Planetesimals to planets: Numerical simulation of collisional evolution

Richard Greenberg, John F. Wacker, William K. Hartmann, Clark R. Chapman

Research output: Contribution to journalArticlepeer-review

347 Scopus citations


A simulation of collisional and gravitational interaction in the early solar system generates planets ∼500 km in diameter from an initial swarm of kilometer-sized planetesimals, such as might have resulted from gravitational instabilities in the solar nebula. The model treats collisions according to experimental and theoretical impact results (such as rebound, cratering, and catastrophic fragmentation) for a variety of materials whose parameters span plausible values for early solid objects. Ad hoc sticking mechanisms are avoided. The small planets form in ∼104 yr, during which time most of the mass of the system continues to reside in particles near the original size. The relative random velocities remain of the order of a kilometer-sized body's escape velocity, with random velocities of the largest objects somewhat depressed because of damping by the bulk of the material. The simulation is terminated when the largest objects' random motion is of smaller dimension than their collision cross sections, so that the "particle-in-a-box" statistical methods of the model break down. The few 500-km planets, in a swarm still dominated by kilometer-scale planetesimals, may act as "seeds" for the subsequent, gradual, accretional growth into full-sized planets.

Original languageEnglish (US)
Pages (from-to)1-26
Number of pages26
Issue number1
StatePublished - Jul 1978

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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