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

  title={The K2-138 System: A Near-resonant Chain of Five Sub-Neptune Planets Discovered by Citizen Scientists},
  author={Jessie L. Christiansen and Ian J. M. Crossfield and Geert Barentsen and Chris J. Lintott and Thomas Barclay and Brooke D. Simmons and Erik A. Petigura and Joshua E. Schlieder and Courtney D. Dressing and Andrew M. Vanderburg and Campbell Allen and Adam McMaster and Grant R. M. Miller and Marten Veldthuis and Sarah Allen and Zach Wolfenbarger and Brian Cox and Julia Zemiro and Andrew W. Howard and John H. Livingston and Evan Sinukoff and Timothy Catron and Andrew Grey and Joshua J. E. Kusch and Ivan A. Terentev and Martin Vale{\vs} and Martti H. Kristiansen},
  journal={The Astronomical Journal},
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 ) 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… 
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