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Exploring Lunar Volatiles and Icy Grains in Icy Moons: Insights from Reactive Molecular Dynamics Simulation

Presentation #103.08D in the session Fire and Ice: Io and Beyond (Oral Presentation)

Published onOct 23, 2023
Exploring Lunar Volatiles and Icy Grains in Icy Moons: Insights from Reactive Molecular Dynamics Simulation

Molecular dynamics simulation is a computational technique that allows us to study the behavior of molecules and materials at the atomic and molecular scale. By accurately calculating bond orders and integrating Newton’s equations, reactive molecular dynamics (RMD) simulation provides a unique opportunity for us to understand many planetary problems where chemistry and dynamics are coupled. One particular problem is the origin of water molecules on the moon. We’ve used RMD to examine the contribution of several geophysical processes including solar wind implantation, micrometeoroid impact, and dielectric breakdown [1-3]. In this study, we focus on the hypervelocity impact of water ice, which is essential for future exploration of icy moons like the Europa Clipper Missions.

Our investigation reveals a two-stage fragmentation pattern, with inter-molecular fragmentation occurring at lower velocities and inter-atomic fragmentation occurring at higher velocities. In particular, inter-atomic fragmentation leads to the formation of H2 and O2 starting at a velocity of 6 km/s. We propose using the relative yield of H2 and O2 as an alternative method for estimating impact velocities of ice grains in high-velocity ranges.

We also directly sample the velocity distribution function (VDF) of the released molecules, which is essential for better modeling of the exosphere. We found that the VDF deviates from a Maxwellian distribution due to the strong clustering features observed from reactive molecular dynamics simulation. Combined with the clustering features, we propose a mixed Maxwellian distribution to incorporate the clustering and compare the difference between mixed and single Maxwellian distributions in terms of their contribution to the surface-bonded exosphere.

Reference:

[1] Huang, Z., Nomura, K. I., Nakano, A., & Wang, J. (2021). Molecular dynamics simulations of dielectric breakdown of lunar regolith: Implications for water ice formation on lunar surface. Geophysical Research Letters, 48(3), e2020GL091681.

[2] Huang, Z., Nomura, K. I., & Wang, J. (2021). Molecular dynamics simulations of water formation and retention by micrometeoroid impact on lunar surface. Geophysical Research Letters, 48(15), e2021GL093509.

[3] Huang, Ziyu, et al. “Molecular dynamics simulation of solar wind implantation in the permanently shadowed regions on the lunar surface.” Geophysical Research Letters 49.18 (2022): e2022GL099333.

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