This story can be accessed from several places (see www.physorg.com/print191665880.html and BBC News April 28th http://news.bbc.co.uk/1/hi/science_and_environment/10090128.stm April 28th ‘Asteroid Themis has frosted surface’ and in addition www.sciencedaily.com). Asteroid 24 Themis, in the Themis Belt between Mars and Jupiter, was the space rock where scientists detected water ice and organic material on the outer surface (reporting on a paper in Nature April 29th). NASAs Infrared Telescope on Hawaii examined the 200km wide surface of the asteroid and by measuring the infrared sunlight reflected by the object found the spectrum was consistent with frozen water – and considered it was coated with a thin film of ice. They also detected complex organics with long-chain molecules.
The ice is probably being replenished over time – by ‘outgassing’ from the interior. Perhaps. Until recently asteroids were assumed to be dry and rocky constructs. These findings now blur the differences between comets and asteroids.
Asteroids will remain in the news for a while as a Japanese capsule is winging it’s way back to the earth with a sample picked up from the surface of such a space rock, and the European Rosetta probe will fly past an asteroid later this year. Finally, a NASA spacecraft will go into orbit around an asteroid in 2011.