Europlanet Science Congress 2021
Virtual meeting
13 – 24 September 2021
Europlanet Science Congress 2021
Virtual meeting
13 September – 24 September 2021
EPSC Abstracts
Vol. 15, EPSC2021-176, 2021
European Planetary Science Congress 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Hubble Space Telescope detects sub-solar water atmosphere on Ganymede

Lorenz Roth1, Nickolay Ivchenko1, Randy Gladstone2, Joachim Saur3, Denis Grodent4, Bertrand Bonfond4, Philippa Molyneux2, and Kurt Retherford2
Lorenz Roth et al.
  • 1KTH Royal Institute of Technology, School of Electrical Engineering and Computer Science, Space and Plasma Physics, Stockholm, Sweden (
  • 2Southwest Research Institute, San Antonio, TX, USA
  • 3Universität zu Köln, Germany
  • 4University of Liège, Belgium

Ganymede’s tenuous atmosphere is produced by charged particle sputtering and sublimation of its icy surface. Previous far-ultraviolet observations of the OI1356 Å and OI1304 Å oxygen emissions were used to derive sputtered molecular oxygen, O2, as an atmospheric constituent. We present a new analysis of high-sensitivity spectra and spectral images of Ganymede’s oxygen emissions acquired by the COS and STIS instruments on the Hubble Space Telescope. The COS eclipse observations constrain atomic oxygen, O, to be at least two orders of magnitude less abundant than O2. We then show that dissociative excitation of water vapor, H2O, is found to increase the OI1304 Å emissions relative to the OI1356 Å emissions around the sub-solar point, where H2O is more abundant than O2. Away from the sub-solar region, the emissions are more than two times brighter at OI1356 Å than at OI1304 Å, and O2 prevails as found in previous analyses. A ~6-fold higher H2O/O2 mixing ratio on the warmer trailing hemisphere compared to the colder leading hemisphere, a spatial concentration at the sub-solar region, and the ratio-estimated H2O densities identify icy surface sublimation as a local dayside atmospheric source.
Our analysis provides the first evidence for a sublimated atmosphere on an icy moon in the outer solar system.

How to cite: Roth, L., Ivchenko, N., Gladstone, R., Saur, J., Grodent, D., Bonfond, B., Molyneux, P., and Retherford, K.: Hubble Space Telescope detects sub-solar water atmosphere on Ganymede, European Planetary Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-176,, 2021.

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