Core-powered mass-loss and the radius distribution of small exoplanets

By S. Ginzburg, H. Schlichting, R. Sari. 2017

335 citations recorded by the source corpus.

Recent observations identify a valley in the radius distribution of small exoplanets, with planets in the range $1.5-2.0\,{\rm R}_\oplus$ significantly less common than somewhat smaller or larger planets. This valley may suggest a bimodal population of rocky planets that are either engulfed by massive gas envelopes that significantly enlarge their radius, or do not have detectable atmospheres at all. One explanation of such a bimodal distribution is atmospheric erosion by high-energy stellar photons. We investigate an alternative mechanism: the luminosity of the cooling rocky core, which can completely erode light envelopes while preserving heavy ones, produces a deficit of intermediate sized planets. We evolve planetary populations that are derived from observations using a simple analytical prescription, accounting self-consistently for envelope accretion, cooling and mass loss, and demonstrate that core-powered mass loss naturally reproduces the observed radius distribution, regardless of the high-energy incident flux. Observations of planets around different stellar types may distinguish between photoevaporation, which is powered by the high-energy tail of the stellar radiation, and core-powered mass loss, which depends on the bolometric flux through the planet's equilibrium temperature that sets both its cooling and mass-loss rates.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/66447806e704bc5d79d96cf4d74a3fa72ecacd83

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In Astronomy and Astrophysics

1. D. Huber
2. J. V. van Saders
3. J. Owen
4. E. Petigura
5. B. Fulton
6. E. Gaidos
7. T. Berger
8. L. Weiss

Citations in the corpus

• A Guide to Realistic Uncertainties on the Fundamental Properties of Solar-type Exoplanet Host Stars (2020, background): “Even so, the dominant mechanism causing this gap is still debated, with core-powered mass loss (Ginzburg et al. 2018) and photoevaporation (Owen & Wu 2017) both making predictions consistent with the observations that can only be distinguished by even more precise samples.”
• Atmospheric Escape and the Evolution of Close-In Exoplanets (2018, background): “There is still debate as to whether the observed gap in the exoplanet radius-period distribution is indeed the evaporation valley (e.g. Ginzburg et al. 2018; Zeng et al. 2018).”
• The Gaia–Kepler Stellar Properties Catalog. II. Planet Radius Demographics as a Function of Stellar Mass and Age (2020, background): “…formation in a gas-poor disk (Lee et al. 2014; Lee & Chiang 2016), extreme ultraviolet (EUV) photoevaporation of planet atmospheres (Owen & Wu 2013, 2017; Lopez & Rice 2018; Owen & MurrayClay 2018; Wu 2019), and core-powered mass loss (Ginzburg et al. 2016, 2018; Gupta & Schlichting 2019, 2020).”
• The California-Kepler Survey. VII. Precise Planet Radii Leveraging Gaia DR2 Reveal the Stellar Mass Dependence of the Planet Radius Gap (2018, methodology): “Ginzburg et al. (2018) performed a population synthesis with comparisons to the F17 radius distribution and demonstrated that core-powered mass loss could explain the bimodal radius distribution.”
• Revised Radii of Kepler Stars and Planets Using Gaia Data Release 2 (2018, background): “This supports XUV-driven photoevaporation as the dominant mechanism sculpting the radii of the exoplanet population, while other mechanisms such as core-powered mass loss (Ginzburg et al. 2016, 2018) seem less important.”