木卫四表面溅射外大气层环境的三维建模
Three-Dimensional Modeling of Callisto's Surface Sputtered Exosphere Environment
摘要：
我们研究释放的各种元素从木卫四的表面到它的外逸层等离子体溅射。冷木星等离子体模拟与三维等离子体行星相互作用的混合模型，产生二维表面降水磁层H+，O+，O++，和S++。对于热木星等离子体，我们假设各向同性沉淀到完整的球面。研究了两种情况：一个是没有电离层屏蔽，因此实现了完全的等离子体穿透（“无电离层”场景），另一个是电离层几乎没有冷等离子体，而是所有的热等离子体到达木卫四的表面（“电离层”场景）。在3D散逸层模型中，中性粒子从表面溅射出来，并沿着它们各自的轨迹运动。三维密度分布表明，而在“无电离层”的情况下，冲压方向是有利的，“电离层”的情况下产生几乎均匀的密度分布。此外，“电离层”情景中的密度分布相对于“无电离层”情景减少了约2.5倍。我们发现，中性气体和离子质谱仪，这是在果汁任务上的粒子环境包的一部分，将能够检测到不同的溅射人口从木卫四的冰表面和主要溅射人口从木卫四的非冰表面。木卫四外逸层的化学成分可以直接与其表面的化学成分联系起来，不仅可以为我们提供木卫四形成场景的信息，还可以为我们提供木星系统的构建模块。
英文摘要：
We study the release of various elements from Callisto's surface into its exosphere by plasma sputtering. The cold Jovian plasma is simulated with a 3D plasma-planetary interaction hybrid model, which produces 2D surface precipitation maps for magnetospheric H+ , O+ , O++ , and S++ . For the hot Jovian plasma, we assume isotropic precipitation onto the complete spherical surface. Two scenarios are investigated: One where no ionospheric shielding takes place and accordingly full plasma penetration is implemented ('no ionosphere' scenario), and one where an ionosphere lets virtually none of the cold plasma but all of the hot plasma reach Callisto's surface ('ionosphere' scenario). In the 3D exosphere model, neutral particles are sputtered from the surface and followed on their individual trajectories. The 3D density profiles show that whereas in the 'no ionosphere' scenario the ram direction is favored, the 'ionosphere' scenario produces almost uniform density profiles. In addition, the density profiles in the 'ionosphere' scenario are reduced by a factor of ~2.5 with respect to the 'no ionosphere' scenario. We find that the Neutral gas and Ion Mass spectrometer, which is part of the Particle Environment Package on board the JUICE mission, will be able to detect the different sputter populations from Callisto's icy surface and the major sputter populations from Callisto's non-icy surface. The chemical composition of Callisto's exosphere can be directly linked to the chemical composition of its surface, and will offer us information not only on Callisto's formation scenario but also on the building blocks of the Jupiter system.
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