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A.-S. Wong, S. K. Atreya (U. of Michigan), Th. Encrenaz (Obs. Paris-Meudon), V. Formisano (IFSI, CNR), N. Ignatiev (IKI)
Although there is no evidence of active outgassing on Mars today, tantalizing clues to the possible existence of "localized" outgassing sources, the hotspots, may exist. A tentative detection of formaldehyde (CH2O) "locally" in the north equatorial region from the Phobos spacecraft in 1989 (1) and the indications of recent ground water seepage and surface runoff particularly at the middle and high latitudes(2) are two examples. Ground-based observations have failed to detect formaldehyde. Those observations were, however, "global", i.e. averaged over large areas, usually the disk or the hemisphere. Therefore, localized outgassing sources may not be ruled out. If the Phobos result is correct, the relatively short lifetime (~13 hrs) of CH2O would require a nearly continuous source of methane (CH4) in the detection region. Other than methane, sulfur species (H2S, SO2) are the likely principal outgassing species. Once in the atmosphere, these molecules and their photoproducts would react with the known martian molecules, producing new species. Starting with the current “global average” upper limits of CH4, SO2 and H2S of, respectively, 0.02, 0.1 and 0.1 ppm, and progressively increasing their abundances above possible hotspots, we calculate the abundances of the new molecules. We find that the introduction of methane into the martian atmosphere results in the formation of mainly formaldehyde, methyl alcohol (CH3OH) and ethane (C2H6), whereas the introduction of the sulfur species produces mainly SO and H2SO4. Depending upon the flux of the outgassed molecules from possible hotspots, some of these species and the resulting new molecules may be detectable locally-for example with the Planetary Fourier Spectrometer on Mars Express.
(1) Korablev, et al., Planet. Space Sci., 41, 441, 1993. (2) Malin and Edgett, Science, 288, 2330, 2000.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.