Can tidal evolution lead to close-in planetary bodies around white dwarfs I: Orbital period distribution

Abstract

The evolution of planetary systems around white dwarfs is crucial to understanding the presence of planetary material in the atmospheres of white dwarfs. These systems uniquely probe exoplanetary compositions. Periodic signals in the photometry of a handful of white dwarfs suggest material blocking the star, potentially from disintegrating planetesimals. Tidal evolution followed by scattering can bring planetesimals onto close-in orbits that would have been within the envelope of the white dwarf progenitor. The orbital period distribution of planetesimals undergoing tidal evolution will peak at short-period (nearly) circularized orbits (~ 10 hour-1 day), with a rising tail towards long-period highly eccentric orbits (~ 100 day). This prediction is generally consistent with the observed white dwarf transiting systems. In order for the planetesimal on the 4.5 hour period around WD 1145+017 to be explained by the tidal evolution of a planetesimal, that planetesimal must have an ultimate tensile strength comparable to that of iron meteorites.