Investigation of lunar ejecta dynamics: Particles reaching the near-Earth space and their effect on Earth-based observation

TL;DR

This study analyzes lunar ejecta particles' orbital evolution, their impact frequency on Earth, and how they influence Earth-based observations, revealing distinct distribution patterns and rapid impact times for small particles.

Contribution

It provides a detailed analysis of lunar ejecta impact dynamics and their observational implications, expanding understanding of near-Earth dust sources and their detectability.

Findings

Most impactors reach Earth within one year.

Small particles (0.2-0.5 μm) impact Earth within one week.

Lunar impactors have distinguishable orbital distributions from interplanetary dust.

Abstract

Aims. Particles ejected from the lunar surface via hypervelocity impacts form a torus between the Earth and the Moon. According to our previous study (Yang et al., A\&A, 659, A120), among them about $2.3\times10^{-4}\,\mathrm{kg/s}$ particles impact the Earth after long-term orbital evolution. We mainly focus on these Earth impactors, analyze their orbital element distribution, and estimate their influence on Earth-based observations. Methods. In previous work we simulated the long-term orbital evolution of particles ejected from the lunar surface, and obtained their steady-state spatial distribution in the Earth-Moon system. In this work, we analyze the simulation results about the Earth impactors, including the fraction of impactors with different initial parameters among all impactors, the orbital element distribution, and the projection of particles onto several Earth-based observatories. Results. Particles ejected from the lunar surface are more likely to impact the Earth within a certain range of initial parameters. Most of these lunar-ejected impactors ($\sim70\%$) reach the Earth within one year, while most of the small ones ($87.2\%$ of $0.2\,\mathrm{\mu m}$ particles and $64.6\%$ of $0.5\,\mathrm{\mu m}$ particles) reach the Earth within one week. A large proportion of lunar-ejected Earth impactors can be distinguished from interplanetary dust particles according to the differences in their orbital distributions. Besides, lunar-ejected particles may exhibit distinct configurations and orientations from the perspectives of different Earth-based observatories.