Study of H2O and CO in Martian atmosphere with PFS/MEX data

Details Study of H2O and CO in Martian atmosphere with PFS/MEX data Study of H2O and CO in Martian atmosphere with PFS/MEX data

May 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010eguga..12.3368s&link_type=abstract

EGU General Assembly 2010, held 2-7 May, 2010 in Vienna, Austria, p.3368

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Scientific paper

In the history of the Mars exploration its atmosphere and planetary climatology has from time aroused particular interest. In the study of the minor gas abundance in the Martian CO2 atmosphere, the water vapour assumes particular importance, both because it is the most variable trace gas, and because it is involved in several processes characterizing the planetary atmosphere. The water vapour photolysis regulates the Martian atmosphere photochemistry, and so it is strictly bounded to the carbon monoxide. The CO study is very important for the so called "atmosphere stability problem" (the whole CO2 atmosphere should be destroyed in 6000 years by photolysis), solved by the theoretical modelling involving photochemical reactions in which the H2O and the CO gases are main characters. The Planetary Fourier Spectrometer (PFS) on board of ESA Mars Express (MEX) mission can probe the Mars atmosphere in the infrared spectral range between 200 and 2000 cm-1 (5-50 μm) with the Long wavelength channel (LWC) and between 1700 and 8000 cm-1 (1.2-5.8 μm) with the Short wavelength channel (SWC). Although there are several H2O and CO absorption bands in the spectral range covered by PFS, we chose to use the 3845 cm-1 (2.6 μm) band for the water vapour and the 4235 cm-1 (2.36 μm) band for the CO analysis, because these ranges are less affected by instrumental problems respect to other ones. The gaseous abundances are retrieved by using a particular algorithm developed for this purpose. The analysis procedure is based on the best fit between the measured averaged spectrum and a synthetic one appositely generated in each step of the fitting loop. The averaged water vapour mixing ratio results to be about 130 ppm, while the averaged carbon monoxide mixing ratio results to be about 1000 ppm, but with strong seasonal variations at high latitudes. The seasonal water vapour map reproduces very well the known seasonal water cycle. In the northern summer the water vapour and CO show a good anticorrelation most of the time, i.e. water has its maximum and carbon monoxide has its minimum mixing ratio over the north pole. This behaviour is due to the carbon dioxide and water sublimation from the north polar ice cup, which dilutes noncondensible species including carbon monoxide. An analogous process takes place during the winter polar cup, but in this case the carbon dioxide and water condensation causes an increase of the abundance of noncondensible species. Therefore, the carbon monoxide mixing ratio varies in response to the mean seasonal cycle of surface pressure. Occasionally the CO has a second maximum also at the north pole. The study of these unexpected features is in progress.

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