Our moon formed by planetary collision
By Sid Perkins
UPI Science News
CAMBRIDGE, Mass., July 28 (UPI) -- Scientists say a rogue planet three
times as massive as Mars probably sideswiped Earth 4.5 billion years ago,
and our moon is the result.
The researchers from the University of Colorado at Boulder say an "oblique
impact" vaporized the upper portions of Earth's crust and mantle. Molten
material then sprayed into orbit and formed several small, extremely hot
moonlets that eventually formed a single, large moon.
Robin Canup, lead researcher for the study, presented the results at the
annual meeting of the American Astronomical Society's Division of
Planetary Sciences in Cambridge, Mass.
Many theories on the moon's formation have been proposed. Canup says
detailed analyses of lunar rocks in the 1970s helped astronomers develop
the theory that a giant collision with another planet formed the moon. In
the late 1980s, Harvard researchers proposed that the object that struck
Earth was about the size of Mars. The new CU calculations show that
proposed object is not massive enough to account for our unusually large
moon.
The CU researchers say the "protoplanet" that struck Earth probably was
orbiting the sun somewhere between Earth and Mars before the collision
occurred.
Canup says the CU model does not answer all of the questions about our
moon's formation, however. Although the proposed size of the protoplanet
gives the correct amount of material needed to form the moon, she says the
model also yields an Earth that is spinning too quickly.
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