Large impact crater could hold clues about moon’s mantle

Washington – Researchers sifting through data from the Moon Mineralogy Mapper that flew aboard India’s Chandrayaan-1 lunar orbiter found a diverse mineralogy in the subsurface of the giant South Pole Aitken basin.

According to researchers, the differing mineral signatures could be reflective of the minerals dredged up at the time of the giant impact 4 billion years ago.

If that’s true, then the South Pole Aitken (SPA) basin could hold important information about the Moon’s interior and the evolution of its crust and mantle.

Using Moon Mineralogy Mapper data, the researchers looked at the light reflected from each of the four central peaks. The spectra of reflected light give scientists clues about the makeup of the rocks. The spectra showed substantial differences in composition from peak to peak.

Some crater peaks were richer in magnesium than others. One of the four craters, located toward the outer edge of the basin, contained several distinct mineral deposits within its own peak, possibly due to sampling a mixture of both upper and lower crust or mantle materials.

Brown graduate student Dan Moriarty said that if impact scaling is done, [the SPA impact] should have excavated into the mantle.
He said that the team believes that the upper mantle is rich in a mineral called olivine, but they don’t see much olivine in the basin, asserting that’s one of the big mysteries about the South Pole Aitken basin.

He added that one of the things they’re trying to figure out is how deep did the impact really excavate adding that if it melted and excavated any material from the mantle, why aren’t they seeing it?

If the impact did excavate mantle material, and it doesn’t contain olivine, that would have substantial implications for models of how the Moon was formed, Moriarty said.

The study has been published online in the Journal of Geophysical Research: Planets.