Characterizing the current systems in the Martian ionosphere

When the solar wind encounters the ionosphere of an unmagnetized planet, it induces currents, forming an induced magnetosphere. These currents, along with their associated magnetic fields, play a crucial role in controlling the movement of charged particles, and are essential for understanding the escape of planetary ions. Unlike the well-documented magnetospheric current systems, the ionospheric current systems on unmagnetized planet remain less understood, limiting our ability to quantify electrodynamic energy transfer. Here, using 8 years of data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we provide the first global map of the Martian ionospheric currents. We identified two current systems coexist within the ionosphere: one aligning with the solar wind electric field, with asymmetries between the west-east electric hemispheres and driven by the solar wind; and one characterized by two current vortices on the dayside, powered by the atmospheric neutral winds. Our findings indicate that the Martian ionospheric dynamics are influenced by both the neutral winds from below and the solar wind from above, emphasizing the intricate nature of current systems on unmagnetized planets.