Results of the Galileo EPI Experiment

We have measured energy and directional distributions of energetic charged particles in the innermost part of the Jovian radiation belt. The observations started as planned during the very last portion of the Galileo Probe's trajectory at a distance of five Jupiter radii (the radius rj is 71714 km) near the orbit of the moon Io. The last samples were taken at 1.25  radii just on top of the Jovian atmosphere at 4.94°W and 6.5°N. The region below 1.8 rj had not been reached by any other spacecraft before.

As shown in the following diagram the EPI instrument was activated for two minutes at five, four and three Jupiter radii. From two radii down to the innermost edge of the radiation belt the instrument measured continuously.

EPI measurements

The data show a new zone of the inner radiation belt below 2.5 rj. Closer to the planet dust ring particles reduce the particle density. The well defined inner edge of the particle population at 1.25 rj is mainly due to absorption by the atmosphere and possibly by a higher material density in the dust rings. The observed particle fluxes along the flight path of the Galileo Probe are given in the diagram for energetic electrons (E1-P1), protons (P1), helium particles (HE) and heavier particles (HV).

EPI-Messungen

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