S. Ida et al., Evidence for early stellar encounters in the orbital distribution of Edgeworth-Kuiper Belt objects, ASTROPHYS J, 528(1), 2000, pp. 351-356
We show that early stellar encounters can explain the high eccentricities a
nd inclinations observed in the outer part (>42 AU) of the Edgeworth-Kuiper
Belt (EKB). We consider the proto-Sun as a member of a stellar aggregation
that undergoes dissolution on a timescale of similar to 10(8) yr, such tha
t the solar nebula experiences a flyby encounter at pericenter distance (cl
) on the order of 100 AU. Using numerical simulations we show that a stella
r encounter pumps up the velocity dispersion in the young solar nebula in t
he outer parts. In the case of a nearly parabolic encounter with a solar ma
ss companion, the velocity dispersion at a greater than or equal to 0.25q i
s pumped up to such an extent that collisions between planetesimals would b
e expected to become highly disruptive, halting further growth of planetesi
mals. This has the consequence that planet formation is forestalled in that
region. We also find that a stellar encounter with pericenter distance q s
imilar to 100-200 AU could have pumped up the velocity dispersion of EKB ob
jects outside 42 AU to the observed magnitude while preserving the velocity
dispersion magnitude inside Neptune's 3:2 mean motion resonance (located a
t 39.5 AU). This allows for the efficient capture of objects by the resonan
ce during a phase of orbital migration by proto-Neptune, which we also test
with simulations. We point out that such a stellar encounter generally aff
ects the dynamical and material structure of a protoplanetary disk, and the
planetesimal distribution can remain imprinted with this signature over mu
ch of the main-sequence lifetime of the star. In particular, our results su
pport the notion that an analogous process has operated in some recently ob
served extrasolar dust disks.