Corotation of Bright Features in the Io Plasma Torus

Electron energy distribution in the Io plasma torus (IPT) is non‐Maxwellian. The “hot” components induce extreme ultraviolet radiation, although their energy source remains unknown. One potential mechanism that may preserve the energy of hot electrons is inwardly directed plasma motion in the Jovian...

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Bibliographic Details
Published in:Journal of geophysical research. Space physics 2018-11, Vol.123 (11), p.9420-9429
Main Authors: Suzuki, F., Yoshioka, K., Hikida, R., Murakami, G., Tsuchiya, F., Kimura, T., Yoshikawa, I.
Format: Article
Language:English
Subjects:
Brightening
Cooling
Corotation
Coulomb collisions
Electron energy
Electron energy distribution
Energy sources
Extreme ultraviolet radiation
Hot electrons
Jupiter
Magnetosphere
Planetary magnetospheres
Radiative cooling
Rotating plasmas
Satellite observation
Toruses
Ultraviolet radiation
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Summary:Electron energy distribution in the Io plasma torus (IPT) is non‐Maxwellian. The “hot” components induce extreme ultraviolet radiation, although their energy source remains unknown. One potential mechanism that may preserve the energy of hot electrons is inwardly directed plasma motion in the Jovian magnetosphere. Therefore, understanding the high‐energy component of the electron energy distribution is important. The extreme ultraviolet spectrometer onboard the HISAKI satellite has started the observation of the IPT. We show that bright transient features in one ansa of the IPT correlate with those in the other ansa after 5 hr. Because it takes 5 hr (one half of the rotation cycle of Jupiter) for a batch of plasma to move from one ansa to the other, the correlation indicates that the transient features are identical and that they survive for greater than 5 hr. Since the time scale of the radiative cooling process is ~3 hr, this fact suggests that injected hot electrons survive against cooling via Coulomb collision with ambient electrons for greater than 2 hr. Assuming the relationship with the cooling time, we can deduce the hot electron temperature from the brightening duration. Here we report the occasional hot electron injections, presumed to exceed 150 up to 650 eV, into the IPT (approximately 15% out of all events). For the most of events, the temperature of injected electron is lower than 150 eV. Key Points Continuous and long‐term observation by HISAKI led to the discovery of the corotation of bright spots in the Io plasma torus Most of the spots (~85%) survived for shorter than 5 hr, suggesting that “warm” (10 hr), indicating that the hot electron temperature reaches 650 eV
ISSN:2169-9380
2169-9402
DOI:10.1029/2018JA025363