By Ron Cowen
Like a crab scuttling through sand, an orbiting planet leaves a telltale trail in the dust surrounding its parent star. Astronomers began scouring nearby stars for such trails nearly 2 decades ago, but telescopes provided only fuzzy images. With the keen-sighted instruments available today, however, the dust trails are coming into sharper focus, opening the way to finding and characterizing the properties of hundreds of planets beyond the solar system.
Doughnut-shape patterns of dust, or debris disks, are much easier to detect than planets themselves because the disks have a much larger surface area. Recent pictures of debris disks around 10 or so nearby stars show gaps, arcs, rings, warps, clumps, and bright patches.