1,2,3,4,1,5,1,- 1KTH Royal Institute of Technology, Stockholm, Sweden
- 2Southwest Research Institute, USA
- 3Institute of Geophysics and Meteorology, University of Cologne, Cologne, Germany
- 4Department of Earth and Planetary Sciences, The Johns Hopkins University, Baltimore, MD, USA
- 5Space Research Institute, Austrian Academy of Sciences, Graz, Austria
- 6SETI Institute, Mountain View, CA, USA
- 7Department of Earth and Planetary Sciences, University of California Santa Cruz, CA, USA
- 8formerly at American University, Washington, DC, USA
- 9Central Arizona College, Coolidge, AZ, USA
An image of Lyman-α (Lyα, 1216 Å) emission from Europa obtained with the Hubble Space Telescope’s Space Telescope Imaging Spectrograph (HST/STIS) provided the first evidence for localized water vapor (H2O) aurora, potentially originating from plume outgassing. Subsequent HST/STIS observations revealed the presence of a global atomic hydrogen (H) exosphere at Europa. We present a comprehensive analysis of STIS Lyα observations of Europa acquired in 1999 and between 2012 and 2020 to search for localized auroral emissions and to constrain the properties of Europa’s H exosphere. We construct a model that accounts for all known sources of Lyα emission, including resonantly scattered sunlight from Europa’s H exosphere. To identify localized anomalies such from an outgassing plume, we subtract the modeled Lyα emission and analyze the residuals.
We find evidence to support a persistent hydrogen exosphere at Europa, but no evidence of localized water vapor.
How to cite: Roth, L., Retherford, K., Saur, J., Strobel, D., Becker, T., Bergman, S., Blöcker, A., Carberry Mogan, S., Grava, C., Ivchenko, M., Joshi, S., McGrath, M., Nimmo, F., Paganini, L., Pryor, W., and Spencer, J.: Europa’s Lyman-α emissions: Insights into the Hydrogen Exosphere but No Sign of a Plume, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-780, https://doi.org/10.5194/epsc2026-780, 2026.
