The water vapor is likely to form when ice sublimes from the surface of Ganymede that is from solid state to gaseous state. The results were made using new and archived data sets from the National Aeronautics and Space Administration’s (NASA) Hubble Space Telescope.
Previous studies had suggested that Ganymede, which is the largest moon in the solar system contains more water than all of the world’s oceans combined. Though, the temperatures there are so cold that the water is in the frozen state to the surface of the moon.
The Ganymede Ocean is believed to be 160 kilometers down the lunar crust. To which, this means that the water vapor that NASA’s Hubble had located is unlikely to represent the evaporation of that ocean.
The surface temperature of Ganymede fluctuates greatly during the day and around midday it can get so warm near the equator that the surface of the ice may releases small amounts of water molecules.
The JUpiter ICy moons Explorer (JUICE) which is an upcoming mission of the European Space Agency is scheduled to start in 2022 that will confirm these results. It will reach the planet in 2029 where it will spend at least three years. JUICE mission will make detailed observations of Jupiter and its three largest moons.
The Jupiter has at least 79 moons out of which Ganymede is the largest one, followed by Io, Europa.