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Title:
Evolution of Planetesimals. II. Numerical Simulations
Authors:
Aarseth, S. J.; Lin, D. N. C.; Palmer, P. L.
Affiliation:
AA(INST. OF ASTRONOMY, MADINGLEY RD., CAMBRIDGE CB3 0HA, UK)
Publication:
Astrophysical Journal v.403, p.351 (ApJ Homepage)
Publication Date:
01/1993
Category:
Planets
Origin:
APJ
Astronomy Keywords:
SOLAR SYSTEM: FORMATION, STARS: PLANETARY SYSTEMS
Keywords:
PLANETS, PLANETESIMALS, SOLAR SYSTEM, PLANETARY SYSTEMS, DISTANCE, ORIGIN, FORMATION, NUMERICAL METHODS, SIMULATION, DYNAMICS, EVOLUTION, COAGULATION, GRAVITY EFFECTS, SCATTERING, COLLISIONS, VELOCITY, ENERGY, EQUILIBRIUM, FRICTION, MASS, ACCRETION, TIMESCALE, THEORETICAL STUDIES, CALCULATIONS, PROCEDURE, PARAMETERS, MODEL, BOUNDARIES
DOI:
10.1086/172208
Bibliographic Code:
1993ApJ...403..351A

Abstract

We continue our investigation of the dynamical evolution and coagulation process of planetesimals With a numerical N-body scheme, we simulate gravitational scattering and physical collisions among a system of planetesimals. The results of these simulations confirm our earlier analytical results that dynamical equilibrium is attained with a velocity dispersion comparable to the surface escape velocity of those planetesimals which contribute most of the system mass. In such an equilibrium, the rate of energy transfer from the systematic shear to dispersive motion, induced by gravitational scattering, is balanced by the rate of energy dissipation resulting from physical collisions. We also confirm that dynamical friction can lead to energy equipartition between an abundant population of low-mass field planetesimals and a few collisionally induced mergers with larger masses. These effects produce mass segregation in phase space and runaway coagulation. Collisions also lead to coagulation and evolution of the mass spectrum. The mergers of two field planetesimals can provide sufficient mass differential with other planetesimals for dynamical friction to induce energy equipartition and mass segregation. For small velocity dispersions, the more massive planetesimals produce relatively large gravitational focusing factors. Consequently, the growth time scale decreases with mass and runaway coagulation is initiated. Our numerical simulations show that, provided there is sufficient supply of low-mass planetesimals, runaway coagulation can lead to the formation of protoplanetary cores with masses comparable to a significant fraction of an Earth mass. We estimate that, at 1 AU, the characteristic time scale for the initial stages of planetesimal growth is ˜104 yr and ˜105 yr for the growth to protoplanetary cores. At Jupiter's present distance, these time scales are an order of magnitude longer.

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