A Comparative Study of the Influence of the Active Young Sun on the Early Atmospheres of Earth, Venus, and Mars

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 CO 2 , 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 H 2 , He, C, N, O, etc. The duration of this blow-off phase for atomic hydrogen depends essentially on the mixing ratios of CO 2 , N 2 and H 2 O 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 Yu.N. Kulikov et al. erosion. We find that the early martian magnetic field could decrease the ion-related nonthermal 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 × 10 24 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.

Habitability of planets on eccentric orbits: Limits of the mean flux approximation

“…It is therefore possible that these planets experience little water escape, as on Earth (Lammer et al 2003;Kulikov et al 2007;Selsis et al 2007). We note that an extreme case for water escape has been observed for a hot Neptune (Ehrenreich et al 2015).…”

Variability of solar/stellar activity and magnetic field and its influence on planetary atmosphere evolution

“…In recent studies by Kulikov et al (2006Kulikov et al ( , 2007, Lammer et al (2006Lammer et al ( , 2008, Lundin et al (2007), Tian et al (2008a, b) and illustrated in Fig. 4 it was shown that enhanced solar EUV radiation and plasma (winds, CMEs) should result in permanent forcing of the upper planetary atmospheres, which can ionize, heat, expand, chemically modify, and erode it during the early phase of a planetary lifetime.…”

“…When the temperature of the thermosphere is large, a significant fraction of the light constituents of the upper atmosphere attain velocities above the escape value, and the thermosphere may even become non-hydrostatic and start to expand accompanied by adiabatic cooling to several planetary radii (Chassefière, 1996;Tian et al, 2005Tian et al, , 2008aTian et al, , b, 2009Kulikov et al, 2007;Lammer et al, 2008).…”

“…The increase in solar luminosity over time and its climatological effect on Venus, Earth and Mars have been discussed by various authors in the past (e.g., Sagan and Mullen, 1972;Walker, 1975;Newman and Rood, 1977;Owen, 1979;Chassefière, 1996;Guinan and Ribas, 2002;Lammer et al, 2003;Ribas et al, 2005;Tian et al, 2005;Kulikov et al, 2006Kulikov et al, , 2007Cnossen et al, 2007). The early Sun, with a luminosity of about ∼70% of that today, should have been too faint to prevent the early Earth and Mars from freezing.…”

The extrasolar planet Gliese 581d: a potentially habitable planet?

“…Pepin 1991), atmospheric loss because of escape to space (e.g. Kulikov et al 2007;Kulikov et al 2006) or incorporation into planetary surface material. But these processes are not known for the Gl 581 system.…”