Jupiter's moon, Europa, has an oxygen atmosphere and an icy surface that may cover an ocean. Since the moon is geologically active, there may be thermal volcanic vents to supply energy for life.
Life like the strange worms and crabs living around volcanic vents at the bottom of Earth's oceans?
Yes. And Saturn's moon Titan, which is larger than the planet Mercury, has a nitrogen-rich atmosphere and hydrocarbon lakes. There are some mysterious chemical reactions taking place on Titan that may be a sign that bacteria like organisms are living there.
Titan's pretty cold, though way below water's freezing point. That life would be frigid! The solar system only has eight planets, not counting Pluto, and four of those are gas giants. Saturn alone has fifty three named moons.
Scientists working with the Cassini spacecraft discovered Saturn's moon Enceladus has liquid water under its surface.
How Do They Know That?
It has geysers! The spacecraft used its plasma spectrophotometer to measure an ice plume ejected from the moon. It found negative water ions. These ions are present where liquid water is in motion, like in fountains. The spacecraft also found hydrocarbons, the building blocks for life.