Impact Ejecta Plumes at the Moon

The Lunar Dust Experiment, on-board National Aeronautics and Space Administration's Lunar Atmosphere and Dust Environment Explorer, observed significant enhancements in impact rate measurements of lunar ejecta. These enhancements were attributed to the spacecraft crossing dense ejecta plumes generated by well-timed and well-placed interplanetary meteoroid impacts on the lunar surface. We have used a Monte Carlo approach to implement an initial speed distribution, derived from globally averaged Lunar Dust Experiment observations, in a 3-D dynamical model describing the ballistic motion of ejecta particles. By matching this model to the observed enhancements, we constrained the initial ejecta angular distribution of these plumes. Our results indicate that lunar impact ejecta plumes reaching altitudes exceeding 24 km are far narrower than previously thought, with initial opening half angles of 8°±3°, suggesting that the high-altitude lunar dust cloud may be dominated by reverse plumes.