MOD Principal Investigator:    Dr. Jeffrey L. Bada
                                                Scripps Institute of Oceanography

TDL Spectrometer instrument Co-I:     Dr. Christopher R. Webster
                                                                Jet Propulsion Laboratory

Other MOD Co-Investigators: D.L. Blaney, M. Duke, F.J. Grunthaner, R.A. Mathies, G.D. McDonald, C.P. McKay, D.A. Paige, S.K. Ride, M. Wadhwa

The Mars Organic Detector (MOD) is designed to detect organic compounds in rock and soil samples directly on the surface of Mars, in order to assess the biological potential of the planet. In addition, the MOD Tunable Diode Laser (TDL) spectrometer component will provide information on desorption and decomposition temperatures, as well as the release rates and quantities of water and carbon dioxide that can be liberated from regolith samples, thereby providing the parameters needed for the design of systems for the future large-scale in situ extraction of valuable consumable resources. The MOD TDLS will also measure the atmospheric water, carbon dioxide, and CO₂ isotopic composition in order to determine whether there is an offset between atmospheric and surface carbonates, a finding which could indicate that a reservoir of biotic organic carbon is present in the Mars regolith.

The analyses to be carried out by the MOD instrument are designed to exam three important hypotheses relevant to fundamental biology and in situ resources:

• Organic compounds associated with either extinct or extant life and/or abiotic chemistry are present in Martian regolith samples.
• Extractable water, in amounts needed by future human explorers, can be obtained from the Martian regolith.
• The carbon dioxide in the Martian atmosphere is depleted in the isotope carbon-13 relative to that in surface carbonates.

To test first the two hypotheses, MOD carries out two simultaneous complementary experiments: simple sublimation-based extraction, fluorescence detection and quantitation of the key organic compounds amino acids, amines, and polycyclic aromatic hydrocarbons (PAHs) at sub-picomole (<10 -12 mole) levels— that is, at least 100 times more sensitive then Viking—and the tunable diode laser spectrometer (TDLS) detection and quantification of evolved water and carbon dioxide in order to assess the water and carbonate inventory of the Martian surface. The last hypothesis is tested by direct measurements using the TDLAS of the atmospheric carbon dioxide content and its isotopic composition, and by comparison with the isotopic ratios determined for evolved gas. The unambiguous detection of the organic compounds would be a significant step in assessing whether life ever existed on Mars.

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