Mars Missions May Have Missed Organics

When two Viking mission landers alighted on Mars 30 years ago, they performed experiments searching for the presence of organic compounds in the soil. The protocol involved rapidly heating the soil to vaporize small molecules and break down larger ones, separating the resultant species by gas chromatography, and analyzing them by mass spectrometry. No organic molecules were detected, and scientists used this result as the most compelling argument against the presence of life on the martian surface. Now, researchers have demonstrated that the Viking protocol can be blind to low levels of organics (Proc. Natl. Acad. Sci. USA 2006, 103, 16089). Rafael Navarro-González of the National Autonomous University of Mexico and his colleagues examined soil samples from a variety of Mars-like environments on Earth, using both total organic analysis and the Viking protocol. For a number of samples, the modern analysis uncovered 10-90 µg of carbon per gram of soil—levels that were not detected by the Viking method. Therefore, they conclude, the question of whether the martian surface harbors organic molecules remains open.