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Discovery and Atmospheric Characterization of Giant Planet Kepler-12b: An Inflated Radius Outlier

Fortney, Jonathan J. and Ciardi, David and Howard, Andrew and Knutson, Heather A. (2011) Discovery and Atmospheric Characterization of Giant Planet Kepler-12b: An Inflated Radius Outlier. Astrophysical Journal Supplement Series, 197 (1). Art. No. 9. ISSN 0067-0049.

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We report the discovery of planet Kepler-12b (KOI-20), which at 1.695 ± 0.030 R_J is among the handful of planets with super-inflated radii above 1.65 R_J. Orbiting its slightly evolved G0 host with a 4.438 day period, this 0.431 ± 0.041 M_J planet is the least irradiated within this largest-planet-radius group, which has important implications for planetary physics. The planet's inflated radius and low mass lead to a very low density of 0.111 ± 0.010 g cm^(–3). We detect the occultation of the planet at a significance of 3.7σ in the Kepler bandpass. This yields a geometric albedo of 0.14 ± 0.04; the planetary flux is due to a combination of scattered light and emitted thermal flux. We use multiple observations with Warm Spitzer to detect the occultation at 7σ and 4σ in the 3.6 and 4.5 μm bandpasses, respectively. The occultation photometry timing is consistent with a circular orbit at e < 0.01 (1σ) and e < 0.09 (3σ). The occultation detections across the three bands favor an atmospheric model with no dayside temperature inversion. The Kepler occultation detection provides significant leverage, but conclusions regarding temperature structure are preliminary, given our ignorance of opacity sources at optical wavelengths in hot Jupiter atmospheres. If Kepler-12b and HD 209458b, which intercept similar incident stellar fluxes, have the same heavy-element masses, the interior energy source needed to explain the large radius of Kepler-12b is three times larger than that of HD 209458b. This may suggest that more than one radius-inflation mechanism is at work for Kepler-12b or that it is less heavy-element rich than other transiting planets.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Fortney, Jonathan J.0000-0002-9843-4354
Ciardi, David0000-0002-5741-3047
Howard, Andrew0000-0001-8638-0320
Knutson, Heather A.0000-0002-0822-3095
Additional Information:© 2011 The American Astronomical Society. Received 2011 July 7; accepted 2011 September 29; published 2011 October 26. J.J.F. acknowledges the support of the Kepler Participating Scientist’s program via NASA grant NNX09AC22G. Kepler was competitively selected as the tenth Discovery mission. Funding for the Kepler mission is provided by NASA’s Science Mission Directorate. We thank the many people who gave so generously of their time to make the Kepler mission a success. We thank Carly Chubak for cross-correlation analyses of the Keck spectra for companions. This work incorporates observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. Finally, the authors extend special thanks to those of Hawaiìan ancestry on whose sacred mountain of Mauna Kea we are privileged to be guests. Without their generous hospitality, the Keck observations presented herein would not have been possible.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:planets and satellites: atmospheres; stars: individual (Kepler-12, KOI-20, KIC 11804465); techniques: spectroscopic
Issue or Number:1
Record Number:CaltechAUTHORS:20111214-110945966
Persistent URL:
Official Citation:Discovery and Atmospheric Characterization of Giant Planet Kepler-12b: An Inflated Radius Outlier Jonathan J. Fortney et al. 2011 ApJS 197 9
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:28467
Deposited By: Ruth Sustaita
Deposited On:14 Dec 2011 19:30
Last Modified:03 Oct 2019 03:32

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