On the origin of inner-source pickup ions

Abstract

In situ measurements of pickup ions (PUI) exhibit a component that has nearly thermalized with the solar wind. This implies an origin close to the Sun and is generally ascribed to interaction of the solar wind with interplanetary dust particles (IDPs). We propose a scenario for the origin of inner-source PUIs in which a population of very small IDPs serves as the neutralizing agent for solar wind ions. The size of these IDPs is less than or comparable to the penetration range, of solar wind ions in IDP material. The interaction of the solar wind with such particles results in a net charge exchange in which solar wind ions exit the IDPs as predominantly neutral or singly-charged ions. When the neutralized solar wind is reionized, it is picked up and can then be measured as a PUI.