Alien Aurorae

In Episode 228 we learned the basics of an aurora, the gorgeous, ephemeral dance of the firmaments.

Solar winds slam into Earth’s magnetosphere, a meeting that kicks off a process that excites atoms in our atmosphere, producing fluorescent displays in the sky. Those fortunate few who witness them are mesmerized and thrilled.

But we earthlings are not the only beings in the universe that might be blessed with auroras. In fact, if little green beings inhabited the other orbs in our solar system, they might see big green light shows of their own!

The image above exhibits an ultraviolet aurora on Saturn, spied by the Hubble Telescope in 1997.

Both Saturn and Jupiter feature massive magnetic fields. Jupiter’s magnetosphere is 20,000 times stronger than ours. The field is 15 times wider than the sun! Though both gas giants dwarf our magnetism, Jupiter is the standout auroral planet in our system. Saturn’s auroras are likely caused by the solar wind, just as they are on Earth. Jupiter, however, is a much more intricate situation.

Some of Jupiter’s storms do stem from the solar wind, but the system’s largest planet also receives contributions from its moons. Its closest natural satellite – Io – exhibits large amounts of volcanic activity. The moon’s eruptions spew charged atoms into space; thanks to its proximity to its mother, these ions directly interact with Jupiter’s magnetosphere. The result is not just auroras, but constant auroras! Because the storms are not mainly coming from the solar wind, Jupiter experiences auroras at all times!

The other planets also experience aurora. Even Uranus.

Uranus and Neptune mirror the other planets that have significant magnetic fields; their auroras precipitate on the poles. Info about auroras on Uranus even aided scientists into pinning down where the poles are on the planet, as Uranus spins in a wacky manner.

Venus and Mars do not have magnetic fields, but astrophysicists have still detected auroras there. On Venus, an aurora can appear over the entire planet, often in diffuse patches, because no magnetic field can direct the solar wind. On Mars, the atmosphere is too thin to produce similar shows. Instead, local, weaker magnetic fields can create aurora above a viewer. The Mars Global Surveyor detected auroral activity; if not for such instruments, we might not know about the storms on Mars.

Mercury does have a magnetic field, but it is so close to the sun that no atmosphere can exist, which means no auroras.

So, auroras happen on other planets. Makes sense. It follows, then, that they probably happen in other solar systems, right? Right!

In 2015, scientists discovered the first extra-solar aurora on a brown dwarf in the constellation Lyra. The aurora on the substelar object is a million times brighter than the northern or southern lights on Earth.

By far the strangest instance, though, does not belong to a planet or a brown dwarf.

Between 2014 and 2016, the Rosetta spacecraft monitored a comet, named 67P/Churyumov–Gerasimenko. And, you guessed it, they discovered auroras on the icy ball!

Rosetta observed Oxygen and Hydrogen emissions from water molecules in the comet’s coma. When electrons from the solar wind struck these atoms, auroras popped up! Simply incredible!