The Missing Planet Mystery Is Solved: Where Did Theia Come From?

The Solar System’s Missing Planet: What Was Theia?

Our Solar System has 8 planets. This is fundamental astronomical knowledge children learn in school. However, this was not always the case. 4.5 billion years ago, Earth had another neighbor besides Venus and Mars. Recent discoveries by scientists at the Max Planck Institute shed new light on the mysterious planet, called Theia. Where did it come from, and what happened to it?

Planet Theia: The Catalyst for the Moon’s Creation

Scientists have known the answer to the second question for years. In Greek mythology, the Titaness Theia was the mother of Selene, the goddess of the Moon. This myth inspired the name of the planet believed to have caused the formation of Earth’s satellite. Approximately 4.5 billion years ago, Theia, then Mars-sized, collided with Earth. The resulting rock fragments hurled into space began orbiting our planet, eventually merging to form the Moon.

Nevertheless, the planet’s origin and exact properties remain a mystery. An international research team, led by scientists from the Max Planck Institute in Göttingen, Germany, may provide the answers. Their latest study, published in Science, delivers new information regarding the mysterious planet’s genesis.

The Missing Planet’s Secret Locked in Rocks

To uncover Theia’s secrets, scientists utilized isotope analysis. Isotopes are variations of elements that differ in the number of neutrons. Crucially, isotopes were not evenly distributed in the early Solar System. Therefore, discovering a specific isotope on an object can reveal its formation location within our system.

Astronomers Solve the Mysterious Planet’s Puzzle

Researchers examined rock samples from Earth and the Moon (delivered by the Apollo missions). After a detailed examination, they could deduce Theia’s potential chemical composition. Since the Moon formed from a mixture of rocks originating from these two planets, scientists inferred which isotopes came from the now-nonexistent celestial body.

This process resembles looking at a cooked dish and trying to guess the exact ingredients used to create it. Of course, the German researchers did not rely on blind guessing. They used complex mathematical models. Consequently, they reached a surprising conclusion: Theia formed in the inner Solar System, closer to the Sun than Earth.

Planet Theia Was Our Cosmic Neighbor

Thanks to the Max Planck Institute scientists’ discoveries, we now know that Theia formed closer to the Sun than Earth and was most likely our cosmic neighbor—at least for a short time. Ultimately, Theia collided with Earth around 4.5 billion years ago. How exactly did this happen?

One theory suggests that although Theia formed closer to the Sun, it orbited on the same path as Earth, but at a different point. The system may have remained in equilibrium for some time, but eventually, the second planet gained too much mass, which led to the collision with Earth. According to another hypothesis, Theia had its own orbit that destabilized for unexplained reasons.

The Missing Planet Left Its Mark on Earth

Regardless of which theory is true, thanks to the German researchers’ discoveries, we know that Theia formed in the Solar System and likely neighbored Earth. This information offers a completely new perspective on one of the most important events in our planet’s early history. The collision with Theia not only created our Moon but also slightly tilted Earth’s axis of rotation, which is why we experience seasons today.

Read this article in Polish: Rozwiązano zagadkę zaginionej planety. Skąd wzięła się Teja?