The Evolution of Hot Flow Anomalies in Martian Space Environment

Hot Flow Anomalies (HFAs) are common transient structures in the foreshock region, generated by interactions between solar wind discontinuities and planetary bow shocks. Owing to the scarcity of multi-spacecraft observations at other planets, the evolution of HFAs has only been confirmed near Earth. Using joint observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) and Tianwen-1 missions, we investigate the evolution of a Martian HFA. This HFA was detected first by MAVEN on the dayside, and later observed by Tianwen-1 on the nightside. The HFA’s core region exhibits negligible magnetic fluctuations, with little change in thickness during propagation, while the peak magnetic field magnitude at its trailing edge decreases a lot. Notably, this HFA remains a young-type HFA and does not evolve from the ‘young’ to ‘mature’ type. This indicates that due to the small size of Martian bow shock, HFAs formed upstream of the quasi-parallel shock can rapidly propagate to the quasi-perpendicular shock region, precluding continuous injection of shock-reflected ions.