37th DPS Meeting, 4-9 September 2005
Session 58 Galilean Satellites
Poster, Thursday, September 8, 2005, 6:00-7:15pm, Music Recital Room

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[58.02] Velocity distribution and its spatial extent of sodium atoms originated from Io

Kazuhiro Aoi, Masato Kagitani, Hidetaka Ueto, Shoichi Okano (Planetary Plasma and Atmospheric Research Center, Tohoku University, Japan)

Jovian satellite Io possesses active volcanic activities and the erupted gas supplys neutrals and ions to the Jovian magnetosphere through the interaction between Io plasma torus and Io. Volcanic gas contains neutral sodium atoms and sodium-bearing molecular ions. They escape from Io through several physical processes which have so far been proposed for ejection of sodium from Io. These ejection processes include atmospheric sputtering for producing the banana cloud, pick-up ion neutralization in Io's atmosphere for the sodium jet, pick-up molecular ion destruction in Io plasma torus for the stream, and charge exchange between Io's atmosphere and the torus for the fan shape.

In order to understand these ejection processes more clearly, high dispersion spectroscopic observation was carried out at the Okayama Astrophysical Observatory, National Astronomical Observatory of Japan, using a 188-cm telescope and the High Dispersion Echelle Spectrograph (HIDES: R=100,000) on 4 nights in February, 2004 and 3 nights in February, 2005. A number of high dispersion spectra of sodium D1 and D2 emissions were obtained for a region of ±1.5RJ (1RJ : Jovian radius = 71492km) centered on Io from the two observations. Analysed results show fast velocity component to the direction of Io's orbital motion on the wing of distinctive slow velocity component in Io's rest frame inside the Io's corona.

In the presentation, ejection velocity distributions of neutral sodium atoms at various Io phase angles will be given. Further, the spatial extent of velocity distribution from Io through the Io's corona to the inner Jovian magnetosphere will be discussed in the context of the ejection processes mentioned above.

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.