The ionosphere of Titan hosts a complex ion chemistry leading to the formation of organic dust below 1,200 km. Current models cannot fully explain the observed electron temperature in this dusty environment. To achieve new insight, we have re-analyzed the data taken in the ionosphere of Titan by the Cassini Langmuir probe (LP), part of the Radio and Plasma Wave Science package. A first paper (Chatain et al., 2021) introduces the new analysis method and discusses the identification of four electron populations produced by different ionization mechanisms. In this second paper, we present a statistical study of the whole LP dataset below 1,200 km which gives clues on the origin of the four populations. One small population is attributed to photo- or secondary electrons emitted from the surface of the probe boom. A second population is systematically observed, at a constant density (∼500 cm⁻³), and is attributed to background thermalized electrons from the ionization process of precipitating particles from the surrounding magnetosphere. The two last populations increase in density with pressure, solar illumination and Extreme ultraviolet flux. The third population is observed with varying densities at all altitudes and solar zenith angles (SZA) except on the far nightside (SZA > ∼140°), with a maximum density of 2,700 cm⁻³. It is therefore certainly related to the photo-ionization of the atmospheric molecules. Finally, a fourth population detected only on the dayside and below 1,200 km reaching up to 2000 cm⁻³ could be photo- or thermo-emitted from dust grains.

中文翻译：

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重新分析泰坦电离层中卡西尼号 RPWS/LP 数据：2. 57 次飞越的统计

泰坦的电离层拥有复杂的离子化学，导致在 1,200 公里以下形成有机尘埃。当前的模型无法完全解释在这种多尘环境中观察到的电子温度。为了获得新的见解，我们重新分析了卡西尼朗缪尔探测器 (LP) 在泰坦电离层中获取的数据，该探测器是无线电和等离子波科学包的一部分。第一篇论文（Chatain 等人，2021 年）介绍了新的分析方法，并讨论了由不同电离机制产生的四种电子群的识别。在第二篇论文中，我们对 1,200 公里以下的整个 LP 数据集进行了统计研究，为四个种群的起源提供了线索。一小部分归因于从探针臂表面发射的光电子或二次电子。^-3 )，并且归因于来自周围磁层中粒子沉淀的电离过程的背景热化电子。最后两个种群的密度随着压力、太阳光照和极紫外通量而增加。除了在远夜侧（SZA > ∼140°）外，在所有高度和太阳天顶角（SZA）上都观察到了密度不同的第三类群，其最大密度为 2,700 cm ^-3。因此，它肯定与大气分子的光电离有关。最后，仅在日侧和 1,200 公里以下、达到 2000 cm ^-3范围内检测到的第四个种群可能是从尘埃颗粒中发出的光或热辐射。