Posted at 10:29 AM ET, 08/04/2011

Moon’s lopsided shape may be thanks to collision with another moon (Video)


A full moon rises over the Juscelino Kubitschek Memorial in Brasilia. (Ueslei Marcelino/Reuters)
There always seemed a planetary discrepancy: The Earth got just one measly moon. Sure, it’s lovely and bright in the sky, but it always seemed a bit lonesome. Saturn has 62 moons. Jupiter has 64. Pluto’s not even a full planet anymore and it gets four moons.

Well, a new study published in Nature magazine says our moon might not have always been so solitary a lunar soul.

Researchers propose a second satellite circled early Earth, until the gravitational force of the sun pulled the smaller moon straight into our moon for a cosmic collision. The impact would be to blame for the moon’s funky asymmetry. Here’s a graphic depiction of what the University of Santa Cruz researchers theorize took place:
This diagram provided by Martin Jutzi and Erik Asphaug of the University of California at Santa Cruz via Nature shows a simulation of four stages of a collision between the moon and a companion moon, 4 percent of the lunar mass, about 4 billion years ago. (AP)

This is not the first time science has tried to explain the moon’s different sides. Others have posited tidal forces or the way the moon’s crust cooled when it first formed.

“The fact that the nearside of the moon looks so different to the farside has been a puzzle since the dawn of the space age,” Francis Nimmo, one of the authors of a 2010 paper in Science proposing tidal forces as the cause, told Nature magazine.

(Personally, I like the latest theory best: a space showdown with our moon earning its unique spot in the sky.)

Watch:

By  |  10:29 AM ET, 08/04/2011

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