Hyperbolic Meteoroids Impacting the Moon

Since the discovery of the Moon's asymmetric ejecta cloud, the origin of its sunward-canted density enhancement has not been well understood. We propose impact ejecta from meteoroids on hyperbolic trajectories (β-meteoroids) that hit the Moon's sunward side could explain this unresolved asymmetry. β-meteoroids are submicron in size, comparable to or smaller than the regolith particles they hit, and can impact the Moon at very high speeds ∼100 km s−1. Therefore, their impact regime may differ from the significantly larger and slower sporadic meteoroids responsible for generating the bulk of the lunar impact ejecta cloud. We compare lunar impact ejecta production to β-meteoroid fluxes observed by multiple spacecraft. If β-meteoroids are able to liberate similar sized submicron particles, orbital dust detector measurements from the Lunar Dust Experiment on board the Lunar Atmosphere and Dust Environment Explorer spacecraft only need to detect one ejecta grain out of every 106 β-meteoroid impacts to the lunar surface to explain the sunward asymmetry with this additional population. This finding suggests β-meteoroids may also contribute to the evolution of other airless surfaces in the inner solar system, and by extension, at exozodiacal systems.