Volume 8, Issue 4 p. 409-412

Detection of the Io plasma torus by Pioneer 10

First published: April 1981
Citations: 13


Evidence of corotating ions which appear to be primarily S++ and O++ has been discovered in data from the Pioneer 10 plasma analyzer, recorded as the spacecraft moved inward from 6.9 to 5.4 RJ during its encounter with Jupiter in 1973. H+ or He++ ions or other light ions are also observed during this time. The Pioneer 10 plasma profile shows a relative variation with radial distance remarkably similar to the Voyager density profile. Both show a well-defined peak falling off steeply toward Jupiter and gradually decreasing away from Jupiter. The Pioneer 10 plasma data are also consistent with a constant temperature plasma for at least 0.5 RJ outside Io’s orbit. A radially inward deflection from strict corotation is also evident in our data. Our detailed analysis of the Pioneer 10 plasma instrument’s behavior and data in the inner Jovian magnetosphere indicates that the above results are not seriously distorted by radiation background. The previous study of Pioneer 10 data of the inner Jovian magnetosphere (Frank et al., 1976) did not include the particular telemetered values from which our detection of these ions has been inferred.