[meteorite-list] Deep Impact Reveals Comet's Components

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Jul 14 12:09:12 2006
Message-ID: <200607141513.IAA05167_at_zagami.jpl.nasa.gov>

http://www.sciam.com/article.cfm?chanID=sa003&articleID=000891F1-AEA2-14B6-ABEB83414B7F4945

Deep Impact Reveals Comet's Components
David Biello
Scientific American
July 14, 2006

The Fourth of July last year had some extra fireworks. NASA's Deep
Impact spacecraft sent a hefty projectile--more than 800 pounds--into
the body of the comet known as Tempel 1. The collision delivered 19
gigajoules of energy--the equivalent of nearly five tons of explosive
TNT--into the wandering comet and ejected a plume of its innermost
secrets. Roughly 10 million kilograms of comet stuff (more than 22
million pounds) spread out into space, giving scientists a rare glimpse
of the ingredients that go into making a comet. Now researchers
observing with the Spitzer Space Telescope have revealed their findings:
comets contain a mix of materials that formed under widely divergent
conditions.

Carey Lisse of Johns Hopkins University and his colleagues studied the
collision through 12 infrared spectrographs taken by Spitzer from July 2
through July 5. Prior to impact, Tempel 1 displayed the same streaming
dust as any other comet, pushed back from the cometary body by the sun's
radiation. But after the early-morning impact, Tempel 1 revealed itself
to be made of water ice and gas, carbonates, polyaromatic hydrocarbons,
silicates, sulfides and other elements.

This mix of components does not match current models of comet dust. Some
of the minerals detected require temperatures between 1,100 and 1,400
degrees Kelvin--only found as close to the sun as Mercury--as well as
volatile gases such as methane that only remain stable at temperatures
below 100 K. This means that there must have been some form of mixing
over large distances going on in the nebula that gave birth to the sun
billions of years ago.

The spectra also hint that water must have been abundant in the area
where the comet formed and that Tempel 1 is not as carbon-rich as some
of its peers; carbon-based materials appear to make up only 20 percent
of this comet compared to as much as 50 percent of others. Nevertheless,
the material in Tempel 1 matches that ejected by Comet Hale-Bopp in 1995
and that means that these comets formed in broadly similar ways, the
researchers argue. Science published the paper analyzing the spectra
online yesterday.
Received on Fri 14 Jul 2006 11:13:32 AM PDT