An article published in the journal “Geophysical Research Letters” reports the detection of a stable presence of water vapor in the atmosphere of Jupiter’s moon Europa. Lorenz Roth of the Kth Royal Institute of Technology in Stockholm, Sweden, used ultraviolet observations conducted with the Hubble Space Telescope between 1999 and 2015 to infer the presence of water vapor. Its presence appears to be persistent only in one hemisphere of Europa, the one opposite the moon’s direction of motion in its orbit.