Water vapor found on Jupiter’s moon Ganymede

The largest moon in our solar system is a little less of a mystery.

An international team of astronomers has detected evidence of water vapor in the atmosphere of Jupiter’s massive moon Ganymede — a discovery that could help in the hunt for habitable exoplanets. 

Icy world: Ganymede is the largest moon in our solar system — it’s even bigger than the planet Mercury — and astronomers suspect it may contain more water than all of Earth’s oceans combined.

The discovery of liquid water elsewhere in the universe is a primary objective in the hunt for extraterrestrial life, so the possibility of all that water has made Ganymede a topic of interest for astronomers.

However because the moon is so cold, all they’ve been able to detect so far is ice — if there is any liquid water on the moon, it’s likely buried 100 miles below the surface.

Alien water vapor: Using data collected by the Hubble telescope over the past two decades, astronomers have now detected the first evidence of water vapor — the gaseous state of water — in Ganymede’s atmosphere.

The discovery does more than just change what we know about Ganymede.

They also have a good idea of how it got there. At what would be considered noon on Ganymede, the surface near its equator gets hot enough for some of the ice to transition directly to a gas, skipping the liquid stage.

This process is called “sublimation,” and prior to this, we’d never seen sunlight-triggered sublimation on a moon in the outer solar system before.

Why it matters: The discovery of water vapor in Ganymede’s atmosphere does more than just change what we know about the moon — it affects our understanding of Jupiter-like systems throughout the universe.

“Understanding the Jovian system and unravelling its history, from its origin to the possible emergence of habitable environments, will provide us with a better understanding of how gas giant planets and their satellites form and evolve,” NASA wrote in a press release.

That understanding, in turn, could help us assess the potential habitability of any Jupiter-like exoplanets we discover.

Looking ahead: The astronomers hope their discovery of Ganymede’s water vapor will help inform the ESA’s upcoming JUICE (JUpiter ICy moons Explorer) mission, which is set to launch in 2022.

Once the craft reaches Jupiter in 2029, it’ll spend at least three years studying the planet and three of its moons, including Ganymede.

“Our results can provide the JUICE instrument teams with valuable information that may be used to refine their observation plans to optimize the use of the spacecraft,” study leader Lorenz Roth said in the press release.

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