Enceladus is the sixth-largest of Saturn's moons, and it is so tiny that it could fit lengthwise into the whole of the United Kingdom (shown to scale here). Nevertheless, it isn't size that counts when it comes to life. In fact, Enceladus is one of only three outer solar system bodies where active eruptions have been observed. More importantly, its eruptions are made up largely of water, leading many experts to believe that a liquid ocean exists under the moon's icy surface. And where there's water, there might be life.