Wednesday 05 Dec 2012Modeling the exotic atmosphere of strongly irradiated terrestrial exoplanets: runaway greenhouse and climate bistability

Dr Jeremy Leconte - LMD Paris

Physics, 4th floor 14:00-15:00

Because current exoplanets detection methods are biased toward shorter period orbits, most planets discovered to date have a higher equilibrium temperature than the Earth and Venus. If water is available at the surface, it could be evaporated, leading to the so-called runaway or moist greenhouse that determines the inner edge of the traditional habitable zone. Modeling the climate of such hot, moist atmospheres is thus mandatory to understand the atmospheric properties of hot transiting terrestrial exoplanets for which observation should soon be available.

However, so far, emphasis has been put on 1D radiative convective models, which cannot well predict the impact of clouds, or the non-linear effect of spatial inhomogeneities which can dominate in the case of close in exoplanets for which the rotation rate is synchronized with the orbital motion. Indeed, as we will discuss, this very peculiar radiative forcing can create a strong day-night side temperature contrast and a very efficient cold trap on the night side that cannot be modeled in 1D.

Using a new "generic" 3D GCM developed at LMD for exoplanet studies, we will show how the classical runaway greenhouse can be avoided if water is present only in limited amount. In particular, we will demonstrate that, depending on the flux received and on the atmospheric mass, a bistable climate regime can exist, a "hot" one where all the water is vaporized, and a "cold" one where it is captured in cold traps. Finally, we will discuss several processes that arise on Earth and that could render these hot planets habitable, pushing further in the limits of the habitable zone.

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