The Tidal Venus Phenomenon: Demographics and Case Studies

Abstract

The demographics of terrestrial planets and their orbits reveal a vast diversity in overall planetary energy budgets. Terrestrial exoplanets in short-period or eccentric orbits can experience intense tidal heating that, combined with stellar irradiation, may trigger runaway greenhouse conditions analogous to Venus. We calculate tidal heating rates for 143 terrestrial-sized exoplanets with measured eccentricities and find that, under adopted archive default eccentricities and constant-$Q$ assumptions, 70% exceed the extreme volcanism threshold in tidal flux and 96% exceed the runaway greenhouse limit in total zero-albedo flux. We develop a three-category taxonomy of tidal influence on climate: flux-driven Venus analogs, tidally dominated planets, and historically compromised Habitable Zone (HZ) worlds, and apply this framework to five case studies. TOI-6716 b and TOI-912 b may have exceptionally high tidal fluxes, potentially serving as examples where tidal dissipation alone causes them to exceed the runaway greenhouse threshold. TOI-700 d and LHS 1140 b, though currently below the threshold, were exposed to above-threshold stellar irradiation during their host stars' $\sim$0.5--3~Gyr pre-main-sequence phases; whether their atmospheres survived is testable with JWST. GJ 12 b, already above the threshold from stellar flux alone, experiences a tidal heat flux of $\sim$5~W/m$^2$ (comparable to Io) that drives an independent volcanic pathway to a runaway greenhouse. Three-dimensional climate simulations show that a temperate atmosphere for GJ 12 b fails to achieve radiative balance, while a Venus-like CO$_2$-dominated atmosphere converges to a stable state. We consider observational prospects for these systems and connections to forthcoming Venus in-situ missions.