Self-consistent Growth of Decimeter Bodies in Protoplanetary Disks

Details Self-consistent Growth of Decimeter Bodies in Protoplanetary Disks Self-consistent Growth of Decimeter Bodies in Protoplanetary Disks

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.5201t&link_type=abstract

American Astronomical Society, DPS meeting #41, #52.01

Astronomy and Astrophysics

Astronomy

Scientific paper

The models currently discussed for the formation of km-size planetesimals assume that in one intermediate step decimeter bodies grow in mutual collisions between different sized smaller dust aggregates. Typical collision velocities expected are up to 10 m/s. We show here that such growth indeed readily occurs.
In laboratory experiment we studied the self-consistent formation of mm- to decimeter-size bodies by accreting small 100 µm particles at collision velocities of about 7.7 m/s. Growth occurs due to direct sticking and reaccretion of fragments by gas drag. The reaccretion of impact ejecta by gas drag is well accounted for by gravity in the laboratory experiments.
Most earlier experiments studied collisions as single events. Here, we study the net outcome of literally millions of collisions. Growth for impact angles of up to 70° occurs.
Aggregates grown have a unique volume filling of 31% close to the maximum compaction feasible by applying local pressure on the aggregate surface (33%). This value is independent of the ratio between particles directly sticking or slowly reaccreted indicating that the growth history of an evolving decimeter body is erased by succeeding compacting impacts. We conclude that for coagulation/fragmentation models only one volume filling of 31% (or 69% porosity) has to be considered for larger bodies.
In detail the accretion efficiencies will depend on the disk model (gas pressure, relative velocities) as this determines the number of particles reaccreted by gas drag. Due to the direct sticking fraction growth is possible in the whole disk but due to the gas aided reaccretion it is most efficient in the inner terrestrial planet forming region.
This work was funded by the DFG FOR 759.

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