Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p41b..02m&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P41B-02
Mathematics
Logic
[0343] Atmospheric Composition And Structure / Planetary Atmospheres, [0414] Biogeosciences / Biogeochemical Cycles, Processes, And Modeling, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
On Mars, methane has been sought for nearly 40 years because of its potential biological significance, but it was detected only recently [1-5]. Its distribution on the planet is found to be patchy and to vary with time [1,2,4,5], suggesting that methane is released from the subsurface in localized areas, and is then rapidly destroyed [1,6]. To date, we have detected four spectral lines of the CH4 ν3 band near 3.3 µm, along with H2O and HDO [1,5,7]. Our observational campaign resumed in August 2009, now using CRIRES/VLT along with CSHELL/NASA-IRTF and NIRSPEC/Keck. Our study of methane on Mars now extends over four Mars years, sampling a wide range of seasons (Ls) with significant spatial coverage. For a typical observation, the spectrometer's long entrance slit is held to the central meridian of Mars while spectra are taken sequentially in time. For each snapshot in time, spectra are acquired simultaneously at contiguous positions along the entire slit length, sampling latitudinally resolved spatial footprints on the planet (35 footprints along the N-S meridian, when Mars is 7 arc-sec in diameter). Successive longitudes are presented as the planet rotates, and the combination then permits partial mapping of the planet. In Northern summer 2003, methane was notably enriched over several localized areas: A (East of Arabia Terra, where water vapor is also greatly enriched), B1 (Nili Fossae), and B2 (southeast quadrant of Syrtis Major) [1,5]. The combined plume contained ~19,000 metric tons of methane, and the estimated source strength (≥ 0.6 kilogram per second) was comparable to that of the massive hydrocarbon seep at Coal Oil Point in Santa Barbara, California. By vernal equinox about one-half the released methane had been lost. When averaged over latitude and season, spectral data from Mars Express also imply an enhancement in methane in this longitude range [4]. The most compelling results from these searches are: 1) the unambiguous detection of multiple spectral lines of methane, 2) Evidence for spatial variations that imply active release in discrete regions, and 3) Evidence for seasonal variations that imply a CH4 lifetime of months rather than the 300-plus years implied by photochemistry. The short lifetime may be the result of reaction with strong oxidants such as peroxides located in the soil and/or on airborne dust grains [1,6,8]. The possible origins of Mars methane will be discussed in the context of geologic and biologic terrestrial analogues. Very recent results will be presented. Acknowledgments: NASA's Planetary Astronomy Program (344-32-51-96) and Astrobiology Program (344-53-51); NSF RUI Grant AST-805540. References: [1] Mumma et al. (2009) Science 323, 1041-1045. [2] Formisano et al. (2004) Science 306, 1758-1761. [3] Krasnopolsky et al. (2004) Icarus 172, 537-547. [4] Geminale et al. (2008), Planet. Sp. Sci. 56,1194-1203. [5] Villanueva et al. (2009), submitted. [6] LeFevre and Forget (2009), Nature 460,720-723. [7] Novak et al. 2009, Mars III Workshop. [8] Atreya et al. (2007), Planet. Sp. Sci. 55,358-369.
Mumma Michael J.
Novak Robert E.
Villanueva Geronimo L.
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