Ion energization in Ganymede’s magnetosphere: Using multifluid simulations to interpret ion energy spectrograms
Ion energization in Ganymede’s magnetosphere: Using multifluid simulations to interpret ion energy spectrograms
复制标题
木卫三磁层中的离子赋能：使用多流体模拟解释离子能谱图
DOI：
--
复制
发表时间：
2008
期刊：
影响因子：
--
通讯作者：
R. Winglee
中科院分区：
文献类型：
--
作者：
C. Paty;W. Paterson;R. Winglee
[1] 我们通过检查木卫三的电离层流出物作为重 (O+) 和轻 (H+) 离子源以及木星磁层等离子体作为重离子的外部来源来研究木卫三磁层内的离子数量和能量分布。我们开发了一种方法，用于检查三维多流体模拟中每种离子种类的能量分布，其方式与伽利略航天器上等离子体实验的观测结果直接相当。这为有关木卫三观测到的电离层流出物组成的现有争议提供了新的见解，并能够进一步检查木卫三磁层内离子群的能量特征。模型预测的电离层流出量与伽利略等离子体实验在最接近处观察到的原位离子能量谱图一致，并且要求电离层 H+ 和 O+ 都存在于离开木卫三极冠电离层的离子群中。电离层离子的向外通量经计算约为 1026 个离子/cm2/s，这与独立计算的木卫三冰表面的溅射率一致。建模的谱图定义了木卫三磁层各个区域的特征能量特征和总体，说明了磁层内捕获的离子的主要来源是木卫三的电离层 O+ 和 H+。事实上，在 G8 飞越期间，在木卫三磁层内观察到的等离子体非常少，这是由于该区域被太阳遮挡约 60 小时，这可能表明光电离对于维持木卫三电离层等离子体源的重要性。
[1] We investigate the ion population and energy distribution within Ganymede’s magnetosphere by examining Ganymede’s ionospheric outflow as a source of heavy (O+) and light (H+) ions and the Jovian magnetospheric plasma as an external source of heavy ions. We develop a method for examining the energy distributions of each ion species in a three-dimensional multifluid simulation in a way directly comparable to the observations of the Plasma Experiment on the Galileo spacecraft. This is used to provide new insight to the existing controversy over the composition of Ganymede’s observed ionospheric outflow, and enables further examination of the energetic signatures of the ion population trapped within Ganymede’s magnetosphere. The model-predicted ionospheric outflow is consistent with the in situ ion energy spectrograms observed by the Galileo Plasma Experiment at closest approach, and requires that both ionospheric H+ and O+ are present in the population of ions exiting Ganymede’s ionosphere over the polar cap. The outward flux of ionospheric ions was calculated to be ~1026 ions/cm2/s, which is in agreement with independently calculated sputtering rates of Ganymede’s icy surface. The modeled spectrograms define characteristic energy signatures and populations for various regions of Ganymede’s magnetosphere, which illustrate the major sources of ions trapped within the magnetosphere are Ganymede’s ionospheric O+ and H+. The fact that very little plasma was observed inside Ganymede’s magnetosphere during the G8 flyby is attributed to the region being shadowed from the sun for ~60 h, which may indicate the importance of photoionization for sustaining Ganymede’s ionospheric plasma source.