Solar wind dynamics around a comet - A 2D semi-analytical kinetic model

Abstract

We aim at analytically modelling the solar wind proton trajectories during their interaction with a partially ionised cometary atmosphere, not in terms of bulk properties of the flow but in terms of single particle dynamics. We first derive a generalised gyromotion, in which the electric field is reduced to its motional component. Steady-state is assumed, and simplified models of the cometary density and of the electron fluid are used to express the force experienced by individual solar wind protons during the interaction. A three-dimensional (3D) analytical expression of the gyration of two interacting plasma beams is obtained. Applying it to a comet case, the force on protons is always perpendicular to their velocity and has an amplitude proportional to 1/r^2. The solar wind deflection is obtained at any point in space. The resulting picture presents a caustic of intersecting trajectories, and a circular region is found that is completely free of particles. The particles do not lose any kinetic energy and this absence of deceleration, together with the solar wind deflection pattern and the presence of a solar wind ion cavity, is in good agreement with the general results of the Rosetta mission. The qualitative match between the model and the in situ data highlights how dominant the motional electric field is throughout most of the interaction region for the solar wind proton dynamics. The model provides a simple general kinetic description of how momentum is transferred between these two collisionless plasmas. It also shows the potential of this semi-analytical model for a systematic quantitative comparison to the data.

12 pages, 6 figures

References in corpus (10)

• The Solar Wind Around Pluto (SWAP) Instrument Aboard New Horizons
• Spatial distribution of low-energy plasma around comet 67P/CG from Rosetta measurements
• The birth and growth of a solar wind cavity around a comet -- Rosetta observations
• Mass loading at 67P/Churyumov-Gerasimenko: a case study
• Measurements of the electrostatic potential of Rosetta at comet 67P
• Mass-loading of the solar wind at 67P/Churyumov-Gerasimenko -- Observations and modelling
• The root of a comet tail - Rosetta ion observations at comet 67P/Churyumov--Gerasimenko
• West-east asymmetry of a mini-magnetosphere induced by Hall effects
• Dawn-dusk asymmetry induced by the Parker spiral angle in the plasma dynamics around comet 67P/Churyumov-Gerasimenko
• Solar wind dynamics around a comet: The paradigmatic inverse-square-law model

Cited by in corpus (7)

• The root of a comet tail - Rosetta ion observations at comet 67P/Churyumov--Gerasimenko
• Solar wind charge exchange in cometary atmospheres. II. Analytical model
• Menura: a code for simulating the interaction between a turbulent solar wind and solar system bodies
• Solar wind dynamics around a comet: The paradigmatic inverse-square-law model
• Interaction between the turbulent solar wind and a planetary magnetosphere: a 2D comet example
• Probing Coronal Magnetic Fields with Sungrazing Comets: \hi\ Ly$\alpha$ from Pickup Ions
• Kinetic-Scale Physics of a Multi-Species Solar Wind