Far-Flung Space Crash May Help Solve Mystery of Moon's Formation

Richard A. Lovett
for National Geographic News
March 15, 2007

Scientists have found fragments they say are from a massive, far-flung collision that may help explain the formation of Earth's moon.

The spectacular smashup took place between two dwarf planets, one of them nearly as large as Pluto, near the dawn of the solar system. (Related story: "Pluto Not a Planet, Astronomers Rule" [August 24, 2006].)

The crash may also someday create the biggest and brightest comet of all time.

Astronomer Michael Brown of the California Institute of Technology found the five fragments while studying the Kuiper belt, located in the solar system's outermost reaches.

The fragments resemble 2003 EL61, the Kuiper belt's mysterious third largest object, suggesting all six bodies were formed in a single violent crash, Brown said.

The finding will appear in tomorrow's issue of the journal Nature.

Crash Landing

Measuring about 930 miles (1,500 kilometers) across, 2003 EL61 had puzzled scientists ever since its discovery, because it's oblong and spins end-over-end so fast that it completes a full revolution every four hours.

It's like a U.S. football "that's a bit deflated and stepped on," Brown said.

2003 EL61 is also unusually dense, suggesting it is the former core of a larger planet that got clobbered sometime in its history, Brown added.

The glancing blow made 2003 EL61 spin, knocked off its icy outer mantle, and created two moons that are almost pure chunks of ice, Brown theorizes.

Now, however, Brown says he has found more remnants of the crash. He and his team were studying the surface composition of Kuiper belt objects when they realized that five of them stood out, he said by email.

Continued on Next Page >>


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