Planetary Science

Lunar Exposure

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Science  03 Sep 2010:
Vol. 329, Issue 5996, pp. 1129
DOI: 10.1126/science.329.5996.1129-a

The Lunar Magma Ocean hypothesis postulates that the outer parts of the Moon formed from a global magma ocean that separated and crystallized into a dense olivine- and pyroxene-rich mantle and a buoyant plagioclase-rich crust. The crust has been sampled through rocks collected and returned from the surface of the Moon and through remote sensing, but the mantle, being inaccessible, is still poorly understood. Yamamoto et al. now propose that in some regions of the Moon, meteorite impacts may have penetrated the mantle/crust boundary and exposed olivine-rich material from the upper mantle. Their data, acquired with the visible and near-infrared spectrometer onboard the SELENE/Kaguya satellite, show that olivine-rich rocks on the surface of the Moon are limited to regions around impact craters that are located in areas where the crust is particularly thin. Meteorite impacts would have thus blasted through the thin crust and brought olivine-rich material from the mantle to the surface. It is possible, however, that the Kaguya data are instead sampling troctolites, rocks containing both olivine and plagioclase, which are thought to have formed from molten magma that rose from the mantle into the lower crust and cooled there. According to Lucey, if Kaguya's data are explained by troctolites, then these rocks could have formed from melting induced by impacts that blasted into the regions where the mantle intruded into the crust.

Nat. Geosci. 3, 533; 517 (2010).

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