High Precision Dielectric Permittivity Measurements of Planetary Regolith analogs Using A Split-Cylinder Resonator

Abstract:

Complex relative permittivity is essential for quantitative interpretation of radar data in remote sensing of planetary surfaces. The real part determines the speed of the electromagnetic waves, while the imaginary part is related to the penetration depth. This project is part of NASA’s OSIRIS-REx asteroid sample return mission. Radar is an important tool for asteroid investigation, particularly for detecting and characterizing regolith; but without robust knowledge of dielectric properties, these data cannot be used to their greatest advantage. Here, we present preliminary measurements of complex relative permittivity using the split-cylinder resonator method at 10 GHz. Resonant cavity methods utilize the difference in resonant frequency between an empty cavity and a cavity containing a sample to calculate relative permittivity and loss tangent of the sample, at higher precision than is possible with other methods. We use these split-cylinder measurements of solid samples at a single frequency in conjunction with companion broadband (300 MHz to 14 GHz) measurements of powders. Our goal is to establish a “parameter space” that characterize the effects of various factors such as water content, frequency, and the relative abundances of mineralogical and elemental constituents such as iron and titanium on complex relative permittivity of geological materials that might represent good analogs for the regolith of Bennu, OSIRIS-REx’s target asteroid. Our results will also provide a database for future asteroid exploration with radar.