The missing organic molecules on Mars

GC-MS on the Viking 1976 Mars missions did not detect organic molecules on the Martian surface, even those expected from meteorite bombardment. This r esult suggested that the Martian regolith might hold a potent oxidant that converts all organic molecules to carbon dioxide rapidly relative to the ra te at which they arrive. This conclusion is influencing the design of Mars missions. We reexamine this conclusion in light of what is known about the oxidation of organic compounds generally and the nature of organics likely to come to Mars via meteorite. We conclude that nonvolatile salts of benzen ecarboxylic acids, and perhaps oxalic and acetic acid, should be metastable intermediates of meteoritic organics under oxidizing conditions. Salts of these organic acids would have been largely invisible to GC-MS, Experiments show that one of these, benzenehexacarboxylic acid (mellitic acid), is gen erated by oxidation of organic matter known to come to Mars, is rather stab le to further oxidation, and would not have been easily detected by the Vik ing experiments. Approximately 2 kg of meteorite-derived mellitic acid may have been generated per m(2) of Martian surface over 3 billion years. How m uch remains depends on decomposition rates under Martian conditions, As ava ilable data do not require that the surface of Mars be very strongly oxidiz ing, some organic molecules might be found near the surface of Mars, perhap s in amounts sufficient to be a resource. Missions should seek these and re cognize that these complicate the search for organics from entirely hypothe tical Martian life.