Tonight's Sky
Sun
Sun
Moon
Moon
Mercury
Mercury
Venus
Venus
Mars
Mars
Jupiter
Jupiter
Saturn
Saturn

Tonight's Sky — Change location

OR

Searching...

Tonight's Sky — Select location

Tonight's Sky — Enter coordinates

° '
° '

Mineral analysis of lunar crater deposit prompts a second look at the impact cratering process

Researchers have discovered a rock body across the floor of Copernicus Crater that appears to bear the mineralogical signature of rocks that were present before the impact that made the crater.
RELATED TOPICS: SOLAR SYSTEM | MOON
Lunar-liquid-rock
Pre-existing mineral deposits on the Moon (sinuous melt, above) have survived impacts powerful enough to melt rock. Not detectable in the crater image (inset), deposits are visible only in light at certain wavelengths. // NASA and Deepak Dhingra
Despite the unimaginable energy produced during large impacts on the Moon, those impacts may not wipe the mineralogical slate clean, according to new research led by Brown University geoscientists.

Researchers have discovered a rock body with a distinct mineralogy snaking for 18 miles (29 kilometers) across the floor of Copernicus Crater, a 60-mile-wide (100km) hole on the Moon’s nearside. The sinuous feature appears to bear the mineralogical signature of rocks that were present before the impact that made the crater.

The deposit is interesting because it is part of a sheet of impact melt, the cooled remains of rocks melted during an impact. Geologists had long assumed that melt deposits would retain little pre-impact mineralogical diversity.

Large impacts produce giant cauldrons of impact melt that eventually cool and reform into solid rock. The assumption was that the impact energy would stir that cauldron thoroughly during the liquid phase, mixing all the rock types together into an indistinguishable mass. Identifying any pre-impact mineral variation would be a bit like dumping a four-course meal into a blender and then trying to pick out the potatoes.

But this distinct feature found at Copernicus suggests that pre-existing mineralogy isn’t always blended away by the impact process.

“The takeaway here is that impact melt deposits aren’t bland,” said Deepak Dhingra from Brown University in Providence, Rhode Island, who led the research. “The implication is that we don’t understand the impact cratering process quite as well as we thought.”

Copernicus is one of the best-studied craters on the Moon, yet this deposit went unnoticed for decades. It was imaging in 83 wavelengths of light in the visible and near-infrared region by the Moon Mineralogy Mapper (M3) that made the deposit stand out like a sore thumb.

M3 orbited the Moon for 10 months during 2008–09 aboard India’s Chandrayaan-1 spacecraft and mapped nearly the whole lunar surface. Different minerals reflect light in different wavelengths at variable intensities. So by looking at the variation at those wavelengths, it’s possible to identify minerals.

In the M3 imaging of Copernicus, the new feature appeared as an area that reflects less light at wavelengths around 900 and 2,000 nanometers, an indicator of minerals rich in magnesium pyroxenes. In the rest of the crater floor, there was a dominant dip beyond 950nm and 2400nm, indicating minerals rich in iron and calcium pyroxenes. “That means there are at least two different mineral compositions within the impact melt, something previously not known for impact melt on the Moon,” Dhingra said.

It is not clear exactly how or why this feature formed the way it did. That’s an area for future study. But the fact that impact melt isn’t always homogenous changes the way geologists look at lunar impact craters.

“These features have preserved signatures of the original target material, providing ‘pointers’ that lead back to the source region inside the crater,” said James W. Head III of Brown University. “Deepak’s findings have provided new insight into the fundamentals of how the cratering process works. These results will now permit a more rigorous reconstruction of the cratering process to be undertaken.”

0

JOIN THE DISCUSSION

Read and share your comments on this article
Comment on this article
Want to leave a comment?
Only registered members of Astronomy.com are allowed to comment on this article. Registration is FREE and only takes a couple minutes.

Login or Register now.
0 comments
ADVERTISEMENT

FREE EMAIL NEWSLETTER

Receive news, sky-event information, observing tips, and more from Astronomy's weekly email newsletter.

ADVERTISEMENT
ADVERTISEMENT
BoxProductcovernov

Click here to receive a FREE e-Guide exclusively from Astronomy magazine.

Find us on Facebook

Loading...