paper

Evidence for Morning-to-Evening Limb Asymmetry on the Cool Low-Density Exoplanet WASP-107b

arXiv:2406.09863 · doi:10.1038/s41550-024-02367-9

Abstract

The atmospheric properties of hot exoplanets are expected to be different between the morning and the evening limb due to global atmospheric circulation. Ground-based observations at high spectral resolution have detected this limb asymmetry in several ultra-hot (>2000 K) exoplanets, but the prevalence of the phenomenon in the broader exoplanetary population remains unexplored. Here we use JWST/NIRCam transmission spectra between 2.5 and 4.0 m to find evidence of limb asymmetry on exoplanet WASP-107 b. With its equilibrium temperature of 770 K and low density of 0.126 gm c, WASP-107 b probes a very different regime compared to ultra-hot giant planets and was not expected to exhibit substantial spatial heterogeneity according to atmospheric models. We infer instead a morning-evening temperature difference on the order of 100 K with a hotter evening limb. Further observations on other cooler exoplanets are needed to determine whether WASP-107 b is an outlier or the models underestimate the presence of limb asymmetry in exoplanets.

arXiv commentThis preprint has not undergone any significant improvements or corrections. This article's Version of Record has been published in Nature Astronomy and can be found at https://www.nature.com/articles/s41550-024-02367-9. Enclosed is the main text, 4 main text figures, methods, 3 Extended Data items, and 5 Supplementary Information items

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