Extreme Ultraviolet Observations from the Voyager 2 Encounter with Saturn

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Abstract
Combined analysis of helium (584 angstroms) airglow and the atmospheric occultations of the star δ Scorpii imply a vertical mixing parameter in Saturn's upper atmosphere of K (eddy diffusion coefficient) ∼8 × 10 7 square centimeters per second, an order of magnitude more vigorous than mixing in Jupiter's upper atmosphere. Atmospheric H 2 band absorption of starlight yields a preliminary temperature of 400 K in the exosphere and a temperature near the homopause of ∼200 K. The energy source for the mid-latitude H 2 band emission still remains a puzzle. Certain auroral emissions can be fully explained in terms of electron impact on H 2 , and auroral morphology suggests a link between the aurora and the Saturn kilometric radiation. Absolute optical depths have been determined for the entire C ring and parts of the A and B rings. A new eccentric ringlet has been detected in the C ring. The extreme ultraviolet reflectance of the rings is fairly uniform at 3.5 to 5 percent. Collisions may control the distribution of H in Titan's H torus, which has a total vertical extent of ∼14 Saturn radii normal to the orbit plane.