Planetary radar has provided a growing number of data sets on the inner planets and near‐Earth and main belt asteroid populations in the solar system. Physical interpretation of radar data for inference of surface properties requires constraints on the constitutive parameters of the material making up a given surface. In this study, the complex permittivity of seven minerals as a function of frequency and porosity is measured using the coaxial transmission line method to determine the mixing equation that best describes the relationship between the real part of the complex permittivity of single mineral crystals and granular mineral powders. We find the Looyenga‐Landau‐Lifshitz and Bruggeman symmetric mixing equations to describe our experimental results with the highest accuracy. The variation in the real part of the permittivity of solid mineral crystals between different minerals is shown to depend on the grain density and the chemical composition of the minerals. These mixing relationships are incorporated into an asteroid radar model and used to calculate the porosity in the near‐surface of seven asteroids visited by robotic spacecraft using Earth‐based radar observations. The results of the asteroid radar model support the presence of significant porosity in the boulders on the surface of asteroid 101955 Bennu. This research highlights the ability of radar to measure the porosity on asteroid surfaces and provides theoretical and experimental justification for the inversion of permittivity to bulk density assumed by the asteroid radar model.

中文翻译：

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模拟矿物从晶体到大块粉末的介电特性，以改善对小行星雷达观测的解释

行星雷达已经提供了越来越多的有关内部行星以及太阳系中近地和主带小行星种群的数据集。为了推断表面特性而对雷达数据进行物理解释需要对构成给定表面的材料的本构参数进行约束。在这项研究中，使用同轴传输线方法测量了七种矿物的复介电常数随频率和孔隙率的变化，以确定最能描述单一矿物晶体的复介电常数的实部与粒状矿物之间关系的混合方程。粉末。我们找到了Looyenga-Landau-Lifshitz和Bruggeman对称混合方程来以最高的精度描述我们的实验结果。固体矿物晶体的介电​​常数的实部变化在不同矿物之间显示出取决于矿物的颗粒密度和化学组成。这些混合关系被合并到小行星雷达模型中，并用于使用基于地球的雷达观测来计算机器人航天器访问的七个小行星的近地表孔隙度。小行星雷达模型的结果支持在小行星101955 Bennu表面的巨石中存在明显的孔隙度。这项研究突出了雷达测量小行星表面孔隙率的能力，并为小行星雷达模型假设的介电常数到体积密度的反演提供了理论和实验依据。