Over 4.5 billion years ago, a massive collision changed everything. A body named Theia crashed into Earth, resulting in the formation of the moon. New research suggests that this cosmic intruder might have actually formed nearby in the inner solar system. This finding raises intriguing questions about Theia itself—what was it made of? How big was it? And where exactly did it come from?
A team of scientists recently tackled these questions. They analyzed isotopes—variations of elements with different neutron counts—from 15 rock samples gathered on Earth and six from the moon, thanks to the Apollo astronauts. Their aim was to understand Theia’s composition and origins. “The most convincing scenario is that both Earth and Theia originated in the inner solar system,” said Timo Hopp, the research leader. This suggests they were neighbors long before the collision that altered their fates.
Understanding Theia involves examining how isotopes were distributed in the early solar system. It turns out that these isotopes can reveal a lot about where an object formed. For instance, researchers focused on isotopes of iron, chromium, and zirconium. Their analysis showed that Earth and the moon share a remarkable similarity, confirming what scientists suspected. But the researchers didn’t stop there; they explored different theories about Theia’s size and make-up in light of this data.
One interesting clue emerged from Earth’s molten core, which formed long before the collision. Elements like iron and molybdenum accumulated there, making them rare in the mantle above. If any iron exists in the mantle, it likely came after the core formed, potentially from Theia. Thosten Klein from the Max Planck Institute for Solar System Research emphasized, “The composition of a body holds its entire formation history.”
To further understand Theia’s origins, the scientists compared Earth’s composition to meteorites—pieces from asteroids formed around the same time as the planets. Interestingly, Earth’s makeup aligns with known meteorite types from across the solar system, while Theia’s composition appears distinct, hinting at previously unknown materials. This suggests that Theia might have originated closer to the sun than Earth.
This research shines a light on our cosmic past and helps us piece together not only the history of the moon and Earth but also the early solar system’s dynamics. As scientists continue to unravel the mysteries of Theia, our understanding of planetary formation and our place in the universe continues to expand.
For more on the research, check out the journal Science here.
