Evidence for morning-to-evening limb asymmetry on the cool low-density exoplanet WASP-107 b

December 2024 • 2024NatAs...8.1562M

Authors • Murphy, Matthew M. • Beatty, Thomas G. • Schlawin, Everett • Bell, Taylor J. • Line, Michael R. • Greene, Thomas P. • Parmentier, Vivien • Rauscher, Emily • Welbanks, Luis • Fortney, Jonathan J. • Rieke, Marcia

Abstract • The atmospheric properties of hot exoplanets are expected to be different between the morning and the evening limbs due to their global atmospheric circulation. Ground-based observations at high spectral resolution have detected this limb asymmetry in several ultra-hot (>2,000 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 μm to find evidence of limb asymmetry on exoplanet WASP-107 b. With its equilibrium temperature of 770 K and low density of 0.126 g cm^‒3, 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-to-evening temperature difference of the order of 100 K with a hotter evening limb. Further observations of other cooler exoplanets are needed to determine whether WASP-107 b is an outlier or whether the models have underestimated the presence of limb asymmetry in exoplanets.

Links

• SIMBAD https://simbad.u-strasbg.fr/simbad/sim-ref?querymethod=bib&simbo=on&submit=submit+bibcode&bibcode=2024NatAs...8.1562M
• PREPRINT http://arxiv.org/abs/2406.09863
• DATA http://doi.org/10.5281/zenodo.12747273
• DATA https://archive.stsci.edu/mastbibref.php?bibcode=2024NatAs...8.1562M
• DATA https://archive.stsci.edu/mastbibref.php?bibcode=2024NatAs...8.1562M
• DATA https://irsa.ipac.caltech.edu/applications/Spitzer/SHA/
• DATA https://irsa.ipac.caltech.edu/bibdata/2024/M/2024NatAs...8.1562M.html
• DATA https://mast.stsci.edu
• ELECTR https://doi.org/10.1038%2Fs41550-024-02367-9