Mitigation of the impact of terrestrial contamination on organic measurements from the Mars Science Laboratory

The objective of the 2009 Mars Science Laboratory (MSL), which is planned to follow the Mars Exploration Rovers and the Phoenix lander to the surface of Mars, is to explore and assess quantitatively a site on Mars as a potential habitat for present or past life. Specific goals include an assessment of the past or present biological potential of the target environment and a characterization of its geology and geochemistry. Included in the 10 investigations of the MSL rover is the Sample Analysis at Mars (SAM) instrument suite, which is designed to obtain trace organic measurements, measure water and other volatiles, and measure several light isotopes with experiment sequences designed for both atmospheric and solid-phase samples. SAM integrates a gas chromatograph, a mass spectrometer, and a tunable laser spectrometer supported by sample manipulation tools both within and external to the suite. The sub-part-per-billion sensitivity of the suite for trace species, particularly organic molecules, along with a mobile platform that will contain many kilograms of organic materials, presents a considerable challenge due to the potential for terrestrial contamination to mask the signal of martian organics. We describe the effort presently underway to understand and mitigate, wherever possible within the resource constraints of the mission, terrestrial contamination in MSL and SAM measurements.     

The Mars Science Laboratory Organic Check Material

Mars Science Laboratory’s Curiosity rover carries a set of five external verification standards in hermetically sealed containers that can be sampled as would be a Martian rock, by drilling and then portioning into the solid sample inlet of the Sample Analysis at Mars (SAM) suite. Each organic check material (OCM) canister contains a porous ceramic solid, which has been doped with a fluorinated hydrocarbon marker that can be detected by SAM. The purpose of the OCM is to serve as a verification tool for the organic cleanliness of those parts of the sample chain that cannot be cleaned other than by dilution, i.e., repeated sampling of Martian rock. SAM possesses internal calibrants for verification of both its performance and its internal cleanliness, and the OCM is not used for that purpose. Each OCM unit is designed for one use only, and the choice to do so will be made by the project science group (PSG).