From Scientific American:
An asteroid circling the sun between the orbits of Mars and Jupiter has for the first time been shown to harbor water ice and organic compounds. Those traits had been associated with comets, which spring from colder, more distant reservoirs in the outer solar system, but not their asteroidal cousins. The finding supports the notion that asteroids could have provided early Earth with water for its oceans as well as some of the prebiotic compounds that allowed life to develop.
Two teams of researchers report complementary observations of the 200-kilometer-wide asteroid, known as 24 Themis, in the April 29 issue of Nature. (Scientific American is part of Nature Publishing Group.) Both analyses are based on spectroscopic observations from the NASA Infrared Telescope Facility atop Mauna Kea in Hawaii, which show absorption features that indicate the presence of water and unidentified organic compounds. The ice appears to coat the entire asteroid as a thin layer of frost. The evidence for water on 24 Themis had been presented at conferences by the two groups in 2008 and 2009 but is only now appearing in a peer-reviewed journal.