HST PanCET program: A Cloudy Atmosphere for the Promising JWST Target WASP-101b
Sanz-Forcada, J.; Ehrenreich, D.; Lecavelier des Etangs, A.; Bourrier, V.; Lavvas, P.; Wakeford, H. R.; Sing, D. K.; Nikolov, N.; Henry, G.; Knutson, H.; Ballester, G. E.; López-Morales, M.; Buchhave, L. A.; García Muñoz, A.; Ben-Jaffel, L.; Kataria, T.; Lewis, N. K.; Evans, T.; Stevenson, K. B.; Marley, M.; Mandell, A.; Barstow, J.
United States, United Kingdom, France, Switzerland, Denmark, Germany, Spain
Abstract
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.