升华盐冰类似物的近红外反射光谱。对冰卫星的影响
Near-Infrared reflectance spectroscopy of sublimating salty ice analogues. Implications for icy moons
摘要：
自伽利略计划以来，伽利略冰卫星表面的成分一直存在争议。已经提出了几种化学物质来解释月球表面非冰成分的组成，特别是硫酸水合物和硫酸镁和硫酸钠。最近，有人提出用氯化镁和氯化钠来解释地面观测中观察到的特征。我们已经考虑了四种不同浓度的盐（NaCl，Na2SO4，MgSO4和MgCl2），以产生盐冰类似物。通过快速冷冻程序产生粒状颗粒。此外，盐冰的致密板是由盐溶液的缓慢结晶产生的。这两种方法模拟了在木卫二和木卫三等冰卫星表面产生水合盐冰的端元（羽状物和缓慢的冰块形成）。我们监测了盐冰在升华过程中的近红外（NIR）演化，揭示了颗粒状颗粒和板块之间的差异。板坯形成了更高量的水合物和最高度水合的化合物。粒状冰必须由更浓的盐溶液形成，以增加冰粒中水合物的含量。盐冰的升华有效地去除了所有多余的水冰，但没有观察到盐的脱水。在1.5 μ m和2.0 μm附近，特别是对于Na2SO4、MgCl2和MgSO4，板的最终光谱是最平坦的，这表明存在稳定的、高度水合的化合物。我们发现，Na2SO4，MgCl2和MgSO4是最兼容的非冰组分在冰卫星表面观测的NIMS仪器伽利略和地面观测。
英文摘要：
The composition of the surface of the Galilean icy moons has been debated since the Galileo mission. Several chemistries have been proposed to explain the composition of the non-icy component of the moon's surfaces, notably, sulphuric acid hydrates and magnesium and sodium sulphates. More recently, magnesium and sodium chlorides have been proposed to explain features observed in ground-based observations. We have considered four salts (NaCl, Na2SO4, MgSO4 and MgCl2) with various concentrations, to produce salty ice analogues. Granular particles were produced by a flash-freezing procedure. Additionally, compact slabs of salty ices were produced by a slow crystallisation of salty liquid solution. These two methods mimic the end-members (plumes and slow ice block formation) for producing hydrated salty ices on the surface of icy moons such as Europa and Ganymede. We have monitored the near-infrared (NIR) evolution of our salty ices during sublimation, revealing differences between the granular particles and the slabs. The slabs formed a higher amount of hydrates and the most highly hydrated compounds. Granular ices must be formed from a more concentrated salty solution to increase the amount of hydrates within the ice particles. The sublimation of salty ices removed all excess water ice efficiently, but the dehydration of the salts was not observed. The final spectra of the slabs were most flattened around 1.5 and 2.0 μm, especially for the Na2SO4, MgCl2 and MgSO4, suggesting the presence of stable, highly hydrated compounds. We find that Na2SO4, MgCl2 and MgSO4 are most compatible with the non-icy component at the surface of the icy moons as observed by the NIMS instrument on Galileo and by ground-based observations.
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