A Scaling for Atmospheric Heat Redistribution on Tidally-Locked Rocky Planets

Atmospheric heat redistribution shapes the remote appearance of rocky exoplanets but there is currently no easy way to predict a planet's heat redistribution from its physical properties. This paper proposes an analytical scaling theory for the heat redistribution on tidally-locked rocky exoplanets. The main parameters of the scaling are a planet's equilibrium temperature, surface pressure, and broadband longwave optical thickness. The scaling compares favorably against idealized general circulation model simulations of TRAPPIST-1b, GJ1132b, and LHS 3844b. For these planets heat redistribution generally becomes efficient, and a planet's observable thermal phase curve and secondary eclipse start to deviate significantly from that of a bare rock, once surface pressure exceeds O(1) bar. The scaling additionally points to planetary scenarios for which heat transport can be notably more or less efficient, such as H2 and CO atmospheres or hot lava ocean worlds. The results thus bridge the gap between theory and imminent observations with the James Webb Space Telescope. They can also be used to parameterize the effect of 3D atmospheric dynamics in 1D models, thereby improving the self-consistency of such models.
Comment: Published in ApJ. Note minor changes in scaling since v1. Also see these three companion papers: Mansfield et al (2019) "Identifying Atmospheres on Rocky Exoplanets Through Inferred High Albedo"; Malik et al (2019) "Analyzing Atmospheric Temperature Profiles and Spectra of M dwarf Rocky Planets", Koll et al (2019) "Identifying Candidate Atmospheres on Rocky M dwarf Planets via Eclipse Photometry"