Ray T. Pierrehumbert, Halley Professor of Physics, University of Oxford
Atmospheric Dynamics of Lava Planets
Some of the most interesting among the roughly 3500 known exoplanets are the least habitable, for life as we know it or indeed for any likely form of life. This talk will focus on one particular class of uninhabitable worlds, the Lava Planets. These are rocky exoplanets with radii up to two or three Earth radii, in such close orbits about their stars that they are almost certainly tide-locked and are expected to have permanent magma oceans in the vicinity of the substellar point. The atmospheres of such planets would be strongly influenced by (and perhaps even entirely created by) the volatiles outgassed from the magma ocean. One of the reasons for the importance of such planets is that they are more amenable to characterization by infrared emission spectroscopy than cooler planets, and that they afford us our best chance to know what rocky exoplanets are made of, since (unlike cooler planets) a substantial part of the rocky substance makes it into the atmosphere as rock vapor. The climate dynamics of such planets is novel, and poses interesting questions; I will provide a survey of the associated phenomena. If the magma ocean outgases into a vacuum (apart from the outgassing products) the dynamics has some deep similarities with cryogenic bodies such as Io or Triton, where the atmospheric source is sublimation from SO2 ice or N2 ice respectively (and also volcanism in the former case). However, there is an interesting transition between local atmospheres which condense out near the source and global atmospheres which fill up the nightside before condensing out. The same distinction applies to lava ocean planets. The case in which the magma ocean outgassed into a non condensing background atmosphere is novel and largely unexplored. It appears that the planet 55Cnc-e is such a planet, and the observed characteristics of the atmosphere present several baffling features, which we are exploring from a dynamical standpoint.