Other
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p11g..05g&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P11G-05
Other
[5405] Planetary Sciences: Solid Surface Planets / Atmospheres, [5430] Planetary Sciences: Solid Surface Planets / Interiors, [5455] Planetary Sciences: Solid Surface Planets / Origin And Evolution, [6207] Planetary Sciences: Solar System Objects / Comparative Planetology
Scientific paper
To investigate in what measure the interactions between the mantle and the atmosphere would have caused the divergent evolutions of the terrestrial planets in our solar system, we propose to model the effects of mantle dynamics on the evolution of CO2, H2O and other species like Argon or Nitrogen in the atmosphere, but also of the surface temperature. We consider several processes that are considered to have a strong influence on the atmosphere of terrestrial planets. First, the main source of volatiles in our model is the degassing from the mantle. We use and adapt the StagYY code developed by Tackley (Tackley, 2008) for the geodynamic part of the study. This modeling gives a realistic and advanced account of the mantle convection processes. When possible, we compare those results to published modeling (Breuer and Spohn, 2006; Grott et al., 2011) and observation. Atmospheric escape is considered as the main volatile loss flux. Early escape is thermal, caused by hydrodynamic escape. Its effects can be modeled, as we did for Venus. After the first few hundred of million years, the main atmospheric escape flux becomes non-thermal. We model the evolution of the present escape flux by comparing recent study on these processes and ASPERA (Analyzer of Space Plasma and EneRgetic Atoms) measurements. Differences in present-day escape depending on solar activity are used to extrapolate early escape. We combine these models to calculate the state of the atmosphere of Venus and Mars. This lets us estimate the surface temperature of those planets either from a Mars Global Circulation Model (e.g. Forget at al., 1999), or with a gray radiative-convective atmosphere model, for Venus. In the case of Mars, Ar appears to be a tracer of volcanic degassing. We also show that the present-day atmosphere of Mars is likely to be constituted by a large part of volcanic gases. Even with a low CO2 concentration in the magma (150 ppm), present-day atmosphere is constructed of 50% of volcanic gases emitted since 4 billion years ago, which corresponds to an age of 1.9 to 2.3 Gyr. The variations of CO2 pressure over this period seem relatively low (50 mbar at most). This seems in line with the assumption that the heavy loss of volatiles occurred before 500 Myr. Surface temperature variations are likely to be small (several Kelvin) and would not be responsible for periods of flowing liquid surface water by themselves. Water is abundant on Mars during the whole 4 billion years evolution (between 30% and 150% of the present day water) but is unlikely to reside in the atmosphere or in liquid form. In the case of Venus, we are able to reproduce a mantle convection behaviour showing what could be interpreted as resurfacing events with times of high activity separated by quieter periods. Atmospheric escape is also different; it is much lower than on Mars. During the last 4 Gyr, CO2 pressure doesn't seem to vary significantly, while water pressure decreased by several millibars, which induced a surface temperature variation of several tens of kelvins and illustrates the dry state of present-day Venus.This is in agreement with calculated isotopic ratios for noble gases such as Neon and Argon.
Gillmann Cédric
Lognonné Philippe
Tackley Paul J.
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