Pebbles from Heaven: Tracking planets in the making
By Ron Cowen
Recording radio waves from the region around a young star, astronomers have for the first time documented a key step in the rocky road to planethood: making pebbles. The standard recipe for planet formation starts with a disk of gas, dust, and ice swirling around a newborn star. Particles within the disk coalesce into nuggets and then ever-larger clumps, which over several million years grow into a planet.
Although astronomers have found dusty disks around many young stars, they had never before seen direct evidence that dust grains actually gather into pebbles. To detect the clumps, David Wilner of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and his colleagues relied on the Very Large Array (VLA), a network of radio telescopes near Socorro, N.M. The array picks up centimeter-long radio wave emissions, the radiation that centimeter-size pebbles would tend to emit.