Ida and Dactyl: Spectral reflectance and color variations
Ida and Dactyl: Spectral reflectance and color variations
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Ida 和 Dactyl：光谱反射率和颜色变化
DOI：
10.1006/icar.1996.0037
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发表时间：
1996
期刊：
影响因子：
3.2
通讯作者：
J. Head
中科院分区：
文献类型：
--
作者：
J. Veverka;P. Helfenstein;P. Lee;P. Thomas;A. McEwen;M. Belton;K. Klaasen;T. Johnson;J. Granahan;F. Fanale;P. Geissler;J. Head
伽利略SSI在0.4 ~ 1.0 μm之间的颜色数据表明，Ida和Dactyl都是s型小行星，具有相似但不同的光谱。在Ida本身也观察到小而明确的颜色变化，包括光谱的蓝色部分和1-μm辉石-橄榄石波段的深度。Ida的表面可分为两种颜色地形：地形A比地形b具有较浅的1-μm吸收和更陡峭的可见红色斜坡。定性地，这两种地形的颜色反照率系统遵循Gaspra的颜色单位和Gaffeyet等人（Gaffey， M. J. F. Bell， R. H. Brown， T. H. Burbine， J. Piatek， K. L. Reed和D. A. Chaky 1993）描述的1-μm波段深度随风化的变化。Icarus106, 573 - 602)。与地形B相比，地形A的反照率略低，1-μm波段较浅，可见红色斜坡略陡，可以解释为两个地形中“加工程度更高”、“更成熟”或“风化程度更高”。与这一解释一致的是，地形A似乎是伊达大部分地区普遍存在的背景，而地形B与一些小陨石坑以及可能来自10公里的Azzurra撞击结构的抛射物有关。由于这些趋势，地形A和B之间的差异不太可能是由Ida体内原始成分的不均匀性引起的，尽管它们确实属于已知的Koronis家族的范围。Dactyl的谱与Ida上的B地形相似，但绝对不同。这与地形A和地形B的颜色和反照率之间的关系不符合：卫星的1 μm波段比地形B深，但反照率比地形B低，而不是更高。根据Gaffeyet等人的说法，就其本身而言，较深的波段深度可以解释为Dactyl是Ida上较少风化的地形B的版本，但这种解释与Dactyl较红的光谱斜率不一致。因此，对Dactyl和Ida之间颜色差异的解释可能与解释Ida上两种地形之间差异的解释不同。考虑到Dactyl和Ida具有非常相似的光度特性（Helfenstein， P.， J. Veverka， P. C. Thomas， D. P. Simonelli， K. Klassen， T. V. Johnson， F. Fanale， J. Granahan, a. S. McEwen， M. J. S. Belton和C. R. Chapman 1996icarus120,48 - 65），从而排除了两个表面之间任何显著的纹理差异，最可能的解释是卫星的成分与Ida稍微不同（更多的辉石？）。光谱差异在Binzelet等人（Binzel， R. P.， S. Xu, and S. J. Bus 1993）报道的范围内。（Icarus106, 608-611 .），这可能是由于Koronis母体的成分不均匀性而不是由破碎后的风化过程引起的。
Abstract Galileo SSI color data between 0.4 and 1.0 μm demonstrate that both Ida and Dactyl are S-type asteroids with similar, but distinct spectra. Small but definite color variations are also observed on Ida itself and involve both the blue part of the spectrum and the depth of the 1-μm pyroxene–olivine band. Ida's surface can be classified into two color terrains: Terrain A has a shallower 1-μm absorption and a steeper visible red slope than does Terrain B. Qualitatively, the color–albedo systematics of these two terrains follow those noted for color units on Gaspra and the variations in 1-μm band depth with weathering described by Gaffeyet al.(Gaffey, M. J., J. F. Bell, R. H. Brown, T. H. Burbine, J. Piatek, K. L. Reed, and D. A. Chaky 1993.Icarus106, 573–602). Terrain A, with its slightly lower albedo, its shallower 1-μm band, and its slightly steeper visible red slope relative to Terrain B could be interpreted as the “more processed,” “more mature,” or the “more weathered” of the two terrains. Consistent with this interpretation is that Terrain A appears to be the ubiquitous background on most of Ida, while Terrain B is correlated with some small craters as well as with possible ejecta from the 10-km Azzurra impact structure. Because of these trends, it is less likely that differences between Terrains A and B are caused by an original compositional inhomogeneity within the body of Ida, although they do fall within the range known to occur within the Koronis family. The spectrum of Dactyl is similar to, but definitely different from, that of Terrain B on Ida. It does not conform to the pattern that obtains between the colors and albedos of Terrains A and B: the satellite's 1-μm band is deeper than that of Terrain B, but its albedo is lower, rather than higher. By itself, the deeper band depth could be interpreted, following Gaffeyet al., to mean that Dactyl is a less weathered version of Terrain B on Ida, but such an interpretation is at odds with Dactyl's redder spectral slope. Thus, the explanation for the color difference between Dactyl and Ida is likely to be different from that which accounts for the differences between the two terrains on Ida. Given that Dactyl and Ida have very similar photometric properties (Helfenstein, P., J. Veverka, P. C. Thomas, D. P. Simonelli, K. Klassen, T. V. Johnson, F. Fanale, J. Granahan, A. S. McEwen, M. J. S. Belton, and C. R. Chapman 1996Icarus120, 48–65), thus ruling out any dramatic texture differences between the two surfaces, the most likely explanation is that the satellite has a slightly different composition (more pyroxene?) than Ida. The spectral difference is within the range reported by Binzelet al.(Binzel, R. P., S. Xu, and S. J. Bus 1993.Icarus106, 608–611.) for members of the Koronis family, and could be caused by compositional inhomogeneities of the Koronis parent body rather than by post-breakup regolith processes.