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The K2-138 System: A Near-resonant Chain of Five Sub-Neptune Planets Discovered by Citizen Scientists

Christiansen, Jessie L. and Crossfield, Ian J. M. and Barentsen, Geert and Lintott, Chris J. and Barclay, Thomas and Simmons, Brooke D. and Petigura, Erik and Schlieder, Joshua E. and Dressing, Courtney D. and Vanderburg, Andrew and Allen, Campbell and McMaster, Adam and Miller, Grant and Veldthuis, Martin and Allen, Sarah and Wolfenbarger, Zach and Cox, Brian and Zemiro, Julia and Howard, Andrew W. and Livingston, John and Sinukoff, Evan and Catron, Timothy and Grey, Andrew and Kusch, Joshua J. E. and Terentev, Ivan and Vales, Martin and Kristiansen, Martti H. (2018) The K2-138 System: A Near-resonant Chain of Five Sub-Neptune Planets Discovered by Citizen Scientists. Astronomical Journal, 155 (2). Art. No. 57. ISSN 1538-3881. doi:10.3847/1538-3881/aa9be0.

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K2-138 is a moderately bright (V = 12.2, K = 10.3) main-sequence K star observed in Campaign 12 of the NASA K2 mission. It hosts five small (1.6–3.3 R⊕) transiting planets in a compact architecture. The periods of the five planets are 2.35, 3.56, 5.40, 8.26, and 12.76 days, forming an unbroken chain of near 3:2 resonances. Although we do not detect the predicted 2–5 minute transit timing variations (TTVs) with the K2 timing precision, they may be observable by higher-cadence observations with, for example, Spitzer or CHEOPS. The planets are amenable to mass measurement by precision radial velocity measurements, and therefore K2-138 could represent a new benchmark system for comparing radial velocity and TTV masses. K2-138 is the first exoplanet discovery by citizen scientists participating in the Exoplanet Explorers project on the Zooniverse platform.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Christiansen, Jessie L.0000-0002-8035-4778
Crossfield, Ian J. M.0000-0002-1835-1891
Barentsen, Geert0000-0002-3306-3484
Lintott, Chris J.0000-0001-5578-359X
Barclay, Thomas0000-0001-7139-2724
Simmons, Brooke D.0000-0001-5882-3323
Petigura, Erik0000-0003-0967-2893
Schlieder, Joshua E.0000-0001-5347-7062
Dressing, Courtney D.0000-0001-8189-0233
Vanderburg, Andrew0000-0001-7246-5438
Howard, Andrew W.0000-0001-8638-0320
Sinukoff, Evan0000-0002-5658-0601
Additional Information:© 2018 The American Astronomical Society. Received 2017 May 11; revised 2017 November 14; accepted 2017 November 15; published 2018 January 11. We thank the anonymous referee for thoughtful and detailed comments that have improved the analysis presented in this paper. This project has been made possible by the contributions of approximately 14000 volunteers in the Exoplanet Explorers project. The contributions of those volunteers who registered on the project are individually acknowledged at We thank production teams from the British and Australian Broadcasting Corporations as well as Fremantle Media for their help in including Exoplanet Explorers on the Stargazing Live programs broadcast in 2017 April. This paper includes data collected by the K2 mission. Funding for the K2 mission is provided by the NASA Science Mission directorate. This publication uses data generated via the platform, development of which is funded by generous support, including a Global Impact Award from Google, and by a grant from the Alfred P. Sloan Foundation. B.D.S. acknowledges support from the National Aeronautics and Space Administration (NASA) through Einstein Postdoctoral Fellowship Award Number PF5-160143 issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060. This research has made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has also made use of the NASA Exoplanet Archive and the Exoplanet Follow-up Observation Program website, which are operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS website is Facilities: Kepler - The Kepler Mission, Keck:I (HIRES) - , Gemini:South (NIRI) - , Exoplanet Archive - , IRSA - , MAST - , Sloan. -
Group:Infrared Processing and Analysis Center (IPAC), Astronomy Department
Funding AgencyGrant Number
Alfred P. Sloan FoundationUNSPECIFIED
NASA Einstein FellowshipPF5-160143
Participating InstitutionsUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
Japanese MonbukagakushoUNSPECIFIED
Max Planck SocietyUNSPECIFIED
Higher Education Funding Council for EnglandUNSPECIFIED
Subject Keywords:eclipses – stars: individual (K2-138) – techniques: photometric – techniques: spectroscopic
Issue or Number:2
Record Number:CaltechAUTHORS:20180111-154519402
Persistent URL:
Official Citation:Jessie L. Christiansen et al 2018 AJ 155 57
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84280
Deposited By: Tony Diaz
Deposited On:12 Jan 2018 00:09
Last Modified:15 Nov 2021 20:18

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