BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:The evolution of collision outcomes in the protoplanetary disk - L
 einhardt\, Z (Cambridge)
DTSTART:20090818T130000Z
DTEND:20090818T132000Z
UID:TALK19500@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Although hundreds of extrasolar planets have been detected\, t
 he earlier phases of planet formation are much more difficult to observe. 
 As a result\, theorists and numericists are still struggling to explain th
 e planet formation process in detail. One of the fundamental problems in e
 xplaining the formation of our own solar system is reproducing the low ecc
 entricity and inclination of the terrestrial planets. The dominant growth 
 mechanism of planetesimals in the terrestrial region is collisions. Howeve
 r\, the details of the collisions and the evolution of the post-collision 
 remnants are not well understood. Although there has been a significant am
 ount of work incorporating simple fragmentation models into numerical simu
 lations of planet formation\, thesesimulations have yet to produce the low
  eccentricities and inclinations of our own solar system. In this talk I w
 ill present numerical simulations that show how the criteria for catastrop
 hically disrupting planetesimals can change by orders of magnitude as thei
 mpact velocity and mechanical properties of the planetesimals are varied. 
 These simulations suggest that the collisional response of planetesimals w
 ill change significantly as the protoplanetary disk evolves. The results p
 resented here validate previous work (Benz\, 2000)\, and expand upon their
  conclusions. The critical impact velocity required to begin collisional e
 rosion 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 con
 sidered. Thus\, it seems likely that additional mechanisms (besides collis
 ions) are needed for planetesimals to grow beyond km-sizes in the young pr
 otoplanetary disk. Our result that km-scale aggregates are particularly su
 sceptible to disruption is supported by the observed deficit of small bodi
 es in the outer solar system. With these results in mind we strongly sugge
 st the use of a velocity dependent disruption law in N-body simulations of
  planet formation and evolution.
LOCATION:Seminar Room 1 Newton Institute
END:VEVENT
END:VCALENDAR