Hybrid Simulations of Plasma Environment Around Enceladus
Hybrid Simulations of Plasma Environment Around Enceladus
复制标题
土卫二周围等离子体环境的混合模拟
DOI：
10.1029/2009ja014391
复制
发表时间：
2010
影响因子：
5.2
通讯作者：
W. Kurth
中科院分区：
文献类型：
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作者：
N. Omidi;C. Russell;J. Leisner;Robert L. Tokar;W. Kurth
[1]土卫二周围的等离子体环境是由与月球主体共转的等离子体和与土星延伸的云和从其南极地区喷出的羽流相关的中性气体之间的相互作用控制的。为了理解这种相互作用的性质，我们使用3-D电磁混合模拟，通过粒子细胞方法动力学地处理离子，并将电子视为电荷中和流体。在这些模拟中，等离子体与中性粒子的相互作用通过电荷交换发生。结果表明，土卫二对等离子体的吸收在月球背面形成了一个尾状密度空腔和一个耗尽尾流，该尾流的方向与磁场垂直，但沿磁场延伸沿着多个土卫二半径。除了在空腔尾部，流动并没有被相互作用减慢，而是以对称的方式转向空腔。共转等离子体与扩展中性粒子的相互作用导致产生离子回旋波，等离子体减速到低于共转速度的速度。结果还表明，南极羽流的存在对相互作用性质的影响程度取决于其密度。对于基密度为106/cm 3（6.5 × 1029个分子）或更低的羽流，我们没有发现明显的影响，而基密度为107/cm 3或更大的羽流被发现对相互作用区域有很大的影响。具体地说，相互作用不再是对称的密度空腔尾部在北方半球和密度增强尾部在南半球。在基密度为1008/cm ~ 3时，在相互作用中也产生了强的阿尔芬翼。将模拟结果与2008年3月12日卡西尼号与土卫二相遇时卡西尼号等离子体光谱仪的数据进行初步比较，结果表明羽流的基本密度为105 × 108/cm 3，对应于产生104 kg/s的新离子。
[1] The plasma environment around Enceladus is governed by the interaction between the corotating plasma with the body of the moon and the neutral gas associated with Saturn's extended cloud and plumes ejected from its southern polar region. To understand the nature of this interaction, we use 3-D electromagnetic hybrid simulations that treat ions kinetically through particle-in-cell methods and treat the electrons as a charge-neutralizing fluid. In these simulations, plasma interaction with the neutrals takes place through charge exchange. The results show that plasma absorption by Enceladus forms a tail-like density cavity behind the moon and a depletion wake which is confined in the direction perpendicular to the magnetic field but extends many Enceladus radii along the magnetic field. Except in the cavity tail, the flow is not slowed by the interaction but is diverted toward the cavity in a symmetric fashion. Interaction of the corotating plasma with the extended neutrals results in the generation of ion cyclotron waves and plasma deceleration to velocities below the corotation speed. The results also show that the extent to which the presence of a plume in the southern pole affects the nature of the interaction depends on its density. For plumes with base densities of ∼106/cm3 (6.5 × 1029 molecules in the plume) or lower we find no significant impacts, while plumes with base densities of ∼107/cm3 and larger are found to greatly impact the interaction region. Specifically, the interaction is no longer symmetric with a density cavity tail in the Northern Hemisphere and a density enhancement tail in the Southern Hemisphere. At base densities of ∼108/cm3, a strong Alfven wing is also generated in the interaction. Preliminary comparisons of the simulations with the Cassini Plasma Spectrometer data during the 12 March 2008 encounter with Enceladus suggest plume base densities of ∼5 × 108/cm3 corresponding to production of ∼4 kg/s of new ions.
土卫二不对称等离子体相互作用中的半球耦合
影响因子：
--
作者：
F. M. Neubauer;N. Schilling
通讯作者：
N. Schilling