近月空间带电粒子环境——“嫦娥1号”“嫦娥2号”观测结果

The Lunar Charged Particle Environment by Chang’E-1 and Chang’E-2

"嫦娥1号"(CE-1)、"嫦娥2号"(CE-2)都安装了1台太阳高能粒子探测器(High-energetic Particles Detectors,HPD)和2台太阳风离子探测器(Solar Wind Ion Detectors,SWIDs),进行了月球轨道200 km和100 km空间环境探测,获得了月球轨道空间高能带电粒子(质子、电子和重离子)能谱随时间的演化特征、等离子体与月球相互作用特征以及太阳风离子速度、密度和温度参量。空间环境探测数据分析结果表明:太阳活动低年、空间环境扰动水平相对较低、月球处于太阳风中时,近月空间带电粒子环境的基本特征与行星际空间相比变化不大。CE-1、CE-2在轨运行期间,发现了多起0.1~2 MeV能量电子急剧增加事件,这些事件发生在月球从太阳风运动到磁尾的所有空间区域,其中20%的事件伴随着卫星周围等离子体离子加速。模拟和统计研究表明:能量电子急剧增加使得绕月卫星和月球表面电位大幅下降导致了离子加速现象的发生;能量电子总流量大于1011 cm-2时,绕月卫星和月球表面充电电位可达负的上千伏。此外,月表溅射与反射太阳风离子、太阳风"拾起"离子等空间环境事件的发现,揭示了太阳风离子和月球存在复杂的相互作用过程。

Chang’E-1 and Chang’E-2 are 3-axis stabilized lunar orbiters with a circular polar orbit of an altitude of 200 km and 100 km respectively. The space environment system of Chang’E-1 and Chang’E-2 consists of two Solar wind ion detectors(SWIDs, SWIDA/B) and one high energetic particles detector(HPD). SWIDs were developed to measure the plasma environment around the Moon and the spectrum of the circumambient ions surround the spacecraft. The high energetic particles detector was designed to investigate the Solar energetic particles events and the energetic particles(proton, electron and heavy ions) in space. The basic charged particle environment nearby the lunar was obtained by the space environment system under the Solar minimum, weakly interplanetary magnetic fields(IMF) conditions. The results of the space environment system indicate that the energetic particles radiation environment near the lunar is the same as in the interplanetary when the lunar is in the Solar wind and the similar trend of variation is maintained when the Solar wind go through the interplanetary to the lunar. Hundreds of the bursts of 0. 1~2 MeV energetic electrons(BEE) occurred by Chang’E-1 and Chang’E-2,and 20% of the ambient plasma ions accelerated on lunar orbit during BEE were observed when Chang’E-1 and Chang’E-2 flying through the terrestrial magneto sheath or the transition region of the boundaries. The results indicated that the BEE induced the surface potential increasing of the orbiter,and lunar or the spacecraft surface will charge to negative kilovolts during the BEEs after the temporal integral of the energetic electrons fluxes reach up to > 1011 cm-2 The complex interaction between Solar wind ions and lunar surface was observed,include the lunar sputter ions,reflection ions and Solar wind "pick up" ions.