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- Title
Transient Change of Io's Neutral Oxygen Cloud and Plasma Torus Observed by Hisaki.
- Authors
Koga, Ryoichi; Tsuchiya, Fuminori; Kagitani, Masato; Sakanoi, Takeshi; Yoshioka, Kazuo; Yoshikawa, Ichiro; Kimura, Tomoki; Murakami, Go; Yamazaki, Atsushi; Smith, H. Todd; Bagenal, Fran
- Abstract
Io's atmospheric oxygen atoms are heated by atmospheric sputtering and escape from Io's gravity, forming a neutral oxygen cloud around Io's orbit. This neutral cloud is important as a source of the Io oxygen plasma torus. Previous studies derived the distribution and density of the equilibrium neutral oxygen cloud. However, little is known about the evolution of the neutral cloud. In this study, we analyzed Hisaki satellite observations of the spatial distribution of OI 130.4 nm emissions around Io's orbit during transient strong density enhancement in the torus in 2015 (called high density period). Comparing time variations of OI and OII 83.4 nm emissions, we estimated that the lifetimes of O+ in this period were about 21 days in the high density period and 41 days in the normal density period. Hisaki observations are consistent with a decrease in the lifetime of O+ when the density in the torus increases. The radial distribution showed the neutral oxygen cloud spread outward up to 8.6 Jupiter radii during the high density period. We also show that during the high density period, the neutral oxygen number density at Io's orbit (where north‐south thickness is assumed to be 1.2 Jupiter radii) increased to 91−25+29 cm−3, more than three times the value during the normal density period (27−7+8 cm−3). The azimuthal distribution showed a dense region around Io and a longitudinally uniform, diffuse region distributed along Io's orbit that enlarges during the high density period. Key Points: The lifetime of O+ was estimated from time variations of O and O+, and it shortened during the density enhancement in 2015Io's neutral oxygen cloud spread outward from Jupiter during the high density periodThe number density of O at Io's orbit during the high density period is three times larger than that during the normal density period
- Subjects
ATMOSPHERIC oxygen; SPUTTERING (Physics); OXYGEN plasmas; RADIAL distribution function; JUPITER (Planet)
- Publication
Journal of Geophysical Research. Space Physics, 2019, Vol 124, Issue 12, p10318
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2019JA026877