Ion Escape From Degenerate Induced Magnetospheres: The Case of Mars

Abstract When the cone angle of the interplanetary magnetic field (IMF) becomes small, induced magnetospheres of unmagnetized planets degenerate. Using hybrid simulations, we study ionospheric ion escape in a 4° cone angle case and compare it with the nominal 55° cone angle (Parker spiral) case. The total escape rate is , nearly an order of magnitude higher than the nominal rate of . The escape probability is four times higher. The unique feature of the degenerate induced magnetosphere is the upstream escape driven by the ambipolar electric field, contributing 42% to the total escape, a channel absent in the nominal case. Additionally, 52% of escape occurs through a cross‐flow plume, formed by the drift of ionospheric ions in the weak convective field and IMF. This channel is dominant, exhibiting an intensity seven times greater than that of the plume driven by the convective electric field in the nominal case.