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Thursday, October 29, 2020  Spokane, Washington  Est. May 19, 1883
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When Planets Collide Scientists Now Theorize The Moon Was Formed By Giant Crash

Robert S. Boyd Knight-Ridder

Astronomers have come up with a new answer to an age-old question: Where did the moon come from?

They now suspect that a wandering planet three times bigger than Mars sideswiped the Earth 4.5 billion years ago, destroying itself but blasting enough matter into space to form our lunar companion.

Until recently, the moon was believed to have been formed independently by the slow buildup of particles of gas and dust until it reached its present size and was captured by Earth’s gravity.

If the new theory is correct, the moon that has inspired lovers, poets and myth-makers throughout human history is the result of a massive traffic accident in space - a much more dramatic birth than the conventional view. And similar collisions could explain a lot about how the solar system was shaped.

According to Robin Canup, an astrophysicist at the University of Colorado, the heat created by such a tremendous collision would have vaporized much of the Earth’s crust, which was then just forming.

The fiery material spread into a gaseous disk spinning around the Earth, she suggested. The disk then broke apart into a handful of extremely hot “moonlets” which eventually coalesced into today’s single large moon.

The “giant impact theory” is based on computer simulations performed by Canup and colleagues at Colorado’s Laboratory for Atmospheric and Space Physics. Canup’s paper was made available in advance of her scheduled presentation here Thursday at a meeting of 600 planetary scientists, sponsored by the American Astronomical Society.

The notion that two planet-size objects banged into each other to form the moon was first proposed by Harvard University researchers 10 years ago.

The new computer simulations have strengthened the theory, but indicate that the planet would have to have been much bigger - 2-1/2 to three times the size of Mars.

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