Permittivity Measurements for Oxia Planum Reference Samples

The ExoMars 2028 Mission is a rover mission heading for Oxia Planum on Mars. The ground penetrating radar WISDOM (Water Ice Subsurface Deposit On Mars) will probe at least to three meters depth to provide insight into the shallow subsurface and to support finding suitable drill sites. To determine accurately the drill’s target depth, where the chance to find bio-signatures is higher compared to the surface, the knowledge of the permittivity is essential. Furthermore, it helps to determine the stratification and the respective thickness properties of the soil layers over a larger scale, i. e., when radar data is taken over a long travel distance.

To achieve an overview of the expected permittivity value range, several soil samples will be analyzed over the frequency range of WISDOM (0.5 GHz to 3.0 GHz). These samples were taken during former field tests (such as SAFER, ExoFit) as well as artificial Martian soil samples (e. g., JSC-1). Moreover, members of the Rover Science Operation Working Group provided reference samples from earth that serve as a reference for the landing site “Oxia Planum” according to what is known from remote sensing data.

For that analysis, a device employing a coaxial probe is used, which allow the measurement of the soil samples’ permittivity. The challenge for such measurement lie in the preparation of the samples to achieve a smooth contact area that minimizes the occurrences of air gaps. Depending on the samples’ constitution, either a flat, ground bulk material or a fine-grained powder will be used. For the latter, a drying treatment is applied to reduce the water content. Particularly for the samples in powder form, the pressure with which the coaxial probe is applied may have a non-negligible influence on the result.

In this work, we will present the results of the permittivity measurements with a focus on the WISDOM frequency range.