A substantial ocean most likely exists beneath the icy surface of Saturn's diminutive moon Enceladus, raising the possibility that primitive forms of extraterrestrial life exist in its briny depths.

The ocean lies between the moon's rocky core and a layer of thick ice, and is estimated to be about the size of Lake Superior. That's large for a moon that is only 310 miles (500 kilometers) in diameter and could fit within the borders of Arizona.

In our solar system, the only other moon known to have similar contact between liquid water and rock is Jupiter's Europa. Both the rock and the water are considered to be essential for the chemistry that could, over eons, turn nonliving