A complex dynamo inferred from the hemispheric dichotomy of Jupiter's magnetic field
A complex dynamo inferred from the hemispheric dichotomy of Jupiter's magnetic field
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DOI：
10.1038/s41586-018-0468-5
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发表时间：
2018-09-06
期刊：
影响因子：
64.8
通讯作者：
Levin, Steven M.
中科院分区：
文献类型：
--
作者：
Moore, Kimberly M.;Yadav, Rakesh K.;Levin, Steven M.
朱诺号航天器位于木星的极地轨道上，它直接测量了木星表面附近的磁场(1)。最近对朱诺轨道(前九个轨道中的八个)观测到的木星磁场的分析提供了木星外部磁场的球谐参考模型(JRM09)(2)。这个模型对了解木星磁层的过程特别感兴趣，但要研究行星内部的磁场，从而研究产生木星主磁场的发电机机制，最好使用其他模型。在这里，我们报告了木星内部一定深度的磁场图。我们发现木星的磁场不同于所有其他已知的行星磁场。在木星内部，大部分通量从北半球的发电机区域以狭窄的频带形式出现，其中一些通过赤道附近密集的孤立通量带返回。在其他地方，这一领域要弱得多。磁场的非偶极子部分几乎完全局限于北半球，所以那里的磁场是强烈的非偶极子，而在南半球，它主要是偶极的。我们认为，与地球不同，木星的发电机并不是在厚厚、均匀的壳层中运行，我们认为这种意想不到的场形态是由径向变化引起的，可能包括分层、密度或电导率，或者两者兼而有之。
The Juno spacecraft, which is in a polar orbit around Jupiter, is providing direct measurements of the planet's magnetic field close to its surface(1). A recent analysis of observations of Jupiter's magnetic field from eight (of the first nine) Juno orbits has provided a spherical-harmonic reference model (JRM09)(2) of Jupiter's magnetic field outside the planet. This model is of particular interest for understanding processes in Jupiter's magnetosphere, but to study the field within the planet and thus the dynamo mechanism that is responsible for generating Jupiter's main magnetic field, alternative models are preferred. Here we report maps of the magnetic field at a range of depths within Jupiter. We find that Jupiter's magnetic field is different from all other known planetary magnetic fields. Within Jupiter, most of the flux emerges from the dynamo region in a narrow band in the northern hemisphere, some of which returns through an intense, isolated flux patch near the equator. Elsewhere, the field is much weaker. The non-dipolar part of the field is confined almost entirely to the northern hemisphere, so there the field is strongly non-dipolar and in the southern hemisphere it is predominantly dipolar. We suggest that Jupiter's dynamo, unlike Earth's, does not operate in a thick, homogeneous shell, and we propose that this unexpected field morphology arises from radial variations, possibly including layering, in density or electrical conductivity, or both.