[♩INTRO]
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!
As we come up on the holidays, you might be thinking about what gifts to get for
your friends and family this year.
And if you’ve got any science fans in your life, we can help with that.
We just released a brand-new set of SciShow Magnetic Words over on DFTBA.
It’s a set of magnets with science-related words put together by our whole team.
You can stick them onto your refrigerator or any other magnetic surface and
rearrange them to create fun science sentences and poetry.
We’ve also got a bunch of other SciShow merch if you like that kind of thing.
You can find it at DFTBA.com/SciShow.
[♩OUTRO]