Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA.
Department of Earth, Planetary and Space Sciences, University of California Los Angeles, Los Angeles, CA, USA.
Nature. 2024 Mar;627(8002):64-66. doi: 10.1038/s41586-024-07046-3. Epub 2024 Mar 6.
Planetary magnetic fields provide a window into the otherwise largely inaccessible dynamics of a planet's deep interior. In particular, interaction between fluid flow in electrically conducting interior regions and the magnetic field there gives rise to observable secular variation (time dependency) of the externally observed magnetic field. Secular variation of Jupiter's field has recently been revealed and been shown to arise, in part, from an axisymmetric, equatorial jet. Whether this jet is time dependent has not previously been addressed, yet it is of critical importance for understanding the dynamics of the planet's interior. If steady, it would probably be a manifestation of deep dynamo convective flow (and jets are anticipated as part of that flow) but if time dependent on a timescale much shorter than the convective turnover timescale of several hundred years, it would probably have a different origin. Here we show that the jet has a wavelike fluctuation with a period of roughly 4 years, strongly suggestive of the presence of a torsional oscillation (a cylindrically symmetric oscillating flow about the rotation axis) or a localized Alfvén wave in Jupiter's metallic hydrogen interior. This opens a pathway towards revealing otherwise hidden aspects of the magnetic field within the metallic hydrogen region and hence constraining the dynamo that generates Jupiter's magnetic field.
行星磁场为研究行星内部深处通常难以接近的动力学提供了一个窗口。特别是，在导电内部区域的流体流动与磁场之间的相互作用，导致了外部观测到的磁场的可观测的长期变化（时间依赖性）。木星磁场的长期变化最近已经被揭示出来，并且部分是由轴对称的赤道喷流引起的。这个喷流是否具有时间依赖性以前尚未得到解决，但对于理解行星内部的动力学至关重要。如果是稳定的，它可能是深部发电机对流流动的表现（喷流预计是该流动的一部分），但如果时间依赖性比几百年来的对流翻转时间尺度短得多，它可能具有不同的起源。在这里，我们表明喷流具有大约 4 年的波动，强烈表明存在扭转振动（关于旋转轴的圆柱对称振动流）或木星金属氢内部的局部阿尔文波。这为揭示金属氢区域内磁场的其他隐藏方面开辟了道路，从而限制了产生木星磁场的发电机。
