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Massive impact may have shaped the face of the Moon

The Moon has two different faces — the near side that always faces towards the Earth, and the far side that always faces away from the Earth — and they are quite different from one another. There has been some debate among scientists regarding the reason for this, primarily about the origin of the dark lunar maria. In a new study published this week though, a team of Japanese researchers reveals what could be the first concrete evidence that a massive impact created one of the large lunar mare on the near side of the Moon, called Oceanus Procellarum, the 'Sea of Storms'.

Compared to the near side of the Moon, the far side is very uniform in appearance. It is peppered with craters of all sizes, but other than a couple of tiny mare that only make up about 1 per cent of the entire area of that side (compared to over 30 per cent of the near side), it is made up of fairly-uniformly old and light-coloured material.

In the new study, published in Nature Geoscience, the research team — led by Ryosuke Nakamura, who is a planetary scientist at the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan — examined data from Japan's Kaguya/Selene lunar orbiter, which showed that concentrations of a low-calcium type of pyroxene found around Oceanus Procellarum were similar to those found around the edges of the South Pole—Aitken basin and Mare Imbrium. The study said that this low-calcium pyroxene can result due to melting and mixing of material from the lunar crust and mantle, or by cooled lunar magma being 'excavated', and this similarity suggests that Oceanus Procellarum may also be due to an impact.

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Such an impact would have resulted in "a 3,000-kilometer wide magma sea several hundred kilometers in depth," said Nakamura, according to SPACE.com. He and his team also speculate that this impact, along with the ones that formed the other large impact basins, would have stripped away the entire surface of the near side of the moon, forming an entirely new surface from the molten material left behind.

The idea of a large impact creating Oceanus Procellarum isn't new, but there was a lack of evidence for the hypothesis up until now.

"Our discovery provides the first compositional evidence of this idea, which could be confirmed by future lunar sample return missions, such as Moonrise," Nakamura added.

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Moonrise was a proposed NASA mission to land a robotic rover at the south pole of the moon, which would gather and return samples to Earth for study. The project lost out to OSIRIS-REx — a sample-return mission to an asteroid planned to launch in 2016 — however just the other day there was a report that the Canadian Space Agency, which had planned to be involved in Moonrise, was in talks with NASA about other proposed missions. So, something like Moonrise could go forward sometime in the near future, and it could be a Canadian rover that does the work.