Martian atmosphere sputtering escape generated by penetrating hydrogen energetic neutral atoms

Atmospheric escape plays a critical role in shaping the long-term climate evolution of Mars. Among the various escape mechanisms, energetic neutral atoms (ENAs) generated through charge exchange between solar wind ions and exospheric neutrals serve as an important diagnostic for ion–neutral interactions and upper atmospheric loss. This study presents direct observations of hydrogen ENAs (H-ENAs) on the dayside of Mars by using the Mars Ion and Neutral Particle Analyzer (MINPA) onboard China’s Tianwen-1 orbiter. By analyzing H-ENA data during a coronal mass ejection and a stream interaction region from December 29, 2021, to January 1, 2022, and comparing these data with MAVEN/SWIA (Mars Atmosphere and Volatile EvolutioN/Solar Wind Ion Analyzer) solar wind measurements, we examine the temporal evolution of H-ENA flux and the associated sputtered escape of atmospheric constituents. The observed H-ENA velocity is consistent with upstream solar wind ions, and the H-ENA-to-ion intensity ratio is used to infer variations in exospheric density, revealing a delayed response to enhanced solar wind activity. Penetrating H-ENA intensities reach up to 5.3 × 10⁶ s⁻¹ cm⁻², with energy fluxes on the order of (0.5–8.1) × 10⁻³ mW/m². The estimated oxygen sputtered escape rate driven by penetrating H-ENAs ranges from 5.5 × 10²³ s⁻¹ to 5.2 × 10²⁴ s⁻¹, comparable to or exceeding previous estimates based on penetrating ions. The findings highlight the need for low-altitude H-ENA observations to better quantify their atmospheric interactions and refine our understanding of nonthermal escape processes at Mars.