Where Was Theia Born And Why Is She Called The Earth’s Neighbor A Study Showed

For the first time, German and American planetary scientists have used iron isotopes in moon rocks to determine where Theia came from – the same Mars-sized protoplanet that crashed into the young Earth 4.5 billion years ago and literally gave birth to the Moon. The results of the study were published in Sciene.

Why is it even possible to find out after billions of years?

When the Solar System was just forming, the disk of gas and dust around the young Sun was not uniform. In it, like in a layer cake, different proportions of isotopes—light and heavy versions of the same element—predominated at different distances from the center. Closer to the Sun there is one composition, further away there is another. The planets grew from what was nearby, so their chemical signature is still preserved.

What exactly was measured?

Command under the leadership of Timo Hopp from Max Planck Institute and the University of Chicago took six lunar samples that the Apollo astronauts brought back in 1969–1972, and fifteen terrestrial rocks of different types. The main innovation is that for the first time they have achieved ultra-precise measurement of iron isotopes in mantle rocks. Previously, iron was considered “noisy”: there was too much of it, it oxidized easily and was constantly “mixed” in the magma, so small differences were simply lost. Chromium, titanium and zirconium gave a clean signal, but iron did not. Now scientists have learned to remove all this noise and see a clear picture.

Result: The Earth and the Moon are practically indistinguishable in terms of iron. This confirms old data for other elements, but now the picture is complete.

How the disaster was “rewinded”

Instead of running millions of computer simulations of the collision, scientists took a different approach. They asked the question the other way around: what composition and size should Theia and the early Earth have had before the impact, so that after the catastrophe they would have obtained exactly the isotopic proportions that we see today in the Earth’s mantle and lunar rocks.

It turned out there were few options. Most were immediately dropped because they did not fit with what we know about the formation of planets from meteorites.

Where does excess iron come from in the earth’s mantle?

The young Earth’s iron core formed extremely quickly. Almost all the iron originally in the mantle migrated into the core under the influence of gravity. Therefore, the iron found in the upper layers of the Earth today appeared after the completion of the formation of the core, and its origin is associated with material brought by Theia.

It turns out that almost all the iron from which humanity later forged the first knives, built ships and skyscrapers is the wreckage of a lost planet.

To be on the safe side, scientists looked at than just iron. Zirconium hardly moves – it remained in the mantle from the very beginning and records the composition of the Earth before the collision. Molybdenum and chromium add details about exactly how the core formed. Together these elements gave a clear picture.

Where exactly was Theia born?

The most likely scenario is that Theia formed in the inner solar system, closer to the Sun than the orbit of modern Earth. Its building material was similar to that of Earth, but with small but distinct isotope differences.

“Earth and Theia were probably neighbors,” says Timo Hopp, lead author of the study.

“The composition of a body stores the entire history of its formation, including its place of origin,” adds Thorsten Klein, director of the Max Planck Institute.

Previously, it was believed that Theia could arrive from anywhere – from the asteroid belt, from behind Jupiter, even from the outer clouds. Now the circle has narrowed sharply. New discovery makes giant impact theory much credibleand explains why the Moon and Earth are so similar in composition.It also finally settles the debate about the composition of the Moon – approximately 70-80% of it consists of material from Theia, and not from the Earth’s mantle.