The Evaporation Valley in the Kepler Planets
598 citations recorded by the source corpus.
A new piece of evidence supporting the photoevaporation-driven evolution model for low-mass, close-in exoplanets was recently presented by the California–Kepler Survey. The radius distribution of the Kepler planets is shown to be bimodal, with a “valley” separating two peaks at 1.3 and 2.6 R⊕. Such an “evaporation valley” had been predicted by numerical models previously. Here, we develop a minimal model to demonstrate that this valley results from the following fact: the timescale for envelope erosion is the longest for those planets with hydrogen/helium-rich envelopes that, while only a few percent in weight, double its radius. The timescale falls for envelopes lighter than this because the planet’s radius remains largely constant for tenuous envelopes. The timescale also drops for heavier envelopes because the planet swells up faster than the addition of envelope mass. Photoevaporation therefore herds planets into either bare cores (∼1.3 R⊕), or those with double the core’s radius (∼2.6 R⊕). This process mostly occurs during the first 100 Myr when the stars’ high-energy fluxes are high and nearly constant. The observed radius distribution further requires the Kepler planets to be clustered around 3 M⊕ in mass, born with H/He envelopes more than a few percent in mass, and that their cores are similar to the Earth in composition. Such envelopes must have been accreted before the dispersal of the gas disks, while the core composition indicates formation inside the ice line. Lastly, the photoevaporation model fails to account for bare planets beyond ∼30–60 days; if these planets are abundant, they may point to a significant second channel for planet formation, resembling the solar system terrestrial planets.
Subfields: Astronomy and Astrophysics, Instrumentation
View Paper: https://www.semanticscholar.org/paper/4f16722f04dd475b5b73e410fbf70efab56e5561
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Citations in the corpus
- About 30% of Sun-like Stars Have Kepler-like Planetary Systems: A Study of Their Intrinsic Architecture (2018, background): “The typical mass for Kepler planets is ∼ 3 M⊕ (Marcy et al. 2014; Fulton et al. 2017; Hadden & Lithwick 2017; Owen & Wu 2017).”
- Revised Radii of Kepler Stars and Planets Using Gaia Data Release 2 (2018, methodology): “Both results have been tied to processes such as photoevaporation (Lopez et al. 2012; Owen & Wu 2017), but are limited subsamples consisting of less than half of planet candidates.”
- The California-Kepler Survey. IV. Metal-rich Stars Host a Greater Diversity of Planets (2017, methodology): “Owen & Wu (2017) performed a population synthesis starting with 3–10 M⊕ cores and a period distribution of df ∝ P 1.9d logP , which is similar to the power law index presented in this work.”
- 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.”
- The California-Kepler Survey. VII. Precise Planet Radii Leveraging Gaia DR2 Reveal the Stellar Mass Dependence of the Planet Radius Gap (2018, methodology): “If photoevaporation is the dominate mechanism for sculpting planet envelopes, one may fit the observed distribution of planets to constrain important quantities like the distribution of planet core masses, envelope fractions, and core compositions (Owen & Wu 2017).”
- An asteroseismic view of the radius valley: stripped cores, not born rocky (2017, methodology): “This was previously pointed out by Owen & Wu (2017) and Jin & Mordasini (2017), on the condition that the observed valley is indeed primarily caused by photo-evaporation – as the measurement of the valley’s slope in this work appears to confirm.”
- Compositional Imprints in Density–Distance–Time: A Rocky Composition for Close-in Low-mass Exoplanets from the Location of the Valley of Evaporation (2017, result): “After the submission of this paper we became aware of the work of Owen & Wu (2017) who had independently reached the same main conclusions as we do in the present work regarding the composition of the Kepler planets.”
- Photoevaporation and high-eccentricity migration created the sub-Jovian desert (2018, background): “…of either the upper or the lower boundary of the unoccupied region in the radius-period/mass-period plane, then it is the two more massive stable atmospheres (b & c) that designate the boundaries (the lowest mass stable atmosphere is the origin of the photoevaporation valley – Owen & Wu 2017).”
- Predictions of the WFIRST Microlensing Survey. I. Bound Planet Detection Rates (2018, background): “Precise spectroscopic measurements of Kepler’s super Earth hosts has revealed a radius dichotomy between large and small super Earths (Fulton et al. 2017) that is likely due to atmospheric stripping (Owen & Wu 2017).”
- Core-powered mass-loss and the radius distribution of small exoplanets (2017, methodology): “Owen & Wu (2017) consider only the high-energy stellar flux as an energy source that unbinds the atmosphere, while we consider only the cooling luminosity of the planet itself (see also Owen & Wu 2016), and especially of its core.”