Water vapor mapping on Mars using OMEGA/Mars Express

A systematic mapping of water vapor on Mars has been achieved using the imaging spectrometer OMEGA aboard the Mars Express spacecraft, using the depth of the 2.6 μm (ν1, ν3) band of H2O. We report results obtained during two periods: (1) Ls=330–40° (January–June 2004), before and after the equinox, and (2) Ls=90–125°, which correspond to early northern summer. At low latitude, our results are globally consistent with previous measurements from ground-based and space (MAWD/Viking and TES/MGS) observations. However, at early northern summer and at high northern latitude (70–80 °N), the water vapor abundances, which we retrieved, appear to be weaker than MAWD and TES results. At the time of water sublimation during early northern summer, there is a maximum of water vapor content at latitudes 75–80°N and longitudes 210–24°E. This region is not far from the area where OMEGA identified a high abundance of calcium-rich sulfates, most likely gypsum. Our data provide the first high-resolution map of the martian water vapor content above the northern polar cap.