Other
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p23a0035g&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #P23A-0035
Other
0325 Evolution Of The Atmosphere (1610, 8125), 0545 Modeling (4255), 1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 5405 Atmospheres (0343, 1060)
Scientific paper
A simple atmosphere-interior coupling has been implemented for Venus under stagnant lid convection regime; the atmosphere gains water from the degassing, through a parameterized model of mantle convection, including volatile exchanges between the mantle and the atmosphere (additionally, the mean depth of partial melting is taken into account), and a radiative-convective atmosphere model computes the temperature at the planet's surface. This coupling suggests that a strong links exist between inner (the solid part) and outer layers of the planets. It also seems essential to study the atmospheric escape which could be a major parameter constraining the surface conditions during the early evolution of terrestrial planets. The initial model of the escape we used is very basic, so we develop this aspect to try and see if realistic results may be obtained with a more complete approach. Thus we use an energy-limited approach to model the escape of hydrogen out of the primitive atmosphere and its entrainment of rare gazes. We compare the evolution of rare gaze depletion and the final (after 4.6 Gy) isotopic ratios to those measured by Venera missions. Results show that depending on the extent of the exosphere and the temperature it reaches, it is possible to explain the present isotopic ratios with only the hydrodynamic escape, especially with hot (such as 500 K to 1500 K) and extended (4 to 8 times the size of the planet) exospheres. Since hydrodynamic escape mostly takes place during the first hundreds of million years, other processes for atmospheric escape have been considered in order to quantify the loss of volatiles during later periods. Using data from Mars Express and several models such as ones created by Leblanc (2001) or Chassefière, Leblanc and Langlais (2006), a model for the evolution of Martian atmosphere and volatiles has been set up. Crust production rates from a model by Breuer et al. (2006) are taken as input for the mantle degassing and the evolution of the content in water, CO2 and SO2 of the atmosphere is studied through different scenarios. We first focused on the present situation as described by available data such as ones from Mars Express in order to study the late evolution of the Martian atmosphere. It appears that a production of at least 0.05 to 0.1 km3/year is needed for the atmosphere to be at steady state. Our second interest is to have a view of possible evolutions of the Martian environment over the whole history of the planet and to try to relate it to specific features discovered, and especially with sulfate formations detected by the OMEGA spectrometer.
Chassefiere Eric
Gillmann Cédric
Lognonné Philippe
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