Seasonal Mapping of [HDO]/[H2O] in the Martian Atmosphere

Details Seasonal Mapping of [HDO]/[H2O] in the Martian Atmosphere Seasonal Mapping of [HDO]/[H2O] in the Martian Atmosphere

Oct 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.2408n&link_type=abstract

American Astronomical Society, DPS meeting #39, #24.08; Bulletin of the American Astronomical Society, Vol. 39, p.455

Astronomy and Astrophysics

Astronomy

Scientific paper

We report seasonal changes in isotopic water on Mars, based on observations taken at NASA's IRTF using CSHELL. Column densities of HDO and H2O were extracted from individual spectral lines near 3.67 μm and 3.29 μm. The slit was positioned N-S on Mars' central meridian. Data were acquired in an ABBA sequence and their difference constitutes a spectral/spatial image from which each species was quantified. The frames were rectified by re-sampling in wavelength and spatial dimension, and spectra were then extracted at 0.6 arc-second intervals along the slit.
We created atmospheric models for Earth and Mars using GENLN2 atmospheric software. The models include solar continuum (and Fraunhofer lines) with two-way transmission through Mars’ atmosphere, thermal emission from Mars’ surface and atmosphere with one-way transmission through Mars atmosphere, and one-way transmission through Earth's atmosphere for both. Latitudinal maps of [HDO]/[H2O] were constructed.
The [HDO]/[H2O] ratios are always higher than terrestrial and they vary with both latitude and season. The ratio in the southern Martian hemisphere is found to be larger than that in the northern. This difference could be the signature of Rayleigh distillation, a process in which the different mean temperatures of the polar caps cause a different degree of HDO sequestration, resulting in different degrees of enrichment in the polar caps. For Ls =155o in 2003 and Ls =357o in 2006, HDO and H2O column densities were both obtained from CSHELL data. They will be compared with results from other seasons (Ls =67o in 1997, Ls =223o in 2005, and Ls =333o in 2004) when HDO was measured with CSHELL and H2O was measured by MGS-TES.
This work was partially funded by grants from NASA's Planetary Astronomy Program (RTOP 344-32-51-96) and NSF RUI Program (AST-0505765). We acknowledge the NASA-IRTF for observing time and M. Smith for providing TES results.

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