Collisions of small ice particles under microgravity conditions
Collisions of small ice particles under microgravity conditions
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DOI：
10.1051/0004-6361/201424069
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发表时间：
2015-01-01
影响因子：
6.5
通讯作者：
Fraser, H. J.
中科院分区：
文献类型：
--
作者：
Hill, C. R.;Heisselmann, D.;Fraser, H. J.
上下文。行星被认为是由原行星盘的固体物质在尘埃聚集过程中形成的。目前尚不清楚冰川是如何生长到千米大小的，但有人提出，雪线以外的水冰可能会影响这一过程。为了更好地理解原行星盘中导致行星形成的碰撞过程，研究了小冰粒的个别低速碰撞。在微重力条件下，粒子在抛物线飞行运动中碰撞，使用专门建造的低温冷却实验装置。该装置能够在131至160 K的温度下，以0.27至0.51 ms（-1）的相对碰撞速度将小冰粒（直径在4.7至10.8 mm之间）对撞在一起。使用了两种类型的冰粒：冰球和不规则形状的冰片。大多数情况下观察到弹跳，少数情况下观察到碎片。用该装置实现了全范围的归一化冲击参数（b/R = 0.0-1.0）。恢复系数均匀分布在0.08 ~ 0.65之间，平均值为0.36，导致碰撞中最少损失58%的平动能。恢复系数的范围归因于研究中使用的颗粒的表面粗糙度。粒子旋转分析表明，碰撞前粒子高达17%的能量转化为旋转能。在研究范围内，温度对恢复系数没有影响。
Context. Planetisimals are thought to be formed from the solid material of a protoplanetary disk by a process of dust aggregation. It is not known how growth proceeds to kilometre sizes, but it has been proposed that water ice beyond the snowline might affect this process.Aims. To better understand collisional processes in protoplanetary disks leading to planet formation, the individual low velocity collisions of small ice particles were investigated.Methods. The particles were collided under microgravity conditions on a parabolic flight campaign using a purpose-built, cryogenically cooled experimental setup. The setup was capable of colliding pairs of small ice particles ( between 4.7 and 10.8 mm in diameter) together at relative collision velocities of between 0.27 and 0.51 ms(-1) at temperatures between 131 and 160 K. Two types of ice particle were used: ice spheres and irregularly shaped ice fragments.Results. Bouncing was observed in the majority of cases with a few cases of fragmentation. A full range of normalised impact parameters ( b/R = 0.0-1.0) was realised with this apparatus. Coefficients of restitution were evenly spread between 0.08 and 0.65 with an average value of 0.36, leading to a minimum of 58% of translational energy being lost in the collision. The range of coefficients of restitution is attributed to the surface roughness of the particles used in the study. Analysis of particle rotation shows that up to 17% of the energy of the particles before the collision was converted into rotational energy. Temperature did not affect the coefficients of restitution over the range studied.