The effects of solar flares on the upper atmosphere of Mars are large but poorly constrained by observations. These effects are an important aspect of the response of Mars to space weather events and may also influence the escape of volatiles from Mars, particularly in the solar system's early history. Here we report the effects of the X8.2 flare on 10 September 2017 on the density and composition of the thermosphere of Mars. This analysis uses neutral number densities of He, O, N₂, CO, Ar, and CO₂ from the MAVEN Neutral Gas and Ion Mass Spectrometer (NGIMS). From these observations, we investigate how the enhanced solar irradiance during the flare produced changes in the neutral upper atmosphere of Mars due to atmospheric heating and photochemistry. Flare‐produced photochemical changes in the neutral thermosphere of Mars have been previously implied but not quantified. We find that at fixed altitudes, the number densities of all species barring He increase and the O/CO₂ ratio decreases by ∼15–45%, indicating thermal expansion. However, when viewed at fixed total number densities, the densities of CO₂ and Ar decrease, and the O/CO₂ ratio increases by up to a factor of ∼3. The photodissociation of CO₂ is one photochemical process that produces changes resembling those identified. The quantified changes will help to constrain the shifting chemical makeup of the upper atmosphere due to these impactful flare events and may aid modeling of flare behavior and the impact of flares on the evolution of the Martian climate.

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2017年9月10日太阳耀斑对火星热层密度和组成的影响

太阳耀斑对火星高层大气的影响很大，但受观测结果的约束很小。这些影响是火星对太空天气事件做出反应的重要方面，也可能影响挥发物从火星的逸出，尤其是在太阳系的早期历史中。在这里，我们报告了2017年9月10日X8.2耀斑对火星热层密度和成分的影响。该分析使用He，O，N ₂，CO，Ar和CO _2的中性数密度来自MAVEN中性气体和离子质谱仪（NGIMS）。从这些观察结果中，我们研究了火炬期间增强的太阳辐照度如何由于大气加热和光化学作用而在火星的中性高层大气中产生变化。火星在中性热层中由耀斑产生的光化学变化先前被暗示但未被量化。我们发现，在固定高度下，除He之外，所有其他物种的数量密度都会增加，而O / CO _2的比值降低约15–45％，表明存在热膨胀。但是，当以固定的总密度观察时，CO ₂和Ar的密度降低，O / CO _2的比值增加至约3倍。CO的光解离_图2是一种光化学过程，其产生类似于所识别的变化。量化的变化将有助于限制由于这些有影响的耀斑事件而引起的高层大气化学成分的变化，并且可能有助于对耀斑行为以及耀斑对火星气候演变的影响进行建模。