The hot-Jupiter Kepler-17b: Discovery, obliquity from stroboscopic starspots, and atmospheric characterization

Jean Michel Désert, David Charbonneau, Brice Olivier Demory, Sarah Ballard, Joshua A. Carter, Jonathan J. Fortney, William D. Cochran, Michael Endl, Samuel N. Quinn, Howard T. Isaacson, François Fressin, Lars A. Buchhave, David W. Latham, Heather A. Knutson, Stephen T. Bryson, Guillermo Torres, Jason F. Rowe, Natalie M. Batalha, William J. Borucki, Timothy M. BrownDouglas A. Caldwell, Jessie L. Christiansen, Drake Deming, Daniel C. Fabrycky, Eric B. Ford, Ronald L. Gilliland, Michal Gillon, Michal R. Haas, Jon M. Jenkins, Karen Kinemuchi, David Koch, Jack J. Lissauer, Philip Lucas, Fergal Mullally, Phillip J. MacQueen, Geoffrey W. Marcy, Dimitar D. Sasselov, Sara Seager, Martin Still, Peter Tenenbaum, Kamal Uddin, Joshua N. Winn

Research output: Contribution to journalArticlepeer-review

140 Scopus citations


This paper reports the discovery and characterization of the transiting hot giant exoplanet Kepler-17b. The planet has an orbital period of 1.486 days, and radial velocity measurements from the Hobby-Eberly Telescope show a Doppler signal of 419.5+13.3 -15.6 m s-1. From a transit-based estimate of the host star's mean density, combined with an estimate of the stellar effective temperature Teff = 5630 ± 100 from high-resolution spectra, we infer a stellar host mass of 1.06 ± 0.07 M and a stellar radius of 1.02 ± 0.03R . We estimate the planet mass and radius to be M P = 2.45 0.11 M J and RP = 1.31 ± 0.02R J. The host star is active, with dark spots that are frequently occulted by the planet. The continuous monitoring of the star reveals a stellar rotation period of 11.89 days, eight times the planet's orbital period; this period ratio produces stroboscopic effects on the occulted starspots. The temporal pattern of these spot-crossing events shows that the planet's orbit is prograde and the star's obliquity is smaller than 15°. We detected planetary occultations of Kepler-17b with both the Kepler and Spitzer Space Telescopes. We use these observations to constrain the eccentricity, e, and find that it is consistent with a circular orbit (e < 0.011). The brightness temperatures of the planet's infrared bandpasses are = 1880 ± 100 K and = 1770 ± 150 K. We measure the optical geometric albedo Ag in the Kepler bandpass and find Ag = 0.10 ± 0.02. The observations are best described by atmospheric models for which most of the incident energy is re-radiated away from the day side.

Original languageEnglish (US)
Article number14
JournalAstrophysical Journal, Supplement Series
Issue number1
StatePublished - Nov 2011
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • eclipses
  • planetary systems
  • stars: individual (Kepler-17b, KIC 10619192, 2MASS 19533486+4748540)
  • techniques: photometric


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