Revealing the water cycle on Mars via D/H isotopic measurements
Abstract
Deuterium fractionation is a powerful metric revealing information about the cycle of water on Mars, and most importantly informing about its stability on short-term (diurnal) and long-term (seasonal) scales. The vapor pressures of HDO and H2O differ significantly, making the condensation/sublimation cycle of the isotopologues strongly susceptible to the ambient temperature, saturation level and existence of condensation nuclei. Until recently, only isolated (in time and in space) measurements of D/H in the atmosphere were available, which were incorrectly assumed to be representative of the bulk atmosphere. Spatially resolved measurements of D/H at different times of day and seasons are necessary to disentangle local from global phenomena, and to possibly identify newy found sources of water on Mars. We have addressed these concerns by acquiring full 2D maps of Mars for a broad range of seasons using high spectral resolution data at ground-based telescopes (Keck/NIRSPEC, VLT/CRIRES, NASA-IRTF/CSHELL). Our maps sample the full observable disk of Mars on 8 dates, spanning from late northern winter to late northern spring on Mars (Ls = 335°, 50°, 71°, 83°). The dates encompass the critical time as the northern polar cap sublimes and replenishes the atmosphere with water. By stepping the instrument’s slit across the planet, we obtained full E-W and N-S coverage across the observable disk, allowing us to sample the short-term diurnal variations and the hemispheric seasonal effects. Our maps reveal significant diurnal and seasonal variability, together with a noticeable variation of the D/H ratio with topography (that we associate to the formation of clouds). We will present global maps of D/H acquired from 2008-2014, and will discuss possible scenarios to explain the observations.This work was partially funded by grants from NASA's Planetary Astronomy Program (344-32-51-96), NASA’s Mars Fundamental Research Program (203959.02.02.20.29), NASA’s Astrobiology Program (344-53-51), and the NSF-RUI Program (AST-805540). We thank the administration and staff of the European Southern Observatory/VLT, Keck Observatory, and NASA-IRTF for awarding observing time and coordinating our observations.
- Publication:
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AAS/Division for Planetary Sciences Meeting Abstracts #46
- Pub Date:
- November 2014
- Bibcode:
- 2014DPS....4630304V