Crossing barriers in planetesimal formation: The growth of mm-dust aggregates with large constituent grains

Abstract

Collisions of mm-size dust aggregates play a crucial role in the early phases of planet formation. We developed a laboratory setup to observe collisions of dust aggregates levitating at mbar pressures and elevated temperatures of 800 K. We report on collisions between basalt dust aggregates of from 0.3 to 5 mm in size at velocities between 0.1 and 15 cm/s. Individual grains are smaller than 25 \mum in size. We find that for all impact energies in the studied range sticking occurs at a probability of 32.1 \pm 2.5% on average. In general, the sticking probability decreases with increasing impact parameter. The sticking probability increases with energy density (impact energy per contact area). We also observe collisions of aggregates that were formed by a previous sticking of two larger aggregates. Partners of these aggregates can be detached by a second collision with a probability of on average 19.8 \pm 4.0%. The measured accretion efficiencies are remarkably high compared to other experimental results. We attribute this to the rel. large dust grains used in our experiments, which make aggregates more susceptible to restructuring and energy dissipation. Collisional hardening by compaction might not occur as the aggregates are already very compact with only 54 \pm 1% porosity. The disassembly of previously grown aggregates in collisions might stall further aggregate growth. However, owing to the levitation technique and the limited data statistics, no conclusive statement about this aspect can yet be given. We find that the detachment efficiency decreases with increasing velocities and accretion dominates in the higher velocity range. For high accretion efficiencies, our experiments suggest that continued growth in the mm-range with larger constituent grains would be a viable way to produce larger aggregates, which might in turn form the seeds to proceed to growing planetesimals.

arXiv comment9 pages, 20 figures

References in corpus (19)

• Rapid planetesimal formation in turbulent circumstellar discs
• The outcome of protoplanetary dust growth: pebbles, boulders, or planetesimals? II. Introducing the bouncing barrier
• The outcome of protoplanetary dust growth: pebbles, boulders, or planetesimals? I. Mapping the zoo of laboratory collision experiments
• Protoplanetary Disk Turbulence Driven by the Streaming Instability: Linear Evolution and Numerical Methods
• Planetesimal formation by sweep-up: How the bouncing barrier can be beneficial to growth
• The Physics of Protoplanetesimal Dust Agglomerates. III. Compaction in Multiple Collisions
• High Velocity Dust Collisions: Forming Planetesimals in a Fragmentation Cascade with Final Accretion
• Low-velocity collisions of centimeter-sized dust aggregates
• Thermal Processing of Silicate Dust in the Solar Nebula: Clues from Primitive Chondrite Matrices
• Microgravity experiments on the collisional behavior of Saturnian ring particles
• The Physics of Protoplanetesimal Dust Agglomerates II. Low Velocity Collision Properties
• Collisions between equal sized ice grain agglomerates
• Porosities of Protoplanetary Dust Agglomerates from Collision Experiments
• The Physics of Protoplanetesimal Dust Agglomerates. V. Multiple Impacts of Dusty Agglomerates at Velocities Above the Fragmentation Threshold
• Impact Angle Influence in High Velocity Dust Collisions during Planetesimal Formation
• Free Collisions in a Microgravity Many-Particle Experiment. II. The Collision Dynamics of Dust-Coated Chondrules
• Self-sustained Levitation of Dust Aggregate Ensembles by Temperature Gradient Induced Overpressures
• Decimetre dust aggregates in protoplanetary discs
• The four-populations model: a new classification scheme for pre-planetesimal collisions

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• Macroscopic Dust in Protoplanetary Disks - From Growth to Destruction
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