Mars Oxidant and Radical Detector

Introduction: The Mars Oxidant and Radical Detector is an instrument designed to characterize the reactive nature of the martian surface environment. Using Electron Paramagnetic Resonance (EPR) techniques, this instrument can detect, identify, and quantify radical species in soil samples, including those inferred to be present by the Viking experiments. This instrument is currently funded by the Mars Instrument Development Program and is compatible with the Mars Science Laboratory mission. Viking Results: The Viking Landers showed that the addition of water to a martian soil sample produced an unexpected release of excess oxygen [1], that radioactively labeled nutrient solutions were decomposed upon contact with the soil [2], that chemical rather than biological reactions were modifying the liquid reagents of the life detection experiments [3], and that the martian soil was free of detectable organic material [4]. The most widely accepted explanation of these results is the presence of one or more reactive compounds in the soil at the parts-per-million level which actively destroy both primitive and meteoritic organic molecules [5]. The specific nature of this reactive phase, including composition, mechanisms of formation, and interaction with biomolecules, has not yet been identified. Testable hypotheses: A number of explanations for the unusual reactivity of the martian soil have been proposed [6], many of which involve the presence of active oxygen species [1, 4]. Experiments under simulated martian conditions, for example, have shown that superoxide radical ions, O 2-, form readily on mineral grain surfaces [7]. The stability, mobility, and reactivity of O 2-is consistent with the results of the Viking Lander investigations. O 2-as well other likely candidates for the martian oxidant are paramagnetic in nature and can be readily detected in native form by Electron Paramag-netic Resonance (EPR) spectroscopy techniques. EPR: Electron Paramagnetic Resonance spectroscopy is likely the most sensitive technique for characterization of atoms and molecules with unpaired electrons. Detection limits achievable in the laboratory are better than 10 11 unpaired electron spins per cubic centimeter of sample. Thus, active oxygen species present at tens of part-per-trillion are routinely analyzed with laboratory hardware. For the Mars Oxidant and Radical Detector, we expect a sensitivity at the parts-per-billion level, which would easily detect the reactive compounds and other paramagnetic species present at the Viking sites. Spin state transitions: The spins from unpaired electrons (S=1/2) behave as tiny magnets, and when placed in a magnetic field these electrons will align either parallel or …