Kollmann P, Roussos E, Paranicas C, Woodfield E E, Mauk B H, Clark G, Smith D C, Vandegriff J
The Johns Hopkins University, Applied Physics Laboratory Laurel MD USA.
Max Planck Institute for Solar System Research Góttingen Germany.
J Geophys Res Space Phys. 2018 Nov;123(11):9110-9129. doi: 10.1029/2018JA025665. Epub 2018 Nov 9.
The radiation belts and magnetospheres of Jupiter and Saturn show significant intensities of relativistic electrons with energies up to tens of megaelectronvolts (MeV). To date, the question on how the electrons reach such high energies is not fully answered. This is largely due to the lack of high-quality electron spectra in the MeV energy range that models could be fit to. We reprocess data throughout the Galileo orbiter mission in order to derive Jupiter's electron spectra up to tens of MeV. In the case of Saturn, the spectra from the Cassini orbiter are readily available and we provide a systematic analysis aiming to study their acceleration mechanisms. Our analysis focuses on the magnetospheres of these planets, at distances of L > 20 and L > 4 for Jupiter and Saturn, respectively, where electron intensities are not yet at radiation belt levels. We find no support that MeV electrons are dominantly accelerated by wave-particle interactions in the magnetospheres of both planets at these distances. Instead, electron acceleration is consistent with adiabatic transport. While this is a common assumption, confirmation of this fact is important since many studies on sources, losses, and transport of energetic particles rely on it. Adiabatic heating can be driven through various radial transport mechanisms, for example, injections driven by the interchange instability or radial diffusion. We cannot distinguish these processes at Saturn with our technique. For Jupiter, we suggest that the dominating acceleration process is radial diffusion because injections are never observed at MeV energies.
木星和土星的辐射带及磁层显示出相对论电子的显著强度，其能量高达数十兆电子伏特（MeV）。迄今为止，电子如何达到如此高能量的问题尚未得到充分解答。这主要是由于缺乏可供模型拟合的MeV能量范围内的高质量电子能谱。我们对伽利略号轨道器整个任务期间的数据进行重新处理，以得出木星高达数十MeV的电子能谱。对于土星，卡西尼号轨道器的能谱很容易获取，我们进行了系统分析，旨在研究其加速机制。我们的分析聚焦于这些行星的磁层，对于木星和土星，分别在L>20和L>4的距离处，此处电子强度尚未达到辐射带水平。我们发现，在这些距离上，没有证据支持MeV电子在两颗行星的磁层中主要通过波粒相互作用加速。相反，电子加速与绝热输运一致。虽然这是一个常见的假设，但对这一事实的确认很重要，因为许多关于高能粒子源、损失和输运的研究都依赖于此。绝热加热可以通过各种径向输运机制驱动，例如，由交换不稳定性或径向扩散驱动的注入。我们的技术无法在土星上区分这些过程。对于木星，我们认为主要的加速过程是径向扩散，因为在MeV能量下从未观测到注入。
