Dynamical evolution of planetesimals in protoplanetary disks
Astrophysics, abstract
astro-ph/0306244
From: Roman Rafikov <rrr@ias.edu>
Date: Thu, 12 Jun 2003 16:03:30 GMT (84kb)
Dynamical evolution of planetesimals in protoplanetary disks
Authors:
Roman R. Rafikov (IAS)
Comments: 20 pages, 17 figures, 1 table, submitted to AJ
The current picture of terrestrial planet formation relies heavily on our
understanding of the dynamical evolution of planetesimals — asteroid-like
bodies thought to be planetary building blocks. In this study we investigate
the growth of eccentricities and inclinations of planetesimals in spatially
homogeneous protoplanetary disks using methods of kinetic theory. We explore
disks with a realistic mass spectrum of planetesimals evolving in time, similar
to that obtained in self-consistent simulations of planetesimal coagulation. We
calculate the behavior of planetesimal random velocities as a function of the
planetesimal mass spectrum both analytically and numerically; results obtained
by the two approaches agree quite well. Scaling of random velocity with mass
can always be represented as a combination of power laws corresponding to
different velocity regimes (shear- or dispersion-dominated) of planetesimal
gravitational interactions. For different mass spectra we calculate
analytically the exponents and time dependent normalizations of these power
laws, as well as the positions of the transition regions between different
regimes. It is shown that random energy equipartition between different
planetesimals can only be achieved in disks with very steep mass distributions
(differential surface number density of planetesimals falling off steeper than
m^{-4}), or in the runaway tails. In systems with shallow mass spectra
(shallower than m^{-3}) random velocities of small planetesimals turn out to be
independent of their masses. We also discuss the damping effects of inelastic
collisions between planetesimals and of gas drag, and their importance in
modifying planetesimal random velocities.
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