On the distribution of the the near-solar bound dust grains detected with Parker Solar Probe

TL;DR

This study models the flux of near-solar dust grains detected by Parker Solar Probe, revealing that bound dust on non-circular orbits explains the observations and highlighting the importance of detection efficiency and impact speed scaling.

Contribution

Developed a forward-model for dust detection rates using 6D phase space distribution, explaining PSP observations with bound dust on non-circular orbits and analyzing detection efficiency effects.

Findings

Dust flux explained by bound, non-circular dust orbits.

Detection efficiency and impact speed scaling are crucial for flux interpretation.

Flux maxima near perihelion suggest additional effects beyond circular dust models.

Abstract

Parker Solar Probe (PSP) counts dust impacts in the near-solar region, but modelling effort is needed to understand the dust population's properties. We aim to constrain the dust cloud's properties based on the flux observed by PSP. We develop a forward-model for the bound dust detection rates using the formalism of 6D phase space distribution of the dust. We apply the model to the location table of different PSP's solar encounter groups. We explain some of the near-perihelion features observed in the data as well as the broader characteristic of the dust flux between 0.15 AU and 0.5 AU. We compare the measurements of PSP to the measurements of Solar Orbiter (SolO) near 1 AU to expose the differences between the two spacecraft. We found that the dust flux observed by PSP between 0.15 AU and 0.5 AU in post-perihelia can be explained by dust on bound orbits and is consistent with a broad range of orbital parameters, including dust on circular orbits. However, the dust number density as a function of the heliocentric distance and the scaling of detection efficiency with the relative speed are important to explain the observed flux variation. The data suggest that the slope of differential mass distribution ${\delta}$ is between 0.14 and 0.49. The near-perihelion observations, however, show the flux maxima, which are inconsistent with the circular dust model, and additional effects may play a role. We found indication that the sunward side of PSP is less sensitive to the dust impacts, compared to the other PSP's surfaces. Conclusions. We show that the dust flux on PSP can be explained by non-circular bound dust and the detection capabilities of PSP. The scaling of flux with the impact speed is especially important, and shallower than previously assumed.