The new findings provide a boost to the giant-impact theory of the moon’s origin.
Computer models of the giant-impact scenario often say that 70% to 90% of the moon should be made of material from Theia. The problem is that most bodies in the solar system have unique chemical makeups, and so the Earth, Theia — and therefore the moon — should too. However, rock samples that the Apollo missions returned from the moon show that the natural satellite’s composition is uncannily similar to Earth’s, much more similar than such models would predict for versions of elements called isotopes. (Isotopes of an element each have different numbers of neutrons in their atomic nuclei.)
In the new study, researchers conducted new high-precision measurements of oxygen isotope levels in a range of lunar samples. The researchers expanded on previous work by focusing on a wide variety of types of moon rock.
The scientists found that there were subtle but regular differences in oxygen isotopic composition depending on the kind of lunar rock tested, Sharp said. This suggested that prior work that averaged together lunar isotope data while ignoring differences in rock type might not have given an accurate picture of the differences between Earth and the moon.
“Going into this project, it was expected that our results would likely mirror that of previous studies,” study lead author Erick Cano, a stable-isotope geochemist at the University of New Mexico, told Space.com. “The most surprising part of our results was finding the amount of variation that we did between the individual lunar samples.”