Subsurface Oceans on Europa and Callisto: Constraints from Galileo Magnetometer Observations
Subsurface Oceans on Europa and Callisto: Constraints from Galileo Magnetometer Observations
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木卫二和木卫四上的地下海洋：来自伽利略磁力计观测的限制
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发表时间：
2000
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通讯作者：
M. Kivelson
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作者：
C. Zimmer;K. Khurana;M. Kivelson
在木卫二和木卫四伽利略飞行期间测量到的磁场扰动与环境木星磁层磁场的时间变化所产生的偶极场是一致的。这些磁场接近完美传导卫星的预期磁场。我们使用一个简单的壳模型研究了这些观测结果对月球内部电子结构的影响。结果表明，木卫二和木卫四在低于地表200公里和300公里的深度内必须有电导率分别大于0.06和0.02 S/m的区域。这种导电性在冰或硅酸盐中是无法获得的，除非冰层至少部分融化，或者冰下可以保持非常大的温度梯度。电离层或拾取离子云可能也不具有足够的导电性。如果它们至少有几公里厚，两颗卫星表面下类似地球的全球海洋可以解释这些观测结果。C∞2000学术出版社
Magnetic field perturbations measured during Galileo flybys of Europa and Callisto are consistent with dipole fields induced by the temporal variations of the ambient jovian magnetospheric field. These fields are close to those expected for perfectly conducting moons. We investigate the implications of these observations for the electrical structure of the moon’s interiors using a simple shell model. It is found that Europa and Callisto must possess regions where the conductivity exceeds 0.06 and 0.02 S/m at a depth of less than 200 and 300 km below the surface, respectively. This conductivity is unattainable in ice or silicates, unless the ice layer is at least partially molten or very large temperature gradients can be maintained below the ice. An ionosphere or a cloud of pick-up ions are probably also insufficiently conductive. Global Earth-like oceans under the surface of both moons could account for the observations provided they are at least a few kilometers thick. c ∞ 2000 Academic Press