Long-lived particulate or gaseous structure in Saturn's outer magnetosphere?

Abstract

During the encounters with Saturn by the Voyager 1, Voyager 2 and the Pioneer 11 spacecraft, large variations in the number density of low-energy plasma ions were observed in the outer magnetosphere. Those density variations were thought to be due to changing external conditions, remnants of gas from Titan, or detached portions of Saturn's main plasma sheet. We have found evidence which suggests that at least some of the density variations (which appear as dips in a curve which generally shows rising density as Saturn is approached) are due to absorbing material near Saturn's equatorial plane in the region between 10 and 20 Saturn radii (R_s). Although the entire picture is still speculative, we present our evidence to encourage further optical examination of that region near Saturn. Notably, in 1978 Colombo suggested that a deep survey be made of the region between Tethys and Titan (10–20 R_s) because of its similarity to the asteroid belt in the Solar System¹.