A new model of how the Earth's moon formed is challenging the idea that
the early Earth was struck by a Mars-sized body, ejecting material that
would become the moon. The new research, by Dr. Robin M. Canup of the
Southwest Research Institute, indicates that both bodies in the
collision were four to five times the mass of Mars, roughly half the
mass of today's Earth.

After colliding once, the two
similar-sized bodies re-collided and then merged briefly before
separating into an early Earth surrounded by a disk of material that
would coalesce into the Moon. The re-collision and merging left the two
bodies with the similar chemical compositions seen today. One of the
challenges to longstanding theory of the collision is that it likely
would have left the Earth and Moon with different chemical compositions.


The research, funded by NASA’s Lunar Science Institute,
Moffett Field, Calif., was published today in the journal Science
online.

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Image courtesy of Southwest Research .