The formation of a solar system such as ours is believed to have followed a multi-stage process around a protostar and its associated accretion disk. Whipple first noted that planetesimal growth by particle agglomeration is strongly influenced by gas drag, and Cuzzi and colleagues have shown that when midplane particle mass densities approach or exceed those of the gas, solid-solid interactions dominate the drag effect. The size dependence of the drag creates a "bottleneck" at the meter scale with such bodies rapidly spiraling into the central star, whereas much smaller or larger particles do not. Independent of whether the origin of the drag is angular momentum exchange with gas or solids in the disk, successful planetary accretion requires rapid planetesimal growth to kilometer scales. A commonly accepted picture is that for collisional velocities Vc above a certain threshold value, V th~ 0.1-10?cm?s–1, particle agglomeration is not possible; elastic rebound overcomes attractive surface and intermolecular forces. However, if perfect sticking is assumed for all ranges of interparticle collision speeds the bottleneck can be overcome by rapid planetesimal growth. While previous work has dealt with the influences of collisional pressures and the possibility of particle fracture or penetration, the basic role of the phase behavior of matter-phase diagrams, amorphs, and polymorphs—has been neglected. Here, it is demonstrated for compact bodies that novel aspects of surface phase transitions provide a physical basis for efficient sticking through collisional melting/amorphization/polymorphization and subsequent fusion/annealing to extend the collisional velocity range of primary accretion to ΔVc ~ 1-100 m?s–1 V th, which encompasses both typical turbulent rms speeds and the velocity differences between boulder-sized and small grains ~1-50?m?s–1. Therefore, as inspiraling meter-sized bodies collide with smaller particles in this high velocity collisional fusion regime they grow sufficiently rapidly to ~0.1-1?km scale and settle into stable Keplerian orbits in ~105 years before photoevaporative wind clears the disk of source material. The basic theory applies to low and high melting temperature materials and thus to the inner and outer regions of a nebula.
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机译：像我们这样的太阳系的形成被认为是围绕着原恒星及其相关的吸积盘经过了多阶段的过程。 Whipple首先指出，颗粒团聚引起的行星生长受到气体阻力的强烈影响，Cuzzi及其同事表明，当中平面颗粒质量密度接近或超过气体的密度时，固-固相互作用将主导阻力作用。阻力的大小相关性会在米级产生“瓶颈”，使这些物体迅速旋入中心恒星，而较小或较大的粒子则不会。不管阻力的起源是与磁盘中的气体还是固体进行角动量交换，成功的行星吸积都需要快速的行星小数增长到千米尺度。普遍接受的图像是，对于高于一定阈值V th〜0.1-10？cm？s-1的碰撞速度Vc，不可能发生颗粒团聚;弹性回弹克服了有吸引力的表面和分子间作用力。但是，如果假定所有范围的粒子间碰撞速度都具有完美的附着力，则可以通过快速的小行星生长克服瓶颈。尽管先前的工作已经处理了碰撞压力的影响以及粒子破裂或穿透的可能性，但物质相图，非晶形和多晶形的相行为的基本作用却被忽略了。在此，对于紧凑体证明，表面相变的新方面为通过碰撞熔融/非晶化/多晶化以及随后的熔融/退火以将一次积体的碰撞速度范围扩展至ΔVc〜1-100 m进行有效粘结提供了物理基础。 ？s–1 V th，既包括典型的湍流有效值速度，也包括大颗粒和小颗粒之间的速度差〜1-50？m？s-1。因此，当吸气米大小的物体在这种高速碰撞聚变状态下与较小的粒子碰撞时，它们会以足够快的速度生长到〜0.1-1？km的范围，并在光蒸发风清除源盘之前的约105年内沉降到稳定的开普勒轨道。基本理论适用于低熔点和高熔点材料，因此适用于星云的内部和外部区域。
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