Other
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p52a..11g&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P52A-11
Other
[5405] Planetary Sciences: Solid Surface Planets / Atmospheres, [5455] Planetary Sciences: Solid Surface Planets / Origin And Evolution, [5480] Planetary Sciences: Solid Surface Planets / Volcanism, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
We study the long term evolution of the conditions on the surface of Mars through the modeling of the effects of volcanic degassing and atmospheric non-thermal escape during the last four billion years. We propose to use the recent advances due to observation and modeling to constrain possible evolutions of the atmosphere of Mars with the help of isotopic data from Carbon, Nitrogen and Argon. We also have an interest in the balance of water during this evolution. CO2 is the main object of our study, as it represents the bulk of the present, and probably past, atmosphere. Volcanic degassing is obtained from crust production models, observation of the surface, and realistic volatile contents of the lavas. ASPERA measurements and modeling of the escape rates produced by ionic escape, sputtering and dissociative recombination constitute the sink of volatiles. The decrease of Extreme UV flux with time is taken into account. We constrain the maximum escape flux of CO2 with the evolution of Argon and the 40Ar/36Ar ratio in the atmosphere and measurements of the present-day situation. This imposes limited escape flux, consistent with the recent lowering of the expected escape efficiency on Mars. With low escape rates, our model is able to reproduce present day 36Ar abundance and 40Ar/36Ar ratio. We also show that the present-day atmosphere of Mars is likely to be constituted by a large part of volcanic gases, as it only takes 150 ppm CO2 in the lavas to obtain a “volcanic/early” ratio of 50%. Likewise, the estimated mean age of the atmosphere is estimated to be no more than 1.9 to 2.3 billion years old, even without present-day volcanism. Atmospheric pressures and variations on Mars are predicted to be low, as the result of degassing and non-thermal escape. In our model, they do not exceed 50 mbar during the considered period. This seems in line with the assumption of a heavy loss of volatiles during the first 500 Myr. Isotopic ratios lead us to propose that Nitrogen is probably old in the Martian atmosphere and has been subjected to the fractionation of atmospheric escape. The 12C/13C, on the other hand is more stable and indicates that Carbon is younger and that a part of it might come from cometary bodies. Water is moderately abundant on Mars during the whole 4 billion years evolution but is unlikely to reside in the atmosphere or in liquid form unless large scale perturbations occur (changes in obliquity, large input of greenhouse gases due to a short burst of volcanism).
Gillmann Cédric
Lognonné Philippe
Moreira Anamaria Martins
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