2025-08-08 ミネソタ大学
This image from NASA’s Juno spacecraft in 2016 shows the north polar region of Jupiter. The JunoCam obtained this view about two hours before closest approach, when the spacecraft was 120,000 miles from Jupiter. Photo provided by: NASA/JPL-Caltech/SwRI/MSSS
＜関連情報＞
- https://cse.umn.edu/college/news/alien-aurora-researchers-discover-new-plasma-wave-jupiters-aurora
- https://cse.umn.edu/physics/news/alien-aurora-lysak-sulaiman-and-elliott-find-new-plasma-regime-jupiters-aurora
- https://journals.aps.org/prl/abstract/10.1103/fn63-qmb7
木星のオーロラ帯における新たなプラズマ状態 New Plasma Regime in Jupiter’s Auroral Zones
R. L. Lysak, A. H. Sulaiman, S. S. Elliott, W. S. Kurth, and S. J. Bolton
Physical Review Letters Published: 16 July, 2025
DOI: https://doi.org/10.1103/fn63-qmb7
Abstract
Observations from the Juno satellite have indicated very low electron densities, as low as 10−3 cm−3, at high-latitudes in Jupiter’s magnetosphere. This region is strongly magnetized, with surface magnetic fields at the one-bar level up to 20 G, or 2 mT, leading to the unusual situation that the electron plasma frequency is less than the ion gyrofrequency. In this extremely low-density plasma, the Alfven wave becomes a plasma oscillation at the electron plasma frequency at shorter perpendicular wavelengths. Analysis of this mode with a kinetic low-frequency dispersion solver indicates that at large wave number, this mode has the characteristics of the Langmuir wave. Thus, this mode can be called an Alfvén-Langmuir mode. Below the plasma frequency, the high-wave number behavior of this mode exhibits a resonance cone, with frequency determined by the angle of the wave vector with the background magnetic field. These waves can be excited by the upward electron beams observed by Juno.
