Water On 24 Themis

Two independent teams of astronomers have discovered, and therefore confirmed, that the Main Belt asteroid 24 Themis, orbiting between Mars and Jupiter, is almost completely covered in frost. That is, water. This is the first time water has been directly identified on the surface of an asteroid.

Themis-- the twenty-fourth asteroid discovered-- is 123 miles across, so the water there is fairly substantial even if it's only on the surface. At that distance from the Sun, however, scientists say it's unclear how frost could remain on the surface over time. It should sublimate away. If it does, the frost is obviously replenished, which might mean Themis has even more water under the surface.

The discovery also strengthens the argument that Earth's water may have been brought to the planet via collisions with asteroids. In that scenario, life, too, may have arisen elsewhere and been brought to Earth-- possibly in the water.