A team of researchers from Brown University and the University of Hawaii have found some mineralogical surprises in the Moon's largest impact crater that could help uncover secrets about the moon’s evolution.

Researchers have used data from India’s Chandrayaan-1 lunar orbiter and found a diverse mineralogy in the subsurface of the giant South Pole Aitken, or SPA, basin, a huge impact crater on the far side of the moon.

“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,” a statement from Brown, said.

According to the study, published in the Journal of Geophysical Research: Planets, the SPA, at 2,500 kilometers across, is the largest impact basin on the moon and perhaps the largest in the solar system.

The researchers also examined smaller craters within the larger SPA basin made by impacts from millions of years after the giant impact that formed the basin. According to the scientists, the smaller impacts uncovered material from deep within the basin that offered up important clues about what lies beneath the surface.

The researchers used Moon Mineralogy Mapper data from Chandrayaan-1 and looked at the light reflected from four craters within the basin to find that the spectra of reflected light provide clues about the composition of the rocks.

“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,” the researchers said.

The varying mineralogy in these central peaks suggests that the SPA subsurface is much more diverse than previously thought.

“We looked in a little more detail and found significant compositional differences between these central peaks,” Dan Moriarty, a graduate student at Brown who led the study, said. “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.”

According to scientists, it is possible that the distinct minerals formed as molten rock from the SPA impact cooled. Earlier studies have suggested that such mineral formation in impact melt is possible. However, it's also possible that the mineral differences reflect differences in rock types that existed before the giant SPA impact.

Moriarty is currently undertaking a much larger survey of SPA craters in the hope of identifying the source of the diversity.