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Published February 2018 | Submitted + Published
Journal Article Open

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


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.

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 https://www.zooniverse.org/projects/ianc2/exoplanet-explorers/about/team. 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 Zooniverse.org 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 http://www.sdss.org/. Facilities: Kepler - The Kepler Mission, Keck:I (HIRES) - , Gemini:South (NIRI) - , Exoplanet Archive - , IRSA - , MAST - , Sloan. -

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Published - Christiansen_2018_AJ_155_57.pdf

Submitted - 1801.03874.pdf


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August 19, 2023
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