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Earth’s northern and southern lights are some of the most magical sights on our planet. But they’re not unique to Earth, and aside from being beautiful, auroras can also give us unusual insights into these other worlds.

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Earth’s northern and southern lights are some of the most magical sights on our planet. But they’re not unique to Earth.

We’ve seen these auroras throughout  our solar system, and even far beyond. And aside from being beautiful, auroras  can also give us unusual insights into these other worlds. Like, whether or not they have underground oceans.

Here on Earth, we get auroras when  charged particles from the Sun, known as the solar wind, travel  down Earth’s magnetic field lines and collide with molecules in the atmosphere. As they pick up a bunch of energy,  those molecules briefly jump up to a higher energy state and then  relax back to their original state. When they do that, each molecule  gives off a specific color of light.

And that’s what produces those colorful glows. You don’t need very special  circumstances for this to happen, so we generally expect to see auroras  on any body in the solar system that has a magnetic field and  a thick enough atmosphere. But extraterrestrial auroras can be totally  different from the ones we see here, depending on the energies and molecules involved.

Some are different colors, while others  aren’t even visible to the naked eye! Still, by observing them through telescopes  that can pick up various wavelengths, we can gather the clues all  these auroras have to offer. One place we see these auroras is  on Jupiter’s largest moon, Ganymede, which is the only moon in our solar system  that generates its own magnetic field likely thanks to its metallic iron core.

It also has a thin oxygen atmosphere. So as the solar wind collides with  the gases near Ganymede’s poles, it produces auroras in both  visible and ultraviolet light. And by studying the invisible, ultraviolet  part of the aurora using the Hubble.

Space Telescope, scientists spotted  something really interesting. See, they expected Ganymede’s aurora  to wobble quite a bit around the poles. That’s because, as the solar  wind gets near Ganymede, it’s affected by Ganymede’s magnetic  field, but also by Jupiter’s.

So it moves around in complicated ways  as the moon goes around the planet. But the aurora wasn’t nearly  as wobbly as they expected. Something seemed to be damping its motion.

They realized that this damped motion  could be evidence for the long-standing hypothesis that Ganymede has an ocean  of liquid water under its surface. See, if this hypothetical ocean has a lot  of charged atoms or molecules dissolved in it, those particles will move  in response to a magnetic field. And that movement of charged particles  actually induces a second magnetic field oriented opposite the original one.

So in the case of Ganymede, that  secondary magnetic field could be counteracting the effect of the  existing magnetic forces on the moon hence the damped motion of the aurora. The upshot of all of that is that basically,  by looking at pretty lights in the sky above Ganymede, we were able  to uncover something amazing about the interior of the moon. But auroras can also give  us clues about the exteriors of other moons and planets.

And weirdly enough, one of the  places that’s true is Mars. And that is weird because  Mars has no magnetic field and barely any atmosphere… and yet it has auroras. They’re called proton auroras because  they happen when high-energy protons in the solar wind collide with hydrogen in  the outer edge of Mars’ thin atmosphere.

There, they pick up electrons  and become neutral atoms. Then, as they enter deeper into the atmosphere, they lose energy as ultraviolet light. The auroras would be invisible to us, but NASA’s MAVEN spacecraft first  detected this ultraviolet glow in 2016.

And it turns out that these auroras can  actually tell us something important about the Martian atmosphere. See, the intensity of the Martian  aurora appears to be seasonal:. It’s brighter when Mars is closer to the Sun, heating up and releasing more  water vapor into the atmosphere.

The Sun’s ultraviolet light then breaks  some of that water down into oxygen and hydrogen, and that hydrogen  becomes fuel for the incoming protons to produce the aurora. This means that the brightness  of the aurora can tell us about how quickly water is being  lost to the outer atmosphere where it then eventually drifts off into space. And that’s intriguing, because  we know Mars used to have a much denser atmosphere,  and is gradually losing it.

So this aurora turns out to be a good  proxy for studying the rate of that loss. And it may tell us something about how Mars became the cold, dry world it is today. Moving further afield, auroras aren’t  just useful for studying planets and moons in our Solar System.

Scientists think we can also use  auroras to detect and study exoplanets. See, not only can auroras give  off visible and ultraviolet light, they can also produce radio  waves, and Earth’s auroras do. So scientists had thought for a while  that it might be possible to use radio telescopes to detect other auroras from Earth.

And this could reveal exoplanets we  couldn’t find using visible light. In particular, astronomers thought that  this technique could be useful for finding. Jupiter-like exoplanets at far  distances from their host stars.

But in 2020, a team claimed to have  used this method to find a roughly. Earth-sized planet close to a small red  dwarf star about 30 light years away. Scientists still need to test this out  a few more times before declaring it a success, but if all goes well, this  could end up being an even more versatile technique for planet-finding than we thought.

So in the grand scheme of things, the  light shows we get on Earth aren’t really anything out of the ordinary. But what is extraordinary is the fact  that these stunning displays can help us explore the universe, from our own  neighborhood to worlds light-years away. Thanks for watching this episode of SciShow Space!

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