Evolution of the Exoplanet Size Distribution: Forming Large Super-Earths Over Billions of Years

Abstract

The radius valley, a bifurcation in the size distribution of small, close-in exoplanets, is hypothesized to be a signature of planetary atmospheric loss. Such an evolutionary phenomenon should depend on the age of the star-planet system. In this work, we study the temporal evolution of the radius valley using two independent determinations of host star ages among the California-Kepler Survey (CKS) sample. We find evidence for a wide and nearly empty void of planets in the period-radius diagram at the youngest system ages ($\lesssim$2-3 Gyr) represented in the CKS sample. We show that the orbital period dependence of the radius valley among the younger CKS planets is consistent with that found among those planets with asteroseismically determined host star radii. Relative to previous studies of preferentially older planets, the radius valley determined among the younger planetary sample is shifted to smaller radii. This result is compatible with an atmospheric loss timescale on the order of gigayears for progenitors of the largest observed super-Earths. In support of this interpretation, we show that the planet sizes which appear to be unrepresented at ages $\lesssim$2-3 Gyr are likely to correspond to planets with rocky compositions. Our results suggest the size distribution of close-in exoplanets, and the precise location of the radius valley, evolves over gigayears.

arXiv commentAccepted to The Astronomical Journal. 46 pages, 27 figures

References in corpus (77)

• Astropy: A Community Python Package for Astronomy
• The NumPy array: a structure for efficient numerical computation
• Gaia Data Release 2. Summary of the contents and survey properties
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• MESA Isochrones and Stellar Tracks (MIST). I: Solar-Scaled Models
• Gaia Data Release 2: The astrometric solution
• MESA Isochrones and Stellar Tracks (MIST) 0: Methods for the construction of stellar isochrones
• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
• The false positive rate of Kepler and the occurrence of planets
• Kepler Presearch Data Conditioning II - A Bayesian Approach to Systematic Error Correction
• The NASA Exoplanet Archive: Data and Tools for Exoplanet Research
• Prevalence of Earth-size planets orbiting Sun-like stars
• Kepler Presearch Data Conditioning I - Architecture and Algorithms for Error Correction in Kepler Light Curves
• Kepler planets: a tale of evaporation
• Most 1.6 Earth-Radius Planets are not Rocky
• The evaporation valley in the Kepler planets
• The Mass-Radius Relation for 65 Exoplanets Smaller than 4 Earth Radii
• Growth Model Interpretation of Planet Size Distribution
• The Ages of Stars
• 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
• False positive probabilties for all Kepler Objects of Interest: 1284 newly validated planets and 428 likely false positives
• 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
• Ages and fundamental properties of Kepler exoplanet host stars from asteroseismology
• How Thermal Evolution and Mass Loss Sculpt Populations of Super-Earths and Sub-Neptunes: Application to the Kepler-11 System and Beyond
• Kepler-36: A Pair of Planets with Neighboring Orbits and Dissimilar Densities
• Unresolved stellar companions with Gaia DR2 astrometry
• Terrestrial Planet Occurrence Rates for the Kepler GK Dwarf Sample
• The California-Kepler Survey. IV. Metal-rich Stars Host a Greater Diversity of Planets
• Planetary population synthesis coupled with atmospheric escape: a statistical view of evaporation
• The California-Kepler Survey. I. High Resolution Spectroscopy of 1305 Stars Hosting Kepler Transiting Planets
• Super-Earth Atmospheres: Self-Consistent Gas Accretion and Retention
• Breeding Super-Earths and Birthing Super-Puffs in Transitional Disks
• A Revised Effective Temperature Scale for the Kepler Input Catalog
• Asteroseismology and Gaia: Testing Scaling Relations Using 2200 Kepler Stars with TGAS Parallaxes
• Compositional imprints in density-distance-time: a rocky composition for close-in low-mass exoplanets from the location of the valley of evaporation
• Make Super-Earths, Not Jupiters: Accreting Nebular Gas onto Solid Cores at 0.1 AU and Beyond
• Planetary Candidates Observed by Kepler VI: Planet Sample from Q1-Q16 (47 Months)
• About 30% of Sun-like Stars Have Kepler-like Planetary Systems: A Study of their Intrinsic Architecture
• The Kepler Follow-Up Observation Program. I. A Catalog of Companions to Kepler Stars from High-Resolution Imaging
• A Study of the Shortest-Period Planets Found With Kepler
• 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
• Stellar Rotation Periods of the Kepler Objects of Interest: A Dearth of Close-in Planets around Fast Rotators
• Inferring probabilistic stellar rotation periods using Gaussian processes
• Evolutionary Analysis of Gaseous Sub-Neptune-Mass Planets with MESA
• In-situ Accretion of Hydrogen-Rich Atmospheres on Short-Period Super-Earths: Implications for the Kepler-11 Planets
• Signatures of the Core-Powered Mass-Loss Mechanism in the Exoplanet Population: Dependence on Stellar Properties and Observational Predictions
• Rotation Periods, Variability Properties and Ages for Kepler Exoplanet Candidate Host Stars
• The Gaia-Kepler Stellar Properties Catalog. II. Planet Radius Demographics as a Function of Stellar Mass and Age
• The California-Kepler Survey. II. Precise Physical Properties of 2025 Kepler Planets and Their Host Stars
• Evolution of the radius valley around low mass stars from $Kepler$ and $K2$
• When Do Stalled Stars Resume Spinning Down? Advancing Gyrochronology with Ruprecht 147
• How formation time-scales affect the period dependence of the transition between rocky super-Earths and gaseous sub-Neptunes and implications for ${\eta }_{\oplus }$
• Photometric Amplitude Distribution of Stellar Rotation of Kepler KOIs-Indication for Spin-Orbit Alignment of Cool Stars and High Obliquity for Hot Stars
• Towards precise stellar ages: combining isochrone fitting with empirical gyrochronology
• Architectures of Exoplanetary Systems. I: A Clustered Forward Model for Exoplanetary Systems around Kepler's FGK Stars
• Atmosphere Origins for Exoplanet Sub-Neptunes
• 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
• Exoplanet secondary atmosphere loss and revival
• Stealing the Gas: Giant Impacts and the Large Diversity in Exoplanet Densities
• Giant Impact: An Efficient Mechanism for the Devolatilization of Super-Earths
• Water on Hot Rocky Exoplanets
• LAMOST telescope reveals that Neptunian cousins of hot Jupiters are mostly single offspring of stars that are rich in heavy elements
• EUV irradiation of exoplanet atmospheres occurs on Gyr timescales
• Metallicity-Dependent Signatures in the Kepler Planets
• Two Views of the Radius Gap and the Role of Light Curve Fitting
• Current Population Statistics Do Not Favor Photoevaporation over Core-Powered Mass Loss as the Dominant Cause of the Exoplanet Radius Gap
• The initial physical conditions of Kepler-36 b & c
• Examining the Radius Valley: a Machine Learning Approach
• Deep GALEX UV Survey of the Kepler Field I: Point Source Catalog
• Effects of Planetesimal Accretion on the Thermal and Structural Evolution of Sub-Neptunes
• Confirming known planetary trends using a photometrically selected Kepler sample

Cited by in corpus (35)

• The California-Kepler Survey. X. The Radius Gap as a Function of Stellar Mass, Metallicity, and Age
• A deep radius valley revealed by Kepler short cadence observations
• A 20-Second Cadence View of Solar-Type Stars and Their Planets with TESS: Asteroseismology of Solar Analogs and a Re-characterization of pi Men c
• Creating the Radius Gap without Mass Loss
• Stellar Rotation in the Gaia Era: Revised Open Clusters Sequences
• TOI-1452 b: SPIRou and TESS reveal a super-Earth in a temperate orbit transiting an M4 dwarf
• TOI-2076 and TOI-1807: Two young, comoving planetary systems within 50 pc identified by TESS that are ideal candidates for further follow-up
• New Perspectives on the Exoplanet Radius Gap from a Mathematica Tool and Visualized Water Equation of State
• Further Evidence of Modified Spin-down in Sun-like Stars: Pileups in the Temperature-Period Distribution
• Validation of 13 Hot and Potentially Terrestrial TESS Planets
• Planets Across Space and Time (PAST). III. Morphology of the Planetary Radius Valley as a Function of Stellar Age and Metallicity in the Galactic Context Revealed by the LAMOST-Gaia-Kepler Sample
• The mass-radius relation of intermediate-mass planets outlined by hydrodynamic escape and thermal evolution
• A Mini-Neptune from TESS and CHEOPS Around the 120 Myr Old AB Dor member HIP 94235
• A 38 Million Year Old Neptune-Sized Planet in the Kepler Field
• Revising Properties of Planet-Host Binary Systems. III. There is No Observed Radius Gap For Kepler Planets in Binary Star Systems
• The influence of host star activity evolution on the population of super-Earths and mini-Neptunes
• Planetary evolution with atmospheric photoevaporation II: Fitting the slope of the radius valley by combining boil-off and XUV-driven escape
• Revising Properties of Planet-Host Binary Systems. IV. The Radius Distribution of Small Planets in Binary Star Systems is Dependent on Stellar Separation
• Joint Modeling of Radial Velocities and Photometry with a Gaussian Process Framework
• Modeling Asteroseismic Yields for the Roman Galactic Bulge Time-Domain Survey
• The California-Kepler Survey. XI. A Survey of Chromospheric Activity Through the Lens of Precise Stellar Properties
• TOI-712: a system of adolescent mini-Neptunes extending to the habitable zone
• Volatile-rich evolution of molten super-Earth L 98-59 d
• Circumbinary planets: migration, trapping in mean-motion resonances, and ejection
• The emptiness inside: Finding gaps, valleys, and lacunae with geometric data analysis
• Exoplanet Occurrence Rate with Age for FGK Stars in Kepler
• Estimating photoevaporative mass loss of exoplanets with PLATYPOS
• Stellar rotation and its connection to the evolution of hydrogen-dominated atmospheres of exoplanets
• Exploring the habitability and interior composition of exoplanets lying within the extended habitable zone
• Confronting compositional confusion through the characterisation of the sub-Neptune orbiting HD 77946
• The Occurrence-weighted Median Planets Discovered by Transit Surveys Orbiting Solar-type Stars and Their Implications for Planet Formation and Evolution
• Characterizing the bolometric-photoevaporative transition in young sub-Neptunes with radiation-hydrodynamic simulations
• Evidence that Planets in the Radius Gap Do Not Resemble Their Neighbors
• Transit Hunt for Young and Maturing Exoplanets (THYME) VIII: a Pleiades-age association harboring two transiting planetary systems from Kepler
• Revisiting the exoplanet radius valley with host stars from SWEET-Cat