Asymmetric Impacts of Near-earth Asteroids on the Moon

Details Asymmetric Impacts of Near-earth Asteroids on the Moon Asymmetric Impacts of Near-earth Asteroids on the Moon

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.2701m&link_type=abstract

American Astronomical Society, DPS meeting #41, #27.01

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Scientific paper

Recent lunar crater studies have revealed an asymmetric distribution of rayed craters (generally the youngest impacts) on the lunar surface: there is a higher density of rayed craters on the leading hemisphere compared with the trailing hemisphere. We tested the hypotheses that (i) the population of Near-Earth asteroids (NEAs) is the source of the impactors of the rayed craters, and (ii) that impacts by this projectile population account quantitatively for the observed asymmetry. We carried out numerical simulations of the orbital evolution of a large number of test particles representing NEAs to determine the spatial distribution of their impacts on the lunar surface. The simulations were done in two stages. In the first stage, we adopted an N-body model that included the Sun, the eight major planets and test particle NEAs, and we obtained encounter statistics of NEAs on the Earth's activity sphere. In the second stage, we calculated the impact flux of the encountering particles on the surface of the Moon, adopting a restricted four body model consisting of the Earth, Moon, Sun and test particle NEAs within Earth's activity sphere. To represent NEAs' initial conditions, we considered two populations: the currently known NEAs, and a synthetic population created by de-biasing the orbital distribution of the known NEAs. We find that the near-Earth asteroids do have an asymmetry in their impacts on the Moon: apex-to-antapex ratio of 1.3-1.4. However, the observed rayed crater distribution's asymmetry is significantly more pronounced: apex-to-antapex ratio of 1.67. Our results suggest that the population of low impact velocity NEAs (i.e., objects nearly co-orbiting with Earth) are underrepresented - by roughly 50% - in the currently known as well as in the de-biased NEA population.
Reference:Ito, T., and Malhotra, R., 2009, submitted to A & A; preprint at http://arxiv.org/abs/0907.3010

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