Inner source distributions: Theoretical interpretation, implications, and evidence for inner source protons

A new and important source of pickup ions has been recently observed for the first time, the so-called inner source. We examine properties of inner source ions at high heliographic latitudes through analysis of data from the Solar Wind Ion Composition Spectrometer on the Ulysses satellite for a period extending through the year of 1994 while Ulysses achieved its southernmost latitudes. As demonstrated by Gloeckler et al. [this issue], the relative abundances of inner source ions resemble those of the solar wind, which implies that the dominant production mechanism for the inner source ions involves the absorption and reemission of solar wind ions from interplanetary dust grains. A simple transport model is devised that compares favorably to observed distribution functions and provides an important consistency check for the previously mentioned production mechanism. The model comparison also allows for constraints to be placed on the total dust geometric cross section. The observed distribution function of protons reveals a significant contribution from the inner source, but the abundance of inner source protons relative to oxygen falls significantly below the universal abundance. We postulate causes of this low relative abundance. We also find that inner source protons have a sizable pressure and may constitute an important energetic population in the solar wind, particularly near the their source.