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Accretion in Protoplanetary Disks: Sticking Chondrules Together

Tuesday, October 2, 2007
Chris
Ormel (Kapteyn Astronomical Institute, Univ Groningen)

Chondrules, mm-sized igneous particles, are one of the oldest fossils of our solar system. They are a conspicuous component of chondritic meteorites, but, in most cases, not the only one. Micron-sized dust grains permeate chondrites in the form of a densely-packed rim around chondrules and more loose matrix material. How did this dust mix with the chondrules? Moreover, how did these sub-mm grains accrete together into planetesimal sized objects in the nebula?

In my talk, I present an accretion scenario in which the dust enables chondrules to stick together. In it, chondrules accrete a porous rim, which will be compacted upon collisions with other chondrules, dissipating the collisional energy and allowing the chondrules to stick. We investigate how much growth can be achieved through this mechanism by running a parameter study, varying the many (and unknown) parameters characterizing the protoplanetary disk. It is found that, under the most favorable conditions, considerable growth can take place, although even then the planetesimal size is not reached. We discuss implications for the internal structure of the primitive meteorites, especially on the properties of chondrule dust rims.

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