“This is a highly detailed look at the compositional structure of the South Pole-Aitken (SPA) basin using modern, cutting-edge data,” said Dr. Dan Moriarty, a postdoctoral researcher at NASA’s Goddard Space Flight Center.

“Given that it’s such an important target for future exploration and perhaps returning a sample to Earth, we hope this will serve as a framework for more detailed study and landing site selection.”

Measuring approximately 1,550 miles (2,500 km) in diameter, SPA is thought to be the oldest and largest impact basin on the Moon, and scientists have long had their eyes on it as a target for future lunar landers.

The impact that created SPA is thought to have blasted all the way through the Moon’s crust and into the mantle.

Visiting SPA and grabbing a sample of that exposed mantle material could provide critical clues about the Moon’s origin and evolution. A sample could also help scientists put a firm date on the impact.

But in order to get the right samples, it’s important to know the best spots to find them.

That’s what Dr. Moriarty and Brown University’s Professor Carlé Pieters had in mind for this study.

The researchers used detailed data from the Moon Mineralogy Mapper, a spectrometer that flew aboard India’s Chandrayaan-1 spacecraft.

They identified four distinct mineralogical regions that form a bullseye pattern within and around the basin.

At the bulleye’s center is a region of what appears to be deposits of volcanic material, a sign that the center of the basin may have been covered by a volcanic flow sometime soon after the impact. That central region is surrounded by a ring of material dominated by magnesium-rich pyroxene, a mineral thought to be plentiful in the lunar mantle. Outside of that is a ring in which pyroxene mixes with the standard crustal rocks of the lunar highlands. Outside of that ring is the basin exterior, where the signatures of impact-related material disappear.

“The findings have some interesting implications for SPA exploration,” the authors said.

“The research suggests, for example, that finding pristine mantle material in the middle of the basin might be a bit tricky because of the large volcanic deposit.”

“Typically the deepest excavation would be in the middle of the crater. But we show that the middle of SPA has been covered over by what looks like a volcanic flow,” Dr. Moriarty said.

“So if you’re looking for mantle, it might be wise to land in the ring surrounding the center, where what appears to be mantle material is highly concentrated.”

“But an ideal landing site might be a spot that has both mantle and volcanic material, because those volcanics are interesting in their own right. Their composition is a little different than that of other volcanic rocks found on the Moon, which suggests they have a unique origin.”

“If these rocks are indeed volcanic, it means that there was a really interesting kind of volcanism happening at SPA,” he added.

“It could be related to the extreme geophysical environment that would have been in place during the formation of the basin. That would be really interesting to look at in more depth.”

“With that in mind, a good spot to land might be near the border of the volcanic center and the pyroxene ring. Another strategy could be to look for a spot where the volcanic material has been pierced by a subsequent impact.”

The scientists found several such craters in the volcanic patch where the pyroxene material has been re-excavated.

“We think going after both mantle and volcanics would make for a richer science return,” Dr. Moriarty said.

Source: Sci News