Massive Micron Meteoroids in the near-Sun Space as Observed by Parker Solar Probe

The interplanetary dust, together with solar wind plasma, forms the space environment of the inner heliosphere. There are two main particle populations of dust, α-meteoroids in bound orbits with micron size and β-meteoroids in hyperbolic orbits with sub-micron and nano size. Collisions between dust particles and dynamical evolution of their orbits greatly shape the grain size and heliocentric distance distributions of dust cloud, yet the specific mechanism still remains unknown. After Parker Solar Probe (PSP) successfully performed more than 10 encounter missions, plenty of dust impact events have been recognized, providing a glimpse of the complex. In this work, we analyze the geometry feature of streaks captured by the Wide-field Imager for Parker Solar Probe (WISPR) and try to locate the impact origins. In addition, we translate the results of streak storms in WISPR images to dust impact rates so as to compare with those recorded by the PSP FIELDS Experiment (FIELDS). We find there is evidence for the α-meteoroids impact. The debris products are directly observed by WISPR. We also find that the dust impact rates determined by the two methods are in good agreement. A pure α-meteoroid model is used to fit the observed impact rates within about 0.3 AU (~67 solar radii) and the fit is pretty well, especially for the rates near perihelion of PSP. Based on these results, we suggest that α-meteoroids can take a significant proportion of zodiacal dust near the Sun and this may lead to a different size distribution of dust cloud and a different mechanism of meteoritic evolution from what they are observed as at 1 AU.