Double disks

Astronomers have confirmed that the nearby star Beta Pictoris has two disks of dust orbiting it, each of which contains debris that’s probably the remnants of planet formation. The disks orbit the star at slightly different inclinations, an indication that if Beta Pictoris harbors unseen planets, they circle the star in more than one plane.

Scientists first imaged a single debris disk around Beta Pictoris in 1985. A decade later, the Hubble Space Telescope found an apparent warp in the disk. Researchers have suggested that this warp is actually a second dust disk, tilted at about 4° from the main disk (SN: 10/9/04, p. 227: Planet Signs? Sifting a dusty disk).

New images from Hubble’s Advanced Camera for Surveys provide firm evidence of the second disk, David Golimowski of Johns Hopkins University in Baltimore and his colleagues report in the June Astronomical Journal. To image the faint disk, the team had to block the glare from the star, which lies 63 light-years from Earth.

A computer model developed by a separate team of researchers suggests that the second disk was created when a massive, unseen planet in a tilted orbit lured bits of rock and ice—leftovers from the planet-making process—from the main disk. The chunks continually collide to replenish the dust, which the star’s radiation constantly pushes away.

Finding a tilted disk isn’t a great surprise, notes Golimowski. Planets in our solar system have orbits inclined to that of Earth by several degrees.

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