Spatial color variations in the volcanic plume at Loki, on Io

Multicolor Voyager 1 photographs of the Loki volcanic plume, on Io, have been analyzed to determine the nature and quantity of the scattering material within the plume. This work indicates that there are two particle populations. The first population consists of particles with radius of 0.001–0.01 µ m, while the second population, which is concentrated near the source, comprises particles with radius greater than 1 µ m;. The population of smaller particles includes most of the particulate mass in the plume. This work increases the previously estimated particulate mass (Johnson et al., 1979) and suggests that the SO 2 gas spectroscopically identified by Pearl et al. (1979) may represent transient flow from the volcano instead of an atmosphere in stable equilibrium with the local surface.