Plasma and fields in the wake of Rhea: 3-D hybrid simulation and comparison with Cassini data
Plasma and fields in the wake of Rhea: 3-D hybrid simulation and comparison with Cassini data
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土卫五后的等离子体和场：3D 混合模拟以及与卡西尼号数据的比较
DOI：
10.5194/angeo-26-619-2008
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发表时间：
2008
影响因子：
1.9
通讯作者：
M. Dougherty
中科院分区：
文献类型：
--
作者：
E. Roussos;J. Müller;S. Simon;A. Bößwetter;U. Motschmann;N. Krupp;M. Fränz;J. Woch;K. Khurana;M. Dougherty
土卫五的磁层相互作用是使用三维的混合等离子体模拟代码，其中离子被视为粒子和电子作为一个无质量，电荷中和流体。与卡西尼号的观察一致，土卫五被建模为等离子体吸收障碍物。这导致了月球后面等离子体尾流（空腔）的形成。我们发现，这个空腔膨胀与离子声速沿着磁场线，导致在一个扩展的耗尽区北部和南部的月球，只有几个瑞亚半径（R Rh）下游。这是一个直接的后果，可比的热和体等离子体速度在土卫五。在磁场线附近，尾流的延伸受到磁场的约束。在尾流中的磁场压缩和稀疏的尾流侧也观察到在我们的结果。这种配置再现了卡西尼号磁力计数据中的签名，在2005年11月近距离飞越土卫五期间获得。几乎所有的等离子体和场参数都表现出沿着包含共转电场的平面的不对称分布。一个反磁电流系统被发现运行平行于尾流边界。这个电流系统的存在与Rhea下游的磁场结构直接相关，而由此产生的作用在离子上的j × B力是赤道平面上速度和电场矢量场的不对称结构的原因。由于土卫五是土星的众多等离子体吸收卫星之一，我们预计，这种情况下的研究应该是相关的大多数月球型的相互作用在土星。
Rhea's magnetospheric interaction is simulated using a three-dimensional, hybrid plasma simulation code, where ions are treated as particles and electrons as a massless, charge-neutralizing fluid. In consistency with Cassini observations, Rhea is modeled as a plasma absorbing obstacle. This leads to the formation of a plasma wake (cavity) behind the moon. We find that this cavity expands with the ion sound speed along the magnetic field lines, resulting in an extended depletion region north and south of the moon, just a few Rhea radii ( R Rh ) downstream. This is a direct consequence of the comparable thermal and bulk plasma velocities at Rhea. Perpendicular to the magnetic field lines the wake's extension is constrained by the magnetic field. A magnetic field compression in the wake and the rarefaction in the wake sides is also observed in our results. This configuration reproduces well the signature in the Cassini magnetometer data, acquired during the close flyby to Rhea on November 2005. Almost all plasma and field parameters show an asymmetric distribution along the plane where the corotational electric field is contained. A diamagnetic current system is found running parallel to the wake boundaries. The presence of this current system shows a direct corelation with the magnetic field configuration downstream of Rhea, while the resulting j × B forces on the ions are responsible for the asymmetric structures seen in the velocity and electric field vector fields in the equatorial plane. As Rhea is one of the many plasma absorbing moons of Saturn, we expect that this case study should be relevant for most lunar-type interactions at Saturn.