Researchers have now seen water vapor rising from the surface of Ganymede. This moon of Jupiter is the largest moon in our solar system, which probably contains more liquid water than all the oceans of the earth beneath its ice sheets. Ganymede is usually too cold for ice to evaporate. However, studies published in Nature Astronomy have shown that charged particles at high noon and the precipitation of sunlight are sufficient to submerge molecules such as oxygen and water vapor (change from freezing to gas).
The very constant presence of an oxygen atmosphere for Hubble observations of this moon has been known for nearly two decades. The space telescope was able to detect long colored ribbons of ultraviolet light emitted by the auroral band, the electrified gas. The most likely culprits were molecular oxygen, O2 – but there were some emissions that did not match the atmosphere of pure molecular oxygen.
A possibility was raised that atomic oxygen was present so that occasionally a single atom of oxygen was released from the surface. Instead, the latest analysis shows that it is water vapor that is the mysterious element of Ganymede’s thin atmosphere. Lead author Lorenz Roth, from the KTH Royal Institute of Technology in Stockholm, said in a statement, “So far only molecular oxygen has been observed.”
“It is produced when charged particles erode the surface of the ice. The water vapor we have now measured is the result of the thermal escape of water vapor from warm icy regions. The data used for this discovery are from the original 1998 mission and historical observations collected between 2010, plus studies conducted in 2018 to aid observations conducted around Jupiter by NASA Juno. The Juno spacecraft itself provided images closest to the moon’s surface for decades, and visual artists were even able to create reconstructed aircraft all the way from Ganymede to Jupiter.
But it’s not just Juno who is helping Hubble. The mission of discovering Europa, Callisto and Ganymede to unravel the secrets of this moon is important for Jupiter Ice Moon Explorer or JUC to discover this task. Roth added, “Our results could provide JUICE instrument teams with valuable information that could be used to refine their observation plans to optimize the use of spacecraft.”
