More evidence of extrasolar planets.

Still reeling from reports of three planets orbiting nearby stars? Christopher Burrows has some advice: Don't forget about one of the original candidates for a planetary system-the dusty disk surrounding the star Beta Pictoris. Mounting evidence suggests that circumstellar disks provide the spawning ground for planets. Under the right conditions, ice and dust in these doughnut-shaped objects collide and clump together, coalescing into new worlds.

The disk around Beta Pictoris has garnered special attention, in part because it contains an intriguing gap near its center, as if a planet had swept the area clear of debris. Now, the Hubble Space Telescope has taken a closer look at the central part of the disk and has found another piece of tantalizing evidence.

The inner region of the disk, just outside the gap, has a warp, or tilt, of about 3 degrees relative to the outer parts of the disk. Burrows, of the Space Telescope Science Institute in Baltimore, suggests that the gravitational tug of an unseen planet circling Beta Pictoris created the tilt.

The planet, he says, would reside somewhere in the 8-billion-kilometer-wide clear zone in the center of the disk. The size of the warp indicates that the planet has a mass between one-twentieth and 20 times that of Jupiter. Burrows concedes that the tug of a passing star could also have produced the warp, but he argues that such an encounter would have distorted the entire disk, not just the inner part. He adds that for the warp to persist, some object must continually be "twisting the disk and keeping [it] out of a basic flat shape."