Io Atmospheric [O I] 6300Å Emission and the Plasma Torus

Details Io Atmospheric [O I] 6300Å Emission and the Plasma Torus Io Atmospheric [O I] 6300Å Emission and the Plasma Torus

Oct 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000dps....32.3513o&link_type=abstract

American Astronomical Society, DPS Meeting #32, #35.13; Bulletin of the American Astronomical Society, Vol. 32, p.1059

Astronomy and Astrophysics

Astronomy

Scientific paper

Extensive Io [O I] 6300Å observations, covering the period 1990-1999, exhibit significant long-term and short-term intensity variations. The long-term average intensity shows a clear dependence on system III longitude, which establishes conclusively that the emission is produced by the interaction between Io's atmosphere and the plasma torus. Two prominent average intensity maxima, 70-90 degrees wide, are centered at system III longitudes 130 and 295. A comparison of data from October 1998 with a three-dimensional plasma torus model, based upon electron impact excitation of atomic oxygen, suggest a basis for study of the torus interaction with Io's atmosphere. The observed short-term [O I] 6300Å intensity variations are separated from the underlying variations caused by large-scale structure of the plasma torus (e.g., electron ribbon location with local time, magnetic latitude, and system III longitudinal asymmetries), with typical fluctuations of 25-50% on timescales of tens of minutes and 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 PLS data. This connection raises the possibility that time scales of [O I] 6300Å emission fluctuations may be related to scale sizes of inward and outward torus plasma transport cells and/or high magnetic latitude created double-layer electron beams. A positive correlation discovered between the intensity and the emission line width may indicate that molecular dissociation also contributes to the [O I] 6300Å emission. The nonthermal electron energy flux may explain this correlation through production of O(1D) by electron impact dissociation of SO2 and SO, with the excess energy going into excitation of O and its kinetic energy. This work is supported by NASA's Planetary Astronomy program.

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