Exoplanets & Exomoons

Shallower Radius Valley Around Low-mass Hosts Provides Evidence For Icy Planets Or Collisions

By Keith Cowing
Status Report
January 25, 2024
Filed under ,
Shallower Radius Valley Around Low-mass Hosts Provides Evidence For Icy Planets Or Collisions
Planetary radius-orbital period-stellar mass plot of the 444 small planets analysed in this work, which includes 375 with parameters from Ho & Van Eylen (2023) (red) and 69 newly refitted (blue) in this work. The radius valley boundary determined in Ho & Van Eylen (2023) is indicated by the grey planes. — astro-ph.EP

The radius valley, i.e., a dearth of planets with radii between 1.5 and 2 Earth radii, provides insights into planetary formation and evolution. Using homogenously revised planetary parameters from Kepler 1-minute short cadence light curves, we remodel transits of 72 small planets orbiting low-mass stars, improving the precision and accuracy of planet parameters.

By combining this sample with a similar sample of planets around higher-mass stars, we determine the depth of the radius valley as a function of stellar mass. We find that the radius valley is shallower for low-mass stars compared to their higher mass counterparts. Upon comparison, we find that theoretical models of photoevaporation under-predict the number of planets observed inside the radius valley for low-mass stars: with decreasing stellar mass, the predicted fraction of planets inside the valley remains approximately constant whereas the observed fraction increases.

We argue that this provides evidence for the presence of icy planets around low-mass stars. Alternatively, planets orbiting low-mass stars undergo more frequent collisions. We predict that more precise mass measurements for planets orbiting low mass stars would be able to distinguish between these scenarios.

Cynthia S. K. Ho, James G. Rogers, Vincent Van Eylen, James E. Owen, Hilke E. Schlichting

Comments: 18 pages, submitted to MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2401.12378 [astro-ph.EP] (or arXiv:2401.12378v1 [astro-ph.EP] for this version)
Submission history
From: Cynthia Ho
[v1] Mon, 22 Jan 2024 22:03:51 UTC (6,454 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻