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

• Published in: Astronomy and astrophysics (Berlin) Vol. 544; p. A138
• Main Authors: Meisner, T., Wurm, G., Teiser, J.
• Format: Journal Article
• Language: English
• Published: Les Ulis EDP Sciences 01.08.2012
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; methods: laboratory; planets and satellites: formation; protoplanetary disks; Energetics; Grain size; Mechanical properties; Experimental study; Fill factor; Collision processes; Proto planetary nebula; Compression strength; Tensile strength; Sound velocity; Young modulus; Planetesimals; Planetary cosmogony; methods: laboratory; protoplanetary disks; planets and satellites: formation; Strength functions
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201219099

The first macroscopic bodies in protoplanetary disks are dust aggregates. We report on a number of experimental studies with dust aggregates formed from micron-size quartz grains. We confirm in laboratory collision experiments an earlier finding that producing macroscopic bodies by the random impact of sub-mm aggregates results in a well-defined upper-filling factor of 0.31  ±  0.01. Compared to earlier experiments, we increase the projectile mass by about a factor of 100. The collision experiments also show that a highly porous dust-aggregate can retain its highly porous core if collisions get more energetic and a denser shell forms on top of the porous core. We measure the mechanical properties of cm-sized dust samples of different filling factors between 0.34 and 0.50. The tensile strength measured by a Brazilian test, varies between 1 kPa and 6 kPa. The sound speed is determined by a runtime measurement to range between 80 m/s and 140 m/s while Young’s modulus is derived from the sound speed and varies between 7 MPa and 25 MPa. The samples were also subjected to quasi-static omni- and uni-directional compression todetermine their compression strengths and flow functions. Applied to planet formation, our experiments provide basic data for future simulations, explain the specific collisional outcomes observed in earlier experiments, and in general support a scenario where collisional growth of planetesimals is possible.