Zodiacal Fluctuations Should Drive Inner-source Pickup Ion Variability

Abstract Dust near the Sun is implicated in the production of an unexpected “inner source” of pickup ions (PUIs). Multiple mechanisms related to dust have been proposed to explain this phenomenon, and all depend on the amount, along with the spatial and size distributions, of zodiacal dust near the Sun. Leveraging new insight showing the zodiacal cloud is highly spatially structured, we investigate the implications of spatial fluctuations of the zodiacal cloud on temporal variability in the inner source of PUIs. Temporal variability of dust near the Sun is inherited from spatial fluctuations upstream at larger distances. Modulation of the inner source due to dust variability can occur on timescales of days to decades, depending on the relevant dust size responsible for generating the inner source and the spatial characteristics of zodiacal abundance fluctuations. Cometary disruptions occurring every few days are also expected to directly modulate the inner source. Similar variability is expected for the production of nanograins incorporated into the solar wind. These results present a new mechanism for days-to-decades variability in the inner-source abundance and provide a quantitative relationship between inner-source variability and zodiacal fluctuations.