An overview by Pioneers observations of the distant geomagnetic tail

Detailed reinvestigations of Pioneer 8 and Pioneer 7 observations of the geomagnetic tail at large geocentric distances (about 500 and about 1,000 Re, respectively) suggest that that far from the earth the distant tail still preserves most of its near earth typical features. In particular, the presence of low density plasma fluxes in the region of expected tail (which, in the past, were considered a strident deviation from typical near earth conditions) can be interpreted in terms of an extension of the plasma mantle to a large fraction of the distant tail. The distant neutral sheet, moreover, is still oriented along the tail midplane; regular reconnection processes of opposite field lines are also extensively observed. Close to the neutral layer, a higher velocity plasma component is often superimposed to the tail plasma protons. The regions of tail observations might still be consistent with a cylindrical tail geometry; nevertheless, the existence of a superimposed, fragmented tail structure cannot be excluded.