Les aurores de la Terre et des planètes du système solaire

Auroras from Earth and the planets of the solar system

Philippe Zarka
CNRS Research Director, LIRA, Observatoire de Paris-PSL

Visible auroras are, along with eclipses, one of the most beautiful natural astronomical spectacles. But what causes them? Electrons that bombard the atmosphere, making it luminescent. OK, but where do these electrons come from? One popular belief is that the solar wind rushes towards the Earth's magnetic poles. This couldn't be further from the truth! I'll explain their origin, which is more complex. And on Jupiter? The beautiful ultraviolet ovals around its magnetic poles bear a striking resemblance to those on Earth. But here again, intuition fails us: the origin of Jupiter's aurorae is totally different from that of the Earth's! What's more, luminous dots and trails - which have no equivalent on Earth - accompany the Jovian aurorae. What are they? I'll explain their origin later. Finally, we can't talk about the aurora in terms of optics alone: they are accompanied by very powerful radio emissions, which are studied from the ground and from space, and help to reveal the workings of the magnetosphere, of which the aurora is one of the visible manifestations. Our exploration will lead us to talk about the other planets in the solar system, and even exoplanets and stars...