In situ observation of energetic pickup oxygen ions upstream from the Martian bow shock: a case study

The O atoms in the Martian exosphere can be ionized by photoionization, charge exchange, or electron impact. The newborn O+ ions are immediately picked up by the solar wind electromagnetic fields, and are then accelerated by the convection electric field. They are called pickup O+ ions. During 08 :54 :00-10:24:00 UT on 2018 November 17, and Mars Atmosphere and Volatile EvolutioN (MAVEN) observed persistent pickup O+ population with energies of similar to 30 keV. They correspond to precipitating O+ ions coming from the upstream solar wind. In phase space, they are located near the middle phase of partial ring distribution with an initial velocity (i. e., near the maximum energy of the partial ring distribution). Our analysis suggests that these precipitating energetic O+ can overcome the electrostatic bow shock potential and proceed downstream. Then, they are subject to the enhanced magnetic field in the magnetosheath. The results will help better understand the generation and the motion trajectories of energetic O+ ions at Mars.