Formation of icy planetesimals

行星形成的第一个阶段是微米大小的颗粒通过凝聚生长到千米大小的微行星。到目前为止，实验研究涉及尘埃颗粒（主要是硅酸盐）的凝聚，因为硅酸盐在原行星盘的内部占主导地位。在原行星盘的外部，盘中的温度足够低，水冰是主要的固体。在不同的生长阶段（毫米大小和米大小），颗粒生长是很难解释的粘附力，只有碰撞速度变得很大，反弹和破碎是典型的碰撞结果。然而，冰聚集体的凝聚力应该大于硅酸盐，因此凝结效率也应该更高。我们提出了多孔冰团块之间的碰撞实验研究，因为它们预计在外部（超越雪线）的原行星盘。将开发一种产生多孔冰团块的实验装置，以及一种在低温条件下进行多次碰撞的装置。将研究在0.5 m/s和10 m/s之间的速度范围内的多次碰撞以及所得骨料的性质。这些结果对于理解太阳系行星的形成非常重要，并将为理论凝聚模型提供关键投入。

The first phase of planet formation is the growth of micron-size particles to km-size planetesimals by coagulation. So far, experimental studies deal with coagulation of dust particles (mostly silicates), as silicates are dominating in the inner parts of protoplanetary disks. In the outer parts of protoplanetary disks the temperature in the disk is low enough that water ice is the dominant solid. In different growth stages (mm-size and meter size), particle growth is difficult to explain by sticking forces only, as collision velocities get large and bouncing and fragmentation are typical collision outcomes. However, cohesion forces for ice aggregates are supposed to be larger than for silicates and therefore also the coagulation efficiency is supposed to be greater. We propose experimental studies on collisions between porous ice agglomerates as they are expected in the outer parts (beyond the snow line) of protoplanetary disks. An experimental setup to generate porous ice agglomerates will be developed, as well as a setup for multiple collisions under cryogenic conditions. Multiple collisions in the velocity range between 0.5 m/s and 10 m/s will be studied as well as the properties of the resulting aggregates. The results will be important for the understanding of the formation of the planets in the Solar System and will provide crucial input for theoretical coagulation models.