Moon Formed by Ring Spun From Earth, Study Says

The moon is not made of material that broke from the Earth in one piece but from a ring spun off from Earth when the planet was young and fast, an Indiana University astronomer said in a report to be issued today.

In his new explanation of how the moon was formed, Richard H. Durisen, an astronomy professor at the university, used a computer to simulate the Earth when it was fluid and rotating rapidly. He found that the result was a single body surrounded by a ring of material.

“To the extent of the computations we’ve done so far, it demonstrates the moon would not have broken off as a single piece,” Durisen said.

The National Science Foundation, which supported Durisen’s work, said the theory that the moon was a spinoff of Earth was proposed first by George Darwin, son of the English naturalist Charles Darwin, in 1879.

One problem with that theory is that the moon does not have enough angular momentum in its orbit to have been formed in one piece, the foundation said. Under Durisen’s theory, the missing momentum would have been in the rest of the ring, which vanished.

The new theory could also explain why the moon has so little iron, while the Earth has so much. The iron would have settled to the Earth’s core, where it lies now, and the outer part could have broken away to form the ring.