Laboratory Studies of the Heterogeneous Uptake of Methane on Martian Soil Analogs: Determination of Upper Limits of Reactivity

Details Laboratory Studies of the Heterogeneous Uptake of Methane on Martian Soil Analogs: Determination of Upper Limits of Reactivity Laboratory Studies of the Heterogeneous Uptake of Methane on Martian Soil Analogs: Determination of Upper Limits of Reactivity

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p13e..01g&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P13E-01

Physics

5210 Planetary Atmospheres, Clouds, And Hazes (0343), 5405 Atmospheres (0343, 1060), 5470 Surface Materials And Properties

Scientific paper

In order to constrain possible methane sources on Mars, it is necessary to understand the type and magnitude of all possible methane sinks. We have performed laboratory experiments to determine the importance of heterogeneous uptake of methane on mineral surfaces analogous to Martian surface material. The uptake of methane on sodium montmorillonite and Mars soil simulant JSC-1 (a palagonite) was studied using a Knusden cell flow reactor capable of achieving Martian temperature, pressure and relative humidity conditions. A quadrupole mass spectrometer was used to detect any decrease in methane flow due to heterogeneous uptake and infrared spectroscopy was used to detect any adsorbed species on the particles. Experiments were performed under Martian temperatures (from 195 to 215 K), and under both dry conditions and 45% RH. As montmorillonite clay possesses unique swelling properties in the presence of water vapor, experiments were performed in which the clay was simultaneously exposed to water and methane, and also experiments in which the clay was equilibrated with water vapor prior to methane exposure. We found no methane uptake relative to an unreactive blank Si wafer on any of the Martian soil analogs studied under any conditions. These negative results place upper limits on the heterogeneous reactivity of methane on the Martian surface. We have determined that the initial uptake coefficient of methane on palagonite is less than 3.66×10-10 (±1.41×10-11) and the initial uptake coefficient, γ0, of methane on montmorillonite is less than 7.52×10-10 (±2.56×10-11). These studies demonstrate methane uptake by mineral surfaces is not expected to be a significant methane sink, as the process likely occurs on a time scale much longer than photolysis.

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