* Astronomy

Title: Kepler 18-b, c, and d: A System Of Three Planets Confirmed by Transit Timing Variations, Lightcurve Validation, Spitzer Photometry and Radial Velocity Measurements
Authors: William D. Cochran, Daniel C. Fabrycky, Guillermo Torres, Francois Fressin, Jean-Michel Desert, 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 Uddin, Peter Tenenbaum, M. Still, Sara Seager, Samuel N. Quinn, F. Mullally, Neil Miller, Geoffrey W. Marcy, Phillip J. MacQueen, Philip 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 III, Eric B. Ford, Debra A. Fischer, Mark Everett, Michael Endl, et al. (7 additional authors not shown)

We report the detection of three transiting planets around a Sunlike 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, radial-velocity variations, Warm-Spitzer observations, and statistical analysis of false-positive probabilities. The Kepler-18 star has a mass of 0.97 solar masses, radius 1.1 solar radii, 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 ±3.4 earth masses, radius 2.00 ±0.10 earth radii, and mean density 4.9 ±2.4 g cm^-3. The two outer planets "c" and "d" are both low-density Neptune-mass planets. Kepler-18c has a mass of 17.3 ±1.9 earth masses, radius 5.49 ±0.26 earth radii, and mean density 0.59 ±0.07 g cm^-3, while Kepler-18d has a mass of 16.4 ±1.4 earth masses, radius 6.98 ±0.33 earth radii, and mean density 0.27 ±0.03 g cm^-3. Kepler-18c and Kepler-18d have orbital periods near a 2:1 mean-motion resonance, leading to large and readily detected transit timing variations.

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