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Ganymede's magnetosphere: Observations and modeling.

机译：Ganymede的磁层：观测和建模。

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摘要

Ganymede, the largest satellite in the solar system, is unique among the planetary satellites not only because of its great size but also because it is the only satellite in the solar system known to possess an intrinsic magnetic field. Ganymede's intrinsic field is sufficiently strong to stand off Jupiter's magnetospheric plasma above its surface and form a mini-magnetosphere embedded in Jupiter's magnetosphere. In this dissertation, we focus on understanding the interactions between Ganymede's magnetosphere and Jupiter's magnetospheric plasma from the perspective of both observations and numerical simulations.;First, we have used all available observations to establish an overall picture of Ganymede's magnetosphere and to investigate the characteristics of in-situ observations from the Galileo spacecraft obtained on individual flybys. We find that the time of magnetopause crossings inferred from the signatures in different instruments agree well with each other for five of the six Galileo close encounters but not during the G8 encounter. This disagreement leads us to speculate that the background flow during the time when the G8 encounter occurred may have been supermagnetosonic unlike that on the other passes and hence a transient shock formed in front of the magnetosphere.;Second, we have conducted a series of three-dimensional MHD simulations to further our understanding of Ganymede's magnetosphere. Our simulations show that, in addition to the familiar structures such as the magnetopause and equatorial current sheet, Ganymede's magnetosphere extends into an Alfv en wing that mediates the interaction of Ganymede with the plasma and ionosphere of Jupiter. The field-aligned currents in the Alfv en wing close not only through the moon and its ionosphere but also through the magnetopause and tail current sheets. Our model reproduces quite closely the magnetic field and plasma observations from multiple Galileo passes. Moreover, our MHD simulations enable us to interpret the observed boundary fluctuations as direct evidence of magnetic reconnection at the magnetopause. By obtaining evidence in comparing our model results with the observations, we conclude that even under steady upstream conditions, upstream reconnection is intermittent. Using our simulation results to provide a realistic description of the external magnetospheric fields, we have been able to refine earlier determinations of Ganymede's internal field and set better constraints on properties of a likely subsurface ocean.
机译：木卫三是太阳系中最大的卫星，在行星状卫星中是独一无二的，不仅因为它的尺寸很大，而且还因为它是太阳系中唯一已知具有固有磁场的卫星。木卫三的本征场足够强大，足以在其表面上方抵挡木星的磁层等离子体，并形成嵌入木星磁层中的微型磁层。本文从观测和数值模拟的角度着眼于了解木卫三磁层与木星磁层之间的相互作用。首先，我们利用所有可用观测资料建立了木卫三磁层的整体图景，并研究了木卫三磁层的特征。伽利略号航天器在单个飞越中获得的现场观测结果。我们发现，从六种伽利略近距离接触中的五次相遇中，通过不同仪器的信号推断出的磁绝经时间彼此吻合得很好，但在八国集团的相遇中却不一致。这种分歧使我们推测，在八国集团相遇期间，背景流可能是超磁声的，这与其他通过过程不同，因此在磁层的前面形成了短暂的冲击。第二，我们进行了一系列的三个多维MHD模拟，以进一步了解Ganymede的磁层。我们的模拟表明，除了磁层顶和赤道电流表等熟悉的结构之外，木卫三的磁层还延伸到一个Alfv机翼中，该木翼介导了木卫三与木星的等离子体和电离层之间的相互作用。 Alfv机翼中的场对准电流不仅通过月球及其电离层闭合，而且通过磁层顶和尾流板闭合。我们的模型非常精确地重现了来自多个伽利略通道的磁场和等离子体观测结果。此外，我们的MHD模拟使我们能够将观察到的边界波动解释为磁层顶磁重联的直接证据。通过获得将模型结果与观测值进行比较的证据，我们得出结论，即使在稳定的上游条件下，上游重新连接也是间歇性的。使用我们的模拟结果来提供对外部磁层磁场的真实描述，我们已经能够完善木卫三内部磁场的早期测定，并对可能的地下海洋的性质设置更好的约束。

著录项

  • 作者

    Jia, Xianzhe.;

  • 作者单位

    University of California, Los Angeles.;

  • 授予单位 University of California, Los Angeles.;
  • 学科 Geophysics.;Physics Fluid and Plasma.;Planetology.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 250 p.
  • 总页数 250
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

  • 入库时间 2022-08-17 11:38:30

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