A Benchmark Model for the Sunlit Martian Ionosphere: Structure, Composition, and Energetics

Multi-instrument measurements of the Martian upper atmosphere and ionosphere by the Mars Atmosphere and Volatile Evolution (MAVEN) mission demand a self-consistent model capable of simultaneously solving the coupled continuity, momentum, and energy equations for various ions and minor neutrals. Here we introduce a one-dimensional model configured for the near-subsolar, moderate solar activity conditions of the Deep Dip 2 (DD2) campaign. The model incorporates an extensive photochemical network including 63 species and 1643 chemical and microphysical processes. Its nominal setup includes scaling the MAVEN Neutral Gas and Ion Mass Spectrometer-derived background neutral densities downward by a factor of 2; imposing a bottom-side H₂ supply of 2 × 10⁷ cm⁻² s⁻¹ and a H₂O mixing ratio of 2 ppm, allowing atomic H to form solely through photochemistry; imposing a topside outflow velocity of 0.035 km s⁻¹ for all ions, consistent with current estimates of plasma escape and day-to-night transport; and applying topside energy fluxes of 6 × 10⁶ eV cm⁻² s⁻¹ for ions and 3 × 10⁹ eV cm⁻² s⁻¹ for electrons. The nominal configuration reproduces multiple MAVEN observations, including the densities of major ions (O (Formula presented) 2+, CO (Formula presented) 2+, O⁺, and NO⁺), protonated ions (OH⁺, HCO⁺, H₂O⁺, and H₃O⁺), and hydrogen-bearing neutrals (H, H₂, and H₂O), as well as the electron and ion temperatures. The model underscores the critical role of chemical heating and demonstrates that hydrogen-bearing neutrals must be solved self-consistently rather than prescribed as static background species. This work presents a physically consistent reference solution for the DD2 conditions and a flexible modeling framework for interpreting the structure, composition, and energetics of the Martian ionosphere, against which more complex scenarios can be tested in future studies.