  The planet candidate Fomalhaut b is bright in optical light but undetected in
longer wavelengths, requiring a large, reflective dust cloud. The most recent
observations find an extremely eccentric orbit (e ~ 0.8), indicating that
Fomalhaut b cannot be the planet that is constraining the system's eccentric
debris ring. An irregular satellite swarm around a super-Earth has been
proposed, however, explaining the well-constrained debris ring requires an
additional planet on an orbit that crosses that of the putative super-Earth.
This paper expands upon a second theory: Fomalhaut b is a transient dust cloud
produced by a catastrophic collision between planetesimals in the disk. We
perform collisional probability simulations of the Fomalhaut debris disk based
on the structure of our Kuiper belt, finding that the catastrophic disruption
rate of d ~ 100 km bodies in the high-eccentricity scattering component is
several per decade. This model paints a picture of the Fomalhaut system as
having recently (within ~10-100 Myr) experienced a dynamical instability within
its planetary system, which scattered a massive number of planetesimals onto
large, high eccentricity orbits similar to that of Fom b. If Fomalhaut b is
indeed a dust cloud produced by such a collision, we should soon see another
appear, while Fomalhaut b will expand until it is either resolved or becomes
too faint to be seen.
