A SYSTEM OF THREE PLANETS CONFIRMED BY TRANSIT TIMING VARIATIONS, LIGHTCURVE VALIDATION, Warm-Spitzer PHOTOMETRY AND RADIAL VELOCITY MEASUREMENTS

We report the detection of three transiting planets around a Sunlike star, which we designate Kepler18. The transit signals were detected in photometric data from the Kepler satellite, and were confirmed to arise from planets using a combination of large transit-timing variations, radial-velocity variations, Warm-Spitzer observations, and statistical analysis of false-positive probabilities. The Kepler-18 star has a mass of 0.97M⊙, radius 1.1R⊙, effective temperature 5345K, and iron abundance [Fe/H]= +0.19. The planets have orbital periods of approximately 3.5, 7.6 and 14.9 days. The innermost planet “b” is a “super-Earth” with mass 6.9± 3.4M⊕, radius 2.00± 0.10R⊕, and mean density 4.9± 2.4 g cm. The two outer planets “c” and “d” are both low-density Neptune-mass planets. Kepler-18c has a mass of 17.3 ± 1.9M⊕, radius 5.49 ± 0.26R⊕, and mean density 0.59 ± 0.07 g cm, while Kepler-18d has a mass of 16.4 ± 1.4M⊕, radius 6.98 ± 0.33R⊕, and mean density 0.27 ± 0.03 g cm. Kepler-18c and Kepler-18d have orbital periods near a 2:1 mean-motion resonance, leading to large and readily detected transit timing variations. Subject headings: planetary systems — stars: individual (Kepler-18, KIC 8644288, 2MASS J19521906 +4444467) — techniques: photometric — techniques: spectroscopic 1 McDonald Observatory, The University of Texas, Austin, TX 78712 2 Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA 3 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138; [email protected] 4 NASA Ames Research Center, Moffett Field, CA 94035 5 Department of Astronomy, The University of Texas, Austin, TX 78712 6 NASA Exoplanet Science Institute/CalTech, Pasadena, CA 91125 USA 7 Fermilab Center for Particle Astrophysics, P.O. Box 500, MS 127, Batavia, IL 60510 8 Massachusetts Institute of Technology, Cambridge, MA 02139 USA 9 San Diego State Univ., San Diego, CA 92182 USA 10 Orbital Sciences Corporation 11 Bay Area Environmental Research Inst. 12 Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA 13 Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, AL10 9AB, England 14 California Institute of Technology, Pasadena, CA 91109 15 SETI Institute, Mountain View, CA, 94043, USA 16 Southern Connecticut State University, New Haven, CT, 06515 17 Space Telescope Science Institute, Baltimore, MD, 21218, USA 18 Jet Propulsion Laboratory, Calif. Institute of Technology, Pasadena, CA, 91109, USA 19 University of Florida, Gainesville, FL 32611 20 Yale University, New Haven, CT 06510 21 NOAO, 950 N. Cherry Ave., Tucson, AZ 85719 22 Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 23 Niels Bohr Institute, University of Copenhagen, DK-2100