Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p31c0554g&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P31C-0554
Physics
5210 Planetary Atmospheres, Clouds, And Hazes (0343), 5405 Atmospheres (0343, 1060), 5455 Origin And Evolution, 5480 Volcanism (6063, 8148, 8450), 6225 Mars
Scientific paper
Past evolution of terrestrial planets is difficult to study due to the lack of data and in situ measurements. However, it is necessary in order to explain some of the features that are observed by recent missions. This work is meant to show that even with the few data we have and by using simple straightforward models, it is possible to have some answers about the evolution of Mars during the last 3 Gyr. We study possible states of the past Martian atmosphere consistent with present observation through a simple evolution model based on realistic outgassing scenarios and atmospheric loss. We focus on CO2 as the most likely main gas present in the atmosphere at that time and involved in large scale and long term processes. Volcanic degassing is obtained through the use of results from numerical model analysis that yielded the evolutions of crust production rates (Breuer et al., 2003 and 2006, Manga et al., 2006). By evaluating the contents of the lavas, the amount of volatiles that are released can be estimated through different scenarios. The mechanisms leading to the loss of the Martian atmosphere are all thought to be part of the atmospheric escape rather than some surface reservoirs such as carbonate formation as no carbonate has been found on Mars to this day. Atmospheric escape is due to non thermal processes (involving solar emissions) as opposed to thermal processes (such as hydrodynamic escape). We used measurements from ASPERA and Mars Express and models from Chassefière et al. (2006) to estimate the amount of lost atmosphere. Thus we obtain evolutions of the CO2 pressure that are consistent with the present state of the atmosphere. It first appears that a present-day crustal production of at least 0.01 to 0.1 km3/year is needed for the atmosphere to be at steady state. Moreover our models provide us with a rough constraint on the CO2 contents of the Martian mantle. It seems it should be lower than 200ppm in order to fit with present-day conditions. Higher concentrations would lead to thicker atmospheres due to intense release of gases by late volcanism. We also witness around 3 Gyr ago a rapid loss of the primary (and primordial) atmosphere due to atmospheric escape. It is finally found that for most of the scenarios (we investigate a wide range of mantle compositions and atmospheric escape models) the present atmosphere is of volcanic origin and has been created between 1 Gyr and 1.5 Gyr ago. If the volcanic activity and the degassing are intense enough then the atmosphere can even be entirely secondary and as young as 500 Myr, meaning that the present Martian atmosphere can be very young.
Chassefiere Eric
Gillmann Cédric
Lognonné Philippe
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