Fredrik Windmark, Til Birnstiel, Carsten Güttler, Jürgen Blum, Cornelis P. Dullemond, Thomas Henning
The formation of planetesimals is often accredited to collisional sticking of
dust grains. The exact process is unknown, as collisions between larger
aggregates tend to lead to fragmentation or bouncing rather than sticking.
Recent laboratory experiments have however made great progress in the
understanding and mapping of the complex physics involved in dust collisions.
We want to study the possibility of planetesimal formation using the results
from the latest laboratory experiments, particularly by including the
fragmentation with mass transfer effect, which might lead to growth even at
high impact velocities. We present a new experimentally and physically
motivated dust collision model capable of predicting the outcome of a collision
between two particles of arbitrary masses and velocities. It is used together
with a continuum dust-size evolution code that is both fast in terms of
execution time and able to resolve the dust well at all sizes, allowing for all
types of interactions to be studied without biases. We find that for the
general dust population, bouncing collisions prevent the growth above
millimeter-sizes. However, if a small number of cm-sized particles are
introduced, for example due to vertical mixing or radial drift, they can act as
a catalyst and start to sweep up the smaller particles. At a distance of 3 AU,
100-meter-sized bodies are formed on a timescale of 1 Myr. We conclude that
direct growth of planetesimals might be a possibility thanks to a combination
of the existence of a bouncing barrier and the fragmentation with mass transfer
effect. The bouncing barrier is here even beneficial, as it prevents the growth
of too many large particles that would otherwise only fragment among each
other, and creates a reservoir of small particles that can be swept up by
larger bodies. However, for this process to work, a few seeds of cm in size or
larger have to be introduced.
View original:
http://arxiv.org/abs/1201.4282
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