Hubble Finds First Evidence of Water Vapor on Jupiter’s Largest Moon

Ganymede may have more water than all of the Earth's oceans combined.
Derya Ozdemir
Image of Ganymede captured by the JunoCam during Juno’s June 7, 2021, flyby.NASA/JPL-Caltech/SwRI/MSSS

Astronomers have discovered the first-ever evidence of water vapor in the atmosphere of Jupiter's moon Ganymede, the largest moon in the solar system, by looking through the last two decades of data from NASA's Hubble Space Telescope, NASA announced on Monday.

Studies have already offered circumstantial evidence that Ganymede holds more water than all of the Earth's oceans combined: It's covered in an icy crust and scientists believe it may have a liquid ocean 100 miles (161 km) beneath its surface. And in this new exciting discovery, the scientists were able to find evidence of water vapor, which is the result of ice sublimating from the moon’s surface, while there was barely any atomic oxygen in Ganymede’s atmosphere.

"So far only the molecular oxygen had been observed," Lorenz Roth of the KTH Royal Institute of Technology, who led the team who found the vapor, explained to NASA in a press release. "This is produced when charged particles erode the ice surface. The water vapor that we measured now originates from ice sublimation caused by the thermal escape of water vapor from warm icy regions."

This indicates that instead of coming from the subsurface ocean, water vapor, not only oxygen, may be escaping from the moon's warmer areas by converting from a solid to a gas.

These illuminating findings contribute to scientists' knowledge of Ganymede's atmosphere and add to the excitement surrounding ESA's planned JUICE (JUpiter ICy moons Explorer) mission.

JUICE is scheduled to launch in 2022 and reach Jupiter in 2029. It will spend at least three years studying Jupiter and three of its biggest moons, with a special focus on Ganymede as a possible habitat.

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"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," said Roth.

Right now, we have NASA's Juno spacecraft orbiting Jupiter and taking a close look at Ganymede. Juno has been studying Jupiter and its surroundings since 2016 and has recently released new images of the icy moon.

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