Despite produced exclusively on the dayside, photoelectrons, as an important population of the Martian ionosphere, have also been observed on the nightside. Here we present a statistical survey of nightside photoelectrons using the suprathermal electron measurements, made by the Solar Wind Electron Analyzer onboard the Mars Atmosphere and Volatile Evolution. We find that nearly 30% of the available nightside suprathermal electron spectra show clear photoelectron signatures. Nightside photoelectrons have an occurrence rate that decreases with increasing solar zenith angle and they are characterized by a preferentially field‐aligned pitch angle distribution. Our analysis also suggests that nightside photoelectrons are less likely observed under the high solar wind condition. These observations are favorably interpreted by the scenario of photoelectron transport along cross‐terminator magnetic field lines, as supported by a simplified test particle model. Our study highlights a complex plasma environment near Mars modulated by both internal and external conditions.

中文翻译：

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火星夜间的光电子研究

尽管仅在白天产生，但在夜间也观察到了作为火星电离层重要种群的光电子。在这里，我们介绍了利用火星大气和挥发性演化过程中的太阳风电子分析仪进行的超热电子测量对夜间光电子进行的统计调查。我们发现，近30％的可用夜间超热电子光谱显示出清晰的光电子签名。夜侧光电子的发生率随太阳天顶角的增加而降低，其特征是优先场对准的俯仰角分布。我们的分析还表明，在强太阳风条件下，不太可能观察到夜侧光电子。在简化的测试粒子模型的支持下，沿着交叉终止子磁场线进行光电子传输的情景可以很好地解释这些观察结果。我们的研究强调了受内部和外部条件调制的火星附近的复杂等离子体环境。