The atmospheric properties of hot exoplanets are expected to be different between the morning and the evening limbs due to their global atmospheric ci

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

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2024-10-04 00:30:05

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.

The JWST/NIRCam data (JWST GTO programme 1185; PI Greene; Observations 8 and 9), JWST/MIRI data (JWST GTO programme 1280; PI Lagage; Observation 1) and TESS data (PI Caldwell; Observation hlsp_tess-spoc_tess_phot_0000000429302040-s0010_tess_v1) are publicly available from the Mikulski Archive for Space Telescopes (https://mast.stsci.edu). The Spitzer/IRAC data (Programme 13052; PI Werner; AORKEY 62712320) are publicly available from the Spitzer Heritage Archive (https://irsa.ipac.caltech.edu/applications/Spitzer/SHA/). The SOAR data (Programme N23A-840705; PI Murphy) are available from Zenodo at https://doi.org/10.5281/zenodo.12747273 (ref. 72).