Comet Holds Building Block for Life

Aug. 17, 2009 -- An amino acid, one of the essential ingredients to life on Earth, has been found in a comet for the first time, NASA announced Monday.

Since amino acids have already been discovered in meteorites, this new development, reported at the American Chemical Society meeting in Washington, D.C., suggests that early Earth had plenty of opportunities to have been seeded for life by extraterrestrial bodies.

Scientists concluded nearly two years of painstaking research on comet samples returned by the Stardust probe to confirm that glycine -- one of 20 known amino acids that form the building blocks for life on Earth -- was in the comet Wild 2, and not the result of terrestrial contamination.

"We're interested in understanding the inventory of materials that were available on early Earth when life got started," lead researcher Jamie Elsila, with NASA's Goddard Space Flight Center in Greenbelt, Md., told Discovery News.

"It's not a particularly unexpected discovery that glycine is in a comet -- we've found amino acids in meteorites before -- but it does show that comets are another way that amino acids could have come to Earth," she said.

Elsila and colleagues developed a technique to extract and analyze deposits of glycine from bits of aluminum foil that lined the probe's collection plates. They discovered that carbon atoms in the glycine had an extra neutron in its nucleus compared to terrestrial carbon, confirming that the amino acid did not come from Earth.

"This is telling us that the molecular ingredients for life are ubiquitous," Carl Pilcher, who oversees NASA's astrobiology program at the Ames Research Center in Mountain View, Calif., told Discovery News.

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"It is confirming something that people have been suspecting for some time... that these processes that produce biologically important compounds in interstellar space then led to them being incorporated into solid bodies," he said.

The Stardust science probe flew by Comet Wild 2 in January 2004 and gathered samples that were parachuted in a capsule back to Earth two years later.

Analysis is ongoing, but scientists already have learned that this comet is a mish-mash of particles forged in the extreme heat close to the sun. These particles then somehow ended up in the deep freeze of the solar system's back yard where comets formed.

"We see in this comet that amino acids were forming at the earliest time in our solar system," said Mike Zolensky, who studies comet dust and interstellar grains at NASA's Johnson Space Center in Houston.

For an amino acid to form, all it would take is organic compounds and liquid water. Zolensky suspects the radioactive decay of short-lived particles provided the heat to melt a bit of comet ice, allowing the amino acid to brew.

"Comets are a lot stranger than we thought -- or at least this one is," Zolensky said.

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