PICKUP IONS FROM ENERGETIC NEUTRAL ATOMS

The inner source of pickup ions (PUIs) was once thought to derive exclusively from the interaction between solar wind and interplanetary grains near the Sun. Recently, however, Gruntman & Izmodenov suggested that inner source hydrogen may derive from energetic neutral atoms (ENAs) from the outer heliosphere. Here, following up on these authors' proposal, we show that the ENA flux recently observed by the Interstellar Boundary Explorer is sufficiently large to actually produce the observed inner source pickup proton densities. We then go on to examine the possibility that solar wind heavy ions, which undergo multiple consecutive electron captures from neutral interstellar atoms in the outer heliosphere, could constitute another significant source of ENAs, thus producing an inner source PUI composition similar to the solar wind, as observed. Because the ENA source is distributed, the generation of PUIs from ENAs occurs throughout the heliosphere, and the ENA source of PUI likely contributes significantly to the metallic elements of anomalous cosmic rays (ACRs), which were previously unexplained. Thus, we show that ENAs create a large fraction of the inner source PUI and provide an extended source of PUIs in the heliosphere that likely generates the metallic ACRs.