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Spatial Distribution of Io's Neutral Oxygen Cloud Observed by Hisaki
Author(s) -
Koga Ryoichi,
Tsuchiya Fuminori,
Kagitani Masato,
Sakanoi Takeshi,
Yoneda Mizuki,
Yoshioka Kazuo,
Yoshikawa Ichiro,
Kimura Tomoki,
Murakami Go,
Yamazaki Atsushi,
Smith H. Todd,
Bagenal Fran
Publication year - 2018
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2018ja025328
Subject(s) - jupiter (rocket family) , exosphere , oxygen , atmosphere (unit) , physics , airglow , extreme ultraviolet , atomic physics , ion , astronomy , meteorology , optics , laser , space shuttle , quantum mechanics
We report on the spatial distribution of a neutral oxygen cloud surrounding Jupiter's moon Io and along Io's orbit observed by the Hisaki satellite. Atomic oxygen and sulfur in Io's atmosphere escape from the exosphere mainly through atmospheric sputtering. Some of the neutral atoms escape from Io's gravitational sphere and form neutral clouds around Jupiter. The extreme ultraviolet spectrograph called EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics) installed on the Japan Aerospace Exploration Agency's Hisaki satellite observed the Io plasma torus continuously in 2014–2015, and we derived the spatial distribution of atomic oxygen emissions at 130.4 nm. The results show that Io's oxygen cloud is composed of two regions, namely, a dense region near Io and a diffuse region with a longitudinally homogeneous distribution along Io's orbit. The dense region mainly extends on the leading side of Io and inside of Io's orbit. The emissions spread out to 7.6 Jupiter radii ( R J ). Based on Hisaki observations, we estimated the radial distribution of the atomic oxygen number density and oxygen ion source rate. The peak atomic oxygen number density is 80 cm −3 , which is spread 1.2 R J in the north‐south direction. We found more oxygen atoms inside Io's orbit than a previous study. We estimated the total oxygen ion source rate to be 410 kg/s, which is consistent with the value derived from a previous study that used a physical chemistry model based on Hisaki observations of ultraviolet emission ions in the Io plasma torus.