Hybrid simulations of large-scale plasma waves at comets and their connection to magnetosheath jets

Wave activity in the cometary plasma environment occurs across various levels of cometary activity, from large heliocentric distances to perihelion. These waves play a key role in the thermalisation of cometary pick-up ions and energy redistribution. Starting thousands of kilometres upstream of the nucleus, the gyrating motion of solar wind and cometary ions produces highly anisotropic velocity distributions, which can drive various wave phenomena.
In this study, we employ the 3D hybrid particle simulation code Amitis to model a cometary magnetosphere at approximately Mars’ distance in the solar wind, assuming an outgassing rate of Q ≈ 10²⁷ s^-1. The simulations reveal large-scale wave structures extending from far upstream of the comet nucleus to downstream of the bow shock. Wave signatures are most pronounced in the +E hemisphere and near the quasi-parallel bow shock, while the −E hemisphere is dominated by magnetic field pile-up. In the inner magnetosphere, where cometary ions dominate, waves are absent. Magnetic field peaks and solar wind density enhancements are out of phase—characteristics consistent with slow magnetosonic waves.
These waves amplify solar wind density, increasing dynamic pressure and potentially contributing to the formation of magnetosheath jets. Our simulations indicate that magnetosheath jets—similar to those observed at Earth—can also occur at comets. We explore the role of waves for the generation of magnetosheath jets within cometary magnetospheres.