GALILEO MEASUREMENTS OF PLASMA-DENSITY IN THE IO TORUS

The measurements of electron density made by the Plasma Wave Subsystem instruments on Galileo during its pass through the torus on December 7th, 1995 are compared with a model based on Voyager 1 measurements ma de in March 1979. Outside Io's orbit, the plasma densities observed by Galileo are approximately a factor of two higher than the Voyager val ues. Shortly after crossing Io's orbit, the Galileo density profile dr opped sharply and remained at low values for the rest of the inbound l eg, suggesting that the 'ribbon' region was either absent or much fart her from Jupiter than usual. The peak density on the outbound leg is c onsistent with Voyager-based predictions for the cold torus in both lo cation (5.1 RJ) and magnitude (950 cm(-3)). Inside 5 RJ the density dr opped sharply to less than 3 cm(-3).