According to The New Scientist, Saturn’s white moon, Enceladus is surrounded by a thin, watery atmosphere. The moon is so tiny that it would not hold an atmosphere, so scientists think that the atmosphere is being created by more violent means such as volcanos or geysers.
The atmosphere is so thin it is invisible, but Cassini was able to discover it because it bends Saturn’s magnetic fields. When the Sun ionises water molecules in Enceladus’s atmosphere, the ions begin to be pulled by Saturn’s magnetic field lines, which are rotating with the planet at a relative speed of 26 kilometres per second.
The magnetic field near the moon’s atmosphere bends to accelerate the ions on Enceladus to that speed, says Christopher Russell, a Cassini team member and geophysicist at the University of California in Los Angeles, US.
“We can calculate how many ions it would take to bend the magnetic field by the amount seen,” Russell told New Scientist. He estimates the moon is losing about 125 kilograms of water to space every second. That loss is too great for the atmosphere to be formed simply by the Sun’s photons boiling off molecules from the moon’s icy surface.