The signature of water ice on the asteroid 24 Themis has been spotted by two international teams working independently on the NASA Infrared Telescope Facility. As well as detecting ice in the reflected light from the asteroid, a number of organic molecules (not life, just precursors to the molecules involved with life) were also seen evenly distributed across the surface of the rock as it tumbled through space.
Although Ceres, the largest asteroid, is thought to contain water ice locked deep within its dusty surface, the 198km wide 24 Themis showed that some asteroids keep their ice on show. This is quite a surprise since the 150-200 Kelvin temperatures experienced by the asteroid as it warms in the light of the Sun between the orbits of Mars and Jupiter was thought sufficient to cause water to sublimate away.
The discovery may shed some light on a different mystery, however, that of where the oceans on Earth came from. Although we’ve been battered by very icy comets before, the isotopes involved in water on Earth don’t match up with those on Comets enough to suggest they delivered everything to us. Analysis of the water locked in asteroids, which also battered us, might reveal how much came from each source of water in the solar system.