The Dielectric response of the tropical hawaiian mars soil simulant JSC mars-1
The observation of low dielectric values <2, consistent with the bright areas of the surface of Mars, is completely counter to expectation for soils dominated by mafic minerals, especially Fe minerals and pyroxenes that tend to have dielectric values two to three times higher than quartz, which has a value of 4.7. To this day, this observation has not been explained. The recent success of the Phoenix lander in locating water on Mars, however, is renewing interest in the use of sensors to determine Martian soil properties. We took measurements on the Hawaiian JSC Mars-1 soil simulant, considered to reflect the properties of the soils of the bright regions of Mars. Our objective was to determine if soil structure and dielectric phase configuration could account for low dielectric responses. We discovered that low dielectric values can be reconciled with mafic, Fe-bearing silicate mineralogy due to the presence of a palagonite structure with internal porosity. Furthermore, dielectric response as a function of water content is startlingly lower than standard soil calibration equations from Earth, meaning that the application of these equations may significantly underestimate water content determined from dielectric measurements—not because of 'bound water,' but because of the altered dielectric phase configuration due to the palagonite internal pore structure. The implications of this finding for future planetary missions are that all sensors relying on interpreting soil properties from measurements of bulk soil electrical, thermal, or dielectric properties will be similarly affected in the presence of materials with internal porosity.