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Astrophysics Luncheon Seminar
Core Accretion: Contrasting Planetesimal-driven and Fragment-driven Scenarios
Presented by Chris Ormel
University of California, Berkeley
Monday, January 30, 2012
12:00 noon
in 169-336
Abstract
In the core accretion scenario for giant planet formation, the first
critical step is the formation of a solid core -- massive enough to
gravitationally bind the nebular gas. But how do cores acquire their
mass in the first place? It is believed that planet formation proceeds
'oligarchicly', where a few large bodies (embryos) consume liberally
from a reservoir of smaller bodies (planetesimals). Modeling this phase
requires us to understand and synthesise many physical processes
simultaneously. I will show that the outcome of these models is very
sensitive to the choices for key model parameters regarding the gas
(e.g., the turbulent strength) and material properties (e.g., the
planetesimal size). In particular, I will emphasize the role of
collisions and argue that fragments of planetesimals, or small particles
in general, can dominate the solid mass reservoir. Accretion scenarios
in which fragments play the dominant role will be investigated. This
requires a rethinking of the use of the proper gravitational cross
section, since gas drag forces will rival the gravitational (2-body) force.
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