The Photochemical Stability of Carbonates on Mars
| Autor: | Christopher P. McKay, Richard C. Quinn, Aaron P. Zent |
|---|---|
| Rok vydání: | 2006 |
| Předmět: |
Extraterrestrial Environment
Photochemistry Ultraviolet Rays Carbonates Analytical chemistry Mars Mineralogy medicine.disease_cause Calcium Carbonate chemistry.chemical_compound Drug Stability Exobiology medicine Martian Calcite Photolysis Mars Exploration Program Atmosphere of Mars Agricultural and Biological Sciences (miscellaneous) Calcium carbonate chemistry Space and Planetary Science Thermodynamics Carbonate rock Carbonate Ultraviolet |
| Zdroj: | Astrobiology. 6:581-591 |
| ISSN: | 1557-8070 1531-1074 |
| DOI: | 10.1089/ast.2006.6.581 |
| Popis: | Carbonates, predominately MgCO3, have been spectroscopically identified at a level of 2-5% in martian dust. However, in spite of this observation, and a large number of climate studies that suggest 1 to several bars of CO2 should be sequestered in carbonate rocks, no outcrop-scale exposures of carbonate have been detected anywhere on Mars to date. To address one hypothesis for this long-standing puzzle, the effect of ultraviolet (UV) light on the stability of calcium carbonate in a simulated martian atmosphere was experimentally investigated. Using 13C-labeled calcite, we found no experimental evidence of the UV photodecomposition of calcium carbonate in a simulated martian atmosphere. Extrapolating the lower limit of detection of our experimental system to an upper limit of carbonate decomposition on Mars yields a quantum efficiency of 3.5 x 10(-8) molecules/photon over the wavelength interval of 190-390 nm and a maximum UV photodecomposition rate of 1.2 x 10(-13) kg m(-2) s(-1) from a calcite surface. The maximum loss of bulk calcite due to this process would be 2.5 nm year(-1) (Mars year). However, calcite is expected to be thermodynamically stable on the surface of Mars, and potential UV photodecomposition reaction mechanisms indicate that, though calcium carbonate may decompose under vacuum, it would be stable in a CO2 atmosphere. Given the expected stability of carbonate on Mars and our inability to detect carbonate decomposition, we conclude that it is unlikely that the apparent absence of extensive carbonate deposits on the martian surface is due to UV photodecomposition in the current environment. |
| Databáze: | OpenAIRE |
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