Kepler-68: Three planets, one with a density between that of earth and ice giants

Ronald L. Gilliland, Geoffrey W. Marcy, Jason F. Rowe, Leslie Rogers, Guillermo Torres, Francois Fressin, Eric D. Lopez, Lars A. Buchhave, Jørgen Christensen-Dalsgaard, Jean Michel Désert, Christopher E. Henze, Howard Isaacson, Jon M. Jenkins, Jack J. Lissauer, William J. Chaplin, Sarbani Basu, Travis S. Metcalfe, Yvonne Elsworth, Rasmus Handberg, Saskia HekkerDaniel Huber, Christoffer Karoff, Hans Kjeldsen, Mikkel N. Lund, Mia Lundkvist, Andrea Miglio, David Charbonneau, Eric B. Ford, Jonathan J. Fortney, Michael R. Haas, Andrew W. Howard, Steve B. Howell, Darin Ragozzine, Susan E. Thompson

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84 Scopus citations


NASA's Kepler Mission has revealed two transiting planets orbiting Kepler-68. Follow-up Doppler measurements have established the mass of the innermost planet and revealed a third Jovian-mass planet orbiting beyond the two transiting planets. Kepler-68b, in a 5.4 day orbit, has MP = 8.3+1.2-2.4 M, RP = 2.31 +0.06-0.09R, and ρP = 3.32 +0.86-0.98 g cm-3, givingKepler-68b a density intermediate between that of the ice giants and Earth.Kepler-68c is Earth-sized, with a radius RP = 0.953+0.037-0.042 R and transits on a 9.6 day orbit; validation of Kepler-68c posed unique challenges. Kepler-68d has an orbital period of 580±15 days and a minimum mass of MP sin i = 0.947 ±0.035MJ . Power spectra of the Kepler photometry at one minute cadence exhibit a rich and strong set of asteroseismic pulsation modes enabling detailed analysis of the stellar interior. Spectroscopy of the star coupled with asteroseismic modeling of the multiple pulsation modes yield precise measurements of stellar properties, notably Teff = 5793±74 K,M* = 1.079±0.051M, R* = 1.243*0.019 R , and ρ*= 0.7903±0.0054 g cm-3, all measured with fractional uncertainties of only a few percent. Models of Kepler-68b suggest that it is likely composed of rock and water, or has a H and He envelope to yield its density ∼3 g cm-3.

Original languageEnglish (US)
Article number40
JournalAstrophysical Journal
Issue number1
StatePublished - Mar 20 2013

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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