Atmospheric Escape at Mars

Introduction: Several mechanisms have been identified to result in escape of the Martian atmosphere. These mechanisms can be divided in two groups [1]: • Thermal escape or Jeans escape, which corresponds to the loss of atoms in the high energy tail of the energy distribution at the exobase. This mechanism is important only for the light species such as hydrogen or deuterium. • Non-thermal escape, which includes the escape of hot neutral species produced by 1. Chemical reactions, such as dissociative recombination of ions (e.g. O2 + e O + O + ΔE), producing the escape of neutral atoms as O, C, N 2. Ionospheric escape, that is the escape of heavy ions produced above the photochemical equilibrium region and below the ionopause and diffusing to high altitudes where they can be picked up by the solar wind (O2, CO2, O) 3. Exospheric ions escape, that is the escape of exospheric ions produced by ionization (UV, charge exchange or electron impact) of the neutral exosphere and picked up by the solar wind (O, H) 4. Energetic Neutral Atoms (ENA) escape, that is the escape of the hot neutral atoms produced by charge exchange between pick up or solar wind ions and the neutral exosphere (O ; H) 5. Sputtering escape: One part of the pick up ions can reimpact the planet and transfer their energy to the neutral species present at the exobase, leading to additional neutral escape (C, N, O, Ar)