Characteristics of the Heliosheath from Voyager 1 Observations

Voyager 1 crossed the termination shock of the solar wind on December 16, 2004 at a distance of 94.0 AU from the Sun. The low-energy energetic particle component, which dominates the observed energy spectrum below ~30 MeV for protons and which had been observed since mid-2002, has become much less variable and much less anisotropic in the heliosheath than it had been in the solar wind. The energy spectra of the classic anomalous cosmic rays (ACRs) were relatively unaffected at the crossing, being heavily modulated and indicating a source region remote from the crossing point of the termination shock at 34 N in heliolatitude. However, the ACR spectra appear to be evolving towards the expected source spectra as Voyager 1 continues into the heliosheath. The intensity of galactic cosmic rays and ~10 MeV electrons are also increasing. In addition, Voyager 2 appears to be observing termination shock particle precursors, suggesting it too will likely cross the termination shock in the next few years. This work was supported by NASA under contract NAS7-03001.