Removal of Hot Saturns in Mass-Radius Plane by Runaway Mass Loss
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-3. Yet, planet interior structure models can readily construct such objects as the natural result of radius inflation. Here, we investigate the role X-ray and extreme UV irradiation (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-3 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2023
- DOI:
- 10.3847/2041-8213/acbd35
- arXiv:
- arXiv:2211.11770
- Bibcode:
- 2023ApJ...945L..36T
- Keywords:
-
- Exoplanet evolution;
- Exoplanet structure;
- Exoplanets;
- Hot Jupiters;
- Hot Neptunes;
- 491;
- 495;
- 498;
- 753;
- 754;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- 11 pages, 5 figures, Accepted to ApJ Letters. This revision includes the effect of orbital evolution resulting from Roche lobe overflow