Current Population Statistics Do Not Favor Photoevaporation over Core-Powered Mass Loss as the Dominant Cause of the Exoplanet Radius Gap

Abstract

We search for evidence of the cause of the exoplanet radius gap, i.e. the dearth of planets with radii near $1.8R_{\oplus }$. If the cause was photoevaporation, the radius gap should trend with proxies for the early-life high-energy emission of planet-hosting stars. If, alternatively, the cause was core-powered mass loss, no such trends should exist. Critically, spurious trends between the radius gap and stellar properties arise from an underlying correlation with instellation. After accounting for this underlying correlation, we find no trends remain between the radius gap and stellar mass or present-day stellar activity as measured by near-UV emission. We dismiss the nondetection of a radius gap trend with near-UV emission because present-day near-UV emission is unlikely to trace early-life high-energy emission, but we provide a catalog of GALEX near-UV and far-UV emission measurements for general use. We interpret the nondetection of a radius gap trend with stellar mass by simulating photoevaporation with mass-dependent evolution of stellar high-energy emission. The simulation produces an undetectable trend between the radius gap and stellar mass under realistic sources of error. We conclude that no evidence, from this analysis or others in the literature, currently exists that clearly favors either photoevaporation or core powered mass loss as the primary cause of the exoplanet radius gap. However, repeating this analysis once the body of well-characterized $<4R_{\oplus }$ planets has roughly doubled could confirm or rule out photoevaporation.

arXiv comment27 pages, 32 figures, accepted to ApJ

References in corpus (33)

• Astropy: A Community Python Package for Astronomy
• Gaia Data Release 2. Summary of the contents and survey properties
• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
• Kepler planets: a tale of evaporation
• The evaporation valley in the Kepler planets
• Understanding the Mass-Radius Relation for Sub-Neptunes: Radius as a Proxy for Composition
• Constraining the Age-Activity Relation for Cool Stars: The SDSS DR5 Low-Mass Star Spectroscopic Sample
• The Mass-Radius Relation for 65 Exoplanets Smaller than 4 Earth Radii
• The California Kepler Survey VII. Precise Planet Radii Leveraging Gaia DR2 Reveal the Stellar Mass Dependence of the Planet Radius Gap
• An asteroseismic view of the radius valley: stripped cores, not born rocky
• The Role of Core Mass in Controlling Evaporation: the Kepler Radius Distribution and the Kepler-36 Density Dichotomy
• Core-powered mass loss and the radius distribution of small exoplanets
• Planetary evaporation by UV & X-ray radiation: basic hydrodynamics
• Sculpting the Valley in the Radius Distribution of Small Exoplanets as a by-product of Planet Formation: The Core-Powered Mass-Loss Mechanism
• How Thermal Evolution and Mass Loss Sculpt Populations of Super-Earths and Sub-Neptunes: Application to the Kepler-11 System and Beyond
• Super-Earth Atmospheres: Self-Consistent Gas Accretion and Retention
• The Extreme Ultraviolet and X-Ray Sun in Time: High-Energy Evolutionary Tracks of a Solar-Like Star
• The coronal X-ray - age relation and its implications for the evaporation of exoplanets
• How Good a Clock is Rotation? The Stellar Rotation-Mass-Age Relationship for Old Field Stars
• Habitable Evaporated Cores: Transforming Mini-Neptunes into Super-Earths in the Habitable Zones of M Dwarfs
• HAZMAT I: The Evolution of Far-UV and Near-UV Emission from Early M Stars
• Mass and Mass Scalings of Super-Earths
• A Spectroscopic Analysis of the California-Kepler Survey Sample: I. Stellar Parameters, Planetary Radii and a Slope in the Radius Gap
• Far-Ultraviolet Activity Levels of F, G, K, and M dwarf Exoplanet Host Stars
• Testing exoplanet evaporation with multi-transiting systems
• An Ultraviolet Investigation of Activity on Exoplanet Host Stars
• The sub-Neptune desert and its dependence on stellar type: Controlled by lifetime X-ray irradiation
• HAZMAT III: The UV Evolution of Mid- to Late-M Stars with GALEX
• A Catalog of Stellar Unified Properties (CATSUP) for 951 FGK-Stars Within 30 pc
• Close-in sub-Neptunes reveal the past rotation history of their host stars: atmospheric evolution of planets in the HD3167 and K2-32 planetary systems
• HAZMAT. V. The Ultraviolet and X-ray Evolution of K Stars
• Examining the Radius Valley: a Machine Learning Approach
• Two Terrestrial Planet Families With Different Origins

Cited by in corpus (37)

• Density, not radius, separates rocky and water-rich small planets orbiting M dwarf stars
• The Gaia-Kepler Stellar Properties Catalog. II. Planet Radius Demographics as a Function of Stellar Mass and Age
• Exoplanet secondary atmosphere loss and revival
• Photoevaporation vs. core-powered mass-loss: model comparison with the 3D radius gap
• Atmospheric Regimes and Trends on Exoplanets and Brown Dwarfs
• EvryFlare III: Temperature Evolution and Habitability Impacts of Dozens of Superflares Observed Simultaneously by Evryscope and TESS
• A deep radius valley revealed by Kepler short cadence observations
• Creating the Radius Gap without Mass Loss
• A fading radius valley towards M-dwarfs, a persistent density valley across stellar types
• X-ray irradiation and evaporation of the four young planets around V1298 Tau
• Evolution of the Exoplanet Size Distribution: Forming Large Super-Earths Over Billions of Years
• Chemistry of Temperate Super-Earth and Mini-Neptune Atmospheric Hazes from Laboratory Experiments
• To cool is to keep: Residual H/He atmospheres of super-Earths and sub-Neptunes
• The importance of silicate vapor in determining the structure, radii, and envelope mass fractions of sub-Neptunes
• AU Microscopii in the FUV: Observations in Quiescence, During Flares, and Implications for AU Mic b and c
• Caught in the Act: Core-powered Mass-loss Predictions for Observing Atmospheric Escape
• The Demographics of Kepler's Earths and super-Earths into the Habitable Zone
• TOI-1759 b: a transiting sub-Neptune around a low mass star characterized with SPIRou and TESS
• The MOPYS project: A survey of 70 planets in search of extended He I and H atmospheres. No evidence of enhanced evaporation in young planets
• Formation of aqua planets with water of nebular origin: Effects of water enrichment on the structure and mass of captured atmospheres of terrestrial planets
• A multi-wavelength look at the GJ 9827 system -- No evidence of extended atmospheres in GJ 9827 b and d from HST and CARMENES data
• The influence of host star activity evolution on the population of super-Earths and mini-Neptunes
• Scaling K2. III. Comparable Planet Occurrence in the FGK Samples of Campaign 5 and Kepler
• A Spectroscopic Analysis of the California-Kepler Survey Sample: II. Correlations of Stellar Metallicities with Planetary Architectures
• Rotation periods of TESS Objects of Interest from the Magellan-TESS Survey with multiband photometry from Evryscope and TESS
• Physical Properties and Impact Parameter Variations of Kepler Planets from Analytic Light Curve Modeling
• Hiding Planets Near and Far: The Parameter Space of Hidden Companions for Known Planetary Systems
• A primordial radius valley as a consequence of planet formation
• TESS discovery of a super-Earth and two sub-Neptunes orbiting the bright, nearby, Sun-like star HD 22946
• Evidence that Planets in the Radius Gap Do Not Resemble Their Neighbors
• Precise Parameters from Bayesian SED Fitting Indicate Thermally-Driven Mass Loss Likely Driver of Radius Valley
• Oxygen left behind: Atmospheric Enrichment due to Fractionation in Sub-Neptunes using BOREAS
• Rapid Formation of Super-Earths Around Low-Mass Stars
• Revisiting the exoplanet radius valley with host stars from SWEET-Cat
• Constraining stellar rotation and planetary atmospheric evolution of a dozen systems hosting sub-Neptunes and super-Earths
• Atmospheric mass loss and stellar wind effects in young and old systems I: comparative 3D study of TOI-942 and TOI-421 systems
• Atmospheric mass loss and stellar wind effects in young and old systems II: Is TOI-942 the past of TOI-421 system?