Original URL: http://www.theregister.co.uk/2005/09/08/comet_clay/

NASA's crash comet made of clay

Tempel-1 gives up its secrets

By Lucy Sherriff

Posted in Science, 8th September 2005 09:38 GMT

Initial results from NASA's crash landing on Comet Tempel-1 could spell disaster for the European Space Agency's Rosetta mission to Comet 67P/Churyumov-Gerasimenko, NASA scientists say. In addition, the findings about the composition of the comet are not entirely as expected, and could shed new light on the earliest days of our solar system.

Deep Impact's probe collided with Tempel-1 on 4 July, releasing an immense cloud of dust, gas and ice. The analysis of the ejected material, using the Spitzer space telescope, suggests the surface is composed of very fine powder, of a consistency similar to that of freshly fallen snow.

Speaking at a gathering of planetary scientists in Cambridge, principal investigator, Dr. Mike Ahearn said that the comet is made of unbelievably fragile material.

"You could pick up a chunk of it like you were picking up good powdered snow for skiing, except it would mostly be dust. The various pieces are held together so weakly that you could break them up on any spatial scale, big or small," he said.

This could make it very tough for Rosetta to land, as it is designed to cling on to a presumed-to-be rocky surface, the NASA team says.

But a little sparring between the US and European space agencies is not unheard of, and ESA scientists say they have not lost heart. Comets are a diverse group of objects, said ESA's Dr Bernard Foing, and there is no reason to suspect that 67P/Churyumov-Gerasimenko is as fragile as Tempel-1.

The analysis also reveals that the cometary material is more varied than anticipated. Comet Tempel 1 contains clays, carbonates and hydrocarbons, the BBC reports.

The presence of clays and carbonates is particularly surprising. Comets are thought to contain material, unchanged from the very earliest days of the solar system. But clays and carbonates need liquid water to form, suggesting the early solar system was rather different than we currently imagine, with much more mixing of the material that went on to form the planets. ®