POROSITIES OF PROTOPLANETARY DUST AGGLOMERATES FROM COLLISION EXPERIMENTS
POROSITIES OF PROTOPLANETARY DUST AGGLOMERATES FROM COLLISION EXPERIMENTS
复制标题
碰撞实验中原行星尘埃团块的孔隙率
DOI：
10.1088/0004-637x/742/1/5
复制
发表时间：
2011
期刊：
影响因子：
--
通讯作者：
G. Wurm
中科院分区：
文献类型：
--
作者：
J. Teiser;Ilka Engelhardt;G. Wurm
尘埃通过粘附碰撞聚集是行星形成的第一步。形成的粉尘聚集体的基本物理性质强烈地依赖于聚集体的孔隙度;例如，机械强度、热导率和气粒耦合时间。此外，进一步碰撞的结果取决于碰撞聚集体的孔隙度。在实验室实验中，我们研究了尺寸为100 μm的小灰尘聚集体（由μm颗粒组成）在不同冲击速度下连续冲击时，尺寸为0.3 mm至3 cm的大聚集体的生长。实验表明，团聚体的生长既有直接粘附的方式，也有重力再吸积的方式。后者可以被看作是一个合适的模拟碎片的再吸积的气体阻力在原行星盘。实验在1.5 m s-1和7 m s-1之间的速度范围内进行。随着冲击速度的增加，所得附聚物的体积填充因子从1.5 m s-1的ε = 0.2增加到7 m s-1的ε = 0.32。这些值与目标大小无关。外推的体积填充因子的测量速度的依赖性意味着较高的碰撞速度不会导致更紧凑的聚集体。因此，ε = 0.32标志着适合描述在v > 6 m s-1时形成的结构的压实程度。在小于1 m s−1的小碰撞速度下，将形成高度多孔的结构，其孔隙率为0.10。对于中等碰撞速度，孔隙率变化。根据圆盘模型和由此产生的相对速度，原行星圆盘中的物体在分米大小的情况下可能会从高度多孔（ε = 0.10）发展到致密（ε = 0.32），具有更复杂的中间尺寸范围，孔隙度不同。
The aggregation of dust through sticking collisions is the first step of planet formation. The basic physical properties of the evolving dust aggregates strongly depend on the porosity of the aggregates; e.g., mechanical strength, thermal conductivity, and the gas–grain coupling time. Also, the outcome of further collisions depends on the porosity of the colliding aggregates. In laboratory experiments we study the growth of large aggregates of ∼3 mm to 3 cm through continuous impacts of small dust agglomerates of 100 μm in size, consisting of μm grains at different impact velocities. The experiments show that agglomerates grow by direct sticking as well as through gravitational reaccretion. The latter can be regarded as a suitable analog to the reaccretion of fragments by gas drag in protoplanetary disks. Experiments were carried out in the velocity range between 1.5 m s−1 and 7 m s−1. With increasing impact velocities the volume filling factor of the resulting agglomerates increases from ϕ = 0.2 for 1.5 m s−1 to ϕ = 0.32 for 7 m s−1. These values are independent of the target size. Extrapolation of the measured velocity dependence of the volume filling factor implies that higher collision velocities will not lead to more compact aggregates. Therefore, ϕ = 0.32 marks a degree of compaction suitable for describing structures forming at v > 6 m s−1. At small collision velocities below 1 m s−1, highly porous structures with ϕ ≈ 0.10 will form. For intermediate collision velocities porosities vary. Depending on the disk model and resulting relative velocities, objects in protoplanetary disks up to decimeters in size might evolve from highly porous (ϕ ≈ 0.10) to compact (ϕ = 0.32) with a more complex intermediate size range of varying porosity.