Researchers found "mineralogical surprises" in a large crater on the moon's surface.
A research team looked at data from the Moon Mineralogy Mapper that flew aboard India's Chandrayaan-1 lunar orbiter, and found surprising mineral diversity in the South Pole Aitken (SPA) basin, a Brown University news release reported.
The 2,500-kilometers-across (about 1553 miles) impact crater may be the largest in our solar system. The behemoth crater is so hot it turns molten rock into "slush," so researchers weren't hopeful of finding much evidence of ancient minerals.
The team was able to find mineral signatures that could have been from an impact four million years ago.
The team looked at smaller craters within the SPA basin that formed after the large impact. The smaller impacts revealed evidence of the ancient mineral makeup down below. The team focused on four central peaks, which occur "when material under the impact zone rebounds, forming an upraised rock formation in the middle of the crater," the news release reported. The tops of the peaks contain "pristine" material from below the impact zone.
The team looked at how light reflected off the four peaks to determine the mineral makeup of the rocks. The researchers determined the peaks varied in composition; some had high magnesium contents while one contained "distinct mineral deposits." This could be due to a "sampling" of debris from both the moon's upper and lower crusts.
"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," Brown graduate student and study leader Dan 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 team hopes to discover what caused the unexpected mineral diversity. Distinct minerals may have formed in the rock as the SPA impact cooled. The diversity could also indicate mineral makeups that exited long before the giant impact even occurred.
"If you do the impact scaling from models, [the SPA impact] should have excavated into the mantle," Moriarty said. "We think the upper mantle is rich in a mineral called olivine, but we don't see much olivine in the basin. That's one of the big mysteries about the South Pole Aitken basin. So one of the things we're trying to figure out is how deep did the impact really excavate. If it melted and excavated any material from the mantle, why aren't we seeing it?"
If there really was no olivine to be found it would have significant implications as to how the moon was formed.
