Erosion of the Inner Zodiacal Cloud and its Effects at the Moon

Abstract:

Since the discovery of the Moon's asymmetric ejecta cloud, the origin of its sunward-canted density enhancement has not been well understood. We found that impact ejecta from meteoroids on hyperbolic trajectories (β-meteoroids) which impact the Moon's sunward side can explain this unresolved asymmetry. β-meteoroids are formed by catastrophic collisions and/or sublimation of zodiacal grains in the inner solar system and are also released by comets. These small grains are submicron in size, comparable to or smaller than the lunar regolith particles they hit, and can impact the Moon at very high speeds ~100 km s^-1. Incorporating β-meteoroid fluxes observed by the Pioneers 8 & 9, Ulysses, and Parker Solar Probe spacecraft as a newly considered impactor source at the Moon, we found β-meteoroid impacts to the lunar surface are able to explain the sunward asymmetry observed by LADEE/LDEX. We will discuss these observations and how this finding suggests β-meteoroids may also contribute to the evolution of other airless surfaces in the inner solar system.