The story begins in the late 1960s. When the first space probes flew over the poles of our Earth. They detected a flux of particles escaping from our atmosphere. A kind of polar wind directed towards space. And the phenomenon immediately caught the attention of scientists. Not that they were surprised that particles escape from our atmosphere — like steam from a pot of boiling water — but they were surprised to see cold particles shooting off at supersonic speeds.
Physicists quickly suspected an electric field to be responsible for the phenomenon. They imagined it generated at about 250 kilometers altitude. In these regions, the atoms of our atmosphere indeed decompose into electrons and ions. Given the mass differences between the two, one might expect them to move away from each other due to gravity. But since electrons and ions carry opposite charges, they should generate an electric field that prevents their separation. An electric field that physicists call ambipolar because it allows ions to drag electrons towards the ground when they are subject to gravity and, conversely, electrons to lift ions towards the heights when they try to escape into space. As a consequence, there’s an increase in the height of our atmosphere and ions rise high enough to finally escape from it.
A Suborbital Rocket to Reveal Earth’s Electric Field
That’s the theory. In practice, scientists have long sought to detect such an electric field. Without success. Until today. And after several years of developing a new instrument. NASA researchers report in the journal Nature.
They first identified “the only rocket range in the world where you can fly through the polar wind and make the measurements” they needed for this. This place is located in Svalbard. So in May 2022, scientists set course for this Norwegian archipelago just a few hundred kilometers from the North Pole. And after about fifteen minutes of suborbital flight, their rocket, named Endurance, indeed measured a variation in electric potential! Of only 0.55 volts. About what it takes to power a watch. But enough to explain the polar wind.
A Weak Electric Field, But Sufficient to Explain the Polar Wind
“It’s more than enough to counteract the gravity acting on hydrogen ions, which are the most abundant particles in the polar wind,” says Alex Glocer, co-author of the study, in a NASA press release. With an effect ten times greater than that of gravity, “it’s even enough to eject them from our atmosphere at supersonic speeds.”
Researchers believe that the ambipolar field, as a fundamental field of our planet alongside gravity and magnetism, may have continuously shaped our atmosphere over time — in a way they now hope to begin exploring. And since they have now shown that a planet’s internal dynamics can create an ambipolar electric field, they suggest that similar electric fields should exist on other planets, particularly on Venus and Mars. All that remains is to measure them too…