Scientists discovered water vapor for the first time on Ganymede (Jupiter's largest moon). To find the vapor, scientists used archival and new data from the Hubble Space Telescope. This is what happens when the surface ice melts and becomes gas.
Lorenz Roth, of the KTH Royal Institute of Technology (Sweden), examined data from Hubble's Cosmic Origins Spectrograph (2018) and images taken by the Space Telescope Imaging Spectrograph between 1998 and 2010. According to NASA, which launched Hubble in 1998 as a joint project with European Space Agency (ESA), the STIS images of ultraviolet showed auroral bands, which are colorful ribbons made up of electrified gases.
Previous research suggested that atomic oxygen could have caused discrepancies in UV images captured over time. Roth's team discovered that the moon's atmosphere contained very little atomic oxygen using data from the Cosmic origins Spectrograph. This meant that there must be another explanation for the discrepancies.
It is possible that the temperature at Ganymede’s equator could rise enough to allow surface ice to release water molecules. Roth's team discovered that the differences in the distribution of auroras in UV images match the expected location for water in the moon's atmosphere when they reexamined them.
Research has shown that Ganymede could contain more water than all our oceans. It is thought that the moon's ocean lies around 100 miles beneath the surface. The vapor is not from there. The moon's temperature freezes water on the surface.
This discovery was made ahead of JUICE (or Jupiter ICy Moons Explorer), the ESA's upcoming mission. The mission is expected to launch in 2022, and reach Jupiter in 2029. The mission will spend at most three years studying the planet and its three largest moons. JUICE will be paying special attention to Ganymede as both a planetary body, and potential habitat.
Roth stated in a statement that "our results can provide JUICE instrument teams valuable information that may help them refine their observation plans to maximize the use of spacecraft," Roth added.
Since 2016, NASA's Juno mission has been studying Ganymede's environment (aka, the Jovian System) with its Juno mission. According to NASA, studying the Jovian system's history and examining its formation and evolution "will help us understand how gas giant planets and satellites evolve." New insights are expected to be gained about the habitability and potential existence of Jupiter-like exoplanetary system.