There is no definitive answer to the question of whether Earth has a sister planet. Some astronomers believe that Earth may have had a sister planet, called Theia, which collided with Earth early in its history. The collision is thought to have formed the Moon.

Other astronomers believe that Earth never had a sister planet, and that the Moon is the product of a giant impact between Earth and another, smaller body.

There are several pieces of evidence that support the theory of a sister planet. For example, the Moon is very large compared to Earth, and it has a much lower density than Earth. This suggests that the Moon may have formed from a separate planet, rather than from the same material as Earth.

Additionally, the Moon has a very unusual orbit. It is tilted at an angle of about 5 degrees, and its orbit is not circular, but rather elliptical. This could be explained by the fact that the Moon was formed from a collision, which would have caused its orbit to be disrupted.

However, there are also several pieces of evidence that contradict the theory of a sister planet. For example, the Moon's composition is very similar to Earth's, suggesting that they formed from the same material.

Additionally, the Moon's orbit is very stable, which would not be the case if it had formed from a collision.

Ultimately, the question of whether Earth has a sister planet remains a mystery. There is evidence to support both sides of the theory, and it is possible that we may never know for sure.