Atmospheric dynamics of Tide-Locked exoplanets

Ray Pierrehumbert, University of Oxford. Part of the applied mathematics seminar series.

A large proportion of the exoplanets discovered so far are in orbits sufficiently close to their host stars that tidal stresses are sufficiently strong that the spin state of planet will become tide-locked to the star on a time scale short compared to the age of the system.  This includes all habitable-zone planets orbiting M stars, as well as all lava planets orbiting more massive main-sequence stars. Such planets have a permanent dayside and a permanent nightside, leading to a range of novel atmospheric circulations which have observable consequences in terms of the optical or infrared phase curves of the planets. In this talk, I will discuss the fundamental geophysical fluid dynamics underpinning our understanding of the atmospheric circulation and its ability to transport heat and chemical constituents. The theoretical framework draws on deep analogies with theories used to understand the climate of the Earth’s tropics, but also engages a number of novel phenomena including generation of super-rotating equatorial jets. In addition to having consequences for the interpretation of astronomical observations, these circulations can strongly effect the long term evolution of the atmosphere through their influence on such things as the runaway greenhouse threshold, volatile exchange with the crust, and sequestration of condensible substances on the nightside of the planet.