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

Journal Article · Wed Jan 20 00:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/709/1/159· OSTI ID:21392351

Anderson, D R; Hellier, C; Smalley, B; Maxted, P F. L.; Bentley, S J ^[1]; Gillon, M; Queloz, D; Mayor, M; Pepe, F; Segransan, D; Udry, S ^[2]; Hebb, L; Cameron, A Collier; Enoch, B; Horne, K; Parley, N R ^[3]; West, R G ^[4]; Lister, T A ^[5]; Pollacco, D ^[6]

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1. Astrophysics Group, Keele University, Staffordshire, ST5 5BG (United Kingdom)
2. Observatoire de Geneve, Universite de Geneve, 51 Chemin des Maillettes, 1290 Sauverny (Switzerland)
3. School of Physics and Astronomy, University of St. Andrews, North Haugh, Fife, KY16 9SS (United Kingdom)
4. Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH (United Kingdom)
5. Las Cumbres Observatory, 6740 Cortona Dr. Suite 102, Santa Barbara, CA 93117 (United States)
6. Astrophysics Research Centre, School of Mathematics and Physics, Queen's University, University Road, Belfast, BT7 1NN (United Kingdom)

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 (lambda approx -150{sup 0}), 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.

• OSTI ID: 21392351
• Journal Information: Astrophysical Journal, Vol. 709, Issue 1; Other Information: DOI: 10.1088/0004-637X/709/1/159; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ECLIPSE
GRAVITATION
JUPITER PLANET
MASS
ORBITS
RADIAL VELOCITY
SATURN PLANET
SCALE HEIGHT
SPECTROSCOPY
STARS
DIMENSIONS
HEIGHT
PLANETS
VELOCITY