Hundreds of millions of kilometers away and taking advantage of solar eclipses, astronomers have managed to observe the Aurora Borealis glow on four of Jupiter’s moons: Io, Europa, Callisto and Ganymede. The technique was to observe these moons each time they passed behind the giant planet and then reappeared on the other side. “The Northern Lights are always there when you watch an eclipse,” confirms California planetary scientist Katherine R. de Kleer, co-author of two concurrently published studies.
Unlike Earth, which owes its aurora borealis to particles ejected from the Sun and colliding with its magnetic field, Jupiter’s moons owe their aurora borealis to one of them, Io.
Io is this moon characterized by the most violent volcanic activity in the entire solar system. These are volcanic ejecta that become electrically charged through interaction with sunlight and are captured by Jupiter’s magnetic field. Some “bounce off” in the thin layers of gas surrounding the moons, causing this glow. Someone who managed to stand on Io – protected from these multiple eruptions – would see many more colors than on the three moons, says one of the studies, due to the variety of elements rejected by the volcanoes.
While this discovery has the potential to capture artists’ imaginations, it could also offer other planetary scientists the opportunity to study the chemical composition of these thin layers of gas — too thin to be called atmospheres.