Jens Teiser

High-velocity dust collisions: forming planetesimals in a fragmentation cascade with final accretion

In laboratory experiments we determine the mass gain and loss in central collisions between centimetre- to decimetre-size SiO2 dust targets and submillimetre- to centimetre-size SiO2 dust projectiles of varying mass, size, shape and at different collision velocities up to ∼56.5 m s −1 . Dust projectiles much larger than 1 mm lead to a small amount of erosion of the target but decimetre targets do not break up. Collisions produce ejecta, which are smaller than the incoming projectile. Projectiles smaller than 1 mm are accreted by a target even at the highest collision velocities. This implies that net accretion of decimetre and larger bodies is possible. Independent of the original size of a considered projectile, after several collisions, all fragments will be of submillimetre size which might then be (re)accreted in the next collision with a larger body. The experimental data suggest that collisional growth through fragmentation and reaccretion is a viable mechanism to form planetesimals.

Experiments on the photophoretic motion of chondrules and dust aggregates-Indications for the transport of matter in protoplanetary disks

In a set of 16 drop tower experiments the motion of sub-millimeter to millimeter-sized particles under microgravity was observed. Illumination by a halogen lamp induced acceleration of the particles due to photophoresis. Photophoresis on dust-free chondrules, on chondrules, glass spheres and metal spheres covered with SiC dust and on pure SiC dust aggregates was studied. This is the first time that photophoretic motion of millimeter-sized particles has been studied experimentally. The absolute values for the photophoretic force are consistent with theoretical expectations for spherical particles. The strength of the photophoretic force varies for chondrules, dust covered particles and pure dust from low to strong, respectively. The measurements support the idea that photophoresis in the early Solar System can be efficient to transport solid particles outward.

Decimetre dust aggregates in protoplanetary discs

The growth of planetesimals is an essential step in planet formation. Decimetre-size dust agglomerates mark a transition point in this growth process. In laboratory experiments we simulated the formation, evolution, and properties of decimetre-scale dusty bodies in protoplanetary discs. Small sub-mm size dust aggregates consisting of micron-size SiO

Experiments on centimeter-sized dust aggregates and their implications for planetesimal formation

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From Planetesimals to Dust: Low-gravity Experiments on Recycling Solids at the Inner Edges of Protoplanetary Disks

particles randomly interacted with dust targets of varying initial conditions in a continuous sequence of independent collisions. Impact velocities were 7.7 m/s on average and in the range expected for collisions with decimetre bodies in protoplanetary discs. The targets all evolved by forming dust \emph{crusts} with up to several cm thickness and a unique filling factor of 31%

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

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Preplanetary scavengers: Growing tall in dust collisions

3%. A part of the projectiles sticks directly. In addition, some projectile fragments slowly return to the target by gravity. All initially porous parts of the surface, i.e. built from the slowly returning fragments, are compacted and firmly attached to the underlying dust layers by the subsequent impacts. Growth is possible at impact angles from 0

COLLIDING DECIMETER DUST

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MACROSCOPIC DUST IN PROTOPLANETARY DISKS—FROM GROWTH TO DESTRUCTION

(central collision) to 70

Photophoretic Strength on Chondrules. 2. Experiment

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