天王星卫星Ariel上含氨物种的证据支持了最近的地质活动
Evidence for ammonia-bearing species on the Uranian satellite Ariel supports recent geologic activity
摘要：
我们研究了富含氨的成分是否存在于天王星卫星Ariel的表面上，通过分析在宽范围的子观测器的纬度和纬度收集的32个近红外反射光谱。我们测量了这些光谱中2.2-{ \micron }特征的带面积和深度，这归因于其他冰体上的含氨物种。10个谱图显示出显著的2.2-{ \micron }特征，谱带面积和深度> 2σ。我们确定了2.2-{ \micron }条带的纵向分布，发现Ariel的前半球和后半球之间没有统计学上有意义的差异，表明该条带分布在Ariel的整个表面。我们比较了显示最强的2.2-{ \micron }带的五个Ariel光谱的带中心和形状与各种含氨和含铵物种的实验室光谱，发现Ariel光谱的光谱特征与氨水合物和速冻氨水溶液最匹配。我们的分析还表明，四个Ariel光谱显示2.24-{ \micron }带（> 2σ带面积和深度），带中心和形状与氨冰最匹配。由于氨应该在短时间内被紫外线光子、宇宙射线和天王星磁层中捕获的带电粒子有效地去除，这种成分的可能存在支持了最近的地质活动，例如富含氨的低温熔岩的就位和富含氨的沉积物因构造运动、撞击事件和物质坡移而暴露。
英文摘要：
We investigated whether ammonia-rich constituents are present on the surface of the Uranian moon Ariel by analyzing 32 near-infrared reflectance spectra collected over a wide range of sub-observer longitudes and latitudes. We measured the band areas and depths of a 2.2-{\micron} feature in these spectra, which has been attributed to ammonia-bearing species on other icy bodies. Ten spectra display prominent 2.2-{\micron} features with band areas and depths > 2σ. We determined the longitudinal distribution of the 2.2-{\micron} band, finding no statistically meaningful differences between Ariel's leading and trailing hemispheres, indicating that this band is distributed across Ariel's surface. We compared the band centers and shapes of the five Ariel spectra displaying the strongest 2.2-{\micron} bands to laboratory spectra of various ammonia-bearing and ammonium-bearing species, finding that the spectral signatures of the Ariel spectra are best matched by ammonia-hydrates and flash frozen ammonia-water solutions. Our analysis also revealed that four Ariel spectra display 2.24-{\micron} bands (> 2σ band areas and depths), with band centers and shapes that are best matched by ammonia ice. Because ammonia should be efficiently removed over short timescales by ultraviolet photons, cosmic rays, and charged particles trapped in Uranus' magnetosphere, the possible presence of this constituent supports geologic activity in the recent past, such as emplacement of ammonia-rich cryolavas and exposure of ammonia-rich deposits by tectonism, impact events, and mass wasting.
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