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Occurrence and core-envelope structure of 1-4x Earth-size planets around Sun-like stars

Marcy, Geoffrey W. and Weiss, Lauren M. and Petigura, Erik A. and Isaacson, Howard and Howard, Andrew W. and Buchhave, Lars A. (2014) Occurrence and core-envelope structure of 1-4x Earth-size planets around Sun-like stars. Proceedings of the National Academy of Sciences of the United States of America, 111 (35). pp. 12655-12660. ISSN 0027-8424. PMCID PMC4156743. https://resolver.caltech.edu/CaltechAUTHORS:20170619-141634766

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Abstract

Small planets, 1–4× the size of Earth, are extremely common around Sun-like stars, and surprisingly so, as they are missing in our solar system. Recent detections have yielded enough information about this class of exoplanets to begin characterizing their occurrence rates, orbits, masses, densities, and internal structures. The Kepler mission finds the smallest planets to be most common, as 26% of Sun-like stars have small, 1–2 R⊕ planets with orbital periods under 100 d, and 11% have 1–2 R⊕ planets that receive 1–4× the incident stellar flux that warms our Earth. These Earth-size planets are sprinkled uniformly with orbital distance (logarithmically) out to 0.4 the Earth–Sun distance, and probably beyond. Mass measurements for 33 transiting planets of 1–4 R⊕ show that the smallest of them, R < 1.5 R⊕, have the density expected for rocky planets. Their densities increase with increasing radius, likely caused by gravitational compression. Including solar system planets yields a relation: ρ=2.32+3.19R/R⊕ [g cm^(-3)]. Larger planets, in the radius range 1.5–4.0 R⊕, have densities that decline with increasing radius, revealing increasing amounts of low-density material (H and He or ices) in an envelope surrounding a rocky core, befitting the appellation ‘‘mini-Neptunes.’’ The gas giant planets occur preferentially around stars that are rich in heavy elements, while rocky planets occur around stars having a range of heavy element abundances. Defining habitable zones remains difficult, without benefit of either detections of life elsewhere or an understanding of life’s biochemical origins.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1073/pnas.1304197111DOIArticle
http://www.pnas.org/content/111/35/12655PublisherArticle
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4156743/PubMed CentralPMC4156743
ORCID:
AuthorORCID
Marcy, Geoffrey W.0000-0002-2909-0113
Weiss, Lauren M.0000-0002-3725-3058
Petigura, Erik A.0000-0003-0967-2893
Isaacson, Howard0000-0002-0531-1073
Howard, Andrew W.0000-0001-8638-0320
Buchhave, Lars A.0000-0003-1605-5666
Additional Information:© 2014 National Academy of Sciences. Edited by Adam S. Burrows, Princeton University, Princeton, NJ, and accepted by the Editorial Board April 16, 2014 (received for review January 24, 2014). Published online before print May 27, 2014. We thank Leslie Rogers, Eric Lopez, Jonathan Fortney, Dimitar Sasselov, Jack Lissauer, Eugene Chiang, Greg Laughlin, and Sara Seager for valuable conversations. We thank the many observers who contributed to the measurements reported here. The authors wish to extend special thanks to those of Hawai‘ian ancestry on whose sacred mountain of Mauna Kea we are privileged to be guests. Without their generous hospitality, the Keck observations presented herein would not have been possible. We thank the extraordinary group of engineers and scientists who worked tirelessly to produce the Kepler mission. Kepler was competitively selected as the tenth NASA Discovery mission. Funding for this mission is provided by the NASA Science Mission Directorate. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Keck Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We thank the NSF Graduate Research Fellowship, Grant DGE 1106400. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Author contributions: G.W.M., L.M.W., E.A.P., H.I., A.W.H., and L.A.B. contributed to this work by acquiring data at telescopes, analyzing those data, and providing final data products or graphs of their results; and G.W.M. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. A.S.B. is a guest editor invited by the Editorial Board.
Funders:
Funding AgencyGrant Number
NASAUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
NSF Graduate Research FellowshipDGE-1106400
Subject Keywords:extrasolar planets; astrobiology; SETI
Issue or Number:35
PubMed Central ID:PMC4156743
Record Number:CaltechAUTHORS:20170619-141634766
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20170619-141634766
Official Citation:Geoffrey W. Marcy, Lauren M. Weiss, Erik A. Petigura, Howard Isaacson, Andrew W. Howard, and Lars A. Buchhave Occurrence and core-envelope structure of 1–4× Earth-size planets around Sun-like stars PNAS 2014 111 (35) 12655-12660; published ahead of print May 27, 2014, doi:10.1073/pnas.1304197111
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78337
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:19 Jun 2017 22:31
Last Modified:03 Oct 2019 18:07

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