Centaur 29P/Schwassmann–Wachmann 1 and its near-nucleus environment from a stellar occultation

Comets offer valuable insights into the early Solar System’s conditions and processes. Stellar occultations enable detailed study of cometary nuclei typically hidden by their coma. Observing the star’s light passing through the coma helps infer dust’s optical depth near the nucleus and determine dust opacity detection limits. 29P/Schwassmann–Wachmann 1, a Centaur with a diameter of approximately 60 km, lies in a region transitioning from Centaurs to Jupiter-family comets. Our study presents the first-ever observed occultation by 29P, allowing in the future for a more refined orbit and thus better predictions for other occultations. The light curve reveals a solid-body detection lasting 3.65±0.05 s, corresponding to a chord length of approximately 54 km. This provides a lower limit for the object’s radius, measured at 27.0±0.7 km. We identified features on both sides of the main-body occultation around 1700 km from the nucleus in the sky plane for which upper limits on apparent opacity and equivalent width were determined. Gradual dimming within 23 km of the nucleus during ingress only is interpreted as a localized dust cloud/jet above the surface with an optical depth of approximately τ=0.18. This article is part of the theme issue ‘Major advances in planetary sciences thanks to stellar occultations’.