A Possible Dynamical History for the Fomalhaut System

Fomalhautb was long thought to shape the eccentric debris belt in the Fomalhautsystem, but its orbit was found to be too eccentric for it to be the dominant belt-shaping perturber. This indicates that Fomalhautb is Earth-sized at most and that the belt-shaping perturber, hereafter named Fomalhautc, remains to be discovered. In addition, since its orbit more or less crosses that of Fomalhautb, it also indicates that the current configuration of the system is transient and was reached recently. In this talk, we show that this current configuration can be explained if Fomalhautc is Saturn- to Neptune-sized, and Fomalhautb originates from a mean-motionresonance with Fomalhautc.