EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

3D Monte-Carlo Simulations of Ganymede's Water Atmosphere - Predictions for JUICE/PEP/NIM

Audrey Vorburger1,2, Fatemi Shahab2, André Galli1, Lucas Liuzzo3, Andrew Poppe3, and Peter Wurz1
Audrey Vorburger et al.
  • 1Physics Institute, University of Bern, Bern, Switzerland (
  • 2Department of Physics, University of Umeå, Umeå, Sweden
  • 3Space Sciences Laboratory, University of California, Berkeley, Berkeley, CA, USA

We present 3D Monte-Carlo simulation results for the surface-sputtered and sublimated H2O molecules in Ganymede's atmosphere. To calculate particle fluxes onto Ganymede's surface, we use test particle model results for electrons, thermal H+ and O+, energetic H+, O++, and S+++, with unprecedented energy resolution. In addition, besides a thermal model based on Galileo measurements, we use recently published surface water content maps and recently measured water sputter yields.

Our simulations show that for the sputtered atmosphere, it is mainly the impinging O+, O++, and S++ ions that deliver H2O to the atmosphere, while electrons and protons only play a minor role in comparison. With Ganymede's surface temperature ranging from 80 K to 150 K (the latter being an upper bound), most returning H2O molecules stick to the surface. As a consequence of this, the morphology of Ganymede's magnetosphere, and the resulting patterns in the precipitation maps, are well preserved in the exosphere up to altitudes of a few thousand kilometers.

In the sub-solar region, it is the sublimated H2O that dominates the atmosphere by up to four orders of magnitude. The sublimated atmosphere quickly decreases with altitude, though, and sputtering becomes the dominant release process for H2O molecules reaching beyond a few hundred kilometers altitude. The sublimated H2O atmosphere is thus quite substantial but highly limited in spatial extent.

In addition to our most important modeling results concerning Ganymede's H2O atmosphere, we will also discuss their implications for spacecraft observability. Using the recently updated JUICE trajectories (CREMA 5), we will show which atmospheric populations (sublimated and/or sputtered H2O) will be encountered during the different Ganymede orbit phases (elliptical, high polar, and low polar). Finally, we will present expected measurement results for the Neutral and Ion Mass spectrometer (NIM), part of the Particle and Environment Package (PEP) onboard JUICE / ESA.

How to cite: Vorburger, A., Shahab, F., Galli, A., Liuzzo, L., Poppe, A., and Wurz, P.: 3D Monte-Carlo Simulations of Ganymede's Water Atmosphere - Predictions for JUICE/PEP/NIM, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7590,, 2022.


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