Quantifying the Surface Heating of Tidally Migrating White Dwarf Planets

The problem of quantifying planetary habitability has recently extended to include terrestrial-mass exoplanets orbiting white dwarfs (WDs). A plausible formation scenario for such a system is the inward migration of a planet that existed before the progenitor star’s AGB phase. Tidal heating due to migration in this scenario is a double-edged sword for habitability; it extends the habitable zone (HZ) outward, but may also drive extreme atmospheric escape and the loss of volatiles. The goal of the present work is to quantify the surface heat flux of a WD planet as it migrates from beyond the snow line to the HZ, and the implications of this evolution on the planet’s habitability. To this end, we introduce a new module for VPLanet, a code for simulating the coupled processes that drive planetary evolution over long timescales. Our new module retrieves evolutionary tracks for WDs of various mass and metallicity by interpolating over precomputed model grids. This addition to the VPLanet ecosystem allows for simulations that couple WD luminosity evolution with tidal forcing, atmospheric escape, and a litany of other interdependent physical processes that influence habitability. We will present the first results of such simulations, which track the surface effective temperature of a planet over the course of migration to the WD HZ using an array of initial eccentricities and semi-major axes. A possible finding is that in order to remain within the HZ for multiple Gyr, a planet must migrate fast enough that tidal heating will drive off all water. Such a finding would represent a strong argument against the formation of any habitable WD worlds.