Apollo 17 rock sample suggests giant meteorite impacts shaped moon’s surface

Meteorites similar to the one that killed off the dinosaurs may have helped shape what the moon looks like.

A sample of moon rock brought back by the Apollo 17 crew in 1972 may have helped reveal some surprising lunar history. In a study published to Nature Astronomy, a group of international scientists led by the Royal Ontario Museum in Canada has found that the formation of ancient rocks on the moon might be directly linked with powerful meteorite impacts.

In one particular rock, the researchers found historic evidence for cubic zirconia that could only have formed when rocks are heated to temperatures of above 2,300 degrees Celsius. The researchers said this in itself could only be achieved by the melting of the outer layer of a planet in a large impact event, such as the one that killed off the dinosaurs on Earth.

While the sample has since reverted to a more stable phase to become baddeleyite, the crystal retains the distinctive evidence of a high-temperature structure. Closer analysis showed that the baddeleyite formed more than 4.3bn years ago.

‘The largest one I have ever seen’

“Rocks on Earth are constantly being recycled, but the moon doesn’t exhibit plate tectonics or volcanism, allowing older rocks to be preserved,” said researcher Dr Lee White.

“By studying the moon, we can better understand the earliest history of our planet. If large, super-heated impacts were creating rocks on the moon, the same process was probably happening here on Earth.”

Co-author of the study, Dr Ana Cernok, said that when the team first looked at the samples, she was amazed at how differently the rock looked to others collected by the Apollo 17 crew.

“Although smaller than a millimetre, the baddeleyite grain that caught our attention was the largest one I have ever seen in Apollo samples,” she said.

“This small grain is still holding the evidence for formation of an impact basin that was hundreds of kilometres in diameter. This is significant, because we do not see any evidence of these old impacts on Earth.”