Beyond runaway: initiation of the post-runaway greenhouse state on rocky exoplanets

Abstract

The runaway greenhouse represents the ultimate climate catastrophe for rocky, Earth-like worlds: when the incoming stellar flux cannot be balanced by radiation to space, the oceans evaporate and exacerbate heating, turning the planet into a hot wasteland with a steam atmosphere overlying a possibly molten magma surface. The equilibrium state beyond the runaway greenhouse instellation limit depends on the radiative properties of the atmosphere and its temperature structure. Here, we use 1-D radiative-convective models of steam atmospheres to explore the transition from the tropospheric radiation limit to the post-runaway climate state. To facilitate eventual simulations with 3-D global circulation models, a computationally efficient band-grey model is developed, which is capable of reproducing the key features of the more comprehensive calculations. We analyze two factors which determine the equilibrated surface temperature of post-runaway planets. The infrared cooling of the planet is strongly enhanced by the penetration of the dry adiabat into the optically thin upper regions of the atmosphere. In addition, thermal emission of both shortwave and near-IR fluxes from the hot lower atmospheric layers, which can radiate through window regions of the spectrum, is quantified. Astronomical surveys of rocky exoplanets in the runaway greenhouse state may discriminate these features using multi-wavelength observations.

arXiv commentAccepted for publication in ApJ; 19 pages, 11 figures; Summary video available at https://exoplanet-talks.org/talk/379

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Cited by in corpus (21)

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• The runaway greenhouse on subNeptune waterworlds
• A cool runaway greenhouse without surface magma ocean
• Super-Earths and Earth-like Exoplanets
• Water Condensation Zones around Main Sequence Stars
• Bioverse: The Habitable Zone Inner Edge Discontinuity as an Imprint of Runaway Greenhouse Climates on Exoplanet Demographics
• Reduced late bombardment on rocky exoplanets around M-dwarfs
• Large Interferometer For Exoplanets (LIFE): IX. Assessing the Impact of Clouds on Atmospheric Retrievals at Mid-Infrared Wavelengths with a Venus-Twin Exoplanet
• How does the background atmosphere affect the onset of the runaway greenhouse ?
• Convective shutdown in the atmospheres of lava worlds
• First exploration of the runaway greenhouse transition with a GCM
• Imaging of exocomets with infrared interferometry
• Absence of a Runaway Greenhouse Limit on Lava Planets
• Large Interferometer For Exoplanets (LIFE). XIV. Finding terrestrial protoplanets in the galactic neighborhood
• From CO${}_2$- to H${}_2$O-dominated atmospheres and back -- How mixed outgassing changes the volatile distribution in magma oceans around M dwarf stars
• The impact of water clouds on the prospective emission spectrum of Teegarden's Star b as observed by LIFE
• Near the Runaway: The Climate and Habitability of Teegarden's Star b
• What the Solar System Can Teach Us About Rocky Exoplanets
• Convection modeling of pure-steam atmospheres
• The effect of a biosphere on the habitable timespan of stagnant-lid planets and implications for the atmospheric spectrum
• Hidden water in magma ocean exoplanets