May 10, 2010 – Original Source: Astrobiology Magazine
A schematic drawing of Gil Levin’s proposed TWEEL experiment as it might be mounted on a rover. TWEEL, Levin says, would unambiguously determine whether NASA’s 1976 Viking landers detected life on Mars.
The Labeled Release (LR) experiment conducted in 1976 by NASA’s two Viking landers added nutrients to martian soil and analyzed the gases released, looking for evidence of life. Both spacecraft returned positive results, and although in the 40-plus years since a scientific consensus has emerged that Viking did not find martian life, LR Principal Investigator Gil Levin remains unshaken in his belief that it did. Now Levin wants NASA to return to one of the Viking landing sites with a new experiment to settle the question. TWEEL (Twin Wireless Extraterrestrial Experiment for Life) would consist of a set of sterilized dart-like probes that would contain two chirally distinct sets of nutrients, in different chambers. (Life’s building-block molecules come in right- and left-handed, or “chiral” versions, but life’s basic structures incorporate only one chiral alternative of each: L (“left-handed”) amino acids and D (“right-handed”) sugars.) Shot downwind to prevent contamination, upon impact TWEEL’s darts would release the nutrients into the soil, radioing results back to the lander. If only one of the two sets of chiral nutrients induced a reaction, Levin said it would be nearly incontrovertible evidence of life on Mars.