Recent advances in giant planetary space environments
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摘要: 太阳系八大行星分为类地行星和巨行星,巨行星不仅体积和质量大,其磁场也相对更强. 土星的磁矩大约是地球的600倍,而木星的磁矩则有地球的20 000倍之大. 土星和木星巨大的磁矩也让其拥有比地球大很多的巨型磁层空间. 等离子体在巨行星的磁层空间中受到强大的电磁力而产生复杂的加速和输运过程,持续产生空间能量物质扰动. 本文将回顾巨行星磁层空间的能量物质循环基本图像、辐射带高能物理过程、磁层电离层耦合过程以及巨行星磁层空间的关键基本等离子体物理过程,尤其结合中国学者在这一领域的最新研究进展进行介绍.Abstract: Among the eight solar system planets, Jupiter and Saturn are the two most giant planets, which also have the most prominent magnetic moments. Comparing to the Earth dipole magnetic field, the magnetic moment of Saturn is about 600 times larger while Jupiter is about 20 000 times larger. The extremely large magnetic moments of giant planets sustain giant planetary magnetospheres, trapping energetic particles with constant electromagnetic perturbations. In this article, we will review the basic pictures of mass and energy circulations in giant planetary space environments, energetic plasma processes in radiation belt, magnetosphere-ionosphere coupling processes and fundamental plasma processes in magnetospheres.
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Key words:
- giant planets /
- magnetosphere /
- aurora /
- magnetic reconnection
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图 1 低频波动在(a)XKSM-YKSM和(b)XKSM-ZKSM平面分布情况,以及(c)低频波动功率谱密度随地方时的分布. 其中,洋红色曲线为A06模型给出的可能的磁层顶位置(假设太阳风动压为0.009 06 nPa),两条黑色曲线给出了磁层顶位置误差范围(修改自Pan et al., 2021a)
Figure 1. The distribution of low frequency fluctuation in (a) XKSM-YKSM and (b) XKSM-ZKSM plane, and (c) the distribution of low frequency fluctuation power spectral density with local time. Among them, the magenta curve is the possible position of the magnetopause given by the A06 model (assuming that the solar wind dynamic pressure is 0.00906 nPa), and two black curves give the error range of the magnetopause position (modified from Pan et al., 2021a)
图 2 木星极光功率与不同周期阿尔芬波动强度的关系. (a)1~20 min波动;(b)20~40 min波动;(c)40~60 min波动;(d)1~60 min波动(修改自Pan et al., 2021b)
Figure 2. The relation between the power of the aurora of Jupiter and the intensity of Alfven waves in different periods is (a) 1~20 min fluctuation; (b) 20~40 min fluctuation; (c) 40~60 min fluctuation; (d) 1~60 min fluctuation (modified from Pan et al., 2021b)
图 3 土星辐射带大于1 MeV电子径向分布(修改自Yuan et al., 2020)
Figure 3. Radial distribution of electrons larger than 1 MeV in the Saturn radiation belt (modified from Yuan et al., 2020)
图 4 相对论电子频发增强统计结果(修改自Yuan et al., 2020). (a)频发增强发生位置直方图;(b)频发增强相对电子总含量直方图;(c)频发增强径向位移典型个例;(d)频发增强径向位移关于L和地方时的分布
Figure 4. The frequency of relativistic electrons enhances the statistical results (modified from Yuan et al., 2020). (a) Histogram of the location of frequent enhancement; (b) The total content histogram of relativistic electrons is enhanced by frequent emission; (c) Typical cases of frequent enhanced radial displacement; (d) Distribution of frequent enhanced radial displacement with respect to L and local time
图 6 地球和木星的类似极光特征与对应的磁层过程对比(修改自Bonfond et al., 2021)
Figure 6. Comparison of Aurora features of earth and Jupiter with corresponding magnetospheric processes (modified from Bonfond et al., 2021)
图 7 Cassini号飞船在磁重联离子扩散区内外观测到的电子谱图(修改自Guo et al., 2018a)
Figure 7. The electron spectra observed by Cassini spacecraft inside and outside the ion diffusion region of magnetic reconnection (modified from Guo et al., 2018a)
图 8 该示意图显示了小尺度磁重联分布在各个地方时且随磁层旋转(修改自Guo et al., 2019)
Figure 8. The schematic diagram shows that the small-scale magnetic reconnection is distributed at any local time and rotates with the magnetosphere (modified from Guo et al., 2019)
图 9 土星图片来源于Cassini观测,致谢NASA/JPL/SSI,完整图片来源于https://eos.org/editor-highlights/cassini-reveals-a-missing-link-on-saturns-rotating-aurora.
Figure 9. Saturn image from Cassini observation, thanks to NASA / JPL / SSI, full image from https://eos.org/editor-highlights/cassini-reveals-a-missing-link-on-saturns-rotating-aurora
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