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Unveiling the planet population at birth

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2007.11006.pdfAccepted version1.75 MBAdobe PDFView/Open
Unveiling_the_Planet_Population_at_Birth___Supplementary_Material.pdfSupporting information5.25 MBAdobe PDFView/Open
Title: Unveiling the planet population at birth
Authors: Rogers, JG
Owen, JE
Item Type: Journal Article
Abstract: The radius distribution of small, close-in exoplanets has recently been shown to be bimodal. The photoevaporation model predicted this bimodality. In the photoevaporation scenario, some planets are completely stripped of their primordial H/He atmospheres, whereas others retain them. Comparisons between the photoevaporation model and observed planetary populations have the power to unveil details of the planet population inaccessible by standard observations, such as the core mass distribution and core composition. In this work, we present a hierarchical inference analysis on the distribution of close-in exoplanets using forward models of photoevaporation evolution. We use this model to constrain the planetary distributions for core composition, core mass, and initial atmospheric mass fraction. We find that the core-mass distribution is peaked, with a peak-mass of ∼4M⊕. The bulk core-composition is consistent with a rock/iron mixture that is ice-poor and ‘Earth-like’; the spread in core-composition is found to be narrow (⁠≲16 per cent variation in iron-mass fraction at the 2σ level) and consistent with zero. This result favours core formation in a water/ice poor environment. We find the majority of planets accreted a H/He envelope with a typical mass fraction of ∼4 per cent⁠; only a small fraction did not accrete large amounts of H/He and were ‘born-rocky’. We find four times as many super-Earths were formed through photoevaporation, as formed without a large H/He atmosphere. Finally, we find core-accretion theory overpredicts the amount of H/He cores would have accreted by a factor of ∼5, pointing to additional mass-loss mechanisms (e.g. ‘boil-off’) or modifications to core-accretion theory.
Issue Date: 19-Mar-2021
Date of Acceptance: 17-Feb-2021
URI: http://hdl.handle.net/10044/1/87232
DOI: 10.1093/mnras/stab529
ISSN: 0035-8711
Publisher: Oxford University Press (OUP)
Start Page: 1526
End Page: 1542
Journal / Book Title: Monthly Notices of the Royal Astronomical Society
Volume: 503
Issue: 1
Copyright Statement: © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). This is a pre-copy-editing, author-produced version of an article accepted for publication in the Royal Astronomical Society following peer review. The definitive publisher-authenticated version James G Rogers, James E Owen, Unveiling the planet population at birth, Monthly Notices of the Royal Astronomical Society, Volume 503, Issue 1, May 2021, Pages 1526–1542, is available online at: https://doi.org/10.1093/mnras/stab529
Sponsor/Funder: The Royal Society
The Royal Society
Commission of the European Communities
Funder's Grant Number: UF150412
Keywords: 0201 Astronomical and Space Sciences
Astronomy & Astrophysics
Publication Status: Published
Open Access location: https://arxiv.org/abs/2007.11006
Online Publication Date: 2021-02-24
Appears in Collections:Physics