Volcanic satellites tidally venting Na, K, and SO2 in optical and infrared light

Abstract

Recent infrared spectroscopy from the James Webb Space Telescope (JWST) has spurred analyses of common volcanic gases such as carbon dioxide (CO<inf>2</inf>), sulphur dioxide (SO<inf>2</inf>), alongside alkali metals sodium (Nai) and potassium (Ki) surrounding the hot Saturn WASP-39 b. We report more than an order-of-magnitude of variability in the density of neutral Na, K, and SO<inf>2</inf> between ground-based measurements and JWST, at distinct epochs, hinting at exogenic physical processes similar to those sourcing Io’s extended atmosphere and torus. Tidally heated volcanic satellite simulations sputtering gas into a cloud or toroid orbiting the planet are able to reproduce the probed line-of-sight column density variations. The estimated SO<inf>2</inf> flux is consistent with tidal gravitation predictions, with a Na/SO<inf>2</inf> ratio far smaller than Io’s. Although stable satellite orbits at this system are known to be <15.3 h, several high-resolution alkali Doppler shift observations are required to constrain a putative orbit. Due to the Roche limit interior to the planetary photosphere at ~8 h, atmosphere–exosphere interactions are expected to be especially important in this system. © The Author(s) 2025. Published by Oxford University Press on behalf of Royal Astronomical Society.