**AAS 199th meeting, Washington, DC, January 2002**

*Session 63. Solar System*

Display, Tuesday, January 8, 2002, 9:20am-6:30pm, Exhibit Hall
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## [63.12] N-body simulations of planetesimal evolution: Effect of varying impactor mass ratio

*Z. M. Leinhardt, D. C. Richardson (Dept. of Astronomy, University of Maryland)*

We present results from direct N-body simulations of
collisions between gravitational aggregates of varying size
as part of a study to parameterize planetesimal growth in
the solar system. We find that as the ratio of projectile to
target mass departs from unity the impact angle (angular
momentum) has less effect on the outcome. At the same time,
the probability of planetesimal growth increases.
Conversely, for a fixed impact energy, collisions between
impactors with mass ratio near unity are more dispersive
than those with impactor mass ratio far from unity. We
derive an expression for the accretion probability as a
function of mass ratio. For a mass ratio of 1:5 we find an
accretion probability of ~ 60% over all impact
parameters. We also compute the critical specific dispersal
energy Q^{*}_{D} as a function of projectile size.
Extrapolating to a projectile size of 1 m with a 1 km target
we find Q^{*}_{D} = 10^{3}--10^{4} J kg^{-1}, in agreement
with several other collision models that use fundamentally
different techniques. Our model assumes that the components
of each gravitational aggregate are identical and
indestructible over the range of sampled impact speeds. In
future work we hope to incorporate a simple fracture model
to extend the range of applicable speeds and plan to
implement our results into a large-scale planetesimal
evolution code.

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