An asteroseismic view of the radius valley: stripped cores, not born rocky

Abstract

Various theoretical models treating the effect of stellar irradiation on planetary envelopes predict the presence of a radius valley: i.e. a bimodal distribution of planet radii, with super-Earths and sub-Neptune planets separated by a valley at around $\approx 2R_{\oplus }$. Such a valley was observed recently, owing to an improvement in the precision of stellar, and therefore planetary radii. Here we investigate the presence, location and shape of such a valley using a small sample with highly accurate stellar parameters determined from asteroseismology, which includes 117 planets with a median uncertainty on the radius of 3.3%. We detect a clear bimodal distribution, with super-Earths ($\approx 1.5R_{\oplus }$) and sub-Neptunes ($\approx 2.5R_{\oplus }$) separated by a deficiency around $2R_{\oplus }$. We furthermore characterize the slope of the valley as a power law $R\propto P^{\gamma }$ with $\gamma =-0.09_{-0.04}^{+0.02}$. A negative slope is consistent with models of photo-evaporation, but not with the late formation of rocky planets in a gas-poor environment, which would lead to a slope of opposite sign. The exact location of the gap further points to planet cores consisting of a significant fraction of rocky material.

MNRAS accepted. Submitted in original form on 28 November 2016

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• A Spectroscopic Analysis of a Sample of K2 Planet-Host Stars: Stellar Parameters, Metallicities and Planetary Radii
• Searching for Hot Water World Candidates with CHEOPS: Refining the radii and analysing the internal structures and atmospheric lifetimes of TOI-238 b and TOI-1685 b
• TOI-733 b: a planet in the small-planet radius valley orbiting a Sun-like star
• Diversity of disc viscosities can explain the period ratios of resonant and non-resonant systems of hot super-Earths and mini-Neptunes
• Characterization of Low Mass K2 Planet Hosts Using Near-Infrared Spectroscopy
• Stellar rotation and its connection to the evolution of hydrogen-dominated atmospheres of exoplanets
• Estimating photoevaporative mass loss of exoplanets with PLATYPOS
• More planetary candidates from K2 Campaign 5 by tran_k2
• 3D Modeling of Moist Convective Inhibition in Idealized Sub-Neptune Atmospheres
• The New Generation Planetary Population Synthesis (NGPPS) VIII. Impact of host star metallicity on planet occurrence rates, orbital periods, eccentricities, and radius valley morphology
• Homogeneous planet masses I: Reanalysis of archival HARPS radial velocities
• Understanding and predicting cadence effects in the characterization of exoplanet transits
• Scaling K2 VIII: Short-Period Sub-Neptune Occurrence Rates Peak Around Early-Type M Dwarfs
• Is the high-energy environment of K2-18b special?
• Diversities and similarities exhibited by multi-planetary systems and their architectures: I. Orbital spacings
• Formation of organic hazes in CO${}_2$-rich sub-Neptune atmospheres within the graphite-stability regime
• TOI-1743 b, TOI-5799 b, TOI-5799 c and TOI-6223 b: TESS discovery and validation of four super-Earth to Neptune-sized planets around M dwarfs
• Validation of a Temperate Fourth Planet in the K2-133 Multi-planet System
• Three young planets around the K-dwarf K2-198: High-energy environment, evaporation history and expected future
• The strongly irradiated planets in Praesepe
• Takeout and Delivery: Erasing the Dusty Signature of Late-stage Terrestrial Planet Formation
• TESS and HARPS-N unveil two planets transiting TOI-1453. A super-Earth and one of the lowest mass sub-Neptunes
• Exploring the habitability and interior composition of exoplanets lying within the extended habitable zone
• Mass Upper Bounds for Over 50 Kepler Planets Using Low-S/N Transit Timing Variations
• A Pair of Dynamically Interacting Sub-Neptunes Around TOI-6054
• X-ray irradiation of three planets around Hyades star K2-136
• Stellar Characterization and a Chromospheric Activity Analysis of a K2 Sample of Planet-Hosting Stars
• Research Programs Arising from 'Oumuamua Considered as an Alien Craft
• Confronting compositional confusion through the characterisation of the sub-Neptune orbiting HD 77946
• Evidence that Planets in the Radius Gap Do Not Resemble Their Neighbors
• A Search for Planetary Metastable Helium Absorption in the V1298 Tau System
• TOI-1634 b: an Ultra-Short Period Keystone Planet Sitting Inside the M Dwarf Radius Valley
• Precise Parameters from Bayesian SED Fitting Indicate Thermally-Driven Mass Loss Likely Driver of Radius Valley
• Radio prospects of extrasolar aurorae polaris as a probe of planetary magnetism
• The GAPS programme at TNG LXXI. A sub-Neptune suitable for atmospheric characterization in a multiplanet and mutually inclined system orbiting the bright K dwarf TOI-5789 (HIP 99452)
• Gas-depleted planet formation occurred in the four-planet system around the red dwarf LHS 1903
• A Validated Low-to-Intermediate Mass Planetary Interior Structure Model and New Mass-Radius Relations
• Super-earths and mini-neptunes follow different orbital period-eccentricity relations
• Evolution and Observable Properties of Rocky Planet Atmospheres
• Decoding the Future of Exoplanets: Asteroseismic Confirmation of Subgiant and Red Giant Hosts
• Using asteroseismology to characterise exoplanet host stars
• Refining the Masses and Radii of the Star Kepler-33 and its Five Transiting Planets
• Discovery of a multi-planetary system orbiting the aged Sun-like star HD 224018
• The Cohesive Object Sequence: The Mass-Density Distribution of Astronomical Objects from Asteroids to Stars
• Sub-Neptunes Show a Stronger Correlation with Cold Jupiters than Super-Earths Especially in Metal-rich Systems
• The GAPS Programme at the TNG: LXX. TOI-5734b: A hot sub-Neptune orbiting a relatively young K dwarf with an Earth-like density
• TOI-1201 b: A mini-Neptune transiting a bright and moderately young M dwarf
• Revisiting the exoplanet radius valley with host stars from SWEET-Cat
• Using observations of escaping H/He to constrain the atmospheric composition of sub-Neptunes
• Stellar chemistry and planet size: insights from GALAH DR4
• Sibling Sub-Neptunes Around Sibling M Dwarfs: TOI-521 and TOI-912
• Constraining stellar rotation and planetary atmospheric evolution of a dozen systems hosting sub-Neptunes and super-Earths
• Split Peas in a Pod: Intra-System Uniformity of Super-Earths and Sub-Neptunes
• ExoplANETS-A: A VO database for host stars and planetary systems: The effect of XUV on planet atmospheres
• A search for transits among the δ Scuti variables in Kepler
• Friends and Foes: Conditional Occurrence Rates of Exoplanet Companions and their Impact on Radial Velocity Follow-up Surveys
• Chemical diversity of the atmospheres and interiors of sub-Neptunes: a case study of GJ 436 b
• Do Outer Giants Inflate Neptune-sized Planets? An Architecture-Dependent Mass-Radius Relation