15:30 〜 15:45
[MIS16-01] Ground-based observation of Io's volcanic activity and related plasma environment
★Invited Papers
キーワード：イオ、プラズマトーラス、火山
Volcanic gases (mainly composed of SO2, SO and S) originated from jovian satellite Io are ionized by interaction with magnetospheric plasma and then form a donut-shaped region called Io plasma torus. Sulfur and oxgen ions (S+, S++, S+++, O+, O++) in the Io plasma torus are excited by electron impact, and then emit photons in EUV to NIR wavelength. In this study, we focus on variability of brightness and structure of the Io plasma torus through observations using ground-based telescopes from 2015 to 2023 in Hawaii.
The ground-based observation of sulfur ion emission, [SII] 671.6 nm and 673.1 nm was conducted at Haleakala Observatory in Hawaii during December 2014 through July 2022 using Tohoku 60-cm telescope. A monochromatic imager with coronagraph attached onto the telescope enables to measure distribution of singly charged sulfur ion with spatial resolution of 0.03 jovian radii. A digital micro-mirror device DMD was employed to block light from Jupiter disk and Galilean moons. Typical integration time of each frame was 20 minutes and total number of reduced images is about 2500. We also made observation of neutral sodium cloud extending up to several hundred of RJ as a proxy of supply of neutral particles from Io (Yoneda et al., 2015).
From the monitoring observation during 2015 through 2020, we found several brightening events in S+ emission on Io plasma torus. Especially, events in February 2015, August 2019 and June 2020, the S+ brightness increased by a factor of 2-3 in a few weeks. In the three cases, S+ north-south distribution scaleheight started to increase just after S+ brightness peaks suggesting increase of ion temperature. We also observed associated variability in iogenic neutral sodium cloud. Those variability in iogenic neutral gases and Io plasma torus are supposed to be associated with the volcanic activity on Io.
The ground-based observation of sulfur ion emission, [SII] 671.6 nm and 673.1 nm was conducted at Haleakala Observatory in Hawaii during December 2014 through July 2022 using Tohoku 60-cm telescope. A monochromatic imager with coronagraph attached onto the telescope enables to measure distribution of singly charged sulfur ion with spatial resolution of 0.03 jovian radii. A digital micro-mirror device DMD was employed to block light from Jupiter disk and Galilean moons. Typical integration time of each frame was 20 minutes and total number of reduced images is about 2500. We also made observation of neutral sodium cloud extending up to several hundred of RJ as a proxy of supply of neutral particles from Io (Yoneda et al., 2015).
From the monitoring observation during 2015 through 2020, we found several brightening events in S+ emission on Io plasma torus. Especially, events in February 2015, August 2019 and June 2020, the S+ brightness increased by a factor of 2-3 in a few weeks. In the three cases, S+ north-south distribution scaleheight started to increase just after S+ brightness peaks suggesting increase of ion temperature. We also observed associated variability in iogenic neutral sodium cloud. Those variability in iogenic neutral gases and Io plasma torus are supposed to be associated with the volcanic activity on Io.