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The solar system's earliest asteroids may have all been massive

A new analysis offers new clues to how planetary building blocks form

2:00pm, August 3, 2017
asteroid wreckage illustration

ALL IN THE FAMILY  By identifying the wreckage of past asteroid crashes (illustrated) known as asteroid families, astronomers can ignore those fragments and pick out asteroids that have remained intact since the early solar system. 

The solar system’s first asteroids were probably born big.

Rather than slowly amassing bulk over time, the original members of the asteroid belt rapidly formed into rocks hundreds of kilometers across, researchers propose. This finding, reported online August 3 in Science, may help resolve a long-standing debate over the origins of planetesimals — the giant space rocks that populated the asteroid belt and constructed the planets.

Astronomers set out to examine competing explanations for planetesimal formation. One says grains in the dusty disk surrounding the baby sun clumped together bit by bit over millions of years to form objects that ranged from meters to hundreds of kilometers across — about the size range in the asteroid belt today. The second idea argues that swarms of centimeter-sized pebbles almost instantaneously collapsed under their collective weight to

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