Disks of dust: planet-stuff surrounds other sunlike stars.

Two orbiting observatories have for the first time homed in on planetary debris circling sunlike stars. The Hubble Space Telescope has taken the first visible-light image of the dusty debris around a young star with a sunlike mass. Colliding bodies left over from planet formation probably generated the debris. The Spitzer Space Telescope has found the first hints that six much older stars known to have planets also host debris disks.

Most previously detected debris disks had turned up around much more massive stars (SN: 10/23/04, p. 262).

The star examined by Hubble is between 30 million and 250 million years old. Even as planetary bodies around that star slam into each other and generate dust, material there might be forming new planets. In contrast, Spitzer examined the region around stars with an average age of 4 billion years, about as old as our sun, which probably have fewer dust-generating collisions.

The findings illuminate the process by which our solar system evolved, says Spitzer scientist Charles Beichman of NASA's Jet Propulsion Laboratory in Pasadena, Calif. He and Hubble scientist David Ardila of Johns Hopkins University in Baltimore presented the new findings this week during a NASA briefing.

In the Hubble study, Ardila's team used the observatory's Advanced Camera for Surveys to image a disk--more like a fat ring-around the young star HD 107146, 88 light-years from Earth. The disk is thicker and bigger than the Kuiper belt, the dusty reservoir of comets in the outer reaches of our solar system.

With a radius of 130 times the Earth-sun distance, HD 107146's ring extends roughly four times as far from its star as the current Kuiper belt extends from the sun. The ring could contain more than 1,000 times as much dust as our solar system does, notes Ardila.

In a model developed by Scott Kenyon of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and Benjamin Bromley of the University of Utah in Salt Lake City, the ring could arise if HD 107146 is at the older end ofits estimated age range. Such a star could form 25 to 50 Pluto-size planets sprinkled throughout the debris-disk region. The planets' gravity would cause surrounding debris to collide and shatter, generating the doughnut shape.

In the Spitzer study, Beichman's team surveyed 26 mature, sunlike stars known to have giant planets. Spitzer can't directly image disks around these stars, but the excess infrared emission it detected around six of these stars indicates that each has a debris disk.