Abundant rocks from deep below the Moon's surface are exposed in concentric rings around craters according to a paper online this week in Nature Geoscience. These rocks are rich in the mineral olivine, which is thought to originate from within the mantle, underneath the crust. This work gives us an insight into development of the Moon's mantle.
Satoru Yamamoto and colleagues used equipment on board the lunar explorer SELENE/Kaguya to survey the composition of the Moon's surface. Exposures of olivine were limited to concentric regions around impact craters that have thin crust. The researchers suggest that large impacts penetrated the outer crust, exposing the mantle olivine stored deeper below the surface. If true, this finding supports the theory that at some point in the Moon's history its mantle overturned, bringing olivine-rich rocks closer to the surface.
In an accompanying News and Views article, Paul Lucey writes that this work provides "a glimpse at the evolution of the lunar mantle".