Extreme Ultraviolet Observations from Voyager 1 Encounter with Saturn

Abstract

The global hydrogen Lyman alpha, helium (584 angstroms), and molecular hydrogen band emissions from Saturn are qualitatively similar to those of Jupiter, but the Saturn observations emphasize that the H(2) band excitation mechanism is closely related to the solar flux. Auroras occur near 80 degrees latitude, suggesting Earth-like magnetotail activity, quite different from the dominant Io plasma torus mechanism at Jupiter. No ion emissions have been detected from the magnetosphere of Saturn, but the rings have a hydrogen atmosphere; atomic hydrogen is also present in a torus between 8 and 25 Saturn radii. Nitrogen emission excited by particles has been detected in the Titan dayglow and bright limb scans. Enhancement of the nitrogen emission is observed in the region of interaction between Titan's atmosphere and the corotating plasma in Saturn's plasmasphere. No particle-excited emission has been detected from the dark atmosphere of Titan. The absorption profile of the atmosphere determined by the solar occultation experiment, combined with constraints from the dayglow observations and temperature information, indicate that N(2) is the dominant species. A double layer structure has been detected above Titan's limb. One of the layers may be related to visible layers in the images of Titan.

Micrometeorite erosion of the main rings as a source of plasma in the inner Saturnian plasma torus

“…The total density increases to a maximum of 2.8 x 1013 mol./cm 2 above the outer A ring for the upper limit on the source and is -2.8 × 1012 mol./cm 3 for one-tenth the source. These are comparable to the total neutral H abundance -1013/cm 2 (Broadfoot et al 1981). The total column density for the energy spectrum of Eq.…”

Thermal plasma and neutral gas in Saturn's magnetosphere

“…Hydrogen atoms (H) emit Lyman alpha radiation (because of resonance scattering of sunlight) which can be detected by ultraviolet spectrometer (UVS) instruments. The Voyager UVS experiments detected H radiation; the original data interpretation was of a torus of H with density of about 20 atoms cm -3 in the vicinity of Titan's orbit [Broadfoot et al, 1981;Sandel et al, 1982]. Subsequent analysis of additional UVS spectra suggests that the H cloud probably has two components, one associated with Titan which is azimuthally asymmetric and centered on Titan's orbit and one which extends in to Saturn's surface which has an intensity peak on the duskside of Saturn [Shemansky and Hall, 1992] (although there is a discrepancy between preencounter and postencounter data as to whether the observations are brightest on the duskside or dawnside).…”

The global plasma environment of Titan as observed by Cassini Plasma Spectrometer during the first two close encounters with Titan

“…It orbits Saturn at a distance of just over 20 Saturn radii (R S ). Moreover, it is the only satellite with an appreciable atmosphere, one which is composed mostly of nitrogen with some methane and H 2 [see, e.g., Broadfoot et al, 1981]. Titan's interaction with Saturn's magnetosphere was first observed by Voyager 1, Hartle et al [1982] and Neubauer et al [1984] have given the most comprehensive analysis of the Titan interaction based on Voyager 1 data.…”