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arXiv 1403.2610astro-ph.EP
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彗星形成于太阳星云的不稳定性！- 将彗星的活动与其形成过程联系起来的实验和建模尝试（包括勘误表）

Comets formed in solar-nebula instabilities! -- An experimental and modeling attempt to relate the activity of comets to their formation process (corrigendum included)

Jürgen Blum, Bastian Gundlach, Steffen Mühle, Josep M. Trigo-Rodriguez

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The pdf file includes the main document and the corrigendum to the main article (just scroll through the pdf)
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摘要：

当彗星核接近太阳时，通过表面层的能量通量增加，导致底层冰的升华和随后的脱气，促进了观察到的气体和尘埃的排放。尘埃的喷射需要尘埃颗粒与彗星核的结合力必须被升华过程引起的力所克服。这涉及到覆盖灰尘层的抗拉强度有多大的问题。微米级灰尘颗粒的均匀层达到的拉伸强度通常为$10^3$至$10^4$ Pa。这远远超过了彗星中水冰的最大升华压力。因此，尚不清楚彗星尘埃活动是如何驱动的。为了解决这个悖论，我们使用了Skorov和Blum（Icarus 221，1-11，2012）的模型，他们假设彗星是由尘埃云和冰聚集体的引力不稳定性形成的，并计算了尘埃聚集体层的彗星核拉伸强度的相应结构为1 Pa。在这里，我们提出的证据表明，发射的彗星尘埃颗粒确实是聚集体与正确的属性，以适应模型的斯科罗夫和布卢姆。然后，我们实验测量层的实验室灰尘聚集体的拉伸强度，并确认由模型推导出的值。为了解释彗星活动的水冰的蒸发驱动，我们推导出的最小尺寸为$\sim 1$毫米的尘埃聚集，在太阳星云的流星体观测和尘埃凝聚模型的协议。最后，我们得出结论，彗星必须形成的引力不稳定性，因为所有替代的形成模式导致更高的抗拉强度的表面层。

英文摘要：

When comet nuclei approach the Sun, the increasing energy flux through the surface layers leads to sublimation of the underlying ices and subsequent outgassing that promotes the observed emission of gas and dust. The ejection of dust requires that the forces binding the dust particles to the comet nucleus must be overcome by the forces caused by the sublimation process. This relates to the question of how large the tensile strength of the overlying dust layer is. Homogeneous layers of micrometer-sized dust particles reach tensile strengths of typically $10^3$ to $10^4$ Pa. This exceeds by far the maximum sublimation pressure of water ice in comets. It is therefore unclear how cometary dust activity is driven. To solve this paradox, we used the model by Skorov and Blum (Icarus 221, 1-11, 2012), who assumed that cometesimals formed by gravitational instability of a cloud of dust and ice aggregates and calculated for the corresponding structure of comet nuclei tensile strength of the dust-aggregate layers on the order of 1 Pa. Here we present evidence that the emitted cometary dust particles are indeed aggregates with the right properties to fit the model by Skorov and Blum. Then we experimentally measure the tensile strengths of layers of laboratory dust aggregates and confirm the values derived by the model. To explain the comet activity driven by the evaporation of water ice, we derive a minimum size for the dust aggregates of $\sim 1$ mm, in agreement with meteoroid observations and dust-agglomeration models in the solar nebula. Finally we conclude that cometesimals must have formed by gravitational instability, because all alternative formation models lead to higher tensile strengths of the surface layers.

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