The very labile presence of an atmosphere composed of oxygen has been known for over two decades, thanks to observations conducted by Hubble. The space telescope was able to detect auroral bands, long colored ribbons of ultraviolet light emitted by the electrified gas. Probably the cause was molecular oxygen, O2, but there were some emissions that did not correspond to an atmosphere of pure molecular oxygen. The latest analysis, in fact, shows that water vapor is the other mysterious component of the thin atmosphere of Ganymede.
"Until now, only molecular oxygen had been observed," the author said in a note principal Lorenz Roth, of the KTH Royal Institute of Technology in Stockholm. “This is produced when charged particles erode the surface of the ice. The water vapor that we have now measured comes from the sublimation of the ice caused by the thermal escape of water vapor from the icy to the warm regions ”.
The data used to make this discovery are historical observations collected between 1998 and 2010, as well as studies conducted in 2018 to help NASA's Juno observations around Jupiter. The Juno spacecraft itself recently delivered images closest to Ganymede's surface. The results of this work will be crucial for the Jupiter Icy Moons Explorer, or JUICE, a mission to explore Europa, Callisto and Ganymede, entering orbit around the latter to discover the secrets of these moons.
" Our findings can provide JUICE teams with valuable information that can be used to refine their observation plans to optimize spacecraft use, ”added Roth.
JUICE is expected to launch next year, in June and will enter orbit around Jupiter in October 2029.