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Radiation interaction with solar system and exoplanets

Problem description:

In view of the low H20 abundance in the present Venusian and Martian atmospheres several observations by spacecraft and studies suggest that both planets should have lost most of their water over the early active period of the young Sun. During the first Gyr after the Sun arrived at the Zero-Age-Main Sequence high X-ray and EUV fluxes between 10 and 100 times that of the present Sun were responsible for much higher temperatures in the thermosphere-exosphere environments on both planets. The figures below show the response of CO2-rich Martian and Venusian atmospheres for various solar/stellar XUV radiation exposures. By applying a diffusive-gravitational equilibrium and thermal balance model for investigating radiation impact on the early thermospheres by photodissociation and ionization processes, due to exothermic chemical reactions and cooling by CO2 IR emission in the 15µm band one finds expanded thermospheres with exobase levels between about 200km (present) and 2000 km (4.5 Gyr ago). The higher temperatures in the upper atmospheres of both planets could reach "blow-off" conditions for H atoms even at high CO2 mixing ratios of 96%.

Mars EUV exposure: (Temperature, Particle Densities)

1 EUV
2 EUV
5 EUV
10 EUV
30 EUV
50 EUV
100 EUV

Venus EUV exposure: (Temperature, Particle Densities)

1 EUV
2 EUV
5 EUV
10 EUV
30 EUV
50 EUV
100 EUV


See topic SW plasma interaction with CO2-rich (Venus-type) terrestrial planets for further details on the models used to calculate the atmospheres densities at different EUV levels.

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