In Situ Observations of Interplanetary Dust Variability in the Inner Heliosphere

Abstract

This work examines the variation of interplanetary dust count rates and directionality during the first three solar encounters made by the Parker Solar Probe spacecraft, covering distances between 0.65 au (∼140 solar radii, R S ) and 0.16 au (∼35 R S ). Dust detections are made by the FIELDS instrument via plasma clouds, produced by impact ionization of dust grains on spacecraft surfaces and resultant spacecraft potential perturbations. Dust count rates and inferred densities are found to vary by ∼50% between the three solar encounters (∼5 months per orbit), with most of the variation concentrated below 0.23 au (∼50 R S ). Dust count rates and directionality, as well as the encounter-to-encounter variability in both quantities are found to be consistent with β -meteoroids: dust grains exiting the solar system on hyperbolic trajectories. Interpretation of the the dust count rate data and the dust directionality data independently suggest (i) that the β -meteoroid source region is more complex than preliminary models suggest, and (ii) that the primary β -meteoroid source region is approximately located between 10 and 30 solar radii from the Sun. These data offer important clues as to the location and geometry of the β -meteoroid source region, and consequently clues about the collisional and sublimation processing of interplanetary dust grains near the Sun.