Amino Acid from a Comet

August 17, 2009

The New Scientist reports that an in-depth analysis of comet dust, collected by NASA’s Stardust mission, has revealed the presence of the amino acid glycine.  The samples were collected in a fly-by of comet Wild 2 in 2004, and later returned to earth.  Although the presence in space of amino acids – compounds that are key building blocks of proteins, and therefore life – has been predicted for some time, this is the first direct evidence found.

The amount of material recovered was very small; it included less than a microgram of glycine, as well as indications of trace amounts of other amino acids and amines.  The glycine was specifically chosen for further analysis because it was the most prevalent of these compounds in the sample.

In fact, there was not enough material to trace the source of any compound except for glycine, the simplest amino acid.

One difficulty in performing an analysis of any sample returned from space is making sure that it has not been in some way contaminated with material from Earth, either in the initial construction of the probe, or after its return.  In this case, the team was able to check the relative proportions of carbon isotopes in the sample:

With only about 100 billionths of a gram of glycine to study, the researchers were able to measure the relative abundance of its carbon isotopes. It contained more carbon-13 than that found in glycine that forms on Earth, proving that Stardust’s glycine originated in space.

This is potentially an exciting result.  One of the more tantalizing questions in biology is just how and where life got its start.  One theory, called panspermia or exogenesis, posits that life originated somewhere else, and was carried to Earth by comets and meteorites.  A more limited possibility is that, while life itself may not have originated elsewhere, some of its key building blocks were delivered from space.  Assuming that these results check out, they are consistent with this kind of mechanism, and with the idea that life may well exist elsewhere.

The Web site also has an article on this research.

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