SMRTR Science & EngineeringNov 20, 2025Scientific American

Lost Planet Theia that Created the Moon Came From the Inner Solar System

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Scientists have determined that Theia, the ancient planet that collided with Earth 4.5 billion years ago to create the moon, originated from the inner solar system closer to the sun than Earth. By analyzing iron, molybdenum, and zirconium isotopes in Earth rocks and lunar samples, researchers discovered that Theia was a rocky planet with a metallic core containing 5-10% of Earth's mass, solving the long-standing mystery of this lost planet's origins.

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