Astronomers have discovered evidence of water vapor in the atmosphere of Jupiter's moon Ganymede for the first time.

Ganymede, the largest moon in the Solar System, is covered in an icy crust. Scientists believe Ganymede may have a liquid ocean 100 miles (161 km) beneath its surface, and that such an ocean could host aquatic alien life.

On Monday NASA announced that, by looking through the last two decades of data from the Hubble Space Telescope, researchers had discovered evidence of water vapor in the Jupiter moon's thin atmosphere.

This water probably doesn't come from the underground ocean, though. Instead, it's likely ice vaporizing from the moon's surface.

Even though it doesn't say much about the moon's potential for alien life, this water vapor adds to scientists' understanding of Ganymede's atmosphere. Previously, they only knew that it contained oxygen.

Hubble's ultraviolet images of Ganymede from 1998. (NASA/ESA/Lorenz Roth) (NASA/ESA/Lorenz Roth)

Above Hubble's ultraviolet images of Ganymede from 1998 were originally interpreted as displaying the atmosphere's atomic oxygen, however the new analysis found differences in the UV aurora correlate with the warming of Ganymede's surface temperature through the day – exactly when water would sublimate into the atmosphere.

"So far only the molecular oxygen had been observed," Lorenz Roth of the KTH Royal Institute of Technology in Stockholm, Sweden, who led the team who found the vapor, told NASA.

"This is produced when charged particles erode the ice surface."

The research and datasets were published in the journal Nature Astronomy.

This article was originally published by Business Insider.

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