Pebble Dynamics and Accretion Processes near planetary Embryos

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The planets in the Solar System and most of the observed extrasolar planetary systems are believed to have formed through a bottom-up process where growths starts from $\mu$m sized dust grains and proceeds through a long sequence of sticking collisions eventually to full grown planets, or planetary cores. For the outer, gaseous planets this is followed by the rapid accretion of gas that lead finally to Jupiter and Saturn. For this runaway gas accretion to occur a minimum core mass of several earth masses must have been accumulated. In the standard growth scenario, the time to reach this critical core mass is often longer than the typical lifetimes of protoplanetary disks. Hence, it constitutes a bottleneck in the overall planet formation process. Recently, the suggestion that it may be possible to overcome this constraint through the rapid accretion of cm-sized objects (pebbles) has attracted considerable attention.In this proposal we intend to analyze in detail the pebble accretion scenario under realistic astrophysical conditions and study the efficacy of the process with respect to the accretion timescale and heavy element enrichment. For that purpose we plan to calculate the dynamics of particles of different sizes around growing cores that are embedded in three-dimensional protoplanetary disks and calculate the accretion rate onto the core.