Kepler-18b, c, and d: A system of three planets confirmed by transit timing variations, light curve validation, Warm-Spitzer photometry, and radial velocity measurements

William D. Cochran, Daniel C. Fabrycky, Guillermo Torres, François Fressin, Jean Michel Désert, Darin Ragozzine, Dimitar Sasselov, Jonathan J. Fortney, Jason F. Rowe, Erik J. Brugamyer, Stephen T. Bryson, Joshua A. Carter, David R. Ciardi, Steve B. Howell, Jason H. Steffen, William J. Borucki, David G. Koch, Joshua N. Winn, William F. Welsh, Kamal UddinPeter Tenenbaum, M. Still, Sara Seager, Samuel N. Quinn, F. Mullally, Neil Miller, Geoffrey W. Marcy, Phillip J. MacQueen, Phillip Lucas, Jack J. Lissauer, David W. Latham, Heather Knutson, K. Kinemuchi, John A. Johnson, Jon M. Jenkins, Howard Isaacson, Andrew Howard, Elliott Horch, Matthew J. Holman, Christopher E. Henze, Michael R. Haas, Ronald L. Gilliland, Thomas N. Gautier, Eric B. Ford, Debra A. Fischer, Mark Everett, Michael Endl, Brice Oliver Demory, Drake Deming, David Charbonneau, Douglas Caldwell, Lars Buchhave, Timothy M. Brown, Natalie Batalha

Research output: Contribution to journalArticlepeer-review

151 Scopus citations


We report the detection of three transiting planets around a Sun-like star, which we designate Kepler-18. 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 (TTVs), radial velocity variations, Warm-Spitzer observations, and statistical analysis of false-positive probabilities. The Kepler-18 star has a mass of 0.97 M , a radius of 1.1 R , an effective temperature of 5345K, and an iron abundance of [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 a mass of 6.9 ± 3.4 M , a radius of 2.00 ± 0.10 R , and a mean density of 4.9 ± 2.4gcm3. The two outer planets "c" and "d" are both low-density Neptune-mass planets. Kepler-18c has a mass of 17.3 ± 1.9 M , a radius of 5.49 ± 0.26 R , and a mean density of 0.59 0.07gcm 3, while Kepler-18d has a mass of 16.4 ± 1.4 M , a radius of 6.98 ± 0.33 R and a mean density of 0.27 ± 0.03gcm3. Kepler-18c and Kepler-18d have orbital periods near a 2:1 mean-motion resonance, leading to large and readily detected TTVs.

Original languageEnglish (US)
Article number7
JournalAstrophysical Journal, Supplement Series
Issue number1
StatePublished - Nov 2011
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • planetary systems
  • stars: individual (Kepler-18, KIC 8644288, 2MASS J19521906+4444467)
  • techniques: photometric
  • techniques: spectroscopic


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