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Published February 2026 | Version Published
Journal Article Open

Volcanic Satellites Tidally Venting Na, K, SO₂ in Optical & Infrared Light

Creators

  • 1. ROR icon California Institute of Technology
  • 2. ROR icon Jet Propulsion Lab
  • 3. ROR icon Ghent University
  • 4. ROR icon University of Bern
  • 5. ROR icon Carnegie Observatories
  • 6. ROR icon University of California, Santa Cruz
  • 7. ROR icon University of California, Irvine
  • 8. ROR icon University of Tennessee at Knoxville
  • 9. ROR icon Boston University
  • 10. ROR icon Leiden University
  • 11. ROR icon Netherlands Institute for Space Research
  • 12. ROR icon Arizona State University
  • 13. ROR icon University of Chicago
  • 14. Portola High School, Irvine, USA
  • 15. ROR icon Indian Institute of Technology Indore

Abstract

Recent infrared spectroscopy from the James Webb Space Telescope (JWST) has spurred analyses of common volcanic gases such as carbon dioxide (CO₂⁠), sulphur dioxide (SO₂⁠), alongside alkali metals sodium (Na i) and potassium (K i) 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 SO₂ 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 SO₂ flux is consistent with tidal gravitation predictions, with a Na/SO₂ 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.

Copyright and License

© The Author(s) 2025. Published by Oxford University Press on behalf of Royal Astronomical Society.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

Acknowledgement

AVO thanks H. Knutson for valuable insight on HST/STIS and N. Nikolov on VLT/FORS2 data. The research described in this paper was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Copyright 2025. All rights reserved. YM acknowledges support from the European Research Council (ERC) under the European Union’s Horizon 2020 Framework Programme (grant agreement no. 101088557, N-GINE).

Data Availability

Relevant JWST data used in this study can be accessed through the Space Telescope Science Institute (STScI) archive at https://archive.stsci.edu.

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Additional details

Related works

Is new version of
Discussion Paper: arXiv:2509.08349 (arXiv)

Funding

National Aeronautics and Space Administration
European Research Council
101088557

Dates

Submitted
2025-01-03
Accepted
2025-08-04
Available
2025-09-25
Published
Available
2026-01-14
Corrected and typeset

Caltech Custom Metadata

Caltech groups
Division of Geological and Planetary Sciences (GPS)
Publication Status
Published