Seasonal variability of atomic hydrogen and oxygen in the EMM/EMUS cross-exospheric observations during Mars year 36

Susarla Raghuram,Krishnaprasad Chirakkil，Shannon Curry, Hessa Rashid Al Matroushi

crossref（2023）

Cited 0|Views21

Abstract

Atomic hydrogen and oxygen are the dominant species in the Martian exosphere. Atomic hydrogen is essentially produced from the dissociation of H2O, whereas, hot oxygen atoms are populated by non-thermal processes such as the dissociative recombination of O2+ with electrons in the Martian ionosphere. The study of these species helps to understand the evolution of the Martian atmosphere and more specifically the history of water on Mars.  The Emirates Mars Ultraviolet Spectrometer (EMUS), one of the primary instruments onboard the Emirates Mars Mission (EMM), has been observing atomic hydrogen and oxygen in the Martian exosphere over the Mars Year 36. We present the analysis of the cross-exospheric observations by the EMUS for hydrogen Lyman series and oxygen 130.4 nm emissions and their seasonal variability. The EMUS cross-exospheric observations cover the tangent altitude starting from 130 km to more than 35,000 km above the disk (see Fig. 1), with most of the observations below 25,000 km. The observations show that when Mars moved from perihelion to aphelion, the hydrogen emission line intensities increase by an order of magnitude or more whereas, for oxygen, it is an increment by a factor of about 2 at larger altitudes. Based on these observations, we also discuss the retrieval of densities, temperature, and the estimation of escape fluxes of hydrogen and oxygen species by applying 3D hydrogen ballistic corona and 3D Monte Carlo particle transport models, respectively. <img src="" alt="" /> Figure 1: The EMM-observed cross-exosphere emission intensity profiles of atomic hydrogen and oxygen during Mars Year 36

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【要点】：本研究分析了火星大气外层原子氢和氧在火星年36期间的季节性变化，揭示了原子氢和氧在火星大气演化及水历史研究中的重要性。

【方法】：通过使用阿联酋火星任务（EMM）上的主要仪器——阿联酋火星紫外光谱仪（EMUS），对原子氢的Lyman系列和氧的130.4 nm发射线的季节性变化进行了观测分析。

【实验】：研究利用EMUS在火星年36期间进行的跨外层大气观测，数据覆盖了从130 km到超过35,000 km的切向高度，大多数观测在25,000 km以下。实验结果显示，火星从近日点到远日点移动时，原子氢发射线强度增加了10倍以上，而氧在较高高度的增加约为2倍。通过应用3D氢弹道冠层和3D蒙特卡洛粒子传输模型，讨论了氢和氧物种的密度、温度的检索以及逃逸通量的估计。