Interplanetary dust fluxes observed with Parker Solar Probe

Abstract

The mission Parker Solar Probe (PSP) provides a new opportunity to make in-situ measurements of dust impacts closer to the Sun than ever before, eventually going as close as ∼ 10 solar radii or ∼ 0.05 AU. PSP can measure dust impacts from monopole measurements of the spacecraft’s electric potential to one of its antennas using its FIELDS instrument. In this work impact rates data is compared to model calculations of dust flux at the spacecraft. The measurements are best described by dust particles forming inside of the PSP’s orbit. The particles then move in hyperbolic orbits away from the Sun because they are repelled by the radiation pressure force. The dust particles can be pushed outward when the ratio of radiation pressure to gravity force exceeds 0.5. This ratio is often denoted as the beta value and the particles in unbound orbits as beta meteoroids.

In this thesis the dust impact rates measured by PSP during its second orbit are compared to calculated dust fluxes. The flux is influenced by the distance from the Sun, where the particles form, and their radiation pressure to gravity ratio (“beta value”). The finding of the range of these parameters result in well described impact rates. The radiation pressure to gravity ratio is found to be generally higher than previous studies. This suggests that PSP measures highly absorbing particles which could be dust particles freshly released from comets. An alternative suggestion is that the particles are not initially on circular orbits, but rather on highly elliptical orbits which will lead to a higher observed radiation pressure to gravity ratio. Three selected signals from monopole measurements are analyzed to derive dust particle parameters such as radiation pressure to gravity ratio and production distance. The signals are in agreement with beta meteoroids which are produced within 13 solar radii and with a radiation pressure to gravity ratio of above 1. It is shown that for the assumed dust impact signals an increase in production distance has to be met with an increase in the radiation pressure to gravity ratio. Similarly, if the particle is to be produced closer to the Sun it must have a smaller radiation pressure to gravity ratio.