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Found: Mysterious asteroid falling apart at a rate of 1 mile per hour

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Peering deep into the asteroid belt between Jupiter and Mars, scientists have spotted the first disintegrating space rock ever observed.

The rock is crumbing slowly -- its disparate pieces gliding gently away from each other at the sluggish rate of one mile an hour, slower than human walking speed.

The strange space rock first caught scientists' attention in September when the Catalina and Pan STARRS sky survey telescopes detected what looked like an unusually fuzzy object on the far side of the asteroid belt.

PHOTOS: Amazing images from space

A closer inspection with the higher resolution W.M. Keck telescope revealed the fuzziness to be three bodies traveling closely together, enveloped in a cloud of dust the size of Earth.

Further investigation with the even higher resolution Hubble Space Telescope showed that there were actually 10 fragments in the dust cloud and that they were slowly moving away from each other. The largest four pieces were about twice the size of a football field.

"It looks like the asteroid is continuing to break up," said David Jewitt, a planetary scientist at UCLA. "The more recent the pictures, the more pieces we see."

Jewitt explains that the breakup couldn't have been caused by a recent impact because the pieces are moving too slowly away from each other. If an impact were involved, the pieces would have flown apart all at once. The breakup can't be attributed to the gravitational pull of a nearby body either, he said, because there are no other bodies nearby. And the asteroid is too far from the sun for the rapid evaporation of gases that may be trapped inside it to have pushed it apart -- it is simply not warm enough.

So why is this asteroid disintegrating before our eyes? In a paper published in the Astrophysical Journal Letters (and on a very helpful website), Jewitt and his research team suggest that the asteroid's breakup is due to the nearly imperceptible force of tiny photons that have been radiating away from the asteroid toward the sun for billions of years.

"Those departing photons put a little push on the asteroid," Jewitt said. "The force is really very weak, but time is long."

The movement of those photons could have slowly caused the asteroid to spin faster and faster, until its gravity could no longer hold all its pieces together. This explanation only works if the disintegrating asteroid was what's known as a rubble pile -- an assemblage of space rocks loosely held together by gravity, with almost no tensile strength. But rubble piles are abundant in the asteroid belt.

Jewitt said this study helps underscore the power of what he calls "this quite pathetic radiation" to destroy asteroids. On his website, he and his team suggest that rapid rotation may even surpass impact destruction as the way that asteroids die.

This is not the first time Jewitt has spotted something strange in the asteroid belt. He made headlines in November when his discovery of an asteroid with six comet-like tails was released.

"We've been looking at asteroids for 200 years, ever since Ceres was discovered in 1801 -- they are one of the most studied populations in the sky," he said. "But we're still finding things we've never seen before. It is kind of awesome."

If you think asteroids are kind of awesome, you like what I write about. Follow me on Twitter for more like this.

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