Diploma Thesis
Staubdiffusion in protoplanetaren Akkretionsscheiben
Michael Wehrstedt
Abstract:
IR-spectra of many comets show clear evidence of crystalline silicate
(predominantly olivine) in notable quantities, beside the known features of
amorphous silicate dust.
It is likely that the matter in comets represents unaltered pristine material
from the time of the solar nebula, which has been "frozen" since its
integration in cometesimals.
Since the dust in the interstellar medium is exclusively amorphous, the
protoplanetary accretion disc must be the origin of crystalline silicate.
A possible formation process is annealing of amorphous silicate in the warm
inner zone of the accretion disc.
Due to turbulence in the optically thick disc, a fraction of the annealed
silicate dust reaches the cooler outer region of the disc by being carried
along with the gas, where it may be built into larger bodies, e.g. cometesimals.
In the matrix of some chondrites are also indications of silicate dust, which
has experienced an annealing-event under the conditions of the solar nebula.
This work investigates the diffusion and crystallisation of dust in
protoplanetary discs.
For this purpose the diffusion equation of the dust (including annealing) is
linked to the equations for the global evolution of an alpha-disc within an
one-dimensional, time-dependent numerical model.
The results suggest that the diffusive transport spreads the dust globally
throughout the disc, and therefore provides an explanation for crystalline
silicate within the primordial bodies of the solar system.
Thesis: ps.gz file (621328 Bytes)
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