An extra solar system planet once orbited next to Earth — and it may be the reason we have a moon

A new study suggests that Theia, the Mars-sized planet that collided with early Earth 4.5 billion years ago to create the moon, was a neighboring world that formed in our inner solar system rather than a distant wanderer. Researchers analyzed chemical signatures in lunar samples and Earth rocks, focusing on iron, molybdenum, and zirconium isotopes to trace Theia's origins. Their models indicate Theia contained 5-10% of Earth's mass and formed locally, explaining why Earth and the moon share nearly identical chemistry that has long puzzled scientists.