7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

The radial plasma transports in Jupiter’s inner magnetosphere seen byspectroscopic observation.
Kazuo Yoshioka1, and Hisaki Science team1
Graduate School of Frontier Sciences, The University of Tokyoe-mail (speaker): kazuo.yoshioka@edu.k.u-tokyo.ac.jp
The Io plasma torus (IPT), located in the Jovian innermagnetosphere (6-8 Jovian radii (RJ) from the planet), isfilled with electrons and heavy ions such as sulfur andoxygen, a significant portion of which originates fromthe volcanoes on Io. The IPT serves as a crucial region
connecting the primary plasma source (Io) with themiddle and outer magnetosphere, where highly dynamic
phenomena occur. Understanding the behavior of plasma
in the IPT is essential for discussing the plasma
dynamics in the whole Jovian magnetosphere (Fig. 1).

Fig. 1 Schematics of Jovian magnetosphere
A comprehensive understanding of the IPT can beachieved through spectral analysis of ion emissions,which are generated by electron impact excitation. Thismethod is called as “Plasma diagnosis”. The emission
lines from ions in the IPT is mainly in the extreme
ultraviolet (EUV) region. Therefore, EUV spectroscopic
data are important for the study of Jupiter's innermagnetosphere.
Hisaki, an Earth-orbiting spacecraft equipped with theextreme ultraviolet spectroscope EXCEED, have been
providing high-resolution spectra of IPT (Fig.2). Hisaki
has been launched in 2013 and still working in 2023[1].

Fig.2 Optical schematics of EXCEED on Hisaki
It sub-continuously observe the IPT and take spectral
images every 1 minute during almost half of its orbital
period of ~100 minutes. The spectral range of EXCEED
is from 52 to 148 nm and its spatial and spectral
resolutions are around 0.5 RJ and 0.3-1.0nm FWHM,respectively. By using those data and plasma diagnosis
method, we can deduce the plasma parameters such as
electron density and temperature, and ion densities [2-4].
The data also has undergone physical chemistrymodeling, assuming axial symmetry. The investigation
has yielded radial profiles of various parameters,

including electron density, temperature, and ionabundances. Moreover, the transport timescale forinward-moving mid-magnetospheric plasma has been
determined to be 2-40 hours, based on the profile ofsupra-thermal electrons. The physical chemistrymodeling indicates an outward transport timescale ofapproximately 30 days for Io-derived plasma. The ratio
between inward and outward plasma speeds (~ 1%) is
consistent with the occurrence rate of depleted flux tubes
observed through in-situ measurements by instrumentson the Galileo spacecraft [5].
In addition, Hisaki observations also revealed that thedynamics of the Jovian magnetosphere are greatly
influenced in response to the Io's volcanic activity. In
early 2015, when various observations indicated anupsurge in volcanic activity, Hisaki embarked oncontinuous observations of the Jovian magnetosphere,
focusing on the aurora emissions and the emission
emanating from the IPT (Fig.3). By employing plasma
diagnosis to analyze the intensified spectrum, inconjunction with a physical chemistry model used todeduce plasma parameters, the study revealed asignificant increase in plasma density and a radial flowrate approximately 2-4 times faster than during a periodof volcanic quiescence. Subsequently, about a month
later, the aurora emissions, indicative of middle
magnetospheric activities, exhibited multiple peaks ofheightened brightness.

Fig.3 Temporal variation of Io plasma torus brightness
during volcanically quiet and active periods [6]In this presentation, the Hisaki mission, its data analysis,
and the new knowledge about Jupiter's magnetosphereprovided by the Hisaki data will be introduced.
References[1] Yoshioka et al. 2013, PSS 85, 250[2] Yoshioka et al. 2014, Science 345, 6,204[3] Yoshikawa et al. 2014, SSR 184, 237[4] Yamazaki et al. 2014, SSR 184, 259[5] Yoshioka et al. 2017, JGR 122, 2,999[6] Yoshioka et al. 2018, GRL 45, 10,193