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takyon writes:

A new proposed model of the formation of Earth's Moon runs counter to the giant impact hypothesis:

The newly proposed theory by researchers Assistant Prof. Hagai Perets, of the Technion, and Weizmann Institute Raluca Rufu (lead author) and Prof. Oded Aharonson, runs counter to the commonly held "giant impact" paradigm that the moon is a single object that was formed following a single giant collision between a small Mars-like planet and the ancient Earth.

"Our model suggests that the ancient Earth once hosted a series of moons, each one formed from a different collision with the proto-Earth," said co-author Assistant Prof. Perets. "It's likely that such moonlets were later ejected, or collided with the Earth or with each other to form bigger moons." To check the conditions for the formation of such mini-moons or moonlets the researchers ran 800 simulations of impacts with the Earth.

The new model is consistent with science's current understanding of the formation of the Earth. In its last stages of the growth, the Earth experienced many giant impacts with other bodies. Each of these impacts contributed more material to the proto-Earth, until it reached its current size. "We believe the Earth had many previous moons," said Assistant Prof. Perets, who added that, "a previously-formed moon could therefore already exist when another moon-forming giant impact occurs."

A multiple-impact origin for the Moon (DOI: 10.1038/ngeo2866) (DX)

Original Submission