Earth, moon aren't oxgyen twins

March 10 (UPI) -- Until now, most planetary scientists thought Earth and its moon were identical oxygen twins, but new research suggests the pair feature distinct oxygen compositions.

The most popular theory for the moon's formation suggest the satellite was born of debris expelled by a massive collision between early-Earth and a proto-planet called Theia.

Lunar samples returned by the Apollo missions revealed an almost identical composition in oxygen isotopes. That would suggest early Earth and Theia featured similar oxygen compositions, an unlikely coincidence.

It's also possible the composition of oxygen isotopes on Earth and Theia thoroughly mixed in the wake of their collision, but scientists have struggled to model such a scenario.

"Our findings suggest that the deep lunar mantle may have experienced the least mixing and is most representative of the impactor Theia," Erick Cano, planetary scientist at the University of New Mexico, said in a news release. "The data imply the distinct oxygen isotope compositions of Theia and Earth were not completely homogenized by the Moon-forming impact and provides quantitative evidence that Theia could have formed farther from the Sun than did Earth."

For the new research, published this week in the journal Nature Geoscience, Cano and his colleagues reanalyzed lunar samples and precisely measured their oxygen isotopic compositions. The samples featured a variety of different rock types, including basalts, highland anorthosites, norites and volcanic glass.

Their analysis showed the exact oxygen isotope composition depended on the makeup of the rock. Differences in how various types of molten debris mixed with the vapor atmosphere in the wake of the collision could explain the variety of oxygen compositions.

"This data suggests that the deep lunar mantle may have experienced the least mixing and is most representative of the impactor Theia," said Zach Sharp, also a planetary scientist at UNM. "Based on the results from our isotopic analysis, Theia would have an origin farther out from the Sun relative to Earth and shows that Theia's distinct oxygen isotope composition was not completely lost through homogenization during the giant impact."

Without the need to produce an exact match between the oxygen compositions of Earth and its moon, scientists will likely find it easier to produce accurate, high-resolution simulations of Earth-Theia impact scenarios.