VOYAGER ENERGETIC PARTICLE OBSERVATIONS AT INTERPLANETARY SHOCKS AND UPSTREAM OF PLANETARY BOW SHOCKS - 1977-1990

The Voyager 1 and 2 spacecraft include instrumentation that makes comprehensive ion (E greater-than-or-similar-to 28 keV) and electron (E greater-than-or-similar-to 22 keV) measurements in several energy channels with good temporal, energy, and compositional resolution. Data collected over the past decade (1977-1988), including observations upstream and downstream of four planetary bow shocks (Earth, Jupiter, Saturn, Uranus) and numerous interplanetary shocks to approximately 30 AU, are reviewed and analyzed in the context of the Fermi and shock drift acceleration (SDA) models. Principal findings upstream of planetary bow shocks include the simultaneous presence of ions and electrons, detection of "tracter" ions characteristic of the parent magnetosphere (O, S, O+), power-law energy spectra extending to greater-than-or-similar-to 5 MeV, and large (up to 100:1) anisotropies. Results from interplanetary shocks include observation of acceleration to the highest energies ever seen in a shock (greater-than-or-similar-to 22 MeV for protons, greater-than-or-similar-to 220 MeV for oxygen), the "saturation" in energy gain to less-than-or-similar-to 300 keV at quasi-parallel shocks, the observation of shock-accelerated relativistic electrons, and separation of high-energy (upstream) from low-energy (down-stream) populations to within approximately 1 particle gyroradius in a near-perpendicular shock. The overall results suggest that ions and electrons observed upstream of planetary bow shocks have their source inside the parent magnetosphere, with first order Fermi acceleration playing a secondary role at best. Further, that quasi-perpendicular interplanetary shocks accelerate ions and electrons most efficiently to high energies through the shock-drift process. These findings suggest that great care must be exercised in the application of concepts developed for heliosphere shocks to cosmic ray acceleration through shocks at supernova remnants.