A Dynamic Model for the Lunar Ejecta Dust Cloud

Abstract

<p>The return to the Moon pushed forward by space agencies as well as private companies around the world, has rekindled interest in the Lunar dust environment, which was identified as a major factor in spacecraft safety and reliability considerations during the Apollo missions. Orbiting the Moon from 2013 to 2014, the Lunar Atmosphere and Dust Environment Explorer (LADEE) gathered conclusive evidence for the existence of a permanent, asymmetric dust cloud around the Moon [1]. Micron-sized ejecta particles generated at impact of interplanetary meteoroids on the Lunar surface act as the main source of this high-altitude dust exosphere, which shows a variable density in dependence of annual meteoroid showers.</p><p>Here we report on the development of a dynamic model for the lunar ejecta dust cloud. This model simulates cloud particles in a Monte-Carlo fashion, drawing on a combination of existing engineering models and results from hypervelocity impact experiments as model inputs: To emulate the influx of meteoroids we use the Interplanetary Meteoroid Environment Model 2 (IMEM2) [2], developed under ESA contract, as well as a comet stream model based on meteor shower zenith-hourly-rates [3, 4]. To determine angular, velocity, and size distributions of ejecta particles, we resort to three different methods: (1) We use the software <em>Ansys Autodyn</em> to numerically model ejecta particles generated at hypervelocity impacts. (2) Impact experiments with a light-gas gun have been conducted at the Harbin Institute of Technology, to derive ejecta distributions generated by bigger projectiles. (3) We intend to conduct hypervelocity impact experiments with lunar soil simulant at the electrostatic dust-accelerator facility at the University of Stuttgart. The novel experiment set-up, which uses a delay-line-detector to measure micron-sized ejecta particles has recently been verified [5]. Ultimately, the simulated dust ejecta cloud will be fitted to LADEE/LDEX data. This poster-presentation gives an overview of the project and its various modules.</p><p><strong>References:</strong><br>[1] Horányi, M., et al. "A permanent, asymmetric dust cloud around the Moon." <em>Nature</em> 522.7556 (2015): 324-326.<br>[2] Soja, R. H., et al. "IMEM2: a meteoroid environment model for the inner solar system." <em>Astronomy & Astrophysics</em> 628 (2019): A109.<br>[3] Jenniskens, Peter. "Meteor stream activity I. The annual streams." <em>Astronomy and Astrophysics</em> 287 (1994): 990-1013.<br>[4] McBride, Neil. "The importance of the annual meteoroid streams to spacecraft and their detectors." <em>Advances in Space Research</em> 20.8 (1997): 1513-1516.<br>[5] Li, Yanwei, et al. "Measurement of fragments generated by hypervelocity impacts of micron-sized iron particles at grazing incidents." <em>Advances in Space Research</em> 69.6 (2022): 2629-2635.</p>