SO<sub>2</sub>, silicate clouds, but no CH<sub>4</sub> detected in a warm Neptune.
basic_science · Level V
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- Record sourced from PubMed, PMID 37967578.
- Also identified by DOI 10.1038/s41586-023-06849-0.
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Abstract
WASP-107b is a warm (approximately 740 K) transiting planet with a Neptune-like mass of roughly 30.5 M<sub>⊕</sub> and Jupiter-like radius of about 0.94 R<sub>J</sub> (refs. <sup>1,2</sup>), whose extended atmosphere is eroding<sup>3</sup>. Previous observations showed evidence for water vapour and a thick, high-altitude condensate layer in the atmosphere of WASP-107b (refs. <sup>4,5</sup>). Recently, photochemically produced sulfur dioxide (SO<sub>2</sub>) was detected in the atmosphere of a hot (about 1,200 K) Saturn-mass planet from transmission spectroscopy near 4.05 μm (refs. <sup>6,7</sup>), but for temperatures below about 1,000 K, sulfur is predicted to preferably form sulfur allotropes instead of SO<sub>2</sub> (refs. <sup>8-10</sup>). Here we report the 9σ detection of two fundamental vibration bands of SO<sub>2</sub>, at 7.35 μm and 8.69 μm, in the transmission spectrum of WASP-107b using the Mid-Infrared Instrument (MIRI) of JWST. This discovery establishes WASP-107b as the second irradiated exoplanet with confirmed photochemistry, extending the temperature range of exoplanets exhibiting detected photochemistry from about 1,200 K down to about 740 K. Furthermore, our spectral analysis reveals the presence of silicate clouds, which are strongly favoured (around 7σ) over simpler cloud set-ups. Furthermore, water is detected (around 12σ) but methane is not. These findings provide evidence of disequilibrium chemistry and indicate a dynamically active atmosphere with a super-solar metallicity.