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S. Ida (Tokyo Inst. of Tech.), J.D. Larwood (Queen Mary \& Westfield College), A. Burkert (MPIA)
We have investigated effects of early stellar encounters on a protoplanetary disk (planetesimal disk) and found that they can explain the high eccentricities and inclinations observed in the outer part (>42AU) of the Edgeworth-Kuiper Belt (EKB). The proto-sun is considered as a member of a stellar aggregation that undergoes dissolution on a timescale ~108 yrs, such that a planetesimal disk experiences a flyby encounter at pericenter distance (q) on the order of 100AU. We simulated dynamical evolution of a planetesimal (test particle) disk perturbed by a passing star. We show that the stellar encounter pumps the velocity dispersion in the disk in the outer parts (> 0.25q). Planet formation is forestalled in that region. We also find that a stellar encounter with pericenter distance q ~ 100--200AU could have pumped up the velocity dispersion of EKB objects outside 42AU to the observed magnitude while preserving that inside Neptune's 3:2 mean-motion resonance (located at 39.5AU), which allows for the efficient capture of objects by the sweeping of the 3:2 resonance during orbital migration by proto-Neptune. We point out that such a stellar encounter generally affects the dynamical structure of a protoplanetary disk and the planetesimal distribution can remain imprinted with this signature over main sequence lifetime of the star.
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