The nearby main-sequence star beta Pictoris is surrounded by an edge-on dis
k 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
Pie. We present a dynamical model showing that a close stellar flyby with a
quiescent disk of planetesimals can create such rings, along with previous
ly unexplained disk asymmetries. Thus we infer that beta Pie's planetesimal
disk was highly disrupted by a stellar encounter in the last hundred thous
and years.