Laboratory Measurements of Oxygen Gas Release from Basaltic Minerals Exposed to UV- Radiation: Implications for the Viking Gas Exchange Experiments

Details Laboratory Measurements of Oxygen Gas Release from Basaltic Minerals Exposed to UV- Radiation: Implications for the Viking Gas Exchange Experiments Laboratory Measurements of Oxygen Gas Release from Basaltic Minerals Exposed to UV- Radiation: Implications for the Viking Gas Exchange Experiments

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p21a0220h&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P21A-0220

Biology

1000 Geochemistry, 5200 Planetary Sciences: Astrobiology, 6225 Mars

Scientific paper

The biology experiments onboard the Viking Landers determined that the Martian soils at Chryse and Utopia Planitia contain an unknown chemical compound of a highly oxidizing nature. The Gas Exchange Experiments (GEx) demonstrated that the humidification of a 1-cc Martian soil sample resulted in the production of as much as 790 nanomoles of oxygen gas. Yen et al. (2000) have provided experimental evidence that superoxide radicals can be generated on plagioclase feldspar (labradorite) grain surfaces by exposure to ultraviolet (UV) light in the presence of oxygen gas. Adsorbed superoxide radicals are thought to react readily with water vapor, and produce oxygen gas in quantities sufficient to explain the Viking GEx results. Direct evidence for the formation of oxygen gas, however, was not provided in the experiments of Yen et al (2000). Accordingly, the motivation of this study is to determine whether superoxide radicals adsorbed on labradorite surfaces are capable of producing oxygen gas upon exposure to water vapor. We have constructed an experimental apparatus that is capable of monitoring oxygen gas release from basaltic mineral powders that have been exposed to UV-radiation under Martian atmospheric pressure conditions. The apparatus consists of a stainless-steel vacuum chamber with a UV- transparent window where sample radiation exposures are performed. The vacuum chamber has multiple valved ports for injection of gases and water vapor. The vacuum chamber is connected via a precision leak valve to a quadrupole mass spectrometer, which measures changes in the composition of the headspace gases over our mineral samples. We will report on the results of our experiments, which are aimed at detecting and quantifying oxygen gas release from UV-exposed basaltic mineral samples using this new experimental facility. These results will further constrain whether superoxide ions adsorbed on mineral surfaces provide a viable explanation for the Viking GEx results, which have been of considerable controversy in the roughly three decades since the measurements were first made.

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