DSMC Modelling of Gaseous Plumes in Europa’s Icy Vents

In this study, we present preliminary results of Direct Simulation Monte Carlo (DSMC) [1] modelling of plumes through icy vents on Europa.

Jupiter's icy moon Europa is of great interest because of its potentially habitable subsurface oceans. Both ESA's JUpiter Icy Moons Explorer (JUICE) [2] and NASA's Europa Clipper [3] missions will, among a multitude of other measurements, perform mass spectrometry on samples from Europa's atmosphere and potential plumes. For the exciting prospect of determining Europa's habitability, estimating the chemical composition of the subsurface liquid water reservoirs is indispensable.

To infer the abundances of different chemical species in such a reservoir from their abundances far above the surface, it is crucial to understand the change in chemical composition of the gaseous plume content from the subsurface liquid water reservoir to the above-surface plume. To this end, we are simulating the evolution of water plumes erupting from a subsurface reservoir, be that an ocean or a water inclusion, from initial triple-point conditions, through the icy crust and into space. Our group benefits from expertise in simulating plumes from Europa's surface [4]. 

Our chosen method is Direct Simulation Monte Carlo (DSMC), modelling individual gas (macro-)particles and their intereactions to simulate the behaviour of a vastly larger number of (micro-)particles. The DSMC method is more computationally expensive than numerical simulations of macroscopic quantities in a crevasse [5], but naturally allows the incorporation of collisional phenomena and chemical reactions between particles and the icy walls, and is applicable to a wide range of pressures and temperatures. Almost a decade ago, DSMC already proved to be an effective tool for simulating Europa plumes from the surface upward [6]. 

We developed our own new DSMC code to familiarize ourselves with this method. We also made use of the state-of-the-art open-source Stochastic PArallel Rarefied-gas Time-accurate Analyzer (SPARTA) code [7]. Our simulations aim to improve the understanding of how chemical compositions change as gaseous material is transported from Europa’s interior into space, and ultimately to support the scientific analysis of data collected by the mass spectrometers NIM on JUICE and MASPEX on Europa Clipper. We will expand on and compare different models by running them under consistent geometrical and physical initial conditions and by comparing their predictions. The ultimate goal is to subject the modelled plumes to a reversal algorithms, to be able to retrieve predictions about subsurface reservoirs from above-surface measurements.

 

Acknowledgement:

The authors acknowledge the financial support of the SNSF under SNSF starting grant 218336.

 

References:

[1] G. A. Bird (1994). Molecular gas dynamics and the direct simulation of gas flows.

[2] O. Grasset, et al. (2013). Planetary and Space Science, 78, 1-21. https://doi.org/10.1016/j.pss.2012.12.002

[3] C. B. Phillips, and R. T. Pappalardo (2014). Eos, Transactions AGU, 95(20), 165-167. https://doi.org/10.1002/2014EO200002

[4] Vorburger, A., and Wurz, P. (2021). J. Geophys. Res. Space Phys., 126(9).  https://doi.org/10.1029/2021JA029690

[5] N. J. van der Hijden et al. (2024). Icarus 417, 116114. https://doi.org/10.1016/j.icarus.2024.116114

[6] J. J. Berg, et al. (2016). Icarus 277, 370–380. https://doi.org/10.1016/j.icarus.2016.05.030

[7] S. J. Plimpton, et al. (2019). Physics of Fluids 31, 086101. https://doi.org/10.1063/1.5108534