Planetary scientists once thought Earth was an oasis in a dry solar system, as early missions to our neighbors revealed desert-like conditions on the Moon, Mars, and Mercury. In contrast, our Earth is literally covered with water.
Missions in recent years have overturned our view of a dry solar system, returning mounting evidence of ample water from a vast array of locations.
Comets from the remote corners of our solar system are made of water and other ices. Orbiters, landers, and rovers reveal Mars as a watery world in the distant past -- a world that today may contain entire underground oceans of frozen water.
The Moon, once thought dry-as-a-bone, has a water cycle -- with small amounts of water moving across its surface -- and millions of tons of water ice locked into frozen crater floors at its poles. Rings of ice orbit the gas giants, and several moons of these distant worlds have immense oceans of liquid water beneath their frozen crusts.
Even Mercury has ice in the dark craters at its poles, as investigated by the ongoing MESSENGER mission.
Water is critical to life and to future human forays into space. While we now know that Earth is not the only place with water, it is the only oasis that contains life. We should remember to take care of our water resources on our home planet, even as we are discovering water almost everywhere in our solar system!