Survey of Voyager plasma science ions at Jupiter: 3. Protons and minor ions

Abstract

AbstractWhen the Voyager 1 and 2 spacecraft flew through the Jovian system in March and July 1979, the Plasma Science instruments measured ions and electrons in the Io plasma torus and plasma sheet between 4.9 and 42 RJ. The dominant ions in the Jovian magnetosphere comprise the first few ionization states of atomic sulfur and oxygen. We present here an analysis of minor ion species H+, Na+, and SO2+. Protons are 1–20% of the plasma between 5 and 30 RJ with variable temperatures ranging by a factor of 10 warmer or colder than the heavy ions. We suggest that these protons, measured deep inside the magnetosphere, are consistent with a source from the ionosphere of ~1.5–7.5 × 1027 protons s−1 (2.5–13 kg/s). Na+ ions are detected between 5 and 40 RJ at an abundance of 1 to 10%, produced by the ionization of the extended neutral cloud emanating from Io that has been observed since 1974. SO2+ ions are detected between 5.31 and 5.07 RJ at an abundance of 0.1–0.6%. These ions clearly come from the plasma interaction with Io's atmosphere, but the exact processes whereby atmospheric molecules escape Io and end up as ions well inside Io's orbit are not clear.