TY  - GEN
N2  - Planetesimals are the hypothetical building blocks of planets, halfway between dust aggregation and the formation
of planetary embryos. The typical diameter of newborn planetesimals was found to be around 100 km. The timedependent
production of these planetesimals and their radial distribution in disks around young stars is still unclear.
This thesis proposes a semi-analytical model for the planetesimal formation rate that is regulated by the radial pebble
flux. The model is implemented into a code that solves the evolution of gas as well as the growth and radial motion
of grains. Within this model, planetesimals form as soon as micron-sized dust has grown to pebble-size (typically ~
mm?cm) and a critical pebble flux is reached. The resulting spatial planetesimal profile is steeper compared to
the initial dust and gas distribution. E.g., for a temperature profile T?r^-0.5, the planetesimal profile is expected to
follow ?_p?r^-2.25 in the inner disk regions. The maximum local planetesimal production is reached for a planetesimal
formation efficiency that allows the planetesimal formation timescale and the pebbles drift timescale to be equal.
A disk parameter study is performed which enables to set limits on possible parameters for the Solar Nebula by
comparing the produced planetesimal profiles with mass constraints for initial planetesimals. This thesis shows that
the Solar Nebula was not too large, enclosing most of the mass within 50 au. Outside of 50 au, particle traps needed
several hundreds of orbits to form or never formed there. Compared to the mass constraints, the most appealing case
that is analyzed in this thesis has a disk mass of around 0.1 solar masses, a fragmentation speed of particles of 2 m/s,
and moderate to weak turbulence (? = 3?10^-4). The model introduced in this thesis does not require fine tuning in
order to meet mass constraints for the Solar Nebula which stresses the applicability of the proposed parameterization
to models of planet formation. By sorting pebbles by their origins, this thesis shows that a significant amount of pebble
mass passed major ice lines before forming planetesimals in the inner Solar Nebula or before they were accreted by
planetary embryos at the current positions of the asteroid belt and Earth. The relative contribution to planetesimals
from regions of different particle origins changes for different times of planetesimal formation. This thesis concludes
with the importance of pebble transport and the planetesimal formation efficiency for shaping the spatial distribution
of planetesimals. The presented planetesimal formation rate model can be used to bridge the gap between the phases
of dust growth and the formation of planetary embryos.
A1  - Lenz, Christian Tobias
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/28808/
KW  - Protoplanetare Scheiben
KW  -  Solarer Nebel
ID  - heidok28808
CY  - Heidelberg
AV  - public
Y1  - 2020///
TI  - Semi-analytical Modeling of Planetesimal Formation.
Implications for Planet Formation and the Solar Nebula
ER  -