New Delhi, Nov. 21 -- Approximately 4.5 billion years ago, a planet called Theia slammed into the Earth. The impact melted parts of Earth's mantle and sent a massive cloud of debris into space. Over time, this debris came together to form the Moon. Scientists have long wondered what Theia was composed of and where it originated. A new study now suggests that Theia formed in the inner Solar System, closer to the Sun than the Earth.

Early models of the Moon's formation predicted that the Moon should mostly consist of Theia's material. But scientists noticed a puzzle: Earth and the Moon are almost chemically identical, far more alike than two separate planets should be.

"To understand why Earth and the Moon are so similar, we needed to loo...