For the first time, astronomers have uncovered evidence of water vapor in the atmosphere of Jupiter's moon Ganymede. This water vapor forms when ice from the moon's surface sublimates -- that is, turns from solid to gas. Scientists used new and archival datasets from NASA's Hubble Space Telescope to make the discovery, published in the journal Nature Astronomy.
Detections of methane on Mars have excited scientists because, on Earth, the gas is often produced by microbes - its presence could indicate that similar life was, or is, present on the red planet. There are potential geological processes that could produce methane too, but even before identifying the source of the gas on Mars, scientists have been trying to solve another mystery.