Jovian, Solar, and other Possible Sources of Radiation Belt Particles

It is well known that electrons, protons, and heavier ions can be accelerated to high energies (≳1 MeV) throughout the solar system by a variety of mechanisms. We review several of the sources of energetic ions and electrons that can produce enhanced fluxes of particles near the Earth's orbit. Solar energetic particles and particles accelerated at interplanetary shock waves are considered. We also review the properties and potential terrestrial influence of Jovian electrons. Recent measurements from the SAMPEX spacecraft in low-Earth orbit are examined to look for extraterrestrial sources of electrons and ions. We find clear evidence of both solar and Jovian electrons at high latitudes and at high altitudes around the Earth, but the durably trapped outer zone electron population seems best and most completely explained by an internal acceleration mechanism.