The huge Procellarum basin on the nearside of the Moon may be a relic scar from an ancient impact event that shaped the lunar surface, reports a study published online this week in Nature Geoscience. Such an impact may explain why the nearside and farside of the Moon are composed of different kinds of rock.
Ryosuke Nakamura and colleagues used data from the Japanese lunar orbiter KAGUYA/SELENE to study the composition of the Moon’s surface. They show that a certain type of the mineral pyroxene - indicative of the melting and excavation of material from the lunar mantle - is concentrated around large impact craters and the ancient 3,000-km-diameter Procellarum basin. They suggest that the findings point to an impact origin for this basin.
The researchers also conclude that an impact event of this magnitude would have excavated the original crust on the nearside of the Moon, leading to the formation of a new, compositionally-distinct, crust within the basin.