A fully kinetic perspective on weakly active comets: Asymmetric outgassing

Abstract

The European Space Agency’s Rosetta mission measured the complex plasma environment surrounding comet 67P/Churyumov-Gerasimenko for more than two years. In this work, the collisionless dynamics of the plasma interaction during the comet’s weakly outgassing phases is investigated through a fully kinetic semi-implicit particle-in-cell approach. The effects of an asymmetric outgassing profile with respect to the upstream plasma conditions are compared with a spherically symmetric Haser model. The three-dimensional shape of the plasma density and the parallel acceleration potential are used as primary measures. It is found that the four-fluid coupled system is not majorly distorted. The different components of the potential structure can be associated with the large-scale behavior and density profiles of the four simulated plasma species. The implications for the acceleration and cooling of electrons within the cometary plasma environment are identified by contrasting the differences in the shape of the acceleration potential between the distinct asymmetric outgassing models. The analysis provides a detailed overview that can help interpret past Rosetta plasma measurements and could be key to help disentangle the physical drivers active in the plasma environment of comets visited by future exploration missions.