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R. E. Novak (Iona College), M. J. Mumma, M. A. DiSanti, M. D. Smith (NASA's GFSC), B. Bonev (University of Toledo - NASA's GSFC), N. Rauf (Salem College)
We report investigations of the D/H ratio based on column densities of atmospheric HDO and H2O on Mars for March 20-22, 2003 (Ls ~ 155 degrees) and for Jan. 11-15, 2004 (Ls ~ 333 degrees) using CSHELL at the NASA IRTF. The instrument slit was positioned N-S along the central meridian of Mars resulting in one-dimensional maps. Column densities of HDO and H2O are extracted from individual spectral lines measured near 3.67 and 3.29 \mum at 0.6 arc-second intervals along the spectrometer entrance slit. Our retrieved water abundances generally agree with those obtained from the Thermal Emission Spectrometer on the Mars Global Surveyor for these dates. Maps of the D/H ratio were then constructed from the CSHELL results at these opposite seasons of the year. The measured ratio varies with both latitude and season. The higher global D/H value on Mars compared to that of the Earth is usually attributed to differential Jeans escape of D and H over geologic time. The observed differences with latitude and season could be the signature of Rayleigh distillation, a process in which the different mean temperatures of the polar caps causes a different degree of HDO sequestration. The observed latitudinal and seasonal variations may be the signature of different degrees of enrichment in the polar caps.
This work was partially funded by grants from NASA’s Planetary Astronomy Program (RTOP 344-32-51-96 to M. J. Mumma) and NSF RUI Program (AST-0205397 to R. E. Novak).
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.