Ion escape from degenerate induced magnetospheres: The case of Mars

When the cone angle of the solar interplanetary magnetic field (IMF) becomes small, induced magnetospheres of unmagnetized planets degenerate, resulting in a markedly different mode of the interaction. In this case, solar wind protons penetrate all the way to the top of the atmosphere on the dayside of Mars. Ions from the ionosphere propagate upstream in the solar wind, toward the Sun, with a substantial flow perpendicular to the solar wind flow. We investigate the ionospheric ion escape from such an object. This study specifically concentrates on hybrid simulations of the ionospheric ion escape from Mars in the case of the 4° cone angle with the other solar wind conditions typical. The total escape rate is found to be almost one order of magnitude higher than for the typical Parker spiral case. The unique feature of the degenerate induced magnetosphere is the upstream escape driven by the ambipolar field, contributing 42% to the total escape rate, fully absent in the Parker spiral case. Additionally, 52% of the total escape occurs through the cross-flow plume, arising from the drift of ionospheric ions in the weak convective field and IMF. This channel dominates and is seven times more intense than the plume driven by the convective field in the nominal case. Understanding how degenerate magnetospheres operate is important not only for the planets in the solar system, but also for exoplanets.