Convergent Heavy-ion Plume from the Martian Ionosphere

Ion escape is a key consequence of the solar wind interaction with Mars, yet the three-dimensional structure of the heavy-ion plume, a major escape channel, remains poorly constrained. Here, we combine MAVEN observations of the plume with multifluid magnetohydrodynamic simulations to investigate the transport of planetary ions and the morphology of the plume originating from the ionosphere. Based on composition, energy, and ion trajectory diagnostics to distinguish ionospheric plume from exospheric pickup ions, we identify a persistent three-dimensional convergent plume structure in the +E hemisphere. Simulations reproduce this morphology and reveal the underlying mechanism: magnetic-field draping generates a nonzero Bx component, which exerts Lorentz force on the plume ions to overcome the outward expansion driven by the convection electric field and to converge toward the central plane. Parameter-controlled simulations further show that the hemispheric asymmetry of plume convergence increases as the interplanetary magnetic field cone angle departs from 90°, consistent with the role of cone angle in controlling the draping geometry. These results show that Martian plume ions can be organized by a large-scale draped field into a three-dimensional convergent structure, going beyond the conventional picture of simple pickup-driven expansion. Meanwhile, plume ions actively participate in magnetosheath dynamics, modifying energy transfer.