Auroras Light Up Some of the Biggest, Wildest Moons in the Solar System

Artist’s depiction of an aurora on Jupiter’s moon Ganymede, the largest moon in the solar system.
Julie Inglis

Four of the most intriguing worlds in the solar system also boast auroral light shows, according to a team of astronomers observing Jupiter’s Galilean moons. 

The four satellites orbiting Jupiter — Io, Ganymede, Callisto and Europa — are also the gas giant’s largest, having initially been discovered by Galileo in the early 1600s. Io is the most volcanically active world we know of, and the other three are suspected of harboring liquid oceans beneath their surface layers. 

Now astronomers using multiple observatories have added faint auroras to the list of features worth investigating further.

“These observations are tricky because in Jupiter’s shadow the moons are nearly invisible. The light emitted by their faint aurorae is the only confirmation that we’ve even pointed the telescope at the right place,” explains CalTech professor Katherine de Kleer in a statement.

de Kleer is lead author on one of two studies on the discovery published Thursday in the Planetary Science Journal.

The atmospheres on the moons are thinner than Earth’s, leading to dancing lights that are redder than the greens we’re more likely to see from the aurora borealis and aurora australis here on Earth. The ochre display could also be up to 15 times brighter, the scientists estimate. 

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Volcanic gases and dust on Io add more sodium to the atmosphere, lending aurora there a more yellow-orange-ish glow. 

“The brightness of the different colors of aurora tell us what these moons’ atmospheres are likely made up of,” adds de Kleer. “We find that molecular oxygen, just like what we breathe here on Earth, is likely the main constituent of the icy moon atmospheres.”

We can continue to expect more details on these weird worlds as the James Webb Space Telescope and missions like Juno and JUICE target them and help us evaluate humanity’s travel plans for the centuries to come. 

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