facility itself.
Vegetables cultivated on lunar soil
Vegetables and fruits, at least, could make this simpler than previously believed. Plants were successfully grown by Dutch researchers in 2016 using lunar and Martian soil replicas. The difficulty is that the regolith has almost no nutrition since it lacks organic components due to the absence of life on the Moon. However, the astronauts’ own waste products, like urine or leftover food, might make up for the lack of these organic ingredients.
To secure the success of their culture experiment, Wieger Wamelink and his colleagues sent in soil microorganisms from Earth to further enrich their synthetic lunar regolith with such organic material. They then planted a variety of vegetables and grains including tomatoes, peas, rye, radishes, leeks, spinach, lettuce, cress, quinoa, and chives. The end result was that plant life flourished in the artificial lunar soil. About half as much biomass was created as on Earth, but there was still plenty to harvest.
Orbit and Antarctica are being used for test crops
On the International Space Station, astronauts are attempting a new approach. Since 2015, the station has included a miniature greenhouse. Plants are nourished by a nutrient solution and grown in a calcareous mineral mass. Bright red, blue, and green LEDs light up the entire object. The ISS crew has already gotten their hands on fresh lettuce thanks to this “veggie” technology. A completely autonomous automated plant-growing system is the next step. More than 180 sensors monitor the soil, air, and water supplies separately and adjust the flow as needed.
Plant growth on the Moon is being tested again in the Antarctic. The EDEN-ISS greenhouse container has been stationed in the Antarctic since the beginning of 2018, around 1300 feet (400 m) from the German Neumayer III research station. Plants like lettuce, radishes, and cucumbers thrive here because the system is comparable to the one used on the space station. Scientists working in the Arctic have already harvested their first crop, which they have consumed with great gusto.
Gioia Massa, a NASA researcher, notes that the farther and longer people go from Earth, the more important it is to be able to produce plants for food, for processing the atmosphere, and for psychology. So, plant life is crucial to any future extended space missions.
It’s a matter of compromises
The people of the future lunar outpost, however, will need more than just lettuce and cucumbers to sustain themselves. Unfortunately, supplies of food will still need to be sent in from Earth. Therefore, a trip back to the Moon and the construction of a lunar station will not be a cheap luxury. What ultimately matters is whether or not the benefits and insights acquired are worth these expenses.
Because Europa, Jupiter’s moon, is thought to conceal an ocean of liquid water under its icy cover, it may be home to intelligent life from outside our solar system. Europa is perhaps more intriguing than any other moon in the galaxy. The frigid moon may be more habitable than previously believed. Europa, the ice moon, seems frigid and frightening at first view. However, it is misleading. Because there is a massive ocean of liquid water under its crust, providing possible conditions for life. Scientists have been slowly digging into the question of whether or not life exists on Europa in recent years. The outcome of which might be unexpected.
Ocean below Europa’s ice
This might be what it looks like when water vapor and water shoot out from the ice and form springs on Europa. (K. Retherford/SWRI/NASA/ESA)
Jovian satellite Europa is strangely beautiful, with a network of furrows that stretch for miles over its icy surface. These furrows resemble the cracks in a painting. However, this stunning scenery comes at a high cost, since no form of life could survive the -240°F (-150°C) temperatures, solid ice crust, and complete absence of air.
A secret habitat
According to the results, Europa likely has lakes underneath its frozen surface. (NASA/JPL/University of Arizona)
However, at depths of 6 to 9 miles (10 to 15 km), a whole other universe opens up. Here lies a vast ocean of salt water that wraps around Europa and is likely to be at least 60 miles (100 km) deep. This ocean may hold twice as much water as all the seas on Earth combined.
Again, details about this watery supermassive planet were gleaned through Galileo probe magnetic field data. Because it also picked up telltale abnormalities in Jupiter’s magnetic field surrounding Europa, the kind of disturbances usually caused by motions of conductive fluid. A magma ocean is unlikely on Europa since the moon is entirely covered in ice and, unlike Io, has no solid crust to keep the heat in. A subglacial sea of liquid salt water, on the other hand, would be conductive but also allow ice crusts to exist.
Since Europa is Jupiter’s second-most inner moon, powerful tidal forces are at play there. (NASA)
The key question, though, is: what exactly is it that keeps the water liquid under the ice in Europa? Tidal forces from Jupiter are a likely cause. Europa’s orbit is very elliptical and somewhat eccentric around its host planet. Because of this, the strength of Jupiter’s gravitational attraction varies throughout the orbit. Thus, the interior of Europa varies according to how squeezed it is by Jupiter at a given moment.
There is a little elliptical deformation of the whole moon when Jupiter is near enough to cause the ice, water, and rock on the side facing it to rise. However, when Europa migrates away from Jupiter, its form once again becomes roughly spherical. These continuous motions produce heat through subsurface friction, which may be sufficient to maintain a liquid water layer under the ice of Europa.
Europa’s cracks and their meaning
When did the cracks start taking on such a peculiar form?
This colorized Galileo satellite picture shows that the ice crust is fractured along many directions. (NASA/JPL/University of Arizona)
Europa’s ice crust is so stiff that it cannot adapt to the movement and fissures caused by the subglacial ocean’s continual ups and downs. Images taken by the Galileo spacecraft reveal a fascinating pattern of elongated trenches and furrows formed by these fissures. Water from the ocean rises to the surface at these fissures regularly and solidifies, thus, causing the darker hue of the lines.
Mysterious directional shifts in the fractures
But there’s something off about these lines. It’s unclear why these fractures have changed direction over time. Since Jupiter’s moon rotates in a tidal lock with the planet, the tidal pressures are always exerted in the same direction. Then why are the cracks not constantly forming in the same direction?
There are theoretically three potential causes: To begin, Europa’s icy crust may revolve a little faster than the rest of the moon. As a result, Jupiter’s tidal forces would gradually shift the crust’s orientation relative to the planet over time. Another idea is that, like Earth’s axis of rotation, Europa’s is somewhat inclined relative to its orbital motion. As a result, Europa would wobble more over time, and its crustal areas would alternately begin to draw closer to Jupiter.
A third prospect is that the fractures are scattered at random and that their direction is not related to lunar activities but could be related to local weak points in the ice sheet.
Europa’s wobbling axis
But this crust hypothesis came up on the losing end, with the models based on this scenario consistently failing to reproduce Europa’s usual cracking pattern. However, if the simulations were modified in a way that Europa’s axis swung back and forth by around 1 degree over time, the results would get quite similar to the fracture pattern seen in the ice crust, suggesting that the wobbling axis is more likely the reason for the directional changes in Europa’s fractures and ridges. Even a little axial tilt (or obliquity) accounts for a lot of this current phenomenon on Europa.
Liquid water under Europa’s ice sheet
What maintains the ocean’s fluidity on Europa? Sloshing water, or even subsea volcanoes. It’s from NASA and the Jet Propulsion Laboratory.
The usual breaking pattern of the ice crust may have been caused by Europa’s mild tumbling, which may also have led to the creation of a subglacial ocean. That’s because the heating impact of tidal forces can be amplified even by tiny variations in Europa’s orientation with regard to Jupiter.
Some scientists think that the subglacial ocean in Europa is continually sloshing back and forth under the unyielding crust due to the ice moon’s wobbling. Instead of being relatively motionless, the water would be marked by powerful currents. Also, the energy released by the motion of the water might be enough to keep Europa’s ocean liquid. Thus, the liquid water on Europa could be heated by the ocean itself, not by the surface or the subsurface. But, this is still only a theory at this point.
The possibility of life on Europa
Organisms under the ice
If water exists as a liquid on Europa, then there might be life on this icy moon of Jupiter. But there is more to it when it comes to subglacial lakes or seas. For thriving and reproducing, most organisms need either light or air, or at least certain gases. That’s why, for a long time, it was believed that the subterranean lakes of Antarctica were fairly unfriendly to life. But that didn’t turn out to be true.
Proof of life on Lake Vostok
A perspective image of the ice surface of Lake Vostok. (Michael Studinger / Lamont-Doherty Earth Observatory)
Lake Vostok, the biggest subglacial lake in the Antarctic on Earth has always been frozen solid. Having been covered by ice almost 2 miles (3 km) thick for the last 15 million years, its waters have been cut off from the surface. No light can make it through this ice sheet, the air pressure is very high, and food is probably in short supply. It’s undeniable that species on Earth that call Lake Vostok home must thrive under very harsh circumstances.
No samples of the lake’s liquid had been obtained due to concerns about contamination, so it was unclear whether or not there were organisms living in the waters of Vostok. However, in recent years, scientists have drilled just above the water level, collecting the first samples of frozen lake water from the boundary layer. This layer forms when the lake water freezes at the points of contact with the glacier ice and then collects on the underside of that glacier ice.
Incredible variety
The samples at depths of around 11,700 to 11,900 ft (3,550 to 3,600 m) came from the ice formed by the lake water and when the samples were studied, the scientists deciphered the DNA and RNA sequences frozen in the ice to discover the kind of species living in the Lake Vostok.
What they uncovered instead of an area devoid of diversity was the DNA of thousands of species living in impossible conditions. 94% of the species were bacteria, while the remaining 6% were either fungus or archaea, a unique class of single-celled creatures. This finding has forever changed our view of what is and isn’t deemed liveable.
Evidence of higher life
Future autonomous diving robots may help us learn more about the ecosystem of Lake Vostok, and potentially Europa as well. (NASA / JPL-Caltech)
What’s more, the investigations also uncovered the fact that many of the bacterial species detected in the ice are generally found in close connection with multicellular creatures. They are parasites and commensals that inhabit fish and other marine organisms such as crabs and worms. Some of the DNA samples could have even originated from these higher species.
This leads to the conclusion that there may be some complex organisms than single cells living in Lake Vostok which also suggests that life may exist on Europa’s cold surface if terrestrial creatures have colonized such purportedly hostile and severe habitats on Earth.
Europa’s ice crust is vital for possibility of life
Is it blocking life or safeguarding it?
Jupiter’s moon Europa has an ice cover that is 3,300 ft (1 km) thick, and it has a crucial role in the search for life on this icy moon. The ice cover serves as a blanket, protecting the subglacial ocean from the deadly cold of space and the lethal effects of radiation. As an added bonus, the ice crust, together with the rocky core, is likely the primary source of chemical building blocks for life. This is due to the coating of chemical compounds left on the surface of Europa’s ice sheet by meteorite strikes, radiation, and particles from Jupiter and the solar wind.
Does Europa have oxygen?
Those fissures in the ice are a hint that the crust of Europa regularly tears open and becomes permeable. (NASA/JPL)
When this radiation splits the water molecules in the ice, this in theory should release oxygen into Europa’s atmosphere. These gases and liquids can as well reach the ocean below if the ice sheet is thin enough to allow them to escape through its countless fractures. Yet, this thick ice crust can still be detrimental to life. And Europa’s ice crust is not precisely a thin sheet, being at least 6 miles (10 km) in thickness.
Recent models showed that enough oxygen could make its way down to the subglacial water from the glacier surface, and it is simply a matter of how long it would take. This is because tidal pressures on Europa could be causing the ice crust to shift and break apart on a regular basis, sending new, frozen ice to the top while pushing other sections of the surface layer deeper into the underwater ocean.
The upheaval in Europa
Numerous new bulges and seams can be seen all throughout Europa’s surface, proving that similar upheaval processes are still happening right now. In theory, oxygen was once restricted to the atmosphere’s outermost layers in Europa. But the simulations reveal that free oxygen might have been mixed in over the full thickness of the ice crust during the span of around 1 to 2 billion years of irradiation and upheaval.
Meanwhile, similar to the underside of ice floes in our terrestrial (surface) seas, a persistent, quicker interchange of thawing and freezing happens at the boundary layer between water and ice on Europa’s icy crust. In as short as half a million years enough oxygen might have been dissolved in Europa’s ocean water during this exchange at the ice-water interface to provide minimum oxygen saturation for life.
Getting ready for life
This amount of oxygen would support life on Earth for even the smallest crustaceans. In under 12 million years, oxygen levels in Europa’s atmosphere may have risen to match those of our seas, making breathing comfortable for even the biggest aerobic organisms. If Europa had started out without oxygen for 1 or 2 billion years, that may have been the perfect amount of time for life to evolve there since this is similar to the history of Earth.
The chemically hostile oxygen wasn’t there when the original building blocks of life developed on Earth. Circumstances altered and the increasing oxygen content of the atmosphere produced the conditions for the genesis of higher life forms only after the earliest single-celled creatures had existed. The water under Europa to possibly have enough oxygen to allow for the formation of even bigger life forms is, therefore, not inconceivable.
Lakes under Europa’s ice
Chaos Terrain for clues
To what extent the ice on Europa can be penetrated is a key aspect of the survival of any life on Jupiter’s moon. Europa’s icy shell may be more permeable than previously assumed. Images taken by the Galileo probe reveal strange landscapes on Europa such as uneven ridges, cracks, and plains that appear jumbled. This topography is called “Chaos Terrain.” The planets Mars and Mercury, as well as the dwarf planet Pluto, all have Chaos Terrains.
Scientists find the ice sheet mechanisms remarkably similar to those structures. This is because similar processes occur on glaciers and ice shelves that sit above subglacial volcanoes.
Caves under Europa’s ice
It is hypothesized that Europa may have subsurface lakes, like ice-filled caverns that sit about midway between the surface and the ocean. There are many cracks in the rough topography of the Chaos Terrain formations above the lakes, which might enable abundant oxygen and organic substances to infiltrate the waters in these shallow caves in the ice.
However, this may also mean that these subglacial lakes of Europa may support life. As time goes on, these tunnels might eventually burst apart due to massive fractures in the ice, allowing for a passageway to the ocean below. Even though Europa has a strong crust, scientists can now see that it may be home to enormous shallow lakes that facilitate “mixing.” This mechanism of mixing has the potential to improve the habitability of Europa’s ocean.
Connection to the ocean under the ice
Springs of water
Image data from the Hubble Space Telescope revealed that water vapor is coming from Europa’s south pole, sometimes in gigantic springs that reach heights of over 125 miles (200 km), providing more proof of a connection between Europa’s surface and its subglacial ocean.
A blue glow
The map above depicts the area where water vapor was found over the southernmost part of Europa. (Credits: NASA/ESA/L. Roth/SWRI/University of Cologne)
The spectrometer on the Hubble telescope picked up the faint light of excited oxygen and hydrogen atoms near the pole of Europa. In most cases, this is brought on by the disintegration of water molecules in response to a magnetic field. That implies that water vapor is present on Europa but at very low temperatures.
The moon Enceladus of Saturn is reported to experience a similar phenomenon. Geysers that are currently active here also send clouds of steam, ice, and dust hurtling into the void. However, only water vapor was found on Europa; whether the springs also include ice and dust particles is still unknown. Also, the origin of these springs remains unknown.
Connection to a hidden ocean
But do these openings reach the ocean under Europa’s ice crust? Or they might be created in the ice as a result of frictional stress close to the surface. In that case, there would be no need to delve into the subglacial ocean to learn more about its composition.
The water vapor auroras always appear when Jupiter’s moon is at the farthest point in its eccentric orbit. This phenomenon is likely caused by Jupiter’s tremendous gravitational pull and its tidal forces. Scientists believe that the large fractures and fissures on Europa’s ice are stretched farther away from the planet, allowing water vapor to escape. But as Europa returns to its orbit around Jupiter, the planet’s gravity squeezes the moon, causing the fractures to close.
Water vapor escaping near Europa’s south pole reinforces its status as a top contender for life in the Solar System.
Europa’s subglacial ocean may provide favorable circumstances for the emergence of life, if it were connected to the surface.
Chemical reactions taking place in the ice of Europa
A dynamic surface
There are possibly more than simply an ocean and lakes full of liquid water under Europa’s ice crust: Deep under the ice, the chemical reactions could be occurring at a remarkable rate between the frozen objects. This is thought to be invaluable. For one thing, at -305°F to -225°F (-187°C to -143°C), chemical processes just cannot take place on their own and extra energy would be required for them to happen.
Jupiter as an energy supplier
The areas where chemical substances have altered the ice are highlighted in false color. Acids and salts are seen in red. (NASA/JPL)
In theory, Jupiter provides one such energy supply. There is a steady release of radiation and energetic particles into the atmosphere through its radiation belts. If they were to land on Europa, they would set off chemical reactions. Nonetheless, these particles often only go down a few millimeters into the ice. For this reason, it was widely believed that considerable chemical activity could not have persisted in the depths of Europa’s ice crust.
However, this extra energy is actually still achievable without radiation and particle flow from Jupiter. Scientists conducted experiments in a high-vacuum room cooled to 50 to 100 Kelvin (minus 223° to minus 173°C) by spraying water vapor and sulfur dioxide gas onto mirrors. Instantaneously, the vapors froze into solid ice. Previous satellite observations have confirmed the presence of sulfur in Europa’s ice, most likely from the ice volcanoes on Jupiter’s moon Io but also from Europa’s subglacial ocean. However, what happened to this sulfur thereafter was a mystery.
The -280°F reaction
Do chemical processes take place on Europe’s ice cap? (NASA/JPL)
The scientists then observed the changes in the reaction chamber using infrared spectroscopy. Despite the subzero temperatures, the sulfur dioxide nevertheless managed to react with the water molecules, resulting in the formation of positive and negative ions. This reaction occurred very instantly at a temperature of -225°F (-143°C). After around half a day to a day at -280°F (-173°C), the reaction reached saturation.
A day may not seem like a little amount of time, but now compare it to the age of Europa, 4.5 billion years. After all, the process in the laboratory surprisingly transformed around 30% of the sulfur dioxide. What’s more, the positive and negative ions formed in this reaction readily combined with other molecules, triggering even other reactions.
What if the crust were more dynamic than we realized?
After this, they added carbon dioxide to the mixture to see whether the process would still occur in carbon dioxide ice, simulating the circumstances on Europa. This also froze up instantly on the mirrors while not halting the continuing reaction. If the frozen carbon dioxide had prevented the reaction this whole theory would have failed.
This, however, implies that Europa’s ice, and maybe the ice of other frozen moons like Ganymede and Callisto, may be chemically active. This means the sulfur dioxide under the surface of Europa is possibly interacting and forming chemical compounds, paving the way for the possibility of life.
