Survey of Voyager plasma science ions at Jupiter: 1. Analysis method

Abstract

When the Voyager 1 and 2 spacecraft fl ew 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 R J . The dominant ions in the Jovian magnetosphere comprise the fi rst few ionization states of atomic sulfur and oxygen. We present here an analysis of minor ion species H + ,Na + , and SO 2 + . Protons are 1 – 20% of the plasma between 5 and 30 R J 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 × 10 27 protons s 1 (2.5 – 13 kg/s). Na + ions are detected between 5 and 40 R J 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. SO 2 + ions are detected between 5.31 and 5.07 R J 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.