Whistler wave mode generation via large amplitude steepened magnetic structures propagating through the Martian ionosphere

In December 2023 an interplanetary coronal mass ejection impacted Mars and left the magnetosphere in a highly disturbed state that was observed by NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. One consequence of this space weather impact was the driving of large amplitude ( ∼ 50 nT) steepened magnetic structures that propagated into the dayside ionosphere. Here we focus on electromagnetic waves that were observed coincident with some of these magnetic structures. We demonstrate that these waves were the obliquely propagating whistler wave mode, confirmed by wavelet transform and minimum variance analyses. The waves were right hand quasi-circularly polarized with a frequency centered around 1 Hz, and demonstrated the typical dispersion features as a function of time and frequency that are associated with the whistler wave mode. The observations were consistent with the waves being generated by currents running along the steepened edges of the magnetic structures, in analogy to collisionless shocks. The whistler mode waves appeared to play an important role in the evolution of the magnetic structures, acting to smooth out the discontinuity between the up- and downstream sides of the steepened edges. While plasma conditions likely prevented the whistler mode waves from Landau damping with the ambient electrons at periapsis, such damping may have been possible at higher altitudes (600–800 km). This study further highlights the importance of understanding the impact of space weather within our solar system, demonstrating that such events can impact planetary magnetospheres and the ionospheres embedded within them.