A Hazy Sign of Distant Planets?

Long before astronomers detected possible planets around other stars, a hint that they might exist came from the 1984 discovery of a dusty ring around the star beta-Pictoris--perhaps the raw material of a future planetary system. Now two astronomers have found a second dusty ring, this one around a binary star system. The discovery, reported in tomorrow's issue of Nature, heartens planet hunters by suggesting that the first ring wasn't a fluke.

Using the telescope on Hawaii's Mauna Kea, astronomers Paul Kalas and David Jewitt of the University of Hawaii observed two bright blue stars about 1000 light-years away. After filtering out the radiation streaming from the stars themselves, they saw a faint band of light surrounding the darkened patch of sky. The duo concluded that it's probably a ring of dust reflecting the starlight.

"It's an important observation if they've found it," says astronomer Chris Burrows of the Space Telescope Science Institute in Maryland. "It's something people have been looking for for several years ... but I want to see it confirmed." Dana Backman, an astronomer at Franklin and Marshall College in Lancaster, Pennsylvania, agrees: "I tend to believe it's a disk. ... It's hard to believe that there's such symmetry accidentally, but it still needs to be confirmed. I'm rooting for the disk to be real."

The dust may be the stars' primordial gas and dust cloud that just "stayed around for a while," perhaps as raw material of planets, says Jack Lissauer, an astronomer at the NASA Ames Research Center in California. But Kalas, now at the Max Planck Institute for Astronomy in Heidelberg, Germany, argues that's unlikely. The binary stars are about 1 million years old, he says, so their radiation would have had plenty of time to sweep away any remaining primordial dust. Instead, Kalas suggests that the dust ring is replenished by collisions between small planets. "These are not disks where planets form; they are a consequence of planet formation," he says.

Either way, the finding "reinforces the belief that planets are quite abundant," Lissauer says. If binary stars could have planets, he says, then out there could be planetary systems "not even imagined by science-fiction authors."

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