Low-Energy Charged Particle Environment at Jupiter: A First Look

Science  01 Jun 1979:
Vol. 204, Issue 4396, pp. 998-1003
DOI: 10.1126/science.204.4396.998


The low-energy charged particle instrument on Voyager was designed to measure the hot plasma (electron and ion energies15 and30 kiloelectron volts, respectively) component of the Jovian magnetosphere. Protons, heavier ions, and electrons at these energies were detected nearly a third of an astronomical unit before encounter with the planet. The hot plasma near the magnetosphere boundary is predominantly composed of protons, oxygen, and sulfur in comparable proportions and a nonthermal power-law tail; its temperature is about 3 x 108 K, density about 5 x 10–3 per cubic centimeter, and energy density comparable to that of the magnetic field. The plasma appears to be corotating throughout the magnetosphere; no hot plasma outflow, as suggested by planetary wind theories, is observed. The main constituents of the energetic particle population (200 kiloelectron volts per nucleon) are protons, helium, oxygen, sulfur, and some sodium observed throughout the outer magnetosphere; it is probable that the sulfur, sodium, and possibly oxygen originate at 1o. Fluxes in the outbound trajectory appear to be enhancedfrom90° to130° longitude (System III). Consistent low-energy particle flux periodicities were not observed on the inbound trajectory; both 5-and 10-hour periodicities were observed on the outbound trajectory. Partial absorption of > 10 million electron volts electrons is observed in the vicinity of the Io flux tube.

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