Jovian magnetospheric plasma irradiates the surface of Ganymede and is postulated to be the primary agent that changes the surface brightness of Ganymede, leading to asymmetries between polar and equatorial regions as well as between the trailing and leading hemispheres. As impinging ions sputter surface constituents as neutrals, ion precipitation patterns can be remotely imaged using the Energetic Neutral Atoms (ENA) measurement technique. Here we calculate the expected sputtered ENA flux from the surface of Ganymede to help interpret future observations by ENA instruments, particularly the Jovian Neutral Analyzer (JNA) onboard the JUpiter ICy moon Explorer (JUICE) spacecraft. We use sputtering models developed based on laboratory experiments to calculate sputtered fluxes of H₂O, O₂, and H₂. The input ion population used in this study is the result of test particle simulations using electric and magnetic fields from a hybrid simulation of Ganymede’s environment. This population includes a thermal component (H⁺ and O⁺ from 10 eV to 10 keV) and an energetic component (H⁺, O⁺⁺ and S⁺⁺⁺ from 10 keV to 10 MeV). We find a global ENA sputtering rate from Ganymede of 1.42 × 10²⁷ s⁻¹, with contributions from H₂, O₂, and H₂O of 34%, 17%, and 49% respectively. We also calculate the energy distribution of sputtered ENAs, give an estimate of a typical JNA count rate at Ganymede, and investigate latitudinal variations of sputtered fluxes along a simulated orbit track of the JUICE spacecraft. Our results demonstrate the capability of the JNA sensor to remotely map ion precipitation at Ganymede.

中文翻译：

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木卫三中高能中性原子溅射的模拟，为 JUICE 任务做准备

木星磁层等离子体照射木卫三表面，据推测是改变木卫三表面亮度的主要因素，导致极地和赤道区域之间以及后半球和前半球之间的不对称。由于撞击离子溅射表面成分作为中性，离子沉淀模式可以使用高能中性原子 (ENA) 测量技术进行远程成像。在这里，我们计算了来自木卫三表面的预期溅射 ENA 通量，以帮助解释 ENA 仪器的未来观测结果，特别是木星 ICy 月球探索者 (JUICE) 航天器上的木星中性分析仪 (JNA)。我们使用基于实验室实验开发的溅射模型来计算 H ₂ O、O _{2 的}溅射通量, 和 H ₂。本研究中使用的输入离子群是使用来自木卫三环境混合模拟的电场和磁场的测试粒子模拟的结果。该群体包括热成分（H ⁺和 O ⁺从 10 eV 到 10 keV）和能量成分（H ⁺、O ⁺⁺和 S ⁺⁺⁺从 10 keV 到 10 MeV）。我们发现来自 Ganymede 的全局 ENA 溅射速率为 1.42 × 10 ²⁷ s ^-1，其中 H ₂、O ₂和 H _{2 的}贡献O 分别为 34%、17% 和 49%。我们还计算了溅射 ENA 的能量分布，估计了木卫三的典型 JNA 计数率，并研究了沿 JUICE 航天器模拟轨道轨迹的溅射通量的纬度变化。我们的结果证明了 JNA 传感器能够远程绘制木卫三的离子降水图。