Laboratory predictions for the night-side surface ice glow of Europa

Europa’s surface continuously experiences high fluxes of charged particles due to the presence of Jupiter’s strong magnetic field. These high-energy charged particles, including electrons, interact with ice- and salt-rich surface, resulting in complex physical and chemical processes. Here we report that Europa ice analogs emit characteristic spectral signatures in the visible region when exposed to high-energy electron radiation. The strongest emission (ice glow) we observed was centered at ~525 nm. We found that the presence of sodium chloride and carbonate strongly quenched, while epsomite enhanced, the radiation-induced ice glow. These emission characteristics could be used to determine the chemical composition of Europa’s surface during night-time low-altitude flybys of spacecraft such as the Europa Clipper. We estimate that the Europa Clipper Wide Angle Camera could record between 500 and 280,000 counts per second through different color filters, depending on the chemical composition of Europa’s surface. Though we focus here on Europa, our study may be relevant to other bodies exposed to high doses of ionizing radiation, such as Io and Ganymede. With its extreme radiation environment, rich surface geology, and compositional diversity, the radiation-induced ice glow on Europa could enable more precise surface characterization and provide unique night-time views.

木卫二（Europa）的表面因木星强磁场的作用，持续暴露于高强度带电粒子流中。这些包括电子在内的高能带电粒子与富含冰与盐类的表面发生相互作用，引发复杂的物理与化学过程。本研究报道，木卫二冰类似物在经受高能电子辐射时，会在可见光波段呈现出特征光谱信号。我们观测到的最强辐射（冰辉）峰值位于约525纳米处。研究发现，氯化钠与碳酸盐的存在会显著淬灭辐射诱导的冰辉，而泻利盐（epsomite）则会增强该信号。这些辐射特征可用于在“欧罗巴快帆”（Europa Clipper）等航天器进行夜间低空飞越任务时，反演木卫二表面的化学组成。我们估算，“欧罗巴快帆”的广角相机通过不同颜色滤光片进行观测时，每秒可记录500至280000个计数，具体数值取决于木卫二表面的化学组成。尽管本研究聚焦于木卫二，但其结论同样适用于其他暴露于高剂量电离辐射的天体，如木卫一（Io）与木卫三（Ganymede）。鉴于木卫二极端的辐射环境、丰富的表面地质特征与多样的表面组分，其表面由辐射诱导产生的冰辉可助力实现更精准的表面成分表征，并提供独特的夜间观测视角。