Cool to moderately warm hydrothermal vents circulating water through the seabed could sustain habitable conditions on moons such as Jupiter's Europa and Saturn's Enceladus for billions of years.

If alien life exists on Europa, we may find it in hydrothermal vents

Source: space
Source Link: https://www.space.com/alien-life-europa-enceladus-hydrothermal-vents