Free Astronomy Magazine January-February 2022

JANUARY-FEBRUARY 2022 that is always opposite to its direc- tion of motion. The asymmetric distribution of water vapour was predicted by pre- vious studies based on computer simulations, but had not previously been detected observationally. “The observation of water vapour on Ganymede and on the trailing side of Europa advances our under- for the first time, an astronomer has discovered evidence for persistent water vapour in the atmosphere of Europa. Using a technique that re- cently resulted in the discovery of water vapour in the atmosphere of Jupiter’s moon Ganymede, an as- tronomer has found evidence of water in Europa’s trailing hemi- sphere — the portion of the moon with a smooth, icy surface scarred by cracks and fissures. The surface of the moon is a bleak environment with an average temperature of −170 °C and only a tenuous atmos- phere. However, astronomers sus- pect that Europa harbours a vast ocean underneath its icy surface, which some scientists speculate could host extraterrestrial life. Now,