Moon’s largest dark spot may be an impact crater

Daily Mail : The Moon’s 3 000–km dark spot is known as Oceanus Procellarum, or the “Ocean of Storms.” Japanese scientists led by Ryosuke Nakamura from the National Institute of Advanced Industrial Science and Technology believe they have found evidence the mare was created by a massive impact. They analyzed soil composition data collected by the Japanese lunar orbiter SELENE, better known in Japan as Kaguya. The data showed the presence of low-calcium varieties of the mineral pyroxene around the Ocean of Storms as well as other known major impact craters. That form of pyroxene is associated with the melting and excavation of material from the lunar mantle, which suggests that the Ocean of Storms was formed by a similar process. Nakamura’s team estimates that the impact was caused by a 180-km-diameter asteroid some 3.9 billion years ago. The researchers believe that future missions to collect samples from the lunar surface will confirm their findings.