By Ron Cowen
Rocky planets such as Earth are born through countless acts of violence—the collision and merging of many smaller bodies. A new study reveals that some planets continue to take a beating hundreds of millions of years after they’ve formed.
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The evidence comes from an infrared survey of 266 youthful stars, revealing that 71 of them have disks of dusty debris. The disks are a sign that newborn planets are being clobbered by asteroids and that the asteroids—planet-formation leftovers—are banging together (SN: 10/9/04, p. 227: Planet Signs? Sifting a dusty disk) and making dust that glows at infrared wavelengths.