Asymmetric Distribution of Lunar Impact Basins Caused by Variations in Target Properties

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Science  08 Nov 2013:
Vol. 342, Issue 6159, pp. 724-726
DOI: 10.1126/science.1243224

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Which Side of the Moon?

The far- and nearsides of the Moon are geologically different. Using high-precision crustal thickness maps derived from NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission, Miljković et al. (p. 724) show that the distribution of lunar impact basins is also highly asymmetrical. Numerical simulations of impact basin formation coupled with three-dimensional simulations of the Moon's asymmetric thermal evolution suggest that lateral variations in temperature within the Moon's crust have a large effect on the final size of an impact basin.


Maps of crustal thickness derived from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission revealed more large impact basins on the nearside hemisphere of the Moon than on its farside. The enrichment in heat-producing elements and prolonged volcanic activity on the lunar nearside hemisphere indicate that the temperature of the nearside crust and upper mantle was hotter than that of the farside at the time of basin formation. Using the iSALE-2D hydrocode to model impact basin formation, we found that impacts on the hotter nearside would have formed basins with up to twice the diameter of similar impacts on the cooler farside hemisphere. The size distribution of lunar impact basins is thus not representative of the earliest inner solar system impact bombardment.

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