The recent inference of sulphur dioxide (SO(2)) in the atmosphere of the hot (∼1100 K), Saturn-mass exoplanet WASP-39b from near-infrared JWST observations (1-3) suggests that photochemistry is a key process in high temperature exoplanet atmospheres (4). This is due to the low (<1 ppb) abundance of SO(2) under thermochemical equilibrium, compared to that produced from the photochemistry of H(2)O and H(2)S (1-10 ppm) (4-9). However, the SO(2) inference was made from a single, small …