A new study published in Science may have solved one of the biggest mysteries in planetary history: where Theia, the planet that collided with early Earth and created the Moon, actually came from.
Researchers from the Max Planck Institute for Solar System Research and the University of Chicago compared the chemical signatures of lunar samples, terrestrial rocks, and meteorites. By examining isotope ratios with unprecedented precision, they reconstructed the likely "ingredient list" of Theia and the proto-Earth before their collision 4.5 billion years ago.
Theia and Earth were neighbors
The analysis points to a clear trend. Most of Theia's building material appears to have originated in the inner solar system, possibly even closer to the Sun than early Earth. The results suggest that the two planets were neighbors long before their violent encounter reshaped the Earth-Moon system.
The team of researchers from the Max Planck Institute for Solar System Research and the University of Chicago reached this conclusion by running multiple formation scenarios and eliminating combinations that did not match the current isotope fingerprints found in lunar and terrestrial rocks.
While Earth's composition can largely be explained using known meteorite classes, Theia's composition appears to include material not yet represented in meteorite collections, another hint of its inner-solar-system origin. Although many details of the giant impact remain uncertain, the findings narrow down Theia's birthplace more than ever before.