When will Halley’s Comet next pass by? What was the spacecraft that arrived on comet 67P, and where is comet Leonard right now? How and where do comets get their distinctive shapes? What is the difference between a comet, an asteroid, or a meteor? Here, we’ll explain the distinctions between them.
They travel through our sky, leaving behind lengthy clouds of gas that provoke intrigue, curiosity, and even fear of a fall depending on the time, and they have humorous names like C/2021 A1, Halley, and 67P. Let’s explore the history of comets, from Halley’s to the more recent Neowise and Leonard, and even the renowned comet 67P, which was outfitted with the Philae spacecraft. These frozen things have captivated and terrified humans for millennia.
In 2023, what comet might we expect to see?
Predicting a comet’s visibility is difficult since it relies on so many variables, and their passage can only be computed a few months in advance. On May 13, 2023, comet 39P Oterma is expected to approach quite close to Earth, raising the possibility that it may be seen from Earth. Comet 103P Hartley may possibly make a close approach to Earth on October 13, 2023.
What is a comet?
The structure of a comet. (Image credit: Pearson Education)
A comet is a heavenly body formed long ago during the formation of the solar system from gases, rocks, and dust that have since frozen solid. These snowballs from space are the real deal. The Sun’s heat causes the comet’s material to melt as it approaches and passes close to the star. After that, the comet starts to eject a massive luminous shape, bigger than most planets, made of dust and gas.
When a comet is in a tight solar orbit, its size may range from a few miles to tens of miles. When its material begins to flow out, it creates a beautiful cloud of gas and dust that follows behind it for millions of miles, making it visible to us on Earth.
The comet develops two tails in its wake: the dust tail and the plasma tail. The first one is made of dust and is proportional to the speed with which the asteroid is moving. Being able to span millions of miles makes it the most impressive. The second is a gaseous structure known as an ionized tail or plasma tail.
These gas molecules are disassembled by the sun’s UV rays, making them emit light. A plasma tail may extend out into space for tens of millions of kilometers. They can reach 100 million miles in length (around 150 million km). Comet Hale-Bopp has been seen with a third sodium tail.
The composition of a comet
Comets emerge from debris left behind from when the Sun and planets were first created. As such, these objects serve as crucial eyewitnesses to the birth of our solar system. Comets are witnesses to those early moments. Because they did not undergo any changes since being frozen in the beginning.
Frozen gases, in the form of ice, boulders, and rock dust, make up a comet’s nucleus. Observations of comet 67P reveal that it is rich in carbon and that several chemical compounds previously unknown everywhere except on Earth have been detected on the comet. Therefore, it is possible that the components that made it possible for life to form on Earth came from space and were carried by heavy bombardment 4 billion years ago. In order to learn more, it would be necessary to analyze the makeup of several additional comets.
The biggest known comet
Comet Bernardinelli-Bernstein compared to other comets. Image credit: NASA / ESA / Zena Levy, STScI.
Currently, comet Bernardinelli-Bernstein or “C/2014 UN271” is the biggest comet in the sky. Observers didn’t directly see it until December 2021, and it wasn’t discovered until 2014. They measured its peculiar diameter and found it to be 85 miles, or 137 kilometers. Because of this, it is the biggest known comet, surpassing even comet C/2002 VQ94 (LINEAR). We now know this based on images collected by the Hubble Telescope in January 2022.
The difference between a meteorite and a comet
A comet is a celestial body that orbits the sun or another star. A core of ice and particles makes up its core. Some of its components transform into gas as it nears the Sun, leaving a bright trail behind the nucleus stretching for millions of miles. Meteorites, on the other hand, are pieces of rock and metal that fall to Earth after entering the atmosphere and burning up. Comets and meteorites are not similar in composition or origin.
The difference between a comet and an asteroid
Asteroid belt
Asteroids, which circle the Sun and may be either rocky or metallic, are one such kind of object. There are two asteroid-rich regions in our solar system, the main asteroid belt, and the Kuiper belt. Both of these regions are now thought to have existed because a planet never formed there. The rocky debris that may have coalesced into a planet during the formation of the other planets is still present in this region. Asteroids are the undeveloped embryos of planets that failed to complete their accretion process.
In contrast, comets are icy entities made of gas trapped in ice and dust from the early solar system’s creation. These objects have been collected from all around the solar system and are now being held in the Oort cloud, a large collection of comets near the solar system’s outskirts. When a comet approaches the Sun, the ice at its core melts and converts to gas, leaving behind a lengthy, distinctive path that can be seen from Earth.
Where do comets come from?
The Oort cloud is where most scientists believe comets originate from. This cloud is a spherical structure that fills the whole solar system with countless frozen particles. As a result, it serves as a genuine comet reservoir. Once in a while, a neighboring planet’s gravitational pull will lead one of these objects to detour from its original path.
The comet’s orbit might shift, bringing it closer to the Sun, where it could be thrown off course. Some comets make a single close approach to the Sun and then continue on their orbits far from the star. While others may be seen from Earth because their orbits are so elliptical that they often pass at a relatively close distance to the Sun.
Were dinosaurs wiped off by a comet?
The Yucatán Peninsula in Mexico was hit by an asteroid 66 million years ago, when Earth was teeming with dinosaurs. The extinction of the dinosaurs and 75% of all other life on Earth can be directly attributed to the collision of this object.
However, in February 2021, two academics released a paper in the journal Scientific Report that offered a new idea to explain the phenomenon. They hypothesized that the object that struck Earth was a piece of a comet that had gotten too close to the Sun and been torn apart by the Sun’s gravity. This impact would have resulted in the formation of the well-known Chicxulub crater and a tsunami, both of which proved to be disastrous for a wide variety of living forms.
When did Halley’s Comet last appear?
Halley’s Comet is without a doubt the most well-known comet in history. Even before it was formally discovered in 1758, this comet had been seen multiple times. The watchers had thought they were seeing a new comet each time.
Many years after this date, in 1835, 1910, and 1986, this comet made fresh crossings that were more or less impressive. Every 76 years, to be precise, and the next one won’t happen until 2061.
Where is Comet Leonard?
Greg J. Leonard, an astronomer, and geologist who discovered comet Leonard in January 2021 and gave it its name, predicted that on January 3, 2022, the comet will come very near to Earth, resulting in a sequence of extraordinary photographs. After that, the comet started to leave our planet and go back to the solar system’s outskirts. It began to dissolve in February 2022, when its nucleus and hair began to fall out.
When did comet Neowise last pass earth
In July 2020, astronomy fans everywhere were giddy about Comet Neowise, also known as C/2020 F3. Many pictures, like the one NASA released, have been inspired by its arrival. The Parker Solar Probe captured the image of the comet, which shows off its distinctive “hair” and “double tail.”
The comet, which had been photographed from every conceivable direction by astronomers all around the globe, has now returned to the Oort cloud. There is a true reservoir of comets in this enormous cloud of tiny ice particles located after Neptune. If Neowise has piqued your interest, you won’t be able to get a glimpse of it for another 6,800 years.
How large is comet 67P?
The weird shaped comet 67P captured by Rosetta. Credit: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0
Comet 67P/Churyumov-Gerasimenko was discovered near Kiev, Ukraine in 1969. This interestingly shaped comet is around 2.5 miles (four kilometers) in length. However, despite its massive size, it is capable of floating. Its density is comparable to that of cork. The comet’s overall form is remodeled when the ice that makes up its surface is sublimated during its many close approaches to the Sun. According to scientists, there are cliffs, plains, and faults to be discovered.
Comet 67P has been explored in great detail by scientists because of the Rosetta probe and its robotic Philae. Following a trip lasting more than a decade aboard the Rosetta probe, the latter finally touched down on the comet’s surface in November of 2014 after traveling 4 billion miles (6.4 billion kilometers) through the Solar System.
The Philae robot, which was equipped with a soil drilling instrument and many pieces of equipment to study the samples it obtained, communicated with Rosetta and relayed crucial data on the comet’s composition until the end of contact in July 2015. In November of 2021, 67P came back to see us again before relocating “permanently”. Since it is unlikely to travel this way again until 2214, it will have a very long voyage ahead of it.
The best way to see a comet in the night sky
The comet’s brightness will determine whether or not it can be seen with the naked eye. This happened in July of 2020 with the very brilliant comet Neowise. To fully appreciate the event, though, astronomical binoculars or a telescope are a must.
When a comet is visible to the human eye, it can be captured on film using just a basic camera and some manual controls. Exposures of 20 seconds or longer at ISO 1600 (minimum 800) need to be used, along with a wide-angle lens. It’s best to reduce the ISO if light pollution is significant.
You may play with the composition by putting the comet in a unique place, such as high in the sky, over a tree, or in a valley between two mountains. To avoid fuzzy photos while taking them without a tripod, try setting the timer on your camera instead.
Asteroids are potentially catastrophic objects of various sizes in our solar system. In spite of how remote the possibility of an asteroid crashing into Earth is, it is still a very real threat. In the neighborhood of 180,000 tons of dust and meteorites fall to Earth each year. These objects tend to be quite diminutive. On the other hand, a massive asteroid may pose a danger to Earth. NASA and other space organizations keep an eye on the paths of some huge objects in case they collide with Earth. Both Apophis and Bennu, asteroids that will pass close to Earth in 2029, fit this description. Even though their paths don’t seem dangerous right now, the planets’ gravitational pull might alter their paths and lead to a collision in the future.
What is an asteroid?
An impression of the asteroid belt. Image credit: NASA/JPL-Caltech
An asteroid is a celestial object with an orbit around a star. Made of metals and rocks, they testify to the birth of our solar system. Asteroids, it is widely believed, are stony debris that failed to coalesce into planets.
These came from the main asteroid belt, which is the region of the solar system between Mars and Jupiter and includes hundreds of thousands of asteroids. Scientists believe that Jupiter’s gravity has stopped a planet from forming in this region. It follows that the asteroids represent the unborn planet’s embryos.
These chunks of rock are now circling the Sun in an area known as the asteroid belt. However, sometimes the gravity of a planet like Mars or Jupiter may cause them to detour from their original path. Once they break off from their original orbit, they are classified as NEOs because they have the potential to enter Earth’s orbit.
The most well-known asteroids
Ceres, the first asteroid ever discovered, was found by Italian astronomer Giuseppe Piazzi in 1801. Since this discovery, astronomers’ attention has shifted away from monitoring asteroids and toward the study of planets and stars. However, asteroids provide insight into the early history of Earth and the Solar System. However, although the vast majority of these aliens maintain their anonymity and quietly develop in their orbit, others are well-recognized and have names. Sometimes scientists would follow them around and watch them from every possible vantage point.
Asteroid Apophis
The asteroid Apophis was first seen in 2004, and its journey has been meticulously tracked ever since. The closer it gets to Earth in its orbit, the more likely it will crash into our planet. Fear and debate are fueled by this possibility, despite NASA’s comforting findings that nixed it years ago.
It’s not a slutty stone, and with good reason. At 1,150 feet (350 meters) in diameter and 27 million tons in mass (30 million US ton), the asteroid is a formidable presence in the solar system. In 2021, it came within 10.5 million mi (17 million km) of Earth (44 times the distance between the Earth and the Moon). Nothing about it posed any kind of danger from this far out. Its future passing has long caused concern among experts. In fact, in 2029, Apophis will be significantly closer to Earth thanks to its orbit, passing within 20,000 mi (32,000 km or one-tenth of the distance between Earth and the Moon) of our planet. To rephrase, it will make a close pass between the Earth and a few geostationary satellites.
However, NASA has told us that a collision is not possible, contrary to the dire predictions of certain periodicals. An American government organization has concluded that this asteroid poses no threat to Earth during the next 100 years.
Asteroid 2001 FO32
Asteroid 2001 FO32
Astronomers were able to get a good look at the strange asteroid 2001 FO32 on March 22, 2021, when it passed within 1.25 million mi (2 million km) of Earth. This asteroid’s unusual quality is its velocity.
The asteroid 2001 FO32 was reportedly the race leader because it was “faster than most asteroids,” as stated by NASA, as reported by the publication Sciences et Avenir. At 79,500 mi/h (128,000 km/h), it was adding about 0.6 miles every second to its total distance traveled. Having a diameter of 0.35 mi (550 m), it was too small to be seen from Earth without a telescope.
Comet 2020 VT4
It is not always possible to predict which asteroids will be seen before they approach the Earth. Some of these asteroids are too near to the Sun for scientists to spot in advance of their arrival. In 2020, asteroid 2020 VT4 made a surprise flyby approximately 235 mi (380 km) over the Pacific Ocean, causing widespread damage. This indicates that it made its way between Earth and a group of geostationary satellites. The distance of VT4 from Earth’s surface is the closest of any passing asteroid.
If this object had impacted Earth, it would not have posed any threat to mankind due to its modest size.
The Little Prince, or Asteroid B612
It’s likely that one of the most well-known asteroids is B612 from Antoine de Saint-Exupéry’s Little Prince. Some readers could suspect that the author has just made up this heavenly body. Still, it does exist, or at least nearly does. The German astronomer who discovered the asteroid in 1906 gave it the designation 612 (without the B). A second asteroid, 46610 Besixdouze, was found on October 15, 1993, and was named after the Little Prince.
Asteroid Bennu
Bennu, found in 1999, is one of the asteroids considered a “danger” to Earth, despite the fact that the probability of a collision remaining at its current level is very low.
After dancing around the asteroid for two years, the Osiris-Rex mission was able to gather surface samples for a NASA investigation. The asteroid measures 1650 ft (500 m) in diameter. In 2023, we’ll bring those samples back to Earth for analysis.
After analyzing its predicted path, NASA determined that the probability of this asteroid colliding with Earth was less than 0.057%. Scientists from NASA have concluded that there is a 99.94% likelihood that Bennu is NOT on an impact trajectory.
NASA warns that if the asteroid’s track changes and it comes closer to Earth, the threat will increase. This is possible if the object enters a region where the Earth’s gravity alters its path. Scientists have estimated that this may happen in 2135. That would put the crash in the year 2182. It is predicted that the crater will be between 3 and 6 mi (5 and 10 km) in diameter.
Which asteroid threatens Earth?
When the Apophis asteroid was discovered in 2004, scientists were alarmed by predictions that it would collide with Earth in 2029. The asteroid is around 1,150 ft (350 m) in length. Despite the many alarmist headlines released in different media, it turns out that these worries are unjustified, since the asteroid’s course rules out any collision with Earth over the next 100 years.
NASA has been keeping a tight check on this asteroid ever since the scare, and it seems like it will come within touching distance of Earth, making it visible to the naked eye. We have a spectacular show in store for us, but there is no end of the world in sight.
What are dangerous asteroids?
Objects that pass through Earth’s orbit, known as near-Earth objects (NEOs), are often mentioned while discussing the dangers posed by falling asteroids. Based on their size and orbital distance from Earth, several of these asteroids pose a threat to our home planet. If an asteroid with an absolute magnitude, or brightness, of less than 22 passes within 0.05 au (4.64 million mi or 7.48 million km) of Earth, it is classified as potentially hazardous. The brighter an object is, the smaller its absolute magnitude value. The bigger the asteroid, the lighter it reflects, hence the brighter it seems.
The likelihood of encountering an object big enough to pose a threat to humanity is low but not zero. The extinction of the dinosaurs occurred 66 million years ago as a result of a catastrophe of this sort.
Since we now have means of avoiding collisions, this danger may be mitigated to some extent. But what would we do if it turned out that a massive asteroid was about to smash into Earth sometime in the next decade? So, what do we have at our disposal?
Evacuating the affected region is now regarded as the only viable option. But what if the danger is much more than that? Planetary defense initiatives are currently researching and developing methods to properly detect potentially hazardous asteroids and deflect them.
The asteroid that wiped off the dinosaurs
Many ideas have been proposed to explain the rapid extinction of the dinosaurs 66 million years ago, with new versions being introduced on a regular basis to account for new findings. One popular theory is that the stunning crater of Chicxulub in the Mexican state of Yucatán was produced by the impact of an asteroid or an asteroid fragment. It would have set off a chain reaction leading to a severe disaster, wiping out numerous animal and plant species, maybe even the non-avian dinosaurs.
The 112 mi (180 km) wide Chicxulub crater was created by an asteroid, but no one knows for sure which one. A report from 2007 in Nature implicates an asteroid with the designation 298 Baptistina. However, this finding has not been accepted universally by the scientific community.
The Deccan Traps, which are volcanic landforms in India, are the focus of the second leading hypothesis that attempts to account for this extinction event by releasing massive amounts of gas into the atmosphere. This time it wasn’t triggered by meteorites; instead, the extinction of the dinosaurs was likely precipitated by a period of massive volcanic eruptions that disrupted the global climate.
How to observe an asteroid?
A number of factors, including the asteroid’s size and distance from the Sun, determine whether or not we can see it. When certain asteroids approach so close to Earth, we may see them with the naked eye.
In other cases, you’ll need binoculars or a telescope to see the spectacle.
The inquisitive may now use a NASA-created online tool to track the motions of several asteroids and comets. You’ll be able to watch for aliens if they ever arrive.
The biggest asteroid in the universe
With a diameter of 587 mi (946 km), Ceres is the biggest main-belt asteroid. In addition, it is the tiniest of the dwarf planets in our solar system. The size of the asteroid that generated the massive Chicxulub crater is believed to be about 7.
This Kuiper belt object is the next one in line after Neptune. A diameter of 775 mi (1,250 km) has been calculated. Larger objects, like Eris, have since been discovered in the Kuiper belt, and these objects are now considered to be dwarf planets. There are a lot of big objects in this faraway region, and studying them is challenging for a number of reasons, not the least of which is their great distance.
The distinction between asteroids and meteorites
The term “asteroid” refers to any astronomical body circling a star that is composed mostly of rock and metal. As a result of course corrections, these objects sometimes approach Earth. A meteorite is an asteroid rock that has survived its fall into Earth’s atmosphere. As a result of the data they provide on the asteroids they came from, these meteorites are of great scientific significance.
Tonight, the DART spacecraft from NASA ended its mission and successfully hit an asteroid. The 540-foot (165-meter) wide asteroid moon Dimorphos was the intended target of the DART probe’s autonomous navigation system. The force of the collision should have been enough to decrease the fragment’s orbital period around Didymos by around 1 percent. As of this moment, only telescope observations can confirm or deny this theory.
This is only a practice run before the big thing: If an asteroid ever threatened Earth, the most promising solution would be a kinetic deflector, which would involve deflecting the asteroid with a massive unmanned space probe. However, it has to strike its target early enough, fast enough, and at the appropriate angle for its impact pulse to send the asteroid far enough out of its orbit for it to miss Earth.
DART’s approach and successful impact
The DART probe collides with the asteroid moon Dimorphos, altering its course.
NASA’s DART mission has now demonstrated that this is possible, even when the asteroid in question is 6.8 million miles (11 million kilometers) from Earth and cannot be seen with ground telescopes. DART arrived Friday night at the 2560-foot (780-meter) asteroid Didymos and its 540-foot (165-meter) moon Dimorphos after a ten-month journey. When the spacecraft was 56,000 miles (90,000 kilometers) from its target, the photos taken by DART’s onboard camera were analyzed by the probe’s autonomous navigation system, which distinguished the two asteroids from each other and headed for the actual target, Dimorphos.
Just after midnight, the moment had come: The DART spacecraft sped at an estimated 14,000 miles (22,500 kilometers) per hour toward its target asteroid and slammed into it. The navigation camera captured the last moments before the DART crashed into Dimorphos, revealing a close-up picture of the asteroid’s surface littered with gritty rubble. NASA scientists now know that they can successfully bring a spacecraft to collide with a rather minor celestial body with precision.
Dimorphos was deflected by how much?
The final photo of the Dimorphos asteroid from the DART camera before the probe collided with the asteroid. (Image: NASA/Johns Hopkins APL)
Even though the DART spacecraft is only around 1,260 pounds (570 kilograms) in weight and the asteroid Dimorphos weighs roughly five billion kilograms, the velocity of the collision and the rebound of the ejected rock should be enough to nudge the asteroid slightly off of its orbit. An asteroid’s course can be drastically altered with even a little increase or decrease in its speed.
Telescopic studies over the next several weeks will indicate whether or not the collision of DART altered the course of the asteroid Dimorphos. The orbital period of Dimorphos can be tracked from Earth by observing the pair’s brightness as Dimorphos passes in front of its bigger parent asteroid. Based on the simulations, the collision between Dimorphos and DART should have shortened its orbit by 1%, which would have shortened its orbital period by 10 minutes.
Compact chunk or porous pile of rubble
The degree to which the rammed asteroid’s trajectory was altered is an important indicator of both the efficacy of kinetic deflection and the composition of the target asteroid. But, the stability and compactness of the target object have a significant impact on the outcome of a deflection operation. Too much porosity allows impact energy to evaporate without an influence, rendering the deflection useless, which would be critical in a crisis situation.
The LICIACube mini-satellite will provide valuable data about the DART-Dimorphos collision. LICIACube is part of the DART mission and positioned itself 15 days before the impact to photograph the crash and its immediate aftermath. This is because the asteroid’s interior may be revealed by factors like the crater’s size and composition and the kind of material that was ejected. However, it will take many weeks to receive all of the photographs due to the tiny CubeSat’s (LICIACube) restricted communication capabilities.
The European space probe HERA will revisit the asteroids in four years to investigate them further.
Validation for the actual test
The critical part of the DART mission has been accomplished with the successful “ramming test” of the asteroid Dimorphos. According to NASA’s first-ever Planetary Defense Officer Lindley Johnson, “DART’s success provides a significant addition to the essential toolbox we must have to protect Earth from a devastating impact by an asteroid.” DART has demonstrated that “we are no longer powerless to prevent this type of natural disaster.”
What is the DART mission? Here is everything there is to know about it. Thousands upon thousands of asteroids speed through space with many of them routinely passing within Earth’s orbit. A regional or perhaps worldwide disaster could be triggered if one of them were to arrive on a collision track with Earth. With its DART mission, NASA is exploring whether or not this may be avoided; for the first time, humankind will seek to alter an asteroid’s course by use of a ram probe.
What could be done if an asteroid is headed in the direction of Earth? According to NASA, a more effective defense would be to use an unmanned spacecraft to deflect the asteroid. On September 26, 2022, NASA’s DART mission will put this kinetic deflector approach to the test.
How do you avoid an asteroid collision?
The risk is real: Earth has been bombarded by space debris several times during its existence. The impact of the 6.2-mile (10-kilometer) wide Chicxulub asteroid 66 million years ago terminated the Cretaceous epoch and wiped out the dinosaurs, while other impacts have created worldwide disasters and monumental mass extinctions. The Tunguska event of 1908 and the Chelyabinsk meteor explosion in February 2013 proved, however, that even tiny fragments may wreak devastating harm.
About 25,000 asteroids, each about 500 feet (150 meters) in size, orbit in the neighborhood of the Earth and often pass through the Earth’s orbit. Although many incidents still go unreported.
It’s just a matter of time
Small chunks up to 3.3 feet (1 meter) in size continue to impact Earth practically daily but are burned up in the atmosphere before reaching the surface. Asteroids up to 1,000 feet (300 meters) in size are expected to strike every few thousand years, and asteroids the size of the Chelyabinsk meteor are seen on average once every 50 years. They are big enough to obliterate a whole city of millions. It’s not a matter of if, but rather when, the next major impact on Earth will occur.
What could be done if an oncoming asteroid is noticed in time? Whether humanity still has time to adopt countermeasures for an approaching asteroid depends on the size of the asteroid and the time left before the impact. When the threat is known decades in advance, the “gentle” “Gravity Tractor” defense could be all that’s needed: Using the gravitational pull of a large probe brought in close proximity to the asteroid, you can divert the asteroid off an Earth collision trajectory.
The kinetic deflector
A spacecraft smashes the asteroid and attempts to divert it off its crash route in an asteroid defense via a kinetic deflector. (Image: INASA/Johns Hopkins University APL)
But in reality, it is more probable that the asteroid will go undetected until it is too late. Because many possible Earth-orbiting asteroids are hard to spot in advance due to their dimness and their orbital distance to the Sun. The 330-foot (100-meter) asteroid called “2019 OK,” for example, was only discovered 12 hours before its closest approach in 2019. Thankfully, it was passing Earth at a distance of barely one-fifth that of the moon. After that point, no amount of protective measures will be able to prevent an impact.
However, there is still hope for an asteroid deflection if an asteroid on a crash track is discovered months or perhaps years in advance. The kinetic deflector approach is generally thought to be the best in such a scenario. As part of the strategy, the heaviest feasible spacecraft is sent in the direction of the asteroid to smash it at a specific angle. If the collision happens early enough, the force of the impact can deviate the fragment off its trajectory, and a deviation of only a few millimeters or a modest slowing is enough to prevent a collision with Earth.
But there is more to it
However, such a deflection is notoriously difficult in reality. The asteroid probe has to make a perfectly timed and hard collision with the asteroid. Too much of an off-angle impact will just alter the asteroid’s spin and not its course. The deflecting impact will be insufficient if the momentum is too low. This method requires the most precise data available regarding the asteroid’s course, spin, and size in order to precisely plan the collision.
If the asteroid is porous, most of the impactor’s energy might be absorbed instead of dissipated. The spacecraft’s collision might cause the asteroid to fracture if it is fragile or made of debris that is only weakly held together. Multiple, potentially catastrophic chunks can still head toward Earth in this case.
Given these challenges, NASA is conducting its first practical tests of kinetic deflection, called the DART Project, as a means of asteroid deflection, serving as a kind of “dress rehearsal” for the real deal.
Target object of the DART
A double asteroid as the impactor
Dimorphos’ new orbit after the collision of the DART satellite. The LICIACube will track the collision and broadcast pictures of the impact back to Earth. (Image: NASA/DART)
This is no easy feat since the whole collision must take place millions of miles from Earth to redirect an asteroid off its crash course with Earth. However, if the asteroid is so far away, the scientists may not be able to determine its exact nature, rotation, or mass before sending out the defensive probe since it will be beyond the precision of current Earth-based telescopes.
The selection of the test asteroid for DART
With the “Double Asteroid Redirection Test,” or DART, NASA is exploring the limits of an asteroid defense mission’s success and the hazards it faces. If an asteroid were to be headed toward Earth, a kinetic deflector, like the one shown by DART, would be the only way to stop it. DART’s mission is to change an asteroid’s orbit, so it can not collide with Earth.
The primary stipulation for the DART is that the experiment must not endanger Earth in any way. Even after an unsuccessful deflection, the target asteroid must follow a course that moves it as far away from Earth as feasible. However, in order to accurately assess the ramming’s effects, the candidate asteroid must be rather near. Thus, it has to be visible with large telescopes.
Didymos and its moon Dimorphos
Size comparisons of DART, Dimorphos, and Didymos. (Image: NASA/Johns Hopkins University APL)
The 1996-discovered twin asteroid Didymos satisfies these requirements for the DART mission. Didymos, the 2560-foot (780-meter) asteroid, and Dimorphos, its moon, measure around 525 feet (160 meters) in diameter. Because of their eccentric orbits, they both swing from the furthest distance from the Sun outside of Mars’ orbit to the closest distance to the Sun within Earth’s orbit. Accordingly, both are circling the Earth and are part of the class of asteroids that, although not immediately dangerous, may one day approach Earth.
This is also why the DART mission isn’t actually aimed at the asteroid Didymos itself. Because there’s too much of a chance that the asteroid may be redirected in such a manner that it would eventually crash on Earth. The moon of the asteroid Dimorphos (Greek for “two forms”) is the actual target of the DART. Due to the stability of its orbit around Didymos, any deviation will only alter the minor-planet moon’s path relative to Didymos.
Observing Dimorphos with transits
When Dimorphos passes in front of his parent asteroid Didymos, the change in brightness allows scientists to calculate its orbital period. (Image: NASA/Johns Hopkins University APL)
While in orbit around Didymos, the asteroid moon also travels directly in front of it. Due to this predictable transit, astronomers have been able to estimate Dimorphos’ orbit and size using just Earth-based telescopes. This tiny moon takes 11 hours and 55 minutes to complete one orbit around its parent asteroid. During this time, the distance between them stays at just approximately 0.73 miles (1.18 kilometers).
The DART mission’s before-and-after planning requires a high level of foreknowledge about the asteroid system. Dimorphos’ orbit around its parent asteroid may be significantly altered if the DART probe collides with the moon at just the proper location and velocity. This deflection, at least in the model predictions, is expected to become apparent during the transit phase. As a result of the impact made by DART on the smaller asteroid in the Didymos system, its orbital period will be altered by at least 73 seconds.
The Didymos-Dimorphos binary asteroids will be within observing distance of Earth at the time of the DART’s collision on September 26, 2022, at a distance of just around 6.85 million miles (11 million kilometers).
Almost indistinguishable from the actual threat
However, there is a second reason why the Didymos system is well suited as a test case for the DART: its two components are illustrative of prospective asteroid impactors on Earth’s course. Dimorphos, with a diameter of around 540 feet (165 meters), is huge enough to cause widespread destruction in the case of an impact on Earth. While its size is comparable to that of probable next-catastrophic-impact asteroids, it is not one of them.
The composition of the target asteroid of the DART mission is also quite similar to that of the asteroids that are flying close to Earth. Didymos’s composition matches that of an “L/LL chondrite” meteorite class according to the analysis of its visible and near-infrared spectra. And this is the composition of most meteorites that strike Earth. The experimental findings of the DART collision will be used for a wide variety of planetary defense research.
Order of events of the DART mission
Specifications of the DART spacecraft
The DART probe places itself at the ideal impact point by autonomously navigating its course. (Image: NASA/Johns Hopkins University APL)
The DART spacecraft has been traveling toward the asteroid Dimorphos since it was launched on November 24, 2021. The asteroid moon Dimorphos will be rammed by the spacecraft on September 26, 2022, at 23:14 UTC, in an attempt to knock it out of orbit. This will be the first-ever test of a technology designed to protect Earth from asteroids. The DART mission is outfitted with various high-tech enhancements that allow this to happen.
The impactor probe used in the DART mission seems plain at first glance: The dimensions of its hull are 3.9 by 4.3 feet (1.2 by 1.3 meters), making it about the size of a soda machine. During the roughly 10-month approach, the DART probe has been powered by two solar panels, each of which is a good 26 feet (8 meters) in length. An experimental ion drive generates thrust by electrostatically accelerating and ejecting xenon ions in a magnetic field. DART has 12 hydrazine-fueled classical maneuvering thrusters for course corrections and fine-tuning of the final approach to Dimorphos.
DART’s autonomous target acquisition and approach
The DART spacecraft from two perspectives. (NASA)
The DART probe has a navigation system that is considerably sophisticated. This is due to DART’s ability to fine-tune its trajectory on its own. The data from the DRACO camera, a tiny telescope with a focal length of around 8.3 inches (21 cm), and a high-resolution digital image sensor are placed on DART for this purpose. High-resolution photos captured by the camera will reveal the precise location and shape of Didymos and Dimorphos.
The spacecraft’s autonomous navigation system records these photos with location and attitude data. About 4 hours before the crash with Dimorphos, at a distance of 56,000 miles (90,000 kilometers) from the target, this SMART Nav system will assume complete control of the DART probe. The navigation system will initially perform an evaluation of the data in order to pinpoint the precise locations of Didymos and its moon Dimorphos using custom algorithms. An hour before impact, Dimorphos will appear as a small 1.5-pixel light point.
The navigation system will then be able to make autonomous decisions about whether or not trajectory modifications are required, and the DART probe’s correction jets will receive new commands. When there are only 930 miles (1,500 kilometers) left between Dimorphos and DART, the asteroid in DRACO images will be around 22 pixels in size and it will be too late for DART to make any changes at this point. When DART is around 460 miles (740 kilometers) away from the target, it will be on a collision track with Dimorphos in two minutes. The probe will now just cover the rest of the distance.
The impact
The DART probe will crash on the surface of Dimorphos at a speed of around 14,000 miles (22,000 kilometers) per hour. DART weighs only 1,260 pounds (570 kilos), whereas the asteroid moon Dimorphos is predicted to weigh over 11 billion pounds (5 billion kilograms). Therefore their collision is more like a bug landing on an elephant. The impact’s relatively small impulse might not seem like it would accomplish anything.
This, however, is not true. The 540 feet (165-meter) rock will receive a little push from the high velocity of the DART collision. In addition to blasting between ten thousand and a hundred thousand pounds of debris into space, the impact will also create a hole in the asteroid’s surface. The force exerted on Dimorphos will be greater than that of the hit alone because of the rebound of this ejection. The combination of this amplified ramming action and the collision is enough to cause a little shift in the asteroid moon’s kinetic energy and knock it off of its orbit.
After DART crashed onto Dimorphos, the spacecraft will be destroyed but the scientific investigation will only be getting started.
Consequences of the DART Impact Event
What will happen to the massive Dimorphos-moon once the tiny DART spacecraft crashes into it? Will the massive asteroid be able to be steered out of orbit by kinetic deflection? How did scientists successfully predict the collision characteristics of the DART-Dimorphos event essential for a deflection?
LICIACube as the direct observer
The Italian Space Agency constructed LICIACube for the impact between DART and Dimorphos to send the collision images to Earth. (Image: (NASA/Johns Hopkins APL/Ed Whitman)
The LICIACube mini-satellite will report back the first data on the DART’s impact results and its effects on Dimorphos’s surface. This mini-satellite will ride behind the DART probe before it collides with the Didymos double asteroid, and its mission is to check out the impact area. Self-propelled with its maneuvering thrusters, it’s programmed to move into an observation point 15 days before the collision, which has already been initiated on September 11th.
LICIACube stands for Light Italian CubeSat for Imaging Asteroids. And the observations and documentation from this courageous little reporter will provide insights scientists couldn’t gain any other way. Using two optical cameras, LICIACube will capture the moment the DART spacecraft crashes on the surface of Dimorphos. Three minutes after the impact, LICIACube will adjust its course to fly near the DART’s crash location.
Images of the crater, the ejected material, and the type of debris of the DART impact are to be provided by this mini-probe. These photographs, together with the last close-ups captured by DART’s DRACO camera before the collision, will provide crucial details regarding the Dimorphos’ make-up, nature, and reaction.
A view of the Dimorphos orbit
Around the same time of the collision, a dozen or more very powerful telescopes on Earth will be aiming toward the Didymos system. The pair of asteroids are 6.85 million miles (11 million kilometers) away from Earth and are only a tiny speck of light even with the best telescopes. But we will be able to see from Earth the periodic variations in brightness of this light, which are set off by the transit of the moon Dimorphos in front of its parent asteroid.
A little shift in transit timing would indicate that the DART probe’s collision deflected the asteroid moon. Astronomers may roughly infer the strength of Dimorphos’ kinetic momentum and the extent to which its trajectory shifted in magnitude to find out whether the asteroid was successfully deflected and the DART mission was a success.
The essentials for the “genuine deal”
The events of DART’s mission definitely won’t be the basis for a Hollywood blockbuster, but the future of Earth’s safety is equally at stake. The ultimate goal of the DART mission is to demonstrate that human beings can deflect an approaching asteroid. If a similar-sized rock is ever found on a collision path with Earth, the knowledge and expertise gained from the DART test in the Didymos system will be invaluable.
Where to watch DART’s collision live
On Monday, September 26, at 4:14 p.m. PT / 7:14 p.m. ET, the spacecraft DART will crash with Dimorphos. Live coverage will start on NASA’s YouTube channel, and the NASA TV at 3 p.m. PT / 6 p.m. ET.
You can also see DART’s position live in the official NASA webpage.
Aftermath of DART
HERA, a spacecraft bound towards the Didymos system
This deflection mission won’t be completed right away despite the DART spacecraft’s collision with the asteroid moon Dimorphos and subsequent studies of the immediate repercussions.
HERA, a European spacecraft, will be launched in 2024 toward the Didymos system and arrive in 2026. For the first time, it will use on-site scientific instrumentation to explore the effects of this kinetic deflection. The HERA spacecraft will scan Dimorphos’s surface topography to an accuracy of within 33 feet (10 meters) using its LIDAR measuring system, camera, and mid-infrared scanner in order to examine the impact crater and any other changes to the surface that may have resulted from the collision.
More crucially, HERA will finally provide us with more accurate information on how far the DART probe steered away from its intended target. The rotation, mass, and orbit of Dimorphos and Didymos will be directly measured, unlike with terrestrial observatories. One way HERA will achieve this is by pointing its laser towards the parent asteroid and picking up the minute wobble caused by the small moon’s gravity. Additionally, HERA will do many near flybys of Dimorphos, transmitting data back to Earth each time. Scientists on the ground will be able to determine whether the asteroid moon’s gravity has altered the signals and, if so, by how much.
Milani: What are Didymos and Dimorphos made of?
The asteroids’ surface will be mapped by the CubeSat Milani, which will also examine the expelled dust. (Image: ESA/Science Office)
However, HERA isn’t traveling alone; it’s accompanied by two smaller satellites (CubeSats) that carry their own sets of equipment and will take readings that supplement those taken by HERA. The Milani minisatellite will use a hyperspectral camera and spectrometer to determine the elemental make-up of Dimorphos and Didymos.
This will also enable scientists to compare the composition of its surface to that of known meteorites and minerals, such as that of the DART crater and its ejecta. Milani also has an onboard analyzer calibrated to detect dust particles between 200 and 400 microinches (5 to 10 micrometers) in diameter. Scientists can use it to learn more about Dimorphos’ composition by studying the dust thrown up by the collision.
Juventas: First radar view into the interior of an asteroid
For the first time, radar will be used by the CubeSat Juventas to illuminate an asteroid’s interior. (Image: ESA/Science Office)
HERA’s companion CubeSat, Juventas, will be investigating the asteroids’ composition and dynamics up close. It is equipped with a miniature replica of the radar sensor used by ESA’s Rosetta comet mission to survey 67P/Churyumov–Gerasimenko, making it the smallest radar system ever sent into orbit. The Juventas radar system will carry out the same task at Didymos and Dimorphos. To do this, it will set up 4 radar antennas, each measuring 5 feet (1.5 meters) in length, and radiating radar waves with circular polarization. The incoming and outgoing signals from Dimorphos’ interior will be recorded and decoded simultaneously.
In order to get accurate readings, the tiny radar satellite Juventas will fly within 1.85 miles (3 kilometers) of Dimorphos at a slow enough speed to get high-resolution data despite the radar’s low power. The radar scan of an asteroid by Juventas will be the first of its kind which will greatly expand the understanding of asteroids. The reason for this mission is that the outside of an asteroid does not actually portray its interior accurately.
Determining whether Dimorphos is made of solid, compact rock or a loosely formed “pile of debris” will be crucial for future asteroid defense. This data, together with measurements of the DART deflection experiment will aid scientists in improving and adjusting the models and calculations used to plan such defensive operations to protect Earth from asteroids in the future.
