Wednesday 08 Jul 2020[Seminar] Atmospheric collapse on tidally locked rocky planets

Pierre Auclair-Desrotour - University of Bern

Remote seminar 14:00-15:00

Over large timescales, a terrestrial planet may be driven towards spin-orbit synchronous rotation by tidal forces. In this particular configuration, the planet exhibits permanent dayside and nightside, which may induce strong day-night temperature gradients. The nightside temperature depends on the efficiency of the day-night heat redistribution and determines the stability of the atmosphere against collapse. To better constrain the atmospheric stability and surface conditions of terrestrial planets located in the habitable zone of their host star, it is thus crucial to understand the complex mechanism of heat redistribution. While general circulation models (GCMs) are far too costly to be used to explore the parameter space, analytic models offer a global overview of the physics with a fairly reduced computational cost. We present here a new model hierarchy that builds on theoretical studies (e.g. Wordsworth 2015, Koll & Abbot 2016) by including additional physical ingredients such as shortwave radiative transfers, scattering, and advection due to atmospheric circulation. We thus show that the analytic theory captures (i) the dependence of temperatures on atmospheric opacities and scattering, (ii) the behaviour of the collapse pressure observed in GCM simulations at low stellar fluxes, and (iii) the increase of stability generated by dayside sensible heating.

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