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SUMMARY:The crucial role of metallicity for planetesimal formation - Johan
 sen\, A (Leiden)
DTSTART:20090818T084000Z
DTEND:20090818T090000Z
UID:TALK19468@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:The probability of finding exoplanets around a main sequence s
 tar rises sharply for metallicities around solar or higher. I present comp
 uter simulations of particle clumping and planetesimal formation in protop
 lanetary discs with varying amounts of solid material. The sedimentary mid
 -plane layer of pebbles is unstable to both Kelvin-Helmholtz and streaming
  instabilities. For metallicities below the solar value the equilibrium mi
 d-plane layer is thick and displays no clumping. However\, already at slig
 htly super-solar metallicities\, strong clumping occurs in the mid-plane l
 ayer. These particle clumps can locally obtain more than a hundred times t
 he gas density. We interpret the onset of clumping as an effect of a curio
 us trait of the streaming instability: the strength of the turbulence incr
 eases with a decreasing solids-to-gas mass ratio. Particles inside dense c
 lumps have collision speeds of a few meters per second\, and the clumps re
 adily contract gravitationally into a number of interacting 100-km-size pl
 anetesimals. Our results show that the metallicity dependence of exoplanet
 s may have been imprinted already in the early stages of planet formation\
 , or during the dispersal of the gaseous part of the disc. 
LOCATION:Seminar Room 1 Newton Institute
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