Mars 2007 Phoenix Scout mission Organic Free Blank: Method to distinguish Mars organics from terrestrial organics

The Organic Free Blank (OFB) for the Mars 2007 Phoenix Scout mission provides an organic carbon null sample to compare against possible Martian organic signatures obtained by the Thermal and Evolved Gas Analyzer (TEGA). Major OFB requirements are an organic carbon content of <10 ng C g ^-1 of sample, a nonporous structure, and strength and integrity that permits machining by the Robotic Arm (RA) Icy Soil Acquisition Device (ISAD). A specially fabricated form of commercial Macor™ (a machinable glass ceramic), made with nitrate salts replacing carbonate salts, was selected as the OFB material. The OFB has a total inorganic carbon content of approximately 1.6 μg C g^-1 after fabrication, cleaning, and heat treatment in oxygen gas at 550°C. The detection limit for organic carbon is ~100 ng C g^-1 of sample, or about a factor of 10 higher than the design goal. One scenario for OFB use on Mars is subsequent to the first TEGA detection of organic carbon. The OFB sample, acquired by the RA ISAD and delivered to TEGA, would come in contact with all surfaces in the sample transfer chain, collecting residual terrestrial contamination that accompanied the spacecraft to Mars. A second sample of the putative Martian organic-bearing material would then be obtained and analyzed by TEGA. Different organic contents and/or different mass spectrometer fragmentation patterns between the OFB material and the two Martian samples would indicate that the detected organic carbon is indigenous to Mars.