The Asteroid Breakup: Disintegration Right Before Astronomers' Eyes, For The First Time Ever
Billions of asteroids are orbiting the sun in a rocky band between Mars and Jupiter known as the Asteroid Belt. The belt is a would-be planet: when the solar system formed some 4.5 billion years ago, gravity pulled rocks together into planets like Earth and Mars. But Jupiter's gravity stunted these asteroids in the belt, and they've been there ever since, ancient fragments frozen in time.
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Until on Sept. 15, 2013, astronomers saw something strange. Sky survey telescopes caught sight of something fuzzy, and scientists tipped off colleagues at the Keck Observatory in Hawaii. On Oct. 1, those astronomers trained their telescope back on the object and "revealed three co-moving bodies embedded in a dusty envelope that is nearly the diameter of Earth," said the University of California, Los Angeles.
In some ways, it resembled a comet — a kind of icy rock that spends most of its life in the farthest depths of the solar system. When the sun's gravity catches a comet just right, it plunges toward the blazing star, shedding a hazy tail of steam and dust. But this clearly was no comet; those don't have multiple nuclei, and they don't orbit in the Asteroid Belt. To solve the mystery, scientists called in the big guns.
"The Keck telescope showed us that this asteroid was worth looking at with Hubble," said David Jewitt, a UCLA astronomer who wrote about the discovery Wednesday in Astrophysical Journal Letters. The Hubble Telescope, with its resolution capable of seeing galaxies thousands of lightyears away, trained its lens on this strange object just 300 million miles from the sun. When the photos came back, the object was revealed to be 10 objects, all asteroids that were disintegrating extremely slowly, with the largest fragments measuring about 600 feet across.
The breakup was so slow that scientists ruled out collision as the cause — that would have been much more violent. Another potential cause is embedded ice sublimating in the sun's heat and shattering the rock. But they ruled out that, too, because the asteroid has never flinched in its trajectory; it's always been the same distance from the sun, indicating no changes in temperature. In fact, this asteroid, now called P/2013 R3, had been zipping through space unchanged for more than 4 billion years until suddenly last year it all just crumbled. "Seeing this rock fall apart before our eyes is pretty amazing," says Jewitt in a statement.
With the obvious answers eliminated, Jewitt made a best guess. He said the long exposure to sunlight had slowly caused the asteroid's rotation speed to increase. Like children on an ever-accelerating merry-go-round, the components eventually separated. Jewitt figures the integrity of the rock had already been weakened by small, nondestructive collisions with other asteroids. Scientists think a lot of asteroids are loosely held together like this; they call them "rubble piles." In this case, the centrifugal force finally did it in.
According to UCLA: "The asteroid's remnant debris, weighing in at 200,000 tons, in the future will provide a rich source of meteoroids, Jewitt said. Most will eventually plunge into the sun, but a small fraction of the debris may one day enter the Earth's atmosphere to blaze across the sky as meteors."
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