Sunlit Io atmospheric [O I] 6300 Å emission and the plasma torus

Details Sunlit Io atmospheric [O I] 6300 Å emission and the plasma torus Sunlit Io atmospheric [O I] 6300 Å emission and the plasma torus

Nov 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001jgr...10626183o&link_type=abstract

Journal of Geophysical Research, Volume 106, Issue A11, p. 26183-26194

Physics

14

Magnetospheric Physics: Magnetosphere Interactions With Satellites And Rings, Planetology: Fluid Planets: Interactions With Particles And Fields, Planetology: Fluid Planets: Tori And Exospheres, Planetology: Solar System Objects: Jovian Satellites

Scientific paper

A large database of sunlit Io [O I] 6300 Å emission, acquired over the period 1990-1999, with extensive coverage of Io orbital phase angle ϕ and System III longitude λIII, exhibits significant long-term and short-term variations in [O I] 6300 Å emission intensities. The long-term average intensity shows a clear dependence on λIII, which establishes conclusively that the emission is produced by the interaction between Io's atmosphere and the plasma torus. Two prominent average intensity maxima, 70° to 90° wide, are centered at λIII~130° and λIII~295°. A comparison of data from October 1998 with a three-dimensional plasma torus model, based upon electron impact excitation of atomic oxygen, suggests a basis for study of the torus interaction with Io's atmosphere. The observed short-term, erratic [O I] 6300 Å intensity variations fluctuate ~20-50% on a timescale of tens of minutes with less frequent fluctuations of a factor of ~2. The most likely candidate to produce these fluctuations is a time-variable energy flux of field-aligned nonthermal electrons identified recently in Galileo plasma science data. If true, the short-term [O I] intensity fluctuations may be related to variable field-aligned currents driven by inward and outward torus plasma transport and/or transient high-latitude, field-aligned potential drops. A correlation between the intensity and emission line width indicates molecular dissociation may contribute significantly to the [O I] 6300 Å emission. The nonthermal electron energy flux may produce O(1D) by electron impact dissociation of SO2 and SO, with the excess energy going into excitation of O and its kinetic energy. The [O I] 6300 Å emission database establishes Io as a valuable probe of the torus, responding to local conditions at Io's position.

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