Wasp-17b: An Ultra-Low Density Planet in a Probable Retrograde Orbit

doi:10.1088/0004-637X/709/1/159

WASP-17b: AN ULTRA-LOW DENSITY PLANET IN A PROBABLE RETROGRADE ORBIT^*

Author

D. R. Anderson¹, C. Hellier¹, M. Gillon^2,3, A. H. M. J. Triaud², B. Smalley¹, L. Hebb⁴, A. Collier Cameron⁴, P. F. L. Maxted¹, D. Queloz², R. G. West⁵, S. J. Bentley¹, B. Enoch⁴, K. Horne⁴, T. A. Lister⁶, M. Mayor², N. R. Parley⁴, F. Pepe², D. Pollacco⁷, D. Ségransan², S. Udry² and D. M. Wilson^1,8

Affiliations

¹ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
² Observatoire de Genève, Université de Genève, 51 Chemin des Maillettes, 1290 Sauverny, Switzerland
³ Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août, 17, Bat. B5C, Liège 1, Belgium
⁴ School of Physics and Astronomy, University of St. Andrews, North Haugh, Fife, KY16 9SS, UK
⁵ Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK
⁶ Las Cumbres Observatory, 6740 Cortona Dr. Suite 102, Santa Barbara, CA 93117, USA
⁷ Astrophysics Research Centre, School of Mathematics & Physics, Queen's University, University Road, Belfast, BT7 1NN, UK
⁸ Current address: Centre for Astrophysics & Planetary Science, University of Kent, Canterbury, Kent, CT2 7NH, UK.

E-mail

dra@astro.keele.ac.uk

Journal

The Astrophysical Journal Create an alert RSS this journal

Issue

Volume 709, Number 1

Citation

D. R. Anderson et al 2010 ApJ 709 159

doi: 10.1088/0004-637X/709/1/159

Article References Cited By

Tag this article Full text PDF (1.25 MB) HTML with Enhancements

ABSTRACT

We report the discovery of the transiting giant planet WASP-17b, the least-dense planet currently known. It is 1.6 Saturn masses, but 1.5-2 Jupiter radii, giving a density of 6%-14% that of Jupiter. WASP-17b is in a 3.7 day orbit around a sub-solar metallicity, V = 11.6, F6 star. Preliminary detection of the Rossiter-McLaughlin effect suggests that WASP-17b is in a retrograde orbit (λ –150°), indicative of a violent history involving planet-planet or star-planet scattering. WASP-17b's bloated radius could be due to tidal heating resulting from recent or ongoing tidal circularization of an eccentric orbit, such as the highly eccentric orbits that typically result from scattering interactions. It will thus be important to determine more precisely the current orbital eccentricity by further high-precision radial velocity measurements or by timing the secondary eclipse, both to reduce the uncertainty on the planet's radius and to test tidal-heating models. Owing to its low surface gravity, WASP-17b's atmosphere has the largest scale height of any known planet, making it a good target for transmission spectroscopy.

Footnote

* Based in part on data collected with the HARPS spectrograph at ESO La Silla Observatory under programme ID 081.C-0388(A).

Keywords