Theia (hypothetical planet)

A long time ago, a planet hit Earth.

This planet was called Theia. It was a big world. It was about the size of Mars. Theia hit the early Earth. This crash sent bits into space. Those bits came together. They made our Moon.

Some parts of Theia may still be inside Earth. We think this happened a very long time ago. Now we have a Moon in the sky!

A long time ago, a planet hit the early Earth.

Scientists think this planet was named Theia. It was a very big world. Some think it was the size of Mars. Other ideas say it was much larger. It might have been almost as big as Earth!

Theia may have lived near Earth's orbit. It might have stayed at stable spots called Lagrange points. These are special places in space. Then, gravity from other planets changed its path. Theia crashed into the early Earth. This was a giant impact. This crash sent many pieces of rock into space. These pieces joined together to make the Moon. Some parts of Theia may still be inside Earth today. We can see these parts deep in the Earth's mantle. The mantle is the layer below the crust. Rocks from the Moon and Earth look very much alike. This helps us think the crash really happened.

Scientists think a lost planet once lived in our solar system. This planet was named Theia. It is a hypothetical world, which means it is an idea based on clues. Theia may have been the reason we have a Moon today. This idea is called the giant-impact hypothesis.

It is a very important part of our early history. The big crash happened about 4.5 billion years ago. This event changed the Earth forever.

Theia likely stayed in a stable spot near Earth's orbit. These spots are called Lagrange points, specifically L4 or L5. These points are special places where gravity keeps things steady. Then, the gravity from Venus or Jupiter moved Theia. This change sent Theia on a path toward the early Earth.

The two worlds hit each other in a massive collision. This crash threw many pieces of rock into space. Over time, these pieces joined together to form the Moon.

Many people have wondered how the Moon began. For a long time, there were four main ideas. One idea was that a single body split into two. Another idea was that Earth's gravity captured a passing object. Some thought Earth and the Moon formed at the same time. The Theia-impact scenario is the one many scientists study now.

This theory helps explain why the Moon and Earth look similar.

We have many clues about the size of Theia. Some scientists say it was about the size of Mars. This would make its mass 10% of our Earth. Other experts think it was much larger than that. It might have been 30% or even 45% of Earth's mass.

Some studies also suggest Theia might have brought water to Earth. This would happen if it formed far away from the Sun.

We can see the truth of this story in rocks. Apollo astronauts brought lunar rocks back to study them. These rocks look very much like the Earth's crust. This similarity suggests the two worlds were once joined.

Some parts of Theia might still be inside our planet. Scientists found large areas deep in Earth's mantle that might be Theia's remains. These areas are called low-shear-velocity provinces. They are like hidden pieces of a lost world.

Theia is a hypothetical planet from the early history of our Solar System. Scientists use the term hypothetical because we have not seen it directly. Instead, they use clues to build a theory about its existence. This idea is central to the giant-impact hypothesis. This hypothesis explains how our Moon was created.

This event likely occurred about 4.5 billion years ago. It was a moment that fundamentally changed the Earth and its surroundings.

To understand how this happened, we must look at Theia's orbit. It is believed that Theia stayed near Earth's orbit in a stable position. These stable spots are known as the L4 or L5 Lagrange points. At these points, the gravity of the Earth and Sun works together to hold an object in place. However, this stability did not last forever. Gravitational perturbations, or shifts caused by gravity, likely changed its path. The massive gravity of planets like Venus or Jupiter may have pulled Theia away from its stable spot. This set Theia on a collision course with the proto-Earth.

The collision itself was a massive event. Early versions of the theory suggested a glancing blow. In that scenario, pieces of both planets were thrown into space. These pieces might have formed one Moon or two moons that eventually merged. However, newer evidence from 2016 suggests a different story. The impact may have actually been a head-on collision. In this version, the remains of Theia are now part of both the Earth and the Moon.

Such a massive crash would have been incredibly violent.

Scientists have debated the exact size of this lost world. Many suggest Theia was roughly the size of Mars. This would mean its mass was about 10% of the modern Earth. Other researchers propose it was much larger. Some estimates suggest a mass of 30%. Other studies suggest it could be 40% to 45% of Earth's mass. In these larger scenarios, Theia would have been nearly equal to the proto-Earth. Its size and mass change how we model the resulting impact.

Before the Theia theory became popular, astronomers had other ideas. They wondered if the Moon split from a single body. Others thought Earth's gravity simply captured a passing object. Some believed the Earth and Moon grew at the same time from the same disk of material. The Theia-impact scenario gained strength because of lunar samples. Apollo astronauts brought rocks back from the Moon to Earth. These rocks have an isotopic composition very similar to Earth's crust. This similarity suggests the two bodies were once mixed together.

We can still find clues of Theia deep inside our own planet. Scientists have detected large low-shear-velocity provinces in the Earth's lower mantle. These are large areas where seismic waves move differently. Computer simulations in 2023 reinforced the idea that these could be fragments of Theia.

There is also a debate about where Theia formed. If it formed far from the Sun, it might have brought water to Earth. This is based on studies of oxygen isotope composition in lunar rocks. Some rocks show more variation than expected, which might reflect Theia's original composition.

The story of Theia connects many different fields of science. It links planetary geology with the study of orbital mechanics. It also connects the history of our Solar System to the chemistry of rocks. Understanding this collision helps us understand why Earth is the way it is today. It explains our Moon, our water, and even the structure of our deep interior. Theia remains a fascinating piece of a much larger cosmic puzzle.