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SUMMARY:Asteroids formed big - Morbidelli\, A (Observatoire de Nice)
DTSTART:20090929T103000Z
DTEND:20090929T110000Z
UID:TALK20347@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:How big were the first planetesimals? We attempt to answer thi
 s question by conducting coagulation simulations in which the planetesimal
 s grow by mutual collisions and form larger bodies and planetary embryos. 
 The size frequency distribution (SFD) of the initial planetesimals is cons
 idered a free parameter in these simulations\, and we search for the one t
 hat produces at the end objects with a SFD that is consistent with asteroi
 d belt constraints.  We find that\, if the initial planetesimals were smal
 l (e.g. km-sized)\, the final SFD fails to fulfill these constraints. In p
 articular\, reproducing the bump observed at diameter D~100km in the curre
 nt SFD of the asteroids requires that the minimal size of the initial plan
 etesimals was also ~100km. This supports the idea that planetesimals forme
 d big\, namely that the size of solids in the proto-planetary disk ``jumpe
 d'' from sub-meter scale to multi-kilometer scale\, without passing throug
 h intermediate values. Moreover\, we find evidence that the initial planet
 esimals had to have sizes ranging from 100 to several 100km\, probably eve
 n 1\,000km\, and that their SFD had to have a slope over this interval tha
 t was similar to the one characterizing the current asteroids in the same 
 size-range. This result sets a new constraint on planetesimal formation mo
 dels and opens new perspectives for the investigation of the collisional e
 volution in the asteroid and Kuiper belts as well as of the accretion of t
 he cores of the giant planets.
LOCATION:Seminar Room 1\, Newton Institute
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