Volume 519, September 2010
|Number of page(s)||9|
|Section||Planets and planetary systems|
|Published online||14 September 2010|
Asymmetric impacts of near-Earth asteroids on the Moon
National Astronomical Observatory, Osawa 2–21–1, Mitaka, Tokyo 181–8588, Japan e-mail: firstname.lastname@example.org
2 Lunar & Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721–0092, USA
Accepted: 24 May 2010
Context. Recent lunar crater studies have revealed an asymmetric distribution of rayed craters on the lunar surface. The asymmetry is related to the synchronous rotation of the Moon: there is a higher density of rayed craters on the leading hemisphere compared with the trailing hemisphere. Rayed craters represent generally the youngest impacts.
Aims. The purpose of this paper is to test the hypotheses that (i) the population of Near-Earth asteroids (NEAs) is the source of the impactors that have made the rayed craters; and (ii) that impacts by this projectile population account quantitatively for the observed asymmetry.
Methods. We carried out numerical simulations of the orbital evolution of a large number of test particles representing NEAs in order to determine directly their impact flux on the Moon. The simulations were done in two stages. In the first stage we obtained encounter statistics of NEAs on the Earth's activity sphere. In the second stage we calculated the direct impact flux of the encountering particles on the surface of the Moon; the latter calculations were confined within the activity sphere of the Earth. A steady-state synthetic population of NEAs was generated from a debiased orbital distribution of the known NEAs.
Results. We find that the near-Earth asteroids do have an asymmetry in their impact flux on the Moon: apex-to-antapex ratio of 1.32 ± 0.01. However, the observed rayed crater distribution's asymmetry is significantly more pronounced: apex-to-antapex ratio of 1.65 ± 0.16. Our results suggest the existence of an undetected population of slower (low impact velocity) projectiles, such as a population of objects nearly coorbiting with Earth; more observational studies of young lunar craters is needed to secure this conclusion.
Key words: minor planets, asteroids: general / Moon / planets and satellites: surfaces / methods: numerical
© ESO, 2010
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.