Feb 02, 2017 4:00 pm - Nielsen Hall 170 - Colloquium
Kevin Walsh - Southwest Research Institute
Terrestrial Planet Formation with Fragmentation and a Dissipating Nebula

Models of each stage of planet growth have largely been successful at
identifying the important physics in different regions of space at
different times. The earliest stages are dominated by small-body
interactions, where km-size bodies collide with each other but also
interact with the gaseous solar nebula. Later, the gravitational
interaction between planetary embryos on long timescales becomes more
important. However, splitting the problem into different stages, each
modeling subsets of the total physics, has an inherit weakness -
planet growth does not progress at the same speed at all
locations. Rather the inner regions of the Solar System may have many
gravitationally interacting planetary embryos, while outer regions are
still dominated by small-body collisions.
Using a particle-based code that models the fragmentation, accretion
and dynamical evolution of a large number of planetesimals through the
entire growth process, one can avoid the pitfalls of the classical
piece-wise approaches. This technique finds that growth timescales
that are far more dependent on distance from the Sun than previously
expected. This leads to giant collisions between Mars-size planetary
embryos at 1 AU before Ceres-size embryos have formed beyond 2 AU. We
use these results to test classical models of Terrestrial Planet
formation and some of the fundamental assumptions built into most
modern models.



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