Date of the discovery: 11 January 2018

Short Description: K2-138 is a system consisting of 6 planets orbiting close to an early K-type star in a unbroken near-3:2 resonant chain. The innermost planet is likely a rocky Super-Earth, while the other 5 planets likely are gaseous Mini-Neptunes with no solid surface. The masses are not known, but with the Spitzer Space Telescope and an effect called Transit Timing Variation (TTV), it would be possible to measure the masses of these planets. K2-138 is a densely packed system, with the innermost planet completing one orbit in only about 2.3 days and the outermost planet completing one orbit in about 42 days.

Volunteer(s): Joshua Kusch, Edward Heaps, Ivan Terentev, TimothyCatron, James Richmond, Alan Patricio Zetina Floresmarhx, sankalp mohan, seamonkeyluv, traumeule, B Butler, Nicholas Sloan, Kerrie Ryan, Huskynator, Lee Mason, Trudy Frankensteiner, Alan Goldsmith, Gavin Condon, Simon Wilde, Sharon McGuire, helenatgzoo, Melina Thévenot, Niamh Claydon-Mullins, ellieoban, Anastasios D. Papanastasiou, AndyGrey, Angela Crow, Dave Williams, Throbulator, Tim Smith, Erin Thomas, Valentina Saavedra, Carole Riley, sidy2001, bn3, ilgiz, Antonio Pasqua, Peter Bergvall, Stephen Hippisley, sidy2001, bn3, Michael Sarich, IaLaVyu

Researchers in the discovery paper: Jessie L. Christiansen, Ian J. M. Crossfield, Geert Barentsen, Chris J. Lintott, Thomas Barclay, Brooke . D. Simmons, Erik Petigura, Joshua E. Schlieder, Courtney D. Dressing, Andrew Vanderburg, Campbell Allen, Adam McMaster, Grant Miller, Martin Veldthuis, Sarah Allen, Zach Wolfenbarger, Brian Cox, Julia Zemiro, Andrew W. Howard, John Livingston, Evan Sinukoff, Timothy Catron, Andrew Grey, Joshua J. E. Kusch, Ivan Terentev, Martin Vales, and Martti H. Kristiansen

Link to paper in ADS: https://ui.adsabs.harvard.edu/abs/2018AJ….155…57C/abstract

SIMBAD page: http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=K2-138&submit=SIMBAD+search

Telescopes involved: Kepler – The Kepler Mission, Keck:I (HIRES) – , Gemini:South (NIRI)

Figure 1 of the paper, showing the classification window shown to the volunteers. The individual transits are clearly visible
Other pages:

wikipedia: https://en.wikipedia.org/wiki/K2-138

Project website: Exoplanet Explorers

Credit for the header image: NASA/JPL-Caltech/R. Hurt (IPAC)

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