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A New Look at Comet's Core Could Reveal Its Role in Our Planet's Early History

By PETER N. SPOTTS

Sept. 12, 2005 ? Some scientists have long held the notion that comets delivered many of the chemical building blocks of organic life. NASA's Deep Impact mission to comet Tempel 1 has substantially strengthened their case.

Last week, at a meeting in London and in results published in Thursday's edition of Science Express, Deep Impact scientists say they have found high levels of organic chemicals beneath the surface of Tempel 1's core.

-An Abundance of Chemicals

But what they've seen so far makes it "more likely" that comets seeded Earth with the chemical precursors for organic life, says Michael A'Hearn, a University of Maryland planetary scientist and the mission's lead researcher.

Past studies from ground-based observatories and comet flybys have identified many of the chemicals in the halo of dust and gas that surrounds the core, as well as in the bright tails of comets.

But these sightings have had little to say directly about the amounts and relative abundance of the compounds comets contain in their cores.

As the team continues to pour through its data, researchers expect to identify all of the chemicals "that comets brought in abundance to the early Earth," A'Hearn says. "That will be our biggest contribution" to understanding comets' roles in the story of life on Earth.

-The Stuff of Stars

One surprise: The team has detected an unexpectedly high concentration of methyl cyanide. Biologists say methyl cyanide is a key player in reactions that form DNA.

"If methyl cyanide is a particularly abundant component, it would suggest that comets could have delivered an abundance of these highly reactive compounds to the early Earth," notes Tom McCollom, a researcher at the University of Colorado at Boulder's Laboratory of Atmospheric and Space Physics.

Methyl cyanide's abundance may also confirm that comets like Tempel 1 can open a window on conditions from which the sun and solar system formed some 4.6 billion years ago.

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