Northern and Southern Lights observed on Saturn at the same time

I’m going to start with some of the fundamentals on this one, and build towards the titular observation.

Everyone’s familiar with magnets. I’m not, in this post, going to drill down into the Standard Model view of electromagnetism; let’s just go with what we know, that some things – like iron – can produce strong magnetic fields.

The Earth is one of those things that produces a magnetic field. It has one mostly because of the molten metal that’s moving around beneath the surface. The Earth ends up being pretty close to a magnetic dipole, like one of those bar magnets you played with in science class in school, so named because it has a north and south pole (that is, its field has an orientation, and each “end” of the magnetic field acts differently). The Earth’s like that too, with two concentrations of the magnetic field lines all collecting at places somewhat close-ish to the geographic north and south poles.

At the same time we’ve got the Sun producing something called the solar wind. That’s the name given to the constant stream of charged particles – electrons and protons, mostly – that are streaming away from the Sun all the time. They’re coming at the Earth, and everything else in the solar system, all the time. Those particles are affected by magnetic fields, though. If they come close to the Earth’s magnetic poles, the shape and strength of the field in those spots can be just enough pull them into our atmosphere. If they do, and the particles smash into oxygen and nitrogen atoms in our air, they can combine and give off a flash of energy that may manifest itself as visible light. That is what we call the Northern (or Southern) Lights, or the aurora borealis(or australis).

But many planets have a magnetic field, and the solar wind blows everywhere, so it’s not just our planet that has these aurora. Saturn has them too, but we weren’t able to see them until 1997. This is because when the charged particles from the solar wind get caught in Saturn’s magnetic field they slam into different atoms, and the flash of energy they give off isn’t visible light, but ultraviolet light of a frequency that gets absorbed in our atmosphere. The first time Saturn’s aurorae were seen was from the Hubble telescope (which, because it’s in space outside our atmosphere, can see that UV light).

Last year, however, Saturn was in just the right spot that its rings and equator were edge-on from our point of view. This meant that we could see the aurorae of both poles at the same time. In doing so we were able to detectdifferences in the north and south aurora. These observations may help us understand the aurora phenomenon, the solar wind, and the internal structure of Saturn.

Here’s a short video of the Hubble images of both aurorae at once.

Or you can click through to this Guardian Science article that has a longer and more detailed explanation from NASA.