The spectra of exoplanet atmospheres are affected by aerosols (clouds and hazes) of uncertain origin. Proposed aerosol formation mechanisms include gas condensation or photochemical reactions. We measure the transmission spectrum of the tidally locked gas giant exoplanet WASP-94A b and identify asymmetry in its atmosphere. The morning limb is cooler and cloudy, while the evening limb is hotter and exhibits gaseous H2O absorption features. We interpret this difference as due to the formation of cloud droplets near the morning limb, which evaporate during circulation to the evening limb. The dominant aerosols are clouds cycling between the day and night sides of the atmosphere, not photochemical hazes. The resulting asymmetry can severely bias chemical abundance measurements, unless limb-resolved spectroscopy is available.
@article{arxiv.2505.10910,
title = {Cloudy mornings and clear evenings on a gas giant exoplanet},
author = {Sagnick Mukherjee and David K. Sing and Guangwei Fu and Kevin B. Stevenson and Stephen P. Schmidt and Harry Baskett and Mei Ting Mak and Patrick McCreery and Natalie H. Allen and Katherine A. Bennett and Duncan A. Christie and Carlos Gascón and Jayesh Goyal and Éric Hébrard and Joshua D. Lothringer and Mercedes López-Morales and Jacob Lustig-Yaeger and Erin M. May and L. C. Mayorga and Nathan Mayne and Lakeisha M. Ramos Rosado and Henrique Reggiani and Zafar Rustamkulov and Kevin C. Schlaufman and K. S. Sotzen and Daniel Thorngren and Le-Chris Wang and Maria Zamyatina},
journal= {arXiv preprint arXiv:2505.10910},
year = {2026}
}
Comments
This is the author's version of the work. It is posted here by permission of the AAAS for personal use, not for redistribution. The definitive version was published in Science on 21st May, 2026, DOI: 10.1126/science.adx5903