2011/01/31 by D. R. Anderson, A. M. S. Smith, Audrey Lanotte +13
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph.EP
paper · pdf · doi:10.1111/j.1365-2966.2011.19182.x
Accepted for publication in MNRAS (16 pages, 12 figures, 6 tables)
arxiv created 2011/06/03 · openalex publication_date 2011/08/24 · arxiv updated 2015/05/27 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/04
We report the detection of thermal emission at 4.5 and 8 μm from the planet WASP-17b. We used Spitzer to measure the system brightness at each wavelength during two occultations of the planet by its host star. By combining the resulting light curves with existing transit light curves and radial-velocity measurements in a simultaneous analysis, we find the radius of WASP-17b to be 2.0RJup, which is 0.2RJup larger than any other known planet and 0.7RJup larger than predicted by the standard cooling theory of irradiated gas giant planets. We find the retrograde orbit of WASP-17b to be slightly eccentric, with 0.0012 < e < 0.070 (3σ). Such a low eccentricity suggests that, under current models, tidal heating alone could not have bloated the planet to its current size, so the radius of WASP-17b is currently unexplained. From the measured planet–star flux-density ratios we infer 4.5 and 8 μm brightness temperatures of 1881 ± 50 and 1580 ± 150 K, respectively, consistent with a low-albedo planet that efficiently redistributes heat from its day side to its night side.