The runaway greenhouse transition [1,2], the carbonate-silicate cycle [3,4] and CO2 surface condensation [4,5] are thought to be three of the most essential geophysical/geochemical processes shaping planetary habitability both inside and outside the solar system [4,6]. However, to date, very little is known about the degree of universality of these processes.
At first, I will briefly review recent ideas proposing ways to statistically detect each of these processes at play, using observations of nearby rocky exoplanets [7-12]. These observations are based on the precise measurement of density and/or molecular detections (in particular CO2) on a large number of rocky exoplanets. I will then focus more specifically on observational tests of the runaway greenhouse , which we can actually already attempt in the TRAPPIST-1 multiplanetary system using comparative density measurements among the seven planets . Although we do not detect the runaway greenhouse radius inflation effect predicted in , we can use atmospheric model predictions to place strong constraints on the water content of TRAPPIST-1 planets .
While this work has been mostly carried out with the support of 1-D numerical climate models, I will present very recent results obtained with 3D Global Climate Models , taking into account the effect of atmospheric dynamics and clouds.
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