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The Very Low Albedo of WASP-12b from Spectral Eclipse Observations with Hubble

Bell, Taylor J. and Nikolov, Nikolay and Cowan, Nicolas B. and Barstow, Joanna K. and Barman, Travis S. and Crossfield, Ian J. M. and Gibson, Neale P. and Evans, Thomas M. and Sing, David K. and Knutson, Heather A. and Kataria, Tiffany and Lothringer, Joshua D. and Benneke, Björn and Schwartz, Joel C. (2017) The Very Low Albedo of WASP-12b from Spectral Eclipse Observations with Hubble. Astrophysical Journal Letters, 847 (1). Art. No. L2. ISSN 2041-8213. doi:10.3847/2041-8213/aa876c.

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We present an optical eclipse observation of the hot Jupiter WASP-12b using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. These spectra allow us to place an upper limit of A_g < 0.064 (97.5% confidence level) on the planet's white light geometric albedo across 290–570 nm. Using six wavelength bins across the same wavelength range also produces stringent limits on the geometric albedo for all bins. However, our uncertainties in eclipse depth are ~40% greater than the Poisson limit and may be limited by the intrinsic variability of the Sun-like host star—the solar luminosity is known to vary at the 10^(−4) level on a timescale of minutes. We use our eclipse depth limits to test two previously suggested atmospheric models for this planet: Mie scattering from an aluminum-oxide haze or cloud-free Rayleigh scattering. Our stringent nondetection rules out both models and is consistent with thermal emission plus weak Rayleigh scattering from atomic hydrogen and helium. Our results are in stark contrast with those for the much cooler HD 189733b, the only other hot Jupiter with spectrally resolved reflected light observations; those data showed an increase in albedo with decreasing wavelength. The fact that the first two exoplanets with optical albedo spectra exhibit significant differences demonstrates the importance of spectrally resolved reflected light observations and highlights the great diversity among hot Jupiters.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Bell, Taylor J.0000-0003-4177-2149
Nikolov, Nikolay0000-0002-6500-3574
Cowan, Nicolas B.0000-0001-6129-5699
Barstow, Joanna K.0000-0003-3726-5419
Barman, Travis S.0000-0002-7129-3002
Crossfield, Ian J. M.0000-0002-1835-1891
Gibson, Neale P.0000-0002-9308-2353
Evans, Thomas M.0000-0001-5442-1300
Sing, David K.0000-0001-6050-7645
Knutson, Heather A.0000-0002-0822-3095
Kataria, Tiffany0000-0003-3759-9080
Lothringer, Joshua D.0000-0003-3667-8633
Benneke, Björn0000-0001-5578-1498
Schwartz, Joel C.0000-0001-5232-9957
Additional Information:© 2017 American Astronomical Society. Received 2017 June 26; Accepted 2017 August 19; Published 2017 September 14. T.J.B. acknowledges support from the McGill Space Institute Graduate Fellowship and from the FRQNT through the Centre de recherche en astrophysique du Québec. J.K.B. acknowledges support from the Royal Astronomical Society Research Fellowship. I.J.M.C. was supported under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007–2013)/ERC grant agreement No. 336792. This work is based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. The Al_2O_3 and cloud-free models tested in this work were made with the NEMESIS code developed by Patrick Irwin. We have also made use of free and open-source software provided by the Matplotlib, Python, and SciPy communities. Facility: HST(STIS) - Hubble Space Telescope satellite.
Group:Astronomy Department
Funding AgencyGrant Number
McGill Space InstituteUNSPECIFIED
Fonds Québécois de la Recherche sur la Nature et les Technologies (FQRNT)UNSPECIFIED
Royal Astronomical SocietyUNSPECIFIED
European Research Council (ERC)336792
NASANAS 5-26555
Subject Keywords:planets and satellites: atmospheres; stars: individual (WASP-12) ; techniques: photometric
Issue or Number:1
Record Number:CaltechAUTHORS:20170914-153456553
Persistent URL:
Official Citation:Taylor J. Bell et al 2017 ApJL 847 L2
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:81463
Deposited By: Tony Diaz
Deposited On:15 Sep 2017 16:51
Last Modified:15 Nov 2021 19:43

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