Identification of Extreme Ultraviolet Emission Lines of the Io Plasma Torus Observed by Hisaki/EXCEED

• Published in: Journal of geophysical research. Planets Vol. 123; no. 7; pp. 1723 - 1731
• Main Authors: Hikida, R., Yoshioka, K., Murakami, G., Kimura, T., Tsuchiya, F., Yamazaki, A., Yoshikawa, I., Iwagami, N.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-07-2018
• Subjects: Electron density; Emission lines; Emissions; Energy balance; Estimation accuracy; EXCEED; extreme ultraviolet emission lines; Extreme values; Hisaki; Io plasma torus; Jupiter; Oxygen; Oxygen ions; Radiative cooling; Sulfur; Toruses; Ultraviolet emission; Ultraviolet spectra
• ISSN: 2169-9097; 2169-9100
• DOI: 10.1029/2018JE005629

The sulfur and oxygen ions in the Io plasma torus (IPT), which is located at a distance of ~6 RJ from Jupiter, emit light in various wavelength regions. In particular, radiative cooling in the ultraviolet wavelength range plays an important role in the energy balance of the Io torus, and it is important to explore the detailed spectral structure in the ultraviolet region. The ultraviolet spectrum of the IPT in the wavelength range 52.0–148.0 nm with a resolution of 0.3–0.4 nm was obtained by Extreme Ultraviolet Spectroscope for Exospheric Dynamics on the Hisaki satellite. Owing to its instrument performance and long integration time, 10 emission lines from the IPT were detected for the first time. By summarizing previous observations and using the results obtained by Extreme Ultraviolet Spectroscope for Exospheric Dynamics, we updated the term diagrams for S II, S III, and S IV emissions from the IPT. Four excited levels in the IPT were detected for the first time. Detection of the emission lines may improve the estimation accuracy of the fraction of hot electron density using the atomic data.
Key Points
Ten emission lines from the Io plasma torus were detected for the first time through the observation by Hisaki/EXCEED
Four excited levels in the Io plasma torus were detected for the first time through the observation by Hisaki/EXCEED
Detection of the new emission lines may improve estimation accuracy of the fraction of hot electrons in the torus