摘要：Context. In the very first steps of the formation of a new planetary
system, dust agglomerates grow inside the protoplanetary disk that rotates around the
newly formed star. In this disk, collisions between the dust particles, induced by
interactions with the surrounding gas, lead to sticking. Aggregates start growing until
their sizes and relative velocities are high enough for collisions to result in bouncing
or fragmentation. With the aim of investigating the transitions between sticking and
bouncing regimes for colliding dust aggregates and the formation of clusters from multiple
aggregates, the Suborbital Particle and Aggregation Experiment (SPACE) was flown on the
REXUS 12 suborbital rocket.
Aims. The collisional and sticking properties of sub-mm-sized aggregates
composed of protoplanetary dust analogue material are measured, including the statistical
threshold velocity between sticking and bouncing, their surface energy and tensile
strength within aggregate clusters.
Methods. We performed an experiment on the REXUS 12 suborbital rocket.
The protoplanetary dust analogue materials were micrometre-sized monodisperse and
polydisperse SiO2
particles prepared into aggregates with sizes around 120 μm and 330 μm, respectively and volume
filling factors around 0.37. During the experimental run of 150 s under reduced gravity
conditions, the sticking of aggregates and the formation and fragmentation of clusters of
up to a few millimetres in size was observed.
Results. The sticking probability of the sub-mm-sized dust aggregates
could be derived for velocities decreasing from ~22 to 3 cm s-1. The transition from bouncing to sticking collisions
happened at 12.7+2.1-1.4 cm s-1 for the smaller aggregates composed of monodisperse
particles and at 11.5+1.9-1.3 and 11.7+1.9-1.3 cm s-1 for the larger aggregates composed of mono- and
polydisperse dust particles, respectively. Using the pull-off force of sub-mm-sized dust
aggregates from the clusters, the surface energy of the aggregates composed of
monodisperse dust was derived to be 1.6 ×
10-5 J m-2, which can be scaled down to 1.7 × 10-2 J m-2 for the micrometre-sized
monomer particles and is in good agreement with previous measurements for silica
particles. The tensile strengths of these aggregates within the clusters were derived to
be 1.9+2.2-1.2 Pa and 1.6+0.7-0.6 Pa for the small and large dust aggregates,
respectively. These values are in good agreement with recent tensile strength measurements
for ~mm-sized silica
aggregates.
Conclusions. Using our data on the sticking-bouncing threshold,
estimates of the maximum aggregate size can be given. For a minimum mass solar nebula
model, aggregates can reach sizes of ~1 cm.
关键词：protoplanetary disks;accretion, accretion disks;planets and satellites: formation
