Direct Observations of Acceleration of Planetary Ions From Mars' Ionosphere Through Magnetic Reconnection When IMF Rotates

Abstract Mars lacks an intrinsic global magnetic field but possesses crustal magnetic anomalies and an atmosphere. Mars' ionosphere, resulted from interactions between Mars' atmosphere and solar radiation, directly interacts with solar wind and interplanetary magnetic field (IMF). However, the mechanisms governing ion acceleration and escape from Mars' ionosphere remain incompletely understood. By analyzing simultaneous observations from MAVEN and Tianwen‐1 missions, we present observational evidence of magnetic reconnection events in Mars' dayside upper ionosphere above weak crustal field region during IMF rotation, accompanied by acceleration of ionospheric ions. The explosive escape flux exceeds the average plume and tailward escape flux by an order of magnitude and is comparable to that of reconnection processes above strong crustal field regions. Our results provide evidence that IMF rotation‐triggered magnetic reconnection constitutes a significant pathway for ion escape from Mars, offering new insights into planet's atmospheric evolution and potential mechanisms for early water loss on Mars.