General Relativity Can Prevent a Runaway Greenhouse on Potentially Habitable Planets Orbiting White Dwarfs

Abstract

Planets orbiting in the habitable zones of white dwarfs have recently been proposed as promising targets for biosignature searches. However, since the white dwarf habitable zone resides at 0.01–0.1 au, planets residing there are subject to tidal heating if they have any orbital eccentricity. Previous work identified nearby planetary companions as potential roadblocks to habitability of planets around white dwarfs, as such companions could induce secular oscillations in eccentricity for the potentially habitable planet, which could in turn heat a surface ocean and induce a runaway greenhouse for even very low values (e ∼ 10−4) of the eccentricity of the potentially habitable planet. In this work, we examine the potential for general relativistic orbital precession to protect habitable planets orbiting white dwarfs from such a runaway greenhouse and demonstrate that, for some system architectures, general relativity can be protective for planetary habitability.