Photoelectrons are an extensively studied component of planetary ionospheres which have been frequently used as a diagnostic of ambient magnetic fields. We show in this study that they also provide information on atmospheric composition via the altitude variation of photoelectron intensity at specific energies. Such an idea is applied to Mars for which a large observational sample of photoelectrons is available from the Solar Wind Electron Analyzer measurements made by the Mars Atmosphere and Volatile Evolution (MAVEN). Our analysis reveals a strong decline in photoelectron intensity from 160 to 200 km, but this trend is restricted to a narrow energy range of 10–15 eV. By employing analytical yield spectrum calculations, we derive the model variations based on different choices of the background atmosphere. We find that the presence of CO is crucial for reproducing the observed variations. This allows atmospheric CO densities to be estimated from photoelectron measurements, which are a factor of 3–7 lower than the published densities based on the MAVEN Neutral Gas and Ion Mass Spectrometer measurements and in better agreement with existing model results. In general, the usefulness of photoelectron intensity at a specific energy as a tracer of atmospheric composition relies critically on the species‐dependent inelastic electron impact cross section at this energy.

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光电子作为行星大气成分的示踪剂：在火星上的CO应用

光电子是行星电离层的一个被广泛研究的组成部分，它经常被用作环境磁场的诊断。我们在这项研究中表明，它们还通过特定能量下的光电子强度的高度变化来提供有关大气成分的信息。这样的想法适用于火星，通过火星大气和挥发性演化（MAVEN）进行的太阳风电子分析仪测量，可以获得大量的光电子观测样本。我们的分析表明，光电子强度从160 km急剧下降到200 km，但是这种趋势仅限于10-15 eV的狭窄能量范围。通过使用屈服谱分析计算，我们基于背景大气的不同选择得出模型变化。我们发现，CO的存在对于再现观察到的变化至关重要。这使得可以通过光电子测量来估算大气中的CO密度，这比基于MAVEN中性气体和离子质谱仪的测量结果所公布的密度低3-7倍，并且与现有模型结果更好地吻合。通常，在特定能量下光电子强度作为大气成分示踪剂的有用性主要取决于在该能量下依赖于物种的非弹性电子碰撞截面。与MAVEN中性气体和离子质谱仪的测量结果相比，其密度要比已公布的密度低3-7倍，并且与现有模型结果更好地吻合。通常，在特定能量下光电子强度作为大气成分示踪剂的有用性主要取决于在该能量下依赖于物种的非弹性电子碰撞截面。与MAVEN中性气体和离子质谱仪的测量结果相比，其密度要比已公布的密度低3-7倍，并且与现有模型结果更好地吻合。通常，在特定能量下光电子强度作为大气成分示踪剂的有用性主要取决于在该能量下依赖于物种的非弹性电子碰撞截面。