  The Sun and >15 percent of nearby stars are surrounded by dusty debris disks
that must be collisionally replenished by asteroids and comets, as the dust
would otherwise be depleted on <10 Myr timescales (ref. 1). Theoretical studies
show that disk structure can be modified by the gravitational influence of
planets (ref. 2-4), but the observational evidence is incomplete, at least in
part because maps of the thermal infrared emission from disks have low linear
resolution (35 AU in the best case; ref. 5). Optical images provide higher
resolution, but the closest examples (AU Mic and Beta Pic) are edge-on (ref.
6,7), preventing the direct measurement of azimuthal and radial disk structure
that is required for fitting theoretical models of planetary perturbations.
Here we report the detection of optical light reflected from the dust grains
orbiting Fomalhaut (HD 216956). The system is inclined 24 degrees away from
edge-on, enabling the measurement of disk structure around its entire
circumference, at a linear resolution of 0.5 AU. The dust is distributed in a
belt 25 AU wide, with a very sharp inner edge at a radial distance of 133 AU,
and we measure an offset of 15 AU between the belt's geometric centre and
Fomalhaut. Taken together, the sharp inner edge and offset demonstrate the
presence of planet-mass objects orbiting Fomalhaut.
