Diversity of Planetary Climates: New revelations in the era of the James Webb Space Telescope

The new frontier of exoplanet discovery and characterisation  has revealed to us a Universe teaming with planets. It appears that it is quite hard to make a star without leaving enough material behind in a protoplanetary disk to form planets. The bounty of new planets (5500 and counting) has offered up many types of planets and associated climate phenomena unknwon in our own solar system. Nonetheless, these novel planetary climates can be explored in terms of the building blocks of fundamental physics that have long been used to build an understanding of the climates of Earth and other Solar System planets, and their evolution over deep time. This talk will focus on the smaller range of planets, ranging up to 3 Earth radii. This class of planets includes both rocky planets, including super-Earths somewhat larger than Earth, and low density gaseous subNeptunes.

The James Webb Space Telescope has opened a revolutionary new capability to characterise atmospheres of the smaller range of planets.  While subNeptunes, by virtue of their low density, must of necessity have extensive volatile envelopes, it was not known where the atmospheres sat on the continuum between Jupiter-like hydrogen-helium atmospheres and higher molecular weight volatiles such as H₂O, NH₃, CO₂ and CH_4.  For rocky planets, one of the key questions has been whether rocky planets around low-mass M stars could retain atmospheres; since M stars are by far the most common (and long lived) stars in the Universe, if their rocky planets can retain atmospheres, the Universe is surely teeming with habitable territory. I will discuss what has been learned so far, and highlight a few key novel climate phenomena. These include climates of tide-locked planets, of lava planets with thin rock-vapour atmospheres, of water-rich subNeptunes involving a mix of hydrogen and supercritical water, and the key importance of characterizing atmospheric CO₂ and testing theories of its geochemical control on rocky planets.