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We use a dynamical model to characterize the monthly and yearly variations of the lunar meteoroid environment for meteoroids originating from short and long-period comets and the main-belt asteroids. Our results show that if we assume the meteoroid mass flux of 43.3tons per day at Earth, inferred from previous works, the mass flux of meteoroids impacting the Moon is 30 times smaller, approximately 1.4tons per day, and shows variations of the order of 10% over a year. The mass flux difference is due to the combined effect of the smaller cross-section of the Moon (factor of 13.46) and Earth's larger gravitational focusing (factor of 2-2.5). The lunar surface is vaporized by these impactors at an average impact vaporization flux of 11.6x10(-16)g.cm(-2).s(-1), providing a significant source for the rarefied lunar exosphere. Our model predicts acceptable vaporization rates and reproduces the local time dependence of observations of the dust ejecta cloud, measured by the Lunar Dust Experiment on board NASA's Lunar Atmosphere and Dust Environment (LADEE) satellite. However, the predicted density of the lunar ejecta cloud is four orders of magnitude larger than reported values by LADEE. This discrepancy might be attributed to a much lower yield from meteoroid impacts on fluffy lunar regolith and/or a lower detection efficiency of the LADEE dust detector. We suggest an upper limit of 30cm per million years for the soil gardening rate from small meteoroids. Plain Language Summary The lunar surface is continuously bombarded by small but fast and abundant particles at rates that amount to 1.4tons per day. These particles originate from asteroids and comets and after striking the surface produce a variety of observable phenomena such as a thin atmosphere and a dust cloud engulfing our satellite. Our novel model describes for the first time in detail the directions and velocities of particles impacting the Moon, including their variability in time and space. This approach correctly reproduces the shape of the dust cloud that was measured by the Lunar Atmosphere and Dust Environment Explorer mission. However, the density of the dust cloud predicted by this model is thousands of times higher than what was inferred from the measurement. On the other hand, our model provides realistic numbers for the mass of particles delivered daily to the Moon and for the exosphere density, resulting in a disagreement that is yet to be understood.

来源平台：JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS