HST PanCET Program: A Cloudy Atmosphere for the Promising JWST Target WASP-101b

H. R. Wakeford, K. B. Stevenson, N. K. Lewis, D. K. Sing, M. López-Morales, M. Marley, T. Kataria, A. Mandell, G. E. Ballester, J. Barstow, L. Ben-Jaffel, V. Bourrier, L. A. Buchhave, D. Ehrenreich, T. Evans, A. García Muñoz, G. Henry, H. Knutson, P. Lavvas, A. Lecavelier Des EtangsN. Nikolov, J. Sanz-Forcada

Research output: Contribution to journalArticlepeer-review

27 Scopus citations


We present results from the first observations of the Hubble Space Telescope (HST) Panchromatic Comparative Exoplanet Treasury program for WASP-101b, a highly inflated hot Jupiter and one of the community targets proposed for the James Webb Space Telescope (JWST) Early Release Science (ERS) program. From a single HST Wide Field Camera 3 observation, we find that the near-infrared transmission spectrum of WASP-101b contains no significant H2O absorption features and we rule out a clear atmosphere at 13σ. Therefore, WASP-101b is not an optimum target for a JWST ERS program aimed at observing strong molecular transmission features. We compare WASP-101b to the well-studied and nearly identical hot Jupiter WASP-31b. These twin planets show similar temperature-pressure profiles and atmospheric features in the near-infrared. We suggest exoplanets in the same parameter space as WASP-101b and WASP-31b will also exhibit cloudy transmission spectral features. For future HST exoplanet studies, our analysis also suggests that a lower count limit needs to be exceeded per pixel on the detector in order to avoid unwanted instrumental systematics.

Original languageEnglish (US)
Article numberL12
JournalAstrophysical Journal Letters
Issue number1
StatePublished - Jan 20 2017


  • planets and satellites: atmospheres
  • planets and satellites: individual (WASP-101b)
  • techniques: spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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