The First Map of D/H In Mars’ Water

Details The First Map of D/H In Mars’ Water The First Map of D/H In Mars’ Water

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.0603v&link_type=abstract

American Astronomical Society, DPS meeting #40, #6.03; Bulletin of the American Astronomical Society, Vol. 40, p.395

Astronomy and Astrophysics

Astronomy

1

Scientific paper

We present the first map of (D/H)H2O on Mars, and it shows important variations across the planet.
The preferential escape of the lighter isotope of hydrogen controls the global (D/H)H2O abundance ratio and comparison of the present abundance ratio with escape models provides an estimate of the amount of water lost over time. Earlier measurements reported a global atmospheric enrichment (D/H) of five times the mean terrestrial ocean value (VSMOW). Nevertheless, the local (D/H)H2O is strongly dependent on the local temperature because of HDO and H2O different vapor pressures, and spatially resolved measurements are needed to properly locate the sources of water on Mars and their true D/H.
We mapped H2O and HDO on Mars in March/April 2008 using high-resolution infrared spectroscopy with CSHELL at NASA-IRTF. We oriented the spectrometer slit North-South on the planet and took spectra of HDO and H2O at 9 slit-positions across the Mars’ disk. We extracted 43 spectra along the slit sampling a total of 8.6 arcsec North-South, and leading to a disk-map consisting of 387 points for each isotope. The combined map shows important differences in (D/H) H2O between the afternoon (East) and the morning hemispheres (West), with an important correlation between temperature and (D/H)H2O indicative of Rayleigh distillation. In addition, we observe important enrichments of deuterated water in certain regions of the southern (winter) hemisphere. The weighted mean of all points shows a global atmospheric (D/H)H2O enrichment of 5.75 relative to Earth's oceans. But, if we compensate the measurements for Rayleigh distillation, the true (D/H)H2O ratio in the permanent cap is expected to be considerably higher, suggesting a wetter climate in the past.

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