A 10 km deep subsurface ocean is thought to exist at the south pole of Enceladus, below a 30–40 km thick ice crust. This artist’s impression shows hydrothermal activity taking place on the floor at the base of Enceladus’s ocean. As hot water travels upward, it comes into contact with cooler water, causing minerals to condense out and form nano-grains of ‘silica’ floating in the water. These are eventually expelled through the vents that connect the ocean to the surface of Enceladus. After being ejected into space via the moon’s geysers, the ice grains erode, liberating the tiny rocky inclusions subsequently detected by Cassini.
Full story: Hot water activity on icy moon’s seafloor