The Solar Wind and Particle Radiation Environment on the Surface of the Moon—New Observations from Chang’E-4
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摘要: 太阳风、太阳高能粒子、银河宇宙线几乎可以无阻碍地到达月面,与月表发生相互作用。太阳风粒子以能量中性原子的形式被月壤散射的过程与太阳风状态、月表电磁环境、局部地形、月壤特性等因素均有关系;银河宇宙射线、太阳高能粒子与月壤相互作用产生以中子和伽马射线为主的反照辐射,形成特殊的月表粒子辐射环境。介绍了“嫦娥四号”首次在月球背面原位所测量的能量中性原子、粒子辐射环境,分析了月面ENA的能谱等特性、月球微磁层存在的观测证据及月面辐射环境的构成及其随时间的变化。结果表明月表能量中性原子观测为认识太阳风与月球的相互作用,这为研究月球微磁层内部结构及成因提供了新的视角;而月面辐射环境的测量为未来月球探测中航天员和设备的安全保障提供了重要依据。Abstract: The solar wind, solar energetic particles and the galactic cosmic rays can reach the Moon almost unhindered, and interact with the lunar surface. The solar wind is partly scattered by the lunar regolith as hydrogen energetic neutral atoms, and the solar wind can also sputter heavy energetic neutral atoms out of the lunar regolith as well. While the albedo radiation, resulting from impact of the solar energetic particles and the galactic cosmic rays on the lunar regolith, are mainly composed of neutrons and gamma rays, features of the lunar surface radiation environment. The first ever in situ measurements of energetic neutral atoms and particle radiation have been carried out by Chang’E-4 on the lunar farside. Results reveal thata mini-magnetosphere is formed in the vicinity of the Moon, suggesting ENA is a new perspective to study the solar wind - Moon interaction. While the radiation measurements provide valuable information to guarantee the health of future robotic or manned missions to the Moon.Highlights
● Chang’E-4 carried out first time in situ measurements of ENA and particle ration environment on the lunar surface ● Observations reveal that low energy (<100 eV) ENA has high flux; while 100-600eV ENA flux exhibits linear correlation with the solar wind parameters. Thus reduced ENA flux in the afternoon section (lunar local time) suggests the surface might be partly shielded by the mini-magnetosphere formed over the Imbrium antipodal magnetic anomalies. The solar wind penetration into the mini-magnetosphere depends on the inertial length of solar wind protons. ● The lunar surface radiation parameters and their variations over time are measured, supplying valuable information for lunar surface mission design. The lunar surface does not affect the galactic ray spectrum under quiet solar conditions, while the neutral components, resulting from galactic ray and solar energetic particle interaction with the lunar regolith, contributes ~23 % to the lunar surface radiation. -
图 5 “嫦娥四号”着陆点周围的磁场大小分布[17]
Fig. 5 Magnetic field strength around the landing site of Chang’E-4
图 6 太阳风与月球相互作用Hall-MHD模拟结果
Fig. 6 Solar wind interacts with the Moon, simulated by the Hall-MHD model[17].
图 12 LDN对宇宙线各组成分的通量测量与近地航天器观测结果的比值平均值(紫色)[27]; LDN对宇宙线各组成分的通量测量与CRÈME模型预测值的比值平均值[28-29](绿色对应CRÈME96,橙色对应CRÈME2009);红色虚线表示比值为1.0
Fig. 12 Averaged ratio of GCR compositions from LND, to those from the near Earth spacecrafts (magenta) [27], and model predictions [28-29] (Green CRÈME96, orange CRÈME2009). Red dashed line marks the ratio of 1.0.
图 13 太阳质子爆发期间辐射剂量的变化情况[30]
Fig. 13 Radiation changes in the solar energetic particle events
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