Monte Carlo Calculations of Helium Escape on Mars via Energy Transfer from Hot Oxygen Atoms
Hao Gu, Jun Cui, Dandan Niu, Zhaoguo He, Kun Li
Abstract
Abstract Understanding He escape is crucial for deciphering the evolution of the He budget on Mars. A number of viable mechanisms have been proposed to drive He escape, with energy transfer from hot O generally thought to be the dominant one. This study is devoted to a state-of-the-art evaluation of the above process assuming hot O is exclusively produced from the dissociative recombination of O 2 + in the Martian ionosphere. A Monte Carlo model is constructed, with model inputs optimized by the recent Mars Atmosphere and Volatile Evolution measurements. The model calculations reveal a dayside He escape flux of (1–2) × 10 6 cm −2 s −1 referred to the surface, for a possible range of H 2 mixing ratio at an altitude of 80 km from 0 to 40 ppm. The computed He escape flux increases with increasing nascent O energy and decreasing atmospheric H 2 and H abundances. The portion of the atmosphere below the exobase is found to make an exceptionally large contribution of 95% to He escape.