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The Boundary between Gas-rich and Gas-poor Planets

Lee, Eve J. (2019) The Boundary between Gas-rich and Gas-poor Planets. Astrophysical Journal, 878 (1). Art. No. 36. ISSN 1538-4357. doi:10.3847/1538-4357/ab1b40.

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Sub-Saturns straddle the boundary between gas-rich Jupiters and gas-poor super-Earths/sub-Neptunes. Their large radii (4–8 R_⊕) suggest that their gas-to-core mass ratios range ~0.1–1.0. With their envelopes being as massive as their cores, sub-Saturns are just on the verge of runaway gas accretion; they are expected to be significantly less populous than gas giants. Yet, the observed occurrence rates of sub-Saturns and Jupiters are comparable within ~100 days. We show that in these inner regions of planetary systems, the growth of sub-Saturns/Jupiters is ultimately limited by local and global hydrodynamic flows—runaway accretion terminates and the formation of gas giants is suppressed. We derive a simple analytic formula for the hydrodynamic accretion rate—an expression that has been previously reported only as an empirical fit to numerical simulations. Evolving simultaneously the background disk gas and the gas accretion onto planetary cores, we find that both the ubiquity of super-Earths/sub-Neptunes and the rarity of gas-rich planets are best explained if an underlying core-mass distribution is peaked at ~4.3 M_⊕. Within a finite disk lifetime ~10 Myr, massive cores (≳10 M_⊕) can become either gas-poor or gas-rich depending on when they assemble, but smaller cores (≾10 M_⊕) can only become gas-poor. This wider range of possible outcomes afforded by more massive cores may explain why metal-rich stars harbor a more diverse set of planets.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Lee, Eve J.0000-0002-1228-9820
Additional Information:© 2019 The American Astronomical Society. Received 2018 September 9; revised 2019 March 21; accepted 2019 April 19; published 2019 June 11. I thank Konstantin Batygin, Eugene Chiang, Sivan Ginzburg, Brad Hansen, Phil Hopkins, Andrew Howard, Heather Knutson, Dong Lai, Erik Petigura, Jason Wang, and Yanqin Wu for helpful discussions. The anonymous referee provided a careful report that helped to improve the manuscript. E.J.L. is supported by the Sherman Fairchild Fellowship at Caltech. This research used the Savio computational cluster resource provided by the Berkeley Research Computing program at the University of California, Berkeley (supported by the UC Berkeley Chancellor, Vice Chancellor for Research, and Chief Information Officer).
Group:TAPIR, Walter Burke Institute for Theoretical Physics
Funding AgencyGrant Number
Sherman Fairchild FoundationUNSPECIFIED
Subject Keywords:planets and satellites: formation – planets and satellites: gaseous planets – planets and satellites: physical evolution – planets and satellites: terrestrial planets
Issue or Number:1
Record Number:CaltechAUTHORS:20190611-160938113
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Official Citation:Eve J. Lee 2019 ApJ 878 36
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:96304
Deposited By: Tony Diaz
Deposited On:11 Jun 2019 23:17
Last Modified:16 Nov 2021 17:19

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