A Comparative Study of the Influence of the Active Young Sun on the Early Atmospheres of Earth, Venus, and Mars |
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Authors: | Yuri N Kulikov Helmut Lammer Herbert I M Lichtenegger Thomas Penz Doris Breuer Tilman Spohn Rickard Lundin Helfried K Biernat |
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Institution: | (1) Polar Geophysical Institute (PGI), Russian Academy of Sciences, Khalturina Str. 15, 183010 Murmansk, Russian Federation;(2) Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria;(3) Institute of Planetary Research, German Aerospace Center, Rutherfordstr. 2, 12489 Berlin, Germany;(4) Swedish Institute of Space Physics (IRF), P.O. Box 812, 98128 Kiruna, Sweden |
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Abstract: | Because the solar radiation and particle environment plays a major role in all atmospheric processes such as ionization, dissociation,
heating of the upper atmospheres, and thermal and non-thermal atmospheric loss processes, the long-time evolution of planetary
atmospheres and their water inventories can only be understood within the context of the evolving Sun. We compare the effect
of solar induced X-ray and EUV (XUV) heating on the upper atmospheres of Earth, Venus and Mars since the time when the Sun
arrived at the Zero-Age-Main-Sequence (ZAMS) about 4.6 Gyr ago. We apply a diffusive-gravitational equilibrium and thermal
balance model for studying heating of the early thermospheres by photodissociation and ionization processes, due to exothermic
chemical reactions and cooling by IR-radiating molecules like CO2, NO, OH, etc. Our model simulations result in extended thermospheres for early Earth, Venus and Mars. The exospheric temperatures
obtained for all the three planets during this time period lead to diffusion-limited hydrodynamic escape of atomic hydrogen
and high Jeans’ escape rates for heavier species like H2, He, C, N, O, etc. The duration of this blow-off phase for atomic hydrogen depends essentially on the mixing ratios of CO2, N2 and H2O in the atmospheres and could last from ∼100 to several hundred million years. Furthermore, we study the efficiency of various
non-thermal atmospheric loss processes on Venus and Mars and investigate the possible protecting effect of the early martian
magnetosphere against solar wind induced ion pick up erosion. We find that the early martian magnetic field could decrease
the ion-related non-thermal escape rates by a great amount. It is possible that non-magnetized early Mars could have lost
its whole atmosphere due to the combined effect of its extended upper atmosphere and a dense solar wind plasma flow of the
young Sun during about 200 Myr after the Sun arrived at the ZAMS. Depending on the solar wind parameters, our model simulations
for early Venus show that ion pick up by strong solar wind from a non-magnetized planet could erode up to an equivalent amount
of ∼250 bar of O+ ions during the first several hundred million years. This accumulated loss corresponds to an equivalent mass of ∼1 terrestrial
ocean (TO (1 TO ∼1.39×1024 g or expressed as partial pressure, about 265 bar, which corresponds to ∼2900 m average depth)). Finally, we discuss and
compare our findings with the results of preceding studies. |
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Keywords: | Early atmospheres Atmospheric evolution Thermospheric heating Solar induced atmospheric loss |
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