 The later years saw analysis of data from the instrument during the fly-bys of Jupiter (1979 for both Voyager 1 and 2).The elemental abundance of MeV particles in the Jovian magnetosphere was expected to be dominated by hydrogen and helium, so it was a surprise to find oxygen and sulfur dominant.This discovery was found to be related to the Voyager discovery of volcanoes on the moon Io spewing oxygen and sulfur into the magnetosphere.