Pebble Dynamics and Accretion Processes near planetary Embryos

太阳系中的行星和大多数观测到的太阳系外行星系统被认为是通过一个自下而上的过程形成的，在这个过程中，生长从几百万美元大小的尘埃颗粒开始，经过一系列长时间的粘滞碰撞，最终到达完全长大的行星或行星核。对于外部的气态行星来说，紧随其后的是气体的快速积累，最终通向木星和土星。要发生这种失控的气体吸积，必须累积了几个地球质量的最小核心质量。在标准的增长情景中，达到这一临界核心质量的时间通常比原行星盘的典型寿命更长。因此，它构成了整个行星形成过程中的一个瓶颈。最近，关于有可能通过厘米大小的物体(卵石)的快速吸积来克服这一限制的建议引起了相当大的关注。在这个提议中，我们打算详细分析现实天体物理条件下的卵石吸积场景，并研究该过程在吸积时间尺度和重元素浓缩方面的有效性。为此，我们计划计算嵌入三维原行星盘的不断增长的核心周围不同大小粒子的动力学，并计算核心的吸积率。

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.