Ionospheric Plasma Transported Into the Martian Magnetosheath

Abstract Heavy cold ions at Mars are gravitationally bound to the planet unless some process provides energy to them. Observations show that cold (1 cm−3) O+/O2+ ions with bulk velocities equal to energies ∼1 keV can reach deep into the nightside Martian magnetosheath. These ions are co‐located with a change of the sign of the sunward component of the magnetic field. This magnetic field topology implies the persistence of a localized planetary ions escape channel associated with draped magnetic field lines that are convecting tailward. The observed ion populations propagate approximately in the same direction as surrounding magnetosheath flow and are likely to be almost unheated ionospheric ions from low altitudes. The paper discusses planetary ion energization via Hall electric field originated from ions and electron separation associated with magnetic field curvature.