超精细和多孔颗粒表面的可见光和近红外反射率
Visible and near-infrared reflectance of hyperfine and hyperporous particulate surfaces
摘要：
太阳系表面的成分可以通过反射和发射光谱学来推断，通过将这些观测结果与实验室测量和辐射转移模型进行比较。虽然若干物体群似乎被亚微米尺寸的颗粒（称为超微粒）覆盖，但对由小于可见光和红外波长的颗粒组成的微粒表面的反射和发射的研究有限。我们已着手确定超微粒表面的反射率以及高孔隙率，以便模拟彗星表面及其相关小行星（P型和D型）的物理状态。在这项工作中，我们提出了一种技术开发，以产生超精细粒子的天体物理相关材料。制备超精细粉末，并在0.4-2.6微米范围内测量反射率。然后将这些粉末包含在水冰粒中，在真空下升华，以产生超精细材料的多孔样品。当研磨到1微米以下时，所研究的四种材料（橄榄石、蒙皂石、辉石和无定形二氧化硅）显示出它们的吸收特征的强烈降低以及光谱的蓝化。这种小晶粒简并意味着由超精细晶粒覆盖的表面应该仅显示浅吸收特征（如果有的话）。这两个效果，带深和光谱蓝化的减少，出现放大时，晶粒被纳入超多孔残留物。我们解释了不同的行为之间的多孔性和更紧凑的表面由个别晶粒的距离和减少的元素散射体的大小。这项工作意味着S型或V型小行星表面的超精细颗粒并不丰富，B型小行星的蓝色性质可能与物理效应有关，而不是成分效应。
英文摘要：
The composition of Solar System surfaces can be inferred through reflectance and emission spectroscopy, by comparing these observations to laboratory measurements and radiative transfer models. While several populations of objects appear to be covered by sub-micrometre sized particles (referred to as hyperfine), there are limited studies on reflectance and emission of particulate surfaces composed of particles smaller than the visible and infrared wavelengths. We have undertaken an effort to determine the reflectance of hyperfine particulate surfaces in conjunction with high-porosity, in order to simulate the physical state of cometary surfaces and their related asteroids (P- and D-types). In this work, we present a technique developed to produce hyperfine particles of astrophysical relevant materials. Hyperfine powders were prepared and measured in reflectance in the 0.4-2.6 micrometer range. These powders were then included in water ice particles, sublimated under vacuum, in order to produce a hyperporous sample of hyperfine material. When grinded below one micrometre, the four materials studied (olivine, smectite, pyroxene and amorphous silica), show strong decrease of their absorption features together with a blueing of the spectra. This small grain degeneracy implies that surfaces covered by hyperfine grains should show only shallow absorption features if any. These two effects, decrease of band depth and spectral blueing, appear magnified when the grains are incorporated in the hyperporous residue. We interpret the distinct behaviour between hyperporous and more compact surfaces by the distancing of individual grains and a decrease in the size of the elemental scatterers. This work implies that hyperfine grains are unabundant at the surfaces of S- or V-type asteroids, and that the blue nature of B-type may be related to a physical effect rather than a compositional effect.
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