Fundamental changes in the composition of escaping ions at Mars induced by the December 2023 space weather event

Abstract

Mars’ dayside ionosphere is maintained primarily by ionization from solar ultraviolet photons and subsequent chemical reactions, with small contributions from other mechanisms such as impact ionization and charge exchange. In December 2023, the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission observed the impact of an interplanetary coronal mass ejection (ICME) on Mars’ ionosphere, including strongly enhanced ?uxes of suprathermal electrons. We show that this enhancement in suprathermal electron ?uxes increased ion production from electron impact, so that dayside electron impact ionization rates exceeded photoionization rates during the ICME. This change in ion production mechanisms led to unusually high densities of the minor ions C+ and O++. Space weather events are known to increase ion escape rates, so changes in ion composition during space weather events have important implications for atmospheric evolution. We show that scaling nominal loss rates to account for space weather may underestimate carbon loss from Mars’ atmosphere.