Removal of Hot Saturns in Mass-Radius Plane by Runaway Mass Loss
arXiv:2211.11770 · doi:10.3847/2041-8213/acbd35
Abstract
The hot Saturn population exhibits a boundary in mass-radius space, such that no planets are observed at a density less than 0.1 g cm. Yet, planet interior structure models can readily construct such objects as the natural result of radius inflation. Here, we investigate the role XUV-driven mass-loss plays in sculpting the density boundary by constructing interior structure models that include radius inflation, photoevaporative mass loss and a simple prescription of Roche lobe overflow. We demonstrate that planets puffier than 0.1 g cm experience a runaway mass loss caused by adiabatic radius expansion as the gas layer is stripped away, providing a good explanation of the observed edge in mass-radius space. The process is also visible in the radius-period and mass-period spaces, though smaller, high-bulk-metallicity planets can still survive at short periods, preserving a partial record of the population distribution at formation.
arXiv comment11 pages, 5 figures, Accepted to ApJ Letters. This revision includes the effect of orbital evolution resulting from Roche lobe overflow; the overall conclusions are the same
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