The Solar Wind Termination Shock and the Outer Heliosphere

Beginning in mid-2002, Voyager 1 observed an extended period of field-aligned flows of low energy ions and electrons that was unlike previous observations, suggesting that the spacecraft was in the vicinity of the solar wind termination shock. However, the observations differed from expectations and have resulted in differing interpretations as to whether or not Voyager 1 crossed the termination shock and entered the subsonic flow in the heliosheath for a seven month period. The puzzling aspects of the observations suggest that the shock is more complex and dynamic than generally expected and that there could be more surprises as Voyager 1 will likely encounter the shock several times before durably entering the heliosheath sometime in the next few years.