  The nearby main sequence star Beta Pictoris is surrounded by an edge-on disk
of dust produced by the collisional erosion of larger planetesimals. Here we
report the discovery of substructure within the northeast extension of the disk
midplane that may represent an asymmetric ring system around Beta Pic. We
present a dynamical model showing that a close stellar flyby with a quiescient
disk of planetesimals can create such rings, along with previously unexplained
disk asymmetries. Thus we infer that Beta Pic's planetesimal disk was highly
disrupted by a stellar encounter in the last hundred thousand years.
