  We propose that the eccentricity and sharpness of the edge of Fomalhaut's
disk are due to a planet just interior to the ring edge. The collision
timescale consistent with the disk opacity is long enough that spiral density
waves cannot be driven near the planet. The ring edge is likely to be located
at the boundary of a chaotic zone in the corotation region of the planet. We
find that this zone can open a gap in a particle disk as long as the collision
timescale exceeds the removal or ejection timescale in the zone. We use the
slope measured from the ring edge surface brightness profile to place an upper
limit on the planet mass. The removal timescale in the chaotic zone is used to
estimate a lower limit. The ring edge has eccentricity caused by secular
perturbations from the planet. These arguments imply that the planet has a mass
between that of Neptune and that of Saturn, a semi-major axis of approximately
119 AU and longitude of periastron and eccentricity, 0.1, the same as that of
the ring edge.
