Resolved spectrophotometric properties of the Ceres surface from Dawn Framing Camera images
Resolved spectrophotometric properties of the Ceres surface from Dawn Framing Camera images
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从黎明取景相机图像解析谷神星表面的分光光度特性
DOI：
10.1016/j.icarus.2017.01.026
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发表时间：
2017
期刊：
影响因子：
3.2
通讯作者：
Christopher T. Russell
中科院分区：
文献类型：
--
作者：
Stefan Schröder;S. Mottola;U. Carsenty;M. Ciarniello;R. Jaumann;Jian;A. Longobardo;E. Palmer;C. Pieters;F. Preusker;C. Raymond;Christopher T. Russell
我们提出了一个全球性的分光光度表征谷神星表面使用黎明分幅相机（FC）的图像。我们确定的光度模型，产生最好的结果，光度校正图像。在接近谷神星时获得的校正FC图像被组装成全球地图和彩色地图。一般来说，谷神星的反射率和颜色变化是温和的。该地图主要由Vendimia Planitia中的一个大型圆形特征主导，该特征从HST图像中已知（Li等人，2006年），并点缀着较小的明亮特征，主要与新鲜的陨石坑有关。表面上的主要颜色变化是由这些陨石坑内和周围的“蓝色”物质表示的，与平均地形相比，这些陨石坑在可见光波长范围内具有负的光谱斜率。我们还采用指数光度模型绘制了相位曲线的变化，这是一种以前应用于小行星灶神星的技术（Schröder et al.，2013年b）。谷神星的表面散射光线的方式与灶神星不同，因为几个看起来很新鲜的陨石坑的喷出物可能是光滑的而不是粗糙的。高弹性、蓝色和身体光滑度似乎都是年轻的指标。蓝色可能是由喷射物质的干燥造成的，类似于Poch等人实验中的层状硅酸盐/水冰混合物。（2016年）。一些蓝色地形的物理平滑度与最初的液体状态一致，可能是由于地下水冰的撞击融化。我们发现红色地形（正光谱斜率）附近的埃尔努泰特陨石坑，其中德桑克蒂斯等人。（2017）检测到有机物质。大的Vendimia Planitia特征的分光光度特性表明它是一个palimplant，与Marchi等人的结果一致。（2016）影响盆地假说。Occator陨石坑的中央明亮区域Cerealia Facula是谷神星上最明亮的区域，平均视觉正常亮度约为0.6，分辨率为每像素1.3公里（6倍于谷神星平均值）。在最高分辨率的图像（每像素35米）中，在这个区域内看到的新鲜明亮的物质的数量可能是统一的。谷物斑具有异常陡峭的相函数，这可能是由于未解析的地形、高表面粗糙度或大的平均粒度造成的。它有一个强烈的红色光谱，而邻近的，不太明亮的，Vinalia光斑是中性的颜色。我们没有发现证据表明，一个昼夜地面雾型霾在Occator所描述的Nathues等人。（2015年）。我们既不能使用相同的图像重现他们的发现，也不能使用更高分辨率的图像证实它们。FC图像还没有提供直接的证据，目前升华Occator。
We present a global spectrophotometric characterization of the Ceres surface using Dawn Framing Camera (FC) images. We identify the photometric model that yields the best results for photometrically correcting images. Corrected FC images acquired on approach to Ceres were assembled into global maps of albedo and color. Generally, albedo and color variations on Ceres are muted. The albedo map is dominated by a large, circular feature in Vendimia Planitia, known from HST images (Li et al., 2006), and dotted by smaller bright features mostly associated with fresh-looking craters. The dominant color variation over the surface is represented by the presence of “blue” material in and around such craters, which has a negative spectral slope over the visible wavelength range when compared to average terrain. We also mapped variations of the phase curve by employing an exponential photometric model, a technique previously applied to asteroid Vesta (Schröder et al., 2013b). The surface of Ceres scatters light differently from Vesta in the sense that the ejecta of several fresh-looking craters may be physically smooth rather than rough. High albedo, blue color, and physical smoothness all appear to be indicators of youth. The blue color may result from the desiccation of ejected material that is similar to the phyllosilicates/water ice mixtures in the experiments of Poch et al. (2016). The physical smoothness of some blue terrains would be consistent with an initially liquid condition, perhaps as a consequence of impact melting of subsurface water ice. We find red terrain (positive spectral slope) near Ernutet crater, where De Sanctis et al. (2017) detected organic material. The spectrophotometric properties of the large Vendimia Planitia feature suggest it is a palimpsest, consistent with the Marchi et al. (2016) impact basin hypothesis. The central bright area in Occator crater, Cerealia Facula, is the brightest on Ceres with an average visual normal albedo of about 0.6 at a resolution of 1.3 km per pixel (six times Ceres average). The albedo of fresh, bright material seen inside this area in the highest resolution images (35 m per pixel) is probably around unity. Cerealia Facula has an unusually steep phase function, which may be due to unresolved topography, high surface roughness, or large average particle size. It has a strongly red spectrum whereas the neighboring, less-bright, Vinalia Faculae are neutral in color. We find no evidence for a diurnal ground fog-type haze in Occator as described by Nathues et al. (2015). We can neither reproduce their findings using the same images, nor confirm them using higher resolution images. FC images have not yet offered direct evidence for present sublimation in Occator.