It’s not just our bodies that have left-handedness and right-handedness. It has long been known that molecules within living organisms also possess the property of asymmetry, also called chirality. This simply means that a molecule does not match its mirror image. Thus, while the proteins in our body are composed of amino acids that are left-handed, the sugars are right-handed.
The Importance of Handedness in Life
This preponderance in one type of handedness has long been considered as essential property and prerequisite of ‘life’ itself. This is mainly because inorganic substances contain roughly equal quantities of both left-handed and right-handed molecules. Thus the question of why only molecules with one type of ‘handedness’ would arise in living organisms from a nearly equal distribution of molecules continues to be important in studying the origins of life.
This intrinsic asymmetry is actually being used by space missions, like the ExoMars mission, as an elegant way of detecting traces of life in outer space.Meteorites found at Taglish lake in Canada, have however shown results that bring this hypothesis to a screeching halt. Researchers have analysed these meteorites for proportions of left- handed ‘L’ and right-handed ‘R’ amino acids, and found an excess of ‘L’ types for some of them.
Meteors as Remnants of a Pre-Life Universe
Meteors represent parts of the extra-terrestrial universe before the emergence of life. Amino acids in these meteors were confirmed to be extra-terrestrial in origin by studying their carbon isotopes. Researchers are proposing that heating in the early days of the solar system melted ice to produce water which dissolved existing amino acids into populations of chiral asymmetric molecules. The amino acids which were found to be excessively present in one form are susceptible to forming asymmetric populations depending on the chirality of the starting amino acid. Thus, a small quantity of an asymmetric molecule could have set off a cascade leading to a highly asymmetric group of amino acids.
“As 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,” saysAlberto Fairen of the SETI Institute in Mountain View, California.
This does NOT, however, in any way, disprove the existence of extraterrestrial life. Chirality is just one aspect of life, and the search of life in outer space will continue.