Lunar Impact Crater Has A Diverse Subsurface Mineralogy
December 10, 2013

Diverse Mineralogy Could Provide New Insight Into Lunar Evolution

redOrbit Staff & Wire Reports - Your Universe Online

The presence of a diverse group of minerals in the largest lunar impact crater could help scientists gain new insight into the Moon’s interior, as well as the evolution of its crust and mantle, claims new research appearing online in Journal of Geophysical Research: Planets.

Dan Moriarty, a graduate student from Brown University, and his colleagues analyzed data collected from the Moon Mineralogy Mapper instrument aboard India's Chandrayaan-1 lunar orbiter. They discovered a diverse subsurface mineralogy in the South Pole Aitken (SPA) basin, which suggests that the region could hold many clues as to how the Moon evolved and what lies inside of it.

“At 2,500 kilometers across, the SPA is the largest impact basin on the Moon and perhaps the largest in the solar system,” the university explained. “Impacts of this size turn tons of solid rock into molten slush. It has been assumed generally that the melting process would obliterate any distinct signatures of pre-existing mineralogical diversity through extensive mixing, but this latest research suggests that might not be the case.”

As part of their research, Moriarty’s team looked at smaller craters existing within the larger SPA basin – craters formed by impacts that occurred millions of years after the massive one that formed the basin itself. They chose to focus specifically on four of the smaller craters, studying their central peaks in order to examine the pristine material that would have been lifted up from below the impact zone when those craters were first formed.

They used Moon Mineralogy Mapper data to look at the light reflected from each of the four central peaks, and found substantial differences amongst them in terms of mineral composition. Some were found to be richer in magnesium than others, and one of the four craters was found to contain multiple distinct mineral deposits in its peak.

Moriarty and his colleagues believe this could be due to the fact that the central peak contains a mixture of minerals from both the upper and lower crust or mantle. The presence of different mineral types in each of the four central peaks leads the study authors to believe that the SPA subsurface is far more diverse than originally believed.

“Previous studies have suggested that all the central peaks look very similar, and that was taken as evidence that everything's the same across the basin,” Moriarty said. “We looked in a little more detail and found significant compositional differences between these central peaks. The Moon Mineralogy Mapper has very high spatial and spectral resolution. We haven't really been able to look at the Moon in this kind of detail before.”

“The next step is figuring out where that diversity comes from,” the university added. “It's possible that the distinct minerals formed as the molten rock from the SPA impact cooled. Recent research from Brown and elsewhere suggests that such mineral formation in impact melt is possible. However, it's also possible that the mineral differences reflect differences in rock types that were there before the giant SPA impact.”