Plasma vortices in non-magnetic planetary wakes driven by magnetic torsion generated by electric currents.

Abstract:

In this work, we study the vortical structures in the plasma wake of Venus and Mars, which can be observed in the plasma data of the Venus Express (VEX) and the Mars Global Surveyor (MGS) spacecraft.

We propose that the origin of these vortices lies in the configuration of the magnetic field embedded in the plasma due to the mutual interaction between this field and electric currents. The latter is explained considering that plasma currents induce magnetic fields that modify the existing field and also produce a helical field configuration that drives charged particles along vortical trajectories.

We introduce three theorems, which may be applicable to any non-collisional plasma system, that relate the vorticity to electromagnetic variables such as the magnetic field and the electric current density. We also introduce a toy vortex model for the wakes of non-magnetised planetary bodies.

We show that the vortex is always linked to an electric current and that both the vortex and the current always coexist. We show that it is possible to observe the vortex in the magnetic data in single spacecraft wake crossings.