Observations by the NASA/ESA Hubble Space Telescope in far-ultraviolet light of Jupiter’s icy moons were used in the past to detect molecular oxygen in their tenuous atmospheres. The results of an analysis of images and spectra of Jupiter’s moon Ganymede have recently shown that the same observations also contain information that water vapor is abundant in the atmosphere in addition to oxygen. A planetary researcher from the KTH Royal Institute of Technology has now used the same analysis for Jupiter’s moon Europa and found a water vapor atmosphere as well, but, mysteriously, only above the icy moon’s trailing hemisphere (the portion of the moon that is always opposite to its direction of motion).
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