Water is everywhere. So far, scientists know of no living things, even the smallest microorganisms, that can live without liquid water. Until recently, Earth was the only place we thought had liquid water, but now we know of other places.
Europa and Callisto, two of Jupiter's moons, may have liquid water oceans beneath a surface crust of ice. In the case of Europa, this ocean may have twice as much water as the whole Earth! Most of the water in the universe, though, is in the form of ice. This ice can come in many forms.
On Earth, the ice is not as cold or hard as it is elsewhere in our solar system. Here the ice is made up of many grains all tightly pressed together. Between these grains is a thin film of water. It is so thin, we might think it is not even there. But, in fact, there is enough water to allow microorganisms to live there. They feed on the minerals in small amounts of dust trapped within the ice.
Scientists discovered these micro-organisms in Antarctica by drilling far down into glaciers. They pull out ice cores with layers of ice that took hundreds of thousands of years to build up.
Ice cores contain a record of past climate. Micro-organisms have been found living in some ice cores buried deep below the surface.
When you get away from Earth, though, the ice becomes so hard that it is like a rock. So, unlike Earth, this ice contains no liquid water.
The rings of Saturn are made up of rock-hard ice particles that have gathered around the planet.
Comet Hale-Bopp visited Earth's skies in April 1997. Photo taken by Charles White and Terri Formico.
Comets streak through the solar system, releasing small amounts of their ice as it is driven off by the sun's energy, forming a tail. When comets collide with other bodies in the solar system they release all their water to the moon or planet they crashed into. This is one important way in which many planets, like Earth and Mars, and many moons, like Callisto and Europa, may have gotten a lot of their water.
Recently, using a new instrument on the Spitzer Space Telescope, scientists discovered that Enceladus, a moon of Saturn, has water volcanoes spouting up through cracks in its icy surface. The Cassini spacecraft at Saturn has learned more about the water volcanoes during its flyby passes of Enceladus. In fact, the more we look, the more water we see, so it seems more and more that water really is everywhere.
Artist's idea of how an ice geyser would look on Saturn's moon Enceladus.
Europa and Callisto, two of Jupiter's moons, may have liquid water oceans beneath a surface crust of ice. In the case of Europa, this ocean may have twice as much water as the whole Earth! Most of the water in the universe, though, is in the form of ice. This ice can come in many forms. 
