Photochemistry is a fundamental process of planetary atmospheres that regulates the
atmospheric composition and stability. However, no unambiguous photochemical products
have been detected in exoplanet atmospheres so far. Recent observations from the JWST
Transiting Exoplanet Community Early Release Science Program, found a spectral
absorption feature at 4.05 μm arising from sulfur dioxide (SO2) in the atmosphere of WASP-
39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass (0.28 MJ) gas giant exoplanet orbiting a …