  The apparent detection of an exoplanet orbiting Fomalhaut was announced in
2008. However, subsequent observations of Fomalhaut b raised questions about
its status: Unlike other exoplanets, it is bright in the optical and
nondetected in the infrared, and its orbit appears to cross the debris ring
around the star without the expected gravitational perturbations. We revisit
previously published data and analyze additional Hubble Space Telescope (HST)
data, finding that the source is likely on a radial trajectory and has faded
and become extended. Dynamical and collisional modeling of a recently produced
dust cloud yields results consistent with the observations. Fomalhaut b appears
to be a directly imaged catastrophic collision between two large planetesimals
in an extrasolar planetary system. Similar events should be very rare in
quiescent planetary systems of the age of Fomalhaut, suggesting that we are
possibly witnessing the effects of gravitational stirring due to the orbital
evolution of hypothetical planet(s) around the star.
