Moon’s biggest crater exposes its hidden lower crust

WASHINGTON - Reports indicate that the biggest and deepest crater on the Moon can provide glimpses of the hidden lower crust of Earth’s natural satellite.

Shortly after the Moon formed, an asteroid smacked into its southern hemisphere and gouged out a truly enormous crater, the South Pole-Aitken basin, almost 1,500 miles across and more than five miles deep.

Asteroid bombardment over billions of years has left the lunar surface pockmarked with craters of all sizes, and covered with solidified lava, rubble, and dust.

Glimpses of the original surface, or crust, are rare, and views into the deep crust are rarer still.

Fortunately, a crater on the edge of the South Pole-Aitken basin may provide just such a view.

According to Noah Petro of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, “We believe the central part of the Apollo Basin may expose a portion of the Moon’s lower crust. If correct, this may be one of just a few places on the Moon where we have a view into the deep lunar crust, because it’s not covered by volcanic material as many other such deep areas are.”

“Just as geologists can reconstruct Earth’s history by analyzing a cross-section of rock layers exposed by a canyon or a road cut, we can begin to understand the early lunar history by studying what’s being revealed in Apollo,” he said.

Petro and his team made the discovery with the Moon Mineralogy Mapper (M3), a NASA instrument on board India’s Chandrayaan-1 lunar-orbiting spacecraft.

Analysis of the light (spectra) in images from this instrument revealed that portions of the interior of Apollo have a similar composition to the impact melt in the South Pole-Aitken (SPA) basin.

As you go deeper into the Moon, the crust contains minerals have greater amounts of iron. When the Moon first formed, it was largely molten.

Minerals containing heavier elements, like iron, sank down toward the core, and minerals with lighter elements, like silicon, potassium, and sodium, floated to the top, forming the original lunar crust.

“The asteroid that created the SPA basin probably carved through the crust and perhaps into the upper mantle. The impact melt that solidified to form the central floor of SPA would have been a mixture of all those layers,” said Petro.

“We expect to see that it has slightly more iron than the bottom of Apollo, since it went deeper into the crust. This is what we found with M3,” he said.

“However, we also see that this area in Apollo has more iron than the surrounding lunar highlands, indicating Apollo has uncovered a layer of the lunar crust between what is typically seen on the surface and that in the deepest craters like SPA,” he added. (ANI)