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M. J. Mumma (NASA's GSFC), R. E. Novak (Iona College), M. A. DiSanti (NASA's GSFC), B. P. Bonev (Univ. of Toledo at NASA's GSFC), N. Dello Russo (Cath. Univ. at NASA's GSFC)
We detected methane and water on Mars using state-of-the-art infrared spectrometers. The CH4 R0 and R1 lines in the \nu3 vibrational band and lines of H2O 2\nu2 both near 3.3 \mum were searched using CSHELL at the NASA IRTF (Jan. and March 2003, Jan. 2004), and Phoenix at Gemini South (May and December 2003). Preliminary searches for P-branch and additional R-branch lines were initiated (2003) using NIRSPEC at Keck-2. These instruments provide high angular resolution along with high spectral resolving power, permitting a simultaneous search for methane and water at each point along the spectrometer entrance slit. The dates sampled cover both blue and red geocentric Doppler shifts, and the detected lines shift in the expected fashion. The CH4 and H2O abundances are correlated at most spatial locations sampled, but notable exceptions are found. The retrieved water burdens agree well with independent TES data taken at the same time. Details will be presented for several longitude ranges.
Owing to its short photochemical lifetime (~ 300 years), the existence of significant methane requires \underline{recent} release from sub-surface reservoirs; local enhancements are expected if methane is released from discrete regions. The presence of sub-surface hydrogen concentrations on Mars has been inferred from local-enhancements in epithermal neutron fluxes measured on Mars Odyssey, but independent evidence is required to establish its likely chemical form (e.g., water vs. hydrocarbons) in low-latitude sites. We suggest that enhanced methane in such regions could test whether sub-surface hydrogen is chemically bound in hydrocarbon moieties. The present methane release rate (inferred from its atmospheric abundance) provides an important quantitative constraint for assessing models of biogenic vs. primordial or geothermal origins. Measurement of isotopic variations with sufficient accuracy to test origins will likely require investigations from space.
Supported by NASA RTOP 344-32-51-96 to MJM, and NSF RUI Grant AST-0205397to REN.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.