Detecting life on Mars.

Despite ample evidence for liquid water on Mars, scientists remain unsure whether life ever resided there. Results from a 1976 Viking probe to the Red Planet failed to find any chemical sign of life, but many scientists argue that the probe wasn't sensitive enough to do so.

Alison M. Skelley and her colleagues have come up with a new way to search for Martian life. They started with an existing device, the Mars Organic Detector, that would remove trace amino acids--the building blocks of proteins--from Martian soil, if they are there. However, the mere presence of amino acids isn't a definite sign of life, but a key geometric trait of the molecules can be.

So, Skelley's team designed a complementary device, the Mars Organic Analyzer. It would take amino acid residues from the detector and then determine whether the molecules have a left-handed or right-handed configuration. Amino acids can exist in either form in nature. A lifeless setting would have about equal amounts of each, but in living organisms, amino acids invariably assume the left-handed form. Detecting a lopsided abundance of one or the other form of amino acids on Mars, therefore, could be a sign of life, the researchers note in the Jan. 25 Proceeding;s' of the National Academy of Sciences.