The Galileo Energetic Particles Detector is fully described byWilliams et al [WILLIAMSETAL1992].
Jupiter possesses the largest planetary magnetosphere in thesolar system. It is the largest in spatial dimension, has the highesttrapped particle energies and intensities, has the greatestcompositional variety in its major particle populations, displays thelargest co-rotational effects and has the largest number of moonswithin the magnetosphere that provide both strong sources for andlosses of the observed particle populations. These characteristics,uncovered by the Pioneer and Voyager flybys demand an instrumentdesign capable of accommodating the great range in parametric valuesestablished by these extremes.
Within the Jovian magnetosphere, the energetic (>=20 keV)particle populations play an important dual role. First, theyrepresent a major factor in determining the size, shape, and dynamicsof the system. For example, observations of energetic particleintensities and corresponding energy densities show that thesepopulations are important in (1) standing off the solar wind andthereby determining magnetopause position; (2) determining the generalmagnetic field configuration in the evening magnetosphere and (3)establishing the bulk of the ring current responsible for themagnetodisk configuration of the middle-Jovian magnetosphere.
Secondly the energetic particles play an important diagnosticrole in the determination of energization, transport, and lossprocesses active in the Jovian magnetosphere. In this role they alsoprovide a remote sensing capability for identifying magnetosphericstructures through finite gyroradius effects and for diagnosing remoteprocesses through field-aligned flow, E x B drift, and magnetic drifteffects.
The Galileo EPD will provide major extensions to the Jovianenergetic particle data base obtained from the Pioneer and Voyagerflybys. For example:(1) Galileo will be placed into a highly elliptical orbit aroundJupiter. The nominal two-year mission lifetime will allow both adirect measure of time variations in the Jovian magnetosphere and asignificantly larger spatial sample of the system than has beenpossible with the previous flybys.
(2) The nominal mission includes several close ( < 1000 km) flybys ofthe Galilean satellites thereby providing the best opportunity to dateto observe details of the satellite/magnetospheric interactions.