Hundreds of millions of kilometers away, and taking advantage of eclipses, astronomers have managed to observe the glow of the aurora borealis on four moons of Jupiter: Io, Europa, Callisto and Ganymede. The technique involved observing these moons each time they passed behind the giant planet, then re-emerged on the other side. “The Northern Lights are always there when you observe an eclipse”, confirms Californian planetary scientist Katherine R. de Kleerco-authors of two studies published simultaneously.
Unlike the Earth, which owes its aurora borealis to particles ejected by the Sun and colliding with its magnetic field, the moons of Jupiter owe their aurora borealis to one of them, Io.
Io is this moon characterized by the most violent volcanic activity of all the solar system. These are volcanic ejecta which, interacting with sunlight, become electrically charged and are captured by Jupiter’s magnetic field. Some “ricochet” in the thin layers of gas surrounding the moons, causing these glows. Someone who could stand on Io —safe from these multiple eruptions— would see many more colors than on the three moons, one of the studies reads, due to the diversity of elements released by volcanoes.
While this discovery has the potential to fire the imagination of artists, it could also provide an opportunity for other planetary scientists to study the chemical composition of these thin layers of gas—too thin to be called atmospheres.