Dust Directionality and an Anomalous Interplanetary Dust Population Detected by the Parker Solar Probe

Abstract

Abstract Theory and previous space missions indicate there are several populations of zodiacal dust. The most prominent populations are grains on bound elliptic orbits (α-meteoroids), and β-meteoroids on hyperbolic escape trajectories governed largely by their size and composition. Yet, there may be other populations not yet confirmed by observation. The Parker Solar Probe (PSP) spacecraft is able to observe in situ dust populations in the densest part of the zodiacal cloud. Over the first seven orbits, dust count rates are well organized by orbital groups based on orbital parameters of PSP’s shrinking orbit. In particular, the first three orbits and the sixth orbit have a single, preperihelion peak in count rate with a gradual drop off postperihelion, while Orbits 4, 5, and 7 have two distinct count rate peaks on either side of perihelion. The secondary peaks in Orbits 4, 5, and 7 are inconsistent with current zodiacal dust models that account for only two dust populations: α- and β-meteoroids. In examining the directionality of dust impacts on the PSP spacecraft, the presence of an anti-ram impactor anomaly postperihelion during Orbit 4 is evident. This anomaly may indicate another dust population beyond the nominal α- and β-meteoroids, and its origin may be related to the Geminids meteoroid stream associated with the asteroid 3200 Phaethon.