Projet de recherche PX/8/SS/18 (Action de recherche PX)
This work studies the sterilization properties of the Martian environment as well as the role of airborne and deposited dust on the intensity of the UV flux reaching the Martian surface (e.g.: Gillotay et al., 2004; Moreau and Muller, 2003; Muller et al., 2003;; Muller and Moreau, 2001; Muller et al., 2001; Moreau and Fonteyn, 1999; Muller and Moreau, 1997) Today, in view of the renewed speculation on a past or even contemporary life on Mars through the Mars Express PFS detection of reduced carbon species in the Martian Atmosphere, the present Martian atmospheric research program, represented by the SPICAM atmospheric sounder on Mars express (e.g.: Bertaux et al., 2000; Muller at al., 2001) including its infrared channel (Korablev et al,2002), can be used directly and indirectly to study the different aspects of the Martian environment and their compatibility with the atmospheric stability of organic compounds. Even of the MARS 2D model was validated by spacecraft observation (MARINER 9, VIKING, PHOBOS…) Comparing SPICAM observations with theoretical simulations will improve some of the assumptions taken several years ago.
Aeronomy related objectives:
Today, the chemical stability of the current Martian atmosphere remains a significant problem to understand. In this framework, hydrogen peroxide is a key chemical constituent in the lower atmosphere. In the classical photochemical scheme, hydrogen peroxide is almost entirely produced by the HO2 "self-reaction” and destroyed during the day through photolysis. An other important sink for atmospheric H2O2 is its condensation in the cold regions of the atmosphere. This condensation process is obviously crucial in the Martian lower atmosphere because it control the amount of atmospheric odd hydrogen by playing the role of reservoir and also regulates molecular oxygen in the Martian troposphere. It is thus very important; to better know the planetary boundary layer environmental condition, to derive vertical, meridional and seasonal variation of water, ozone and thermal profile from SPICAM observation. Moreover, SPICAM has the capabilities to; at least, qualitatively detect the presence of hydrogen peroxide. Using these data and constraining the MARS 2D model will improve the calculation of vertical and meridional distribution for trace gases improving, consequently, theoretical spectral calculation of UV flux at the surface. The first SPICAM interpretation to reach publication (Bertaux et al, 2005) presents the first observations of NO nightglow in the upper atmosphere, this will help constrain the amount of NO in the lower atmosphere and could relate to the NO role in life processes, which, as an astrobiology objective has not been treated in the already published paper.
Astrobiology related objectives:
From Mars 2D model results (Moreau, 1995b), it is obvious, that reduced carbon species production is directly connected to the oxidizing capacity of the troposphere which is determined by the concentration of atmospheric hydroxyl radicals produced mainly by hydrogen peroxide photolysis. Following previous studies, one source of formaldehyde could arise from subsurface bacterial activities. The simplicity of the bacterial structure allows them to be considerably more resistant to environmental variable such as pH, salinity and temperature that are lethal to more complex organisms. Knowing that the regolith texture could permit a local diffusion depth of several kilometers, it seems plausible that a local methane or acetic acid flux could exist at the regolith surface. It is evidently tempting to take Phobos and MarsExpress (?) detection of formaldehyde as the reduced atmospheric gases that would leak from such a system but their exist some chemical and photochemical constraints weakening this hypothesis. The SPICAM infrared channel detected surface water ice on its first overpass, as the quality and regularity of observations increase, it is hoped that in combination with the middle-infrared PFS instrument, the detection and identification of organic molecules in the atmosphere or surface will be confirmed. From recent laboratory experiments simulating UV destruction of organic compounds under today Martian surface conditions, the quantum efficiency for the decomposition of organic molecule by UV light represents 2.24 +/- 1.2 10-6 g of C m-2 yr-1. This rate is comparable to the slow growing cryptoendolithic microbial communities found in dry Antarctica deserts (the most Mars's like Earth's environment) and thus is one of the critical parameter to better know for exobiology studies purpose.
Satellite(s) or flight opportunity(ies):
- Mars Express
Field of research:
Atmospheric Chemistry / Space Sciences: Solar Physics
