尘埃发射与动力学
Dust Emission and Dynamics
AI总结：
该研究梳理了彗星尘埃发射与动力学领域的进展，介绍了航天器探测带来的新认知，指出了尘埃脱离机制、演化过程及遥感反演等待解决问题。
摘要：
从地球上观测时，我们看到的彗星大部分形态都是尘埃。太阳辐射压对尘埃粒子运动轨迹的影响取决于粒子的横截面积与质量之比，因此太阳辐射压在彗尾内部起到了类似质谱仪的作用。长期以来，研究人员通过研究彗尘埃尾的外观来获取尘埃特性信息，例如粒子特征尺寸以及进入彗尾时的初始速度。\n过去二十年间，多项彗星航天器探测任务让我们得以以远高于地球或近地空间望远镜的分辨率研究目标彗星的尘埃活动，也为1986年造访1P/Halley（哈雷彗星）的航天器所得结果补充了更多细节。目前我们已知，彗星内彗发中的尘埃动力学过程十分复杂，其中有相当一部分粒子最终会落回彗星表面。近表面彗发的丝状结构被认为是气流的地形聚焦、表面活动分布不均以及投影效应共同作用的结果。部分尺寸大于厘米级的碎片从表面被抬升时可能含有冰，这会影响其运动状态。\n目前仍存在诸多待解决的问题：导致尘埃从表面脱离并被抬升的过程的微观物理机制、尘埃在远离彗核过程中的演化情况，以及我们能从外彗发和彗尾的遥感观测中反推出多少彗核活动的相关信息。
英文摘要：
When viewed from Earth, most of what we observe of a comet is dust. The influence of solar radiation pressure on the trajectories of dust particles depends on their cross-section to mass ratio. Hence solar radiation pressure acts like a mass spectrometer inside a cometary tail. The appearances of cometary dust tails have long been studied to obtain information on the dust properties, such as characteristic particle size and initial velocity when entering the tail. Over the past two decades, several spacecraft missions to comets have enabled us to study the dust activity of their targets at much greater resolution than is possible with a telescope on Earth or in near-Earth space, and added detail to the results obtained by the spacecraft visiting comet 1P/Halley in 1986. We now know that the dynamics of dust in the inner cometary coma is complex and includes a significant fraction of particles that will eventually fall back to the surface. The filamented structure of the near-surface coma is thought to result from a combination of topographic focussing of the gas flow, inhomogeneous distribution of activity across the surface, and projection effects. It is possible that some larger-than-centimetre debris contains ice when lifted from the surface, which can affect its motion. Open questions remain regarding the microphysics of the process that leads to the detachment and lifting of dust from the surface, the evolution of the dust while travelling away from the nucleus, and the extent to which information on the nucleus activity can be retrieved from remote observations of the outer coma and tail.
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