PPARC セミナー (2024/10/25)

PPARC セミナー (2024/10/25)

(1) Shinnosuke Satoh

[Title]  
EMIC waves at Io and Ganymede

[Abstract]  
Strong electromagnetic ion cyclotron (EMIC) waves were detected in the plasma downstream of Io during the close flybys of the Galileo spacecraft (e.g.; Kivelson et al., 1996; Huddleston et al., 1997). The EMIC waves at Io are associated with the pickup ions: the pickup ions are accelerated almost perpendicularly to the local magnetic field line, resulting in an initial velocity distribution that is highly unstable and generates the EMIC waves at frequency of the local ion cyclotron frequency (Huddleston et al, 1998). The detection of EMIC waves at the singly-ionized SO frequency revealed Io’s exosphere contains a time-variable neutral SO component (Russell and Kivelson, 2001). To this day, Galileo’s magnetic field observations detected the EMIC waves associated with singly ionized S (mass-over-charge, m/q=32), H_2S (m/q=34), SO (m/q=48), and SO_2 (m/q=64) in the vicinity of Io (e.g.; Russell and Kivelson 2001; Russell et al., 2003).
The EMIC waves at Ganymede, on the other hand, have not yet reported. Our study attempts to detect EMIC waves at Ganymede using the fluxgate magnetometer (MAG) on board the Juno spacecraft (Connerney et al., 2017). We used the Juno/MAG observation data obtained during its only flyby at Ganymede on June 7, 2021 (closest approach at 16:56:07 UTC). Juno went through the plasma downstream of Ganymede and was likely connected with the open field lines during the flyby (Allegrini et al., 2022). We calculated the short-time Fourier transform (STFT) and the discrete wavelet transform (DWT) of the magnetic field components parallel and perpendicular to the time-averaged field line direction. Assuming that the EMIC waves propagate along the magnetic field line, we derived the coherence and phase difference using the cross spectrum of the two perpendicular components to see the polarization. So far, we are looking for the EMIC waves associated with the m/q=1, 2, 3, 8, 16, and 32 ions when Juno is in the Ganymede magnetosphere. Left-hand polarization is clearly confirmed for the m/q=32 EMIC wave, which we speculate is associated with the pickup molecular oxygen ions. The presence of molecular-oxygen EMIC wave is consistent with the particle observation (Allegrini et al., 2022). We are still investigating the EMIC waves associated with the other ions. In this presentation, the current status of the research will be reported.

(2) Yasumasa Kasaba

[Title]
Plasma and radio waves in BepiColombo and JUICE: Recent flybys & Progress

[Abstract]
With Plasma Wave Experiment (PWE) aboard Arase spacecraft, we are running two major collaborations with Europe.
The first is Plasma Wave Investigation (PWI) aboard the Mio spacecraft of BepiColombo, ESA-JAXA joint mission to Mercury, which will observe Mercury on the orbit from the end of 2025. The second is Radio and Plasma Wave Investigations (RPWI) aboard ESA JUpiter ICy moons Explorer (JUICE) mission to Jupiter, which will observe Jovian system on the orbit from 2031. In both Japan and Europe, main players are overlapped and collaborating strongly in both missions and beyond.
In this presentation, we show followings:
(1) BepiColombo/Mio PWI –  recent results of Mercury flybys, including the 4th in Sep 2024  [based on EPSC2024 presentation]
(2) JUICE RPWI –  Lunar-Earth flyby plans in Aug 2024 [based on RPWI Team meeting + preparation for SGEPSS talk]