木卫二表面水冰结晶度及线状体与雨云组成的关系
Europa's Surface Water-ice Crystallinity and Correlations between Lineae and Hydrate Composition
摘要：
木卫二的表面组成和冰火山活动的证据可以提供深入了解地下海洋的性质和组成，从而可以评估其潜在的可居住性。揭示表面处理和地下活动的一个有前途的途径是在表面上观察到的结晶和无定形水冰的相对分数，这是受温度，带电粒子轰击，气相沉积和冰火山活动的影响。在木卫二的前半球上观察到的结晶度不能单独通过热物理和粒子通量模型来再现，这表明可能有其他过程影响表面。我们进行了光谱混合分析的高光谱图像立方体从伽利略近红外测绘光谱仪（NIMS），以确定如何表面结晶度的物理处理在高空间分辨率尺度的影响。我们特别关注两个图像立方体，靠近赤道的15e015和靠近南极的17e009，两者都在领先的半球上。我们进行了非负最小二乘光谱混合分析，揭示了非冰的组成和水冰结晶度的表面。我们发现，无定形水冰占主导地位的光谱在赤道和南极。我们估计15e015 NIMS立方体内的平均结晶度约为35%，17e009 NIMS立方体内的平均结晶度约为15%，这与基于地面的光谱学推导的堆积一致。我们还确定了相关的硫酸镁，氯化镁，和水合硫酸与线和脊，这可能会提供证据的表面处理涌升地下材料。
英文摘要：
Europa's surface composition and evidence for cryovolcanic activity can provide insight into the properties and composition of the subsurface ocean, allowing the evaluation of its potential habitability. One promising avenue for revealing the surface processing and subsurface activity are the relative fractions of crystalline and amorphous water-ice observed on the surface, which are influenced by temperature, charged particle bombardment, vapor deposition, and cryovolcanic activity. The crystallinity observed on Europa's leading hemisphere cannot be reproduced by thermophysical and particle flux modeling alone, indicating that there may be additional processes influencing the surface. We performed a spectral mixture analysis on hyperspectral image cubes from the Galileo Near-Infrared Mapping Spectrometer (NIMS) to identify how surface crystallinity is influenced by physical processing at a high spatial resolution scale. We focus specifically on two image cubes, 15e015 closer to the equator and 17e009 closer to the south pole, both on the leading hemisphere. We performed a nonnegative least-squares spectral mixture analysis to reveal both the non-ice composition and the water-ice crystallinity of the surface. We found that amorphous water-ice dominates the spectrum at the equator and the south pole. We estimated a mean crystallinity of ~35% within the 15e015 NIMS cube and a mean crystallinity of ~15% within the 17e009 NIMS cube, which is consistent with ground-based spectroscopically derived crystallinities. We also identified a correlation of magnesium sulfate, magnesium chloride, and hydrated sulfuric acid with lineae and ridges, which may provide evidence for surface processing by upwelling subsurface material.
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