Never touted as easy, hunting for aliens just got a little bit harder.
It seems an excess of 鈥渓eft-handed鈥� molecules, long assumed to be a signature of life, can be created inside asteroids through a non-biological process. That puts a damper on missions that intended to look for this chemical signature as evidence of biological activity on other worlds.
Molecules have handedness, or chirality, if their mirror-images cannot be superimposed upon each other, rather like your right and left hands. Life on Earth is built almost exclusively on left-handed amino acids, so scientists have assumed that a strong left-handed bias is a fundamental part of biochemistry.
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Instruments on the European Space Agency鈥檚 ExoMars and Rosetta missions are designed to search for an excess of left-handed molecules as an indicator of life.
But a new study found that meteorites collected from Canada鈥檚 Tagish Lake also have a excesses of left-handed aspartic and glutamic acids, two amino acids that are common in terrestrial life.
Natural path
The researchers propose that, in the solar system鈥檚 early days, heating as a result of radioactivity could have melted ice trapped deep inside asteroids. Liquid water then dissolved already present amino acids, which crystallised into mostly left-handed groupings.
Previous studies had seen small chiral excesses in amino acids from meteorites. But the new study is the first to propose a natural path for large left-handed enrichments in nonbiological materials, says team leader of NASA鈥檚 Goddard Space Flight Center in Greenbelt, Maryland.
鈥淎s evidence mounts that [left-handed] excess occurs naturally across bodies in the solar system, any strategies designed to search for life based on looking for this excess require serious rethinking,鈥� says of the SETI Institute in Mountain View, California.
Even without chirality, though, the search for extra-terrestrial life can continue. 鈥淎 swimming pool full of [left-handed] amino acids is not alive,鈥� says Harald Steininger, a project scientist for the on ExoMars. 鈥淟ife shows in many different aspects, and chirality is only one of them.鈥�
Journal reference: Meteoritics & Planetary Science, DOI: 10.1111/j.1945-5100.2012.01400.x
