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

David, Trevor J. and Contardo, Gabriella and Sandoval, Angeli and Angus, Ruth and Lu, Yuxi (Lucy) and Bedell, Megan and Curtis, Jason L. and Foreman-Mackey, Daniel and Fulton, Benjamin J. and Grunblatt, Samuel K. and Petigura, Erik A. (2021) Evolution of the Exoplanet Size Distribution: Forming Large Super-Earths Over Billions of Years. Astronomical Journal, 161 (6). Art. No. 265. ISSN 0004-6256. doi:10.3847/1538-3881/abf439.

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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 (≾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 that appear to be unrepresented at ages ≾2–3 Gyr are likely to correspond to planets with rocky compositions. Our results suggest that the size distribution of close-in exoplanets and the precise location of the radius valley evolve over gigayears.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
David, Trevor J.0000-0001-6534-6246
Contardo, Gabriella0000-0002-3011-4784
Sandoval, Angeli0000-0003-1133-1027
Angus, Ruth0000-0003-4540-5661
Lu, Yuxi (Lucy)0000-0003-4769-3273
Bedell, Megan0000-0001-9907-7742
Curtis, Jason L.0000-0002-2792-134X
Foreman-Mackey, Daniel0000-0002-9328-5652
Fulton, Benjamin J.0000-0003-3504-5316
Grunblatt, Samuel K.0000-0003-4976-9980
Petigura, Erik A.0000-0003-0967-2893
Alternate Title:Small Planet Sizes Evolve Over Billions of Years
Additional Information:© 2021. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2020 November 19; revised 2021 March 18; accepted 2021 March 23; published 2021 May 14. This paper is dedicated to the memory of John Stauffer, a valued mentor whose energy and determination were an inspiration to many. We thank the anonymous referee for a thorough and insightful review, as well as Eric Ford, Christina Hedges, David W. Hogg, and Josh Winn for helpful discussions. T.J.D. is especially grateful to Chelsea Yarnell for her irreplaceable support throughout the COVID-19 pandemic. This paper includes data collected by the Kepler mission, funded by the NASA Science Mission directorate. This work presents results from the European Space Agency (ESA) space mission Gaia. Gaia data are being processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC is provided by national institutions, in particular the institutions participating in the Gaia MultiLateral Agreement (MLA). The Gaia mission website is The Gaia archive website is This work made use of the cross-match database created by Megan Bedell. Facilities: Kepler - The Kepler Mission, Gaia - , GALEX. - Software: astropy (Astropy Collaboration et al. 2013, 2018), jupyter (Kluyver et al. 2016), matplotlib (Hunter 2007), numpy (van der Walt et al. 2011), pandas (pandas Development Team 2020; Wes McKinney 2010), seaborn (Waskom et al. 2017), scikit-learn (Pedregosa et al. 2011), scipy (Jones et al. 2001).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Gaia Multilateral AgreementUNSPECIFIED
Subject Keywords:Exoplanets; Exoplanet evolution; Exoplanet astronomy; Super Earths; Mini Neptunes
Issue or Number:6
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanets (498); Exoplanet evolution (491); Exoplanet astronomy (486); Super Earths (1655); Mini Neptunes (1063)
Record Number:CaltechAUTHORS:20210518-083339018
Persistent URL:
Official Citation:Trevor J. David et al 2021 AJ 161 265
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109166
Deposited By: Tony Diaz
Deposited On:19 May 2021 18:55
Last Modified:19 May 2021 18:55

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