Distribution of Impact Locations and Velocities of Earth Meteorites on the Moon |
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| Authors: | John C Armstrong |
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| Institution: | (1) Department of Physics, Weber State University, 2508 University Circle, Ogden, UT 84408-2508, USA |
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| Abstract: | Following the analytical work of Armstrong et al. (Icarus 160:183–196, 2002), we detail an expanded N-body calculation of the direct transfer of terrestrial material to the Moon during a giant impact.
By simulating 1.4 million particles over a range of launch velocities and ejecta angles, we have derived a map of the impact
velocities, impact angles, and probable impact sites on the moon over the last 4 billion years. The maps indicate that the
impacts with the highest vertical impact speeds are concentrated on the leading edge, with lower velocity/higher-angle impacts
more numerous on the Moon’s trailing edge. While this enhanced simulation indicates the estimated globally averaged direct
transfer fraction reported in Armstrong et al. (Icarus 160:183–196, 2002) is overestimated by a factor of 3–6, local concentrations can reach or exceed the previously published estimate. The most
favorable location for large quantities of low velocity terrestrial material is 50 W, 85 S, with 8.4 times more impacts per
square kilometer than the lunar surface average. This translates to 300–500 kg km−2, compared to 200 kg km−2 from the previous estimate. The maps also indicate a significant amount of material impacting elsewhere in the polar regions,
especially near the South Pole-Aiken basin, a likely target for sample return in the near future. The magnitudes of the impact
speeds cluster near 3 km/s, but there is a bimodal distribution in impact angles, leading to 43% of impacts with very low
(<1 km/s) vertical impact speeds. This, combined with the enhanced surface density of meteorites in specific regions, increases
the likelihood of weakly shocked terrestrial material being identified and recovered on the Moon. |
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