How Do Auroras Work?

When you were a kid learning to name the planets in our solar system (perhaps back when there were 9 of them), the name “Saturn” was nearly synonymous with “rings.” The discs of ice, dust, and rock swirling around Saturn distinguished it from all the other planets. Now, new images released by NASA describe a very different, but much more familiar, kind of ring around Saturn: an aurora.

Here on Earth, the aurora is one of nature’s most beautiful and otherworldly phenomena. So it may come as no surprise that alien auroras exist as well—in fact, they’ve been spotted on all the other planets except Mercury, as well as on several of Jupiter’s moons.

So, what makes an aurora? What do all of these planets have in common?

First of all, the Sun. It’s constantly spewing streams of really hot, really energetic protons and electrons in an outflow known as solar wind.

As the sun’s protons and electrons stream into the atmosphere of a planet, they smash into gas molecules and release energy, resulting in the diffuse light of the aurora. The energy of the collision and the type of gas determines the light’s color—green indicates oxygen and blue indicates nitrogen, for example.

That’s not all it takes to make an aurora, though. Planetary bodies with a relatively weak magnetic field—like Mercury or the Moon—simply get bombarded with solar radiation.

But all the other planets (plus Jupiter’s moons) have a strong magnetosphere—a large region of space that’s influenced by a magnetic field. As the solar winds barrage the planet’s magnetosphere, the particle flow is deflected and reshaped.  This interaction between the solar wind and the magnetosphere results in the fluctuating loops and swirls that grace our polar skies.

Of course, the process is slightly different depending where you are in the solar system. Saturn’s moons, for instance, can stimulate the aurora by their movements through that planet’s magnetosphere, and Jupiter’s aurora gives off 1000 times more energy than Earth’s.

And who knows? Can those delicate arcs and cascades possibly look as beautiful from the terra firma of a planetary neighbor?

For a closer look at Saturn’s light show, watch this video of the aurora shifting over the course of 20 hours (nearly two Saturnian days).