Amino Acid Glycine Found in Comet Material

Confirmation appeared in Astrophysical Journal in May (and reported today) that the amino acid glycine had been found in a cometary halo. The material was captured during a fly-through of comet 81P/Wild 2 by the spacecraft Stardust in 2004.

The glycine molecules that Stardust found came from gas the comet released as the sun warmed it. It was captured in the spacecraft’s sampling gear — akin to an oversized circular ice-cube tray filled with aerogel, a remarkably spongy material that can withstand high heat while at the same time slowing, then cradling, comet material that zips into it at faster-than-bullet speeds.

Stardust passed through the comet’s coma — a halo of dust and gas that surrounds the comet’s core. The team found glycine in the aerogel as well as on some of the foil that lines the aerogel-filled collection chambers.

But the researchers still had to rule out possible contamination from Earth. Glycine consists of carbon, hydrogen, nitrogen, and oxygen. By analyzing the forms of carbon in the glycine molecules, they found that the samples had much higher proportions of a heavy isotope of carbon than does glycine on Earth. The verdict: It’s extraterrestrial, born and bred on the comet itself.