Comets formed in solar-nebula instabilities! – An experimental and modeling attempt to relate the activity of comets to their formation process
Comets formed in solar-nebula instabilities! – An experimental and modeling attempt to relate the activity of comets to their formation process
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彗星在太阳星云不稳定中形成！ - 将彗星活动与其形成过程联系起来的实验和建模尝试
DOI：
10.1016/j.icarus.2014.03.016
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发表时间：
2014
期刊：
影响因子：
3.2
通讯作者：
J. Trigo
中科院分区：
文献类型：
--
作者：
J. Blum;B. Gundlach;S. Muhle;J. Trigo
当彗核接近太阳时，通过表层增加的能量通量导致下面冰的升华和随后的气体释放，从而促进了观测到的气体和尘埃的释放。虽然气体的释放可以通过求解热传递方程来直接理解，并考虑到靠近彗核表面的无冰尘埃层的有限渗透性，但尘埃的喷射还要求将尘埃粒子束缚在彗核上的力必须被升华过程所产生的力所克服。这涉及到上覆粉尘层的抗拉强度有多大的问题。微米大小的均匀粉尘颗粒层的抗拉强度通常达到103至104 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。为了解决这一矛盾，我们使用了Skorov和Blum （Skorov， YV, Blum， J. 2012）的模型。伊卡洛斯（Icarus 221, 361-11），他假设彗星是由尘埃和冰聚集云的引力不稳定形成的，并计算出彗星核相应结构的尘埃聚集层的抗拉强度约为1pa。在这里，我们提供的证据表明，发射的彗星尘埃粒子确实是具有合适性质的聚集体，符合Skorov和Blum的模型。然后，我们通过实验测量了实验室粉尘团聚体各层的抗拉强度，并验证了模型得出的数值。为了解释由水冰蒸发驱动的彗星活动，我们得出了尘埃聚集体的最小尺寸为~ 1毫米，与流星体观测和太阳星云中的尘埃聚集模型一致。最后，我们得出结论，彗星一定是由引力不稳定性形成的，因为所有其他的形成模型都会导致表层的抗拉强度更高。
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. While the release of gas can be straightforwardly understood by solving the heat-transport equation and taking into account the finite permeability of the ice-free dust layer close to the surface of the comet nucleus, the ejection of dust additionally 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 (Skorov, YV, Blum, J. 2012. Icarus 221, 361–11), 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∼ 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.
DOI：
10.1088/0004-637x/764/2/146
发表时间：
2012-08
期刊：
The Astrophysical Journal
影响因子：
--
作者：
P. Garaud;F. Meru;M. Galvagni;C. Olczak
通讯作者：
P. Garaud;F. Meru;M. Galvagni;C. Olczak
原行星尘埃团块的物理 VII 大尘埃团块的低速碰撞行为
DOI：
10.1088/0004-637x/758/1/35
发表时间：
2012
期刊：
The Astrophysical Journal
影响因子：
--
作者：
Schräpler;Seizinger
通讯作者：
Seizinger