Hervé Beust (Grenoble) gave a nice talk about inferring orbital parameters for the (directly detected) exoplanet (or exoplanet-like thing) in the Fomalhaut system and then how those parameters might be related to the morphology of the dust debris ring around Fomalhaut. He can't find a consistent dynamical solution, that explains both the exoplanet and the ring, without adding new planets. His inference makes use of priors on exoplanet parameters with which I don't agree (although they are industry standards, so I am not complaining) and it also assumes that the mass of Fomalhaut is very well known. I would be very interested to see if you could explain the system entirely by (a) relaxing the star-mass prior, (b) sharpening the exoplanet orbital-parameter priors, and (c) insisting that the exoplanet orbit be of a size and shape that could explain the ring. Would that fail? Great (but very difficult-to-answer) question!
(In question period, Beust more-or-less admitted that the formation, origin, lifetimes, and morphologies of these dust debris rings are not well understood: They should be very short-lived objects. And yet they are observed in many systems. Interesting, that.)