Excerpts from an article at Genomeweb.com:
Scientists from NASA this week reported that they have detected the amino acid glycine in samples of the comet Wild 2 gathered by the spacecraft
Stardust, adding ammunition to the theory that life on Earth may have extraterrestrial beginnings and that life may exist elsewhere in space.
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In January 2004 Stardust passed through the dense gas and dust surrounding the icy nucleus of the comet Wild 2. As it did, it collected gas and dust samples in a collection grid filled with a special aerogel. The grid was then stowed in a capsule that detached from Stardust and parachuted to Earth two years later.
…
In preliminary tests, glycine was detected in both the sample of the aerogel and aluminum foil from the sides of the chambers that held the aerogel in the collection grid.
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But though glycine was detected, it was unclear whether that was due to contamination from terrestrial sources. To determine whether the glycine had in fact come from outer space, Elsila and his fellow researchers performed gas chromatography coupled with mass spectrometry and isotope ratio mass spectrometry.
The most common form of carbon, carbon 12, has six protons and six neutrons in its nucleus. A glycine molecule from space, however, tends to have more of the heavier isotope carbon 13, which carries an extra neutron in its nucleus, than a glycine from Earth. Because the glycine from the Stardust samples contained carbon 13, “the carbon isotopic signature was extraterrestrial, proving that this glycine is cometary,” Elsila said.