Hot plasma heavy ion abundance in the inner Jovian magnetosphere (<10 Rj)

Knowledge of the hot plasma components of the Jovian environment is important for several scientific problems, including the acceleration and transport of Jovian plasmas, the stability of the plasma sheet, and the bombardment, implantation, and sputtering of the surfaces of Jovian moons, especially Europa. The multiple flybys of the Jovian moon Europa during the Galileo mission have provided the opportunity to study the time and spatial dependence of the abundance of the dominant hot plasma (∼0.2–10 MeV/nucleon (n)) heavy ions in the innermost region of the Jovian magnetosphere (≲10 Rj). Reported here are measurements made by the CMS ΔE×E telescopes in the EPD instrument on the Galileo orbiter during the first six encounters with the moon Europa, data taken over a period of about 1.5 years. We use these measurements to study the hot plasma oxygen, sulfur, and sodium abundances near and inside the Europa orbit. The values we determine for these species in the energy range of 0.5–1.0 MeV/n are 0.67±0.05 for the S/O abundance and 0.05±0.01 for the Na/O abundance, and are similar to previous determinations made by instruments on the Voyager (measurements in 1979) and Ulysses (measurements in 1992) spacecraft.