Venus as an Exoplanet: I. An Initial Exploration of the 3-D Energy Balance for a CO_2 Exoplanetary Atmosphere Around an M-Dwarf Star
arxiv(2022)
摘要
The chemical evolution of an exoplanetary Venus-like atmosphere is dependent
upon the ultraviolet to near ultraviolet (FUV-NUV) radiation ratio from the
parent star, the balance between CO_2 photolysis and recombination via
reactions that depend on the water abundance, and various catalytic chemical
cycles. In this study, we use a three-dimensional (3-D) model to simulate
conditions for a Venus-like exoplanet orbiting the M-dwarf type star GJ 436 by
varying the star/planet distance and considering the resultant effects on
heating/cooling and dynamics. The simulation includes the middle and upper
atmosphere (<40 mbar). Overall, these model comparisons reveal that the impact
of extreme ultraviolet to ultraviolet (EUV-UV) heating on the energy balance
shows both radiative and dynamical processes are responsible for driving
significant variations in zonal winds and global temperature profiles at <
10^-5 mbar. More specifically, CO_2 15-μm cooling balances EUV/UV
and Near InfraRed (NIR) heating at altitudes below 10^-7 mbar pressure with
a strong maximum balance for pressures at 10^-5 mbar, thus explaining the
invariance of the temperature distribution at altitudes below 10^-5mbar
pressure for all cases. Our model comparisons also show that moderate changes
in NIR heating result in relatively small changes in neutral temperature in the
upper atmosphere, and virtually no change in the middle atmosphere. However,
with larger changes in the NIR heating profile, much greater changes in neutral
temperature occur in the entire upper and middle atmosphere studied.
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