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

• Main Authors: Wakeford, H. R., Stevenson, K. B., Lewis, N. K., Sing, D. K., López-Morales, M., Marley, M., Kataria, T., Mandell, A., Ballester, G. E., Barstow, J., Ben-Jaffel, L., Bourrier, V., Buchhave, L. A., Ehrenreich, D., Evans, T., García Muñoz, A., Henry, G., Knutson, H., Lavvas, P., Lecavelier des Etangs, A., Nikolov, N., Sanz-Forcada, J.
• Other Authors: Univ Arizona, Dept Planetary Sci
• Language: en
• Published: IOP PUBLISHING LTD 2017
• Subjects: planets and satellites: atmospheres; planets and satellites: individual (WASP-101b); techniques: spectroscopic
• Online Access: http://hdl.handle.net/10150/623095; http://arizona.openrepository.com/arizona/handle/10150/623095

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 13 sigma. 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.