Scientists find Water vapor on Ganymede
A team led by the Swedish KTH examined data acquired by NASA's Hubble telescope on Jupiter's and the solar system's largest moon Ganymede, and discovered past occurrences of water vapor in Ganymede's atmosphere.
The discovery was made by analyzing UV light on Hubble's Space Telescope Imaging Spectrograph photos from 1998 to 2010, and data from Hubble's Cosmic Origins Spectrograph in 2018. NASA has released the following statement regarding the discovery:
"Ganymede's surface temperature varies strongly throughout the day, and around noon near the equator it may become sufficiently warm that the ice surface releases (or sublimates) some small amounts of water molecules. In fact, the perceived differences in the UV images are directly correlated with where water would be expected in the moon's atmosphere."
Scientists believe there is more water under the Ganymede ice sheet than there is in all of Earth's oceans combined. In 2022, ESA's (European Space Agency) JUICE (JUpiter ICy moons Explorer) mission will leave Earth to study the presence of water closer to Jupiter's moons. If all goes according to plan, JUICE will arrive on Jupiter sometime in 2029.