collisions between larger bodies, followed by a cascade that grinds down the objects to the observed small grains. For collisions to occur in a debris disk, the bodies must be gravitationally perturbed sufficiently to create relatively large collisional velocities. A planetary system around the star can cause such perturbations, as can a binary star companion or the close approach of another star. The presence of a debris disk may indicate a high likelihood of exoplanets orbiting the star. Furthermore, many debris disks also show structures within the dust (for example, clumps and warps or asymmetries) that point to the presence of one or more exoplanets within the disk. The presence or absence of asymmetries in our own trans-Neptunian belt remains controversial although they might exist. Known belts Belts of dust or debris have been detected around many stars, including the Sun, including the following: The orbital distance of the belt is an estimated mean distance or range, based either on direct measurement from imaging or derived from the temperature of the belt. The Earth has an average distance from the Sun of 1 AU. See also Accretion disk Asteroid belt Protoplanetary disk References External links Debris disk