Observations of extreme ultraviolet emissions from the Saturnian plasmasphere

Emission signals from the Saturnian plasmasphere at wavelengths shortward of 800 A have been detected by the Pioneer ultraviolet photometer. The surface brightness of the emissions is about 0.3±0.2 R. These short-wavelength emissions are interpreted as arising primarily from the radiative decay of electron excited atomic oxygen ions (O++), in the region between 5 and 7 Rs from Saturn. The total power radiated by the Saturnian plasma inferred from these ultraviolet measurements is about ∼2 × 1016 erg s−1, consistent with in situ plasma measurements. From the observed energy loss rate it is estimated that the ions are introduced into the plasma torus at a rate of 8 × 1025 ions/s, possibly through the sputtering of water ice on the surface of Tethys and Dione by particle impact.

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