Enabling new exploration opportunities on planetary surfaces: In situ geochemical characterization in soils by dielectric spectroscopy onboard the AXEL rover system. (August 2020)

• Record Type: Journal Article
• Authors: Chin, Keith B.; Anderson, Robert C.; Schoelen, Dane A.; Kerber, Laura A.; McGarey, Patrick; Paton, Michael; Brown, Travis L.; Nesnas, Issa A.
• Is Part Of: Planetary and space science. Volume 187(2020)
• Publication Date: 2020-08
• Subjects: Space sciences -- Periodicals; Atmosphere, Upper -- Periodicals; Sciences spatiales -- Périodiques; Haute atmosphère -- Périodiques; 523
• DOI: 10.1016/j.pss.2020.104948
• Languages: English
• ISSNs: 0032-0633

Abstract

Abstract: In the work, we present dielectric spectroscopy (DS) is an analytical method capable of characterizing and quantifying electrochemically active materials (water/ice, ions, etc.) in planetary regoliths. Detection of these materials occurs when a small amount of energy is applied to an in situ sample, causing perturbation in the form of potential kinetic energy and inducing polarization and/or relaxation processes in materials of interest. The frequency dispersion on the electrical properties of impendences, relative permittivity, and conductivity spectra represents chemical and physical properties in association with inherent material properties. Therefore, measuring these energetic states can provide a unique fingerprint of the materials, depending on the frequencies that are scanned. In the case of water content in soils, the Debye equivalent circuit model can accurately predict its electrical properties and provide excellent quantification of the water content in soils. Use of DS is enabled by miniaturization of the key components and the low power requirements. DS is therefore capable of offering substantial scientific returns as an in situ sampling and non-destructive measurement technique, making it ideally suitable for deployment onboard many smaller space exploratory platforms. This work reports the first deployment use of DS from a field test for geochemical characterization of in situ soils, specifically on the quantification of water onboard the AXEL mobility system in the Mojave Desert. Laboratory testing has confirmed the sensitivity of DS with respect to particle size (fine vs coarse) determination as well as water content (down to 0.01 ​wt%) under a wide range of environmental conditions. Water content associated with bound and bulk water was uniquely identified in the soil mixture. We also describe a field demonstration using DS using two distinct insertion dielectric probes specifically design for sub-surface measurements, verifying their mechanical robustness and chemical stability. The field measurements are in good agreement with laboratory data and effectively quantified water content at about 3.0 ​wt% and 8.0 ​wt% for field test sites #1 and #2, respectively. Highlights: Dielectric spectroscopy has significant implications for scientific characterization geochemical settings based on electrical properties. Our breadboard DS system combining a low power, miniature instrumentation with subsurface probes suitable for in situ water content analysis. Laboratory measurements substantiate water/ice detection in soil analogues and sensitivity of water content <0.01 ​wt%. Field testing onboard the AXEL system validates water content analysis by conductivity and relative permittivity electrical properties.