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The evolution of collision outcomes in the protoplanetary disk

Leinhardt, Z (Cambridge)
Tuesday 18 August 2009, 14:00-14:20

Meeting Room 2, CMS


Although hundreds of extrasolar planets have been detected, the earlier phases of planet formation are much more difficult to observe. As a result, theorists and numericists are still struggling to explain the planet formation process in detail. One of the fundamental problems in explaining the formation of our own solar system is reproducing the low eccentricity and inclination of the terrestrial planets. The dominant growth mechanism of planetesimals in the terrestrial region is collisions. However, the details of the collisions and the evolution of the post-collision remnants are not well understood. Although there has been a significant amount of work incorporating simple fragmentation models into numerical simulations of planet formation, thesesimulations have yet to produce the low eccentricities and inclinations of our own solar system. In this talk I will present numerical simulations that show how the criteria for catastrophically disrupting planetesimals can change by orders of magnitude as theimpact velocity and mechanical properties of the planetesimals are varied. These simulations suggest that the collisional response of planetesimals will change significantly as the protoplanetary disk evolves. The results presented here validate previous work (Benz, 2000), and expand upon their conclusions. The critical impact velocity required to begin collisional erosion of weak aggregate bodies is only a few metres per second. Therefore, the transition from the coagulation phase to collisional erosion for km-sized bodies begins much earlier during planet formation than usually considered. Thus, it seems likely that additional mechanisms (besides collisions) are needed for planetesimals to grow beyond km-sizes in the young protoplanetary disk. Our result that km-scale aggregates are particularly susceptible to disruption is supported by the observed deficit of small bodies in the outer solar system. With these results in mind we strongly suggest the use of a velocity dependent disruption law in N-body simulations of planet formation and evolution.

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