Could there be life beneath the surface of Mars or moons? I realize radiation and extreme temperatures would probably destroy life on the surface of most planets and moons, but could life exist beneath the surface (e.g. like earth worms on earth)?
That's one of the big questions. ESA scientists, at least, think it's worth looking for underground life. See ExoMars mission.

More likely than earth worms are microbes, since some microbes on Earth live under similar conditions as presumed for underground Mars.