Characterization of the permittivity of controlled porous water ice-dust mixtures to support the radar exploration of icy bodies

Abstract

The internal properties of porous and icy bodies in the solar system can be investigated by ground‐penetrating radars (GPRs), like the COmet Nucleus Sounding Experiment by Radiowave Transmission instrument on board the Rosetta spacecraft which has sounded the interior of the nucleus of comet 67P/Churyumov‐Gerasimenko. Accurate constraints on the permittivity of icy media are needed for the interpretation of the data. We report novel permittivity measurements performed on water ice samples and icy mixtures with porosities in the 31–91% range. The measurements have been performed between 50 MHz and 2 GHz with a coaxial cell on a total of 38 samples with a good reproducibility. We used controlled procedures to produce fine‐grained and coarse‐grained ice samples with a mean diameter of 4.5 μm and 67 μm, respectively, and to prepare icy mixtures. The JSC‐1A lunar regolith simulant was used as the dust component in the mixtures. The results are focused on the real‐part ε′ of the permittivity, which constrains the phase velocity of the radio waves in low‐loss media. The values of ε′ show a nondispersive behavior and are within the range of 1.1 to 2.7. They decrease with the increasing porosity Φ according to E(1 − Φ), with E equal to about 3.13 for pure water ice, and in the 3.8–7.5 range for ice‐dust mixtures with a dust‐to‐ice volumetric ratio in the 0.1–2.8 range, respectively. These measurements are also relevant for radiometers operating in the millimeter‐submillimeter domains, as suggested by the nondispersive behavior of the mixtures and of the pure components.

Broadband Measurements of the Complex Permittivity of Carbonaceous Asteroid Regolith Analog Materials

“…The maximum percentage difference for all samples in ′ r and tan are 4.0% and 2.2%, respectively, and the median percentage difference does not go above 0.43% for ′ r and 0.14% for tan . These low maximum and median differences testify to the homogeneity of our samples in the transmission line, and the maximum differences in ′ r are within those obtained by Brouet et al (2016). As an example, Figure 6 shows ′ r and tan from both sets of S-parameters as well as their averages for the 5.0 wt% kerogen sample measured at 25 ∘ C, which has the highest median difference in ′ r of all samples measured (0.43%).…”

“…For example, Brouet et al (2014) made complex relative permittivity measurements of JSC Mars-1 Martian soil simulant and volcanic ash in three frequency bands (50-500 MHz, 2.45-12 GHz, and 190 GHz), and Brouet et al (2015) made broadband ′ r measurements of JSC-1A lunar regolith simulant and volcanic ash from 0.05 to 6 GHz as well as complex relative permittivity measurements at 190 GHz. Brouet et al (2016) made 12 ′ r measurements of porous ice samples and 26 measurements of dust-ice mixtures at a range of porosities where the dust fraction was made up of JSC-1A lunar regolith simulant. Brouet et al (2016) made 12 ′ r measurements of porous ice samples and 26 measurements of dust-ice mixtures at a range of porosities where the dust fraction was made up of JSC-1A lunar regolith simulant.…”

“…Heggy et al (2012) measured the complex permittivity of four powdered meteorites from 5 to 100 MHz: three ordinary chondrites and one mesosiderite. Brouet et al (2016) made 12 ′ r measurements of porous ice samples and 26 measurements of dust-ice mixtures at a range of porosities where the dust fraction was made up of JSC-1A lunar regolith simulant. See also Heggy et al (2001), Herique et al (2002), and references therein.…”

Buried Ice and Sand Caps at the North Pole of Mars: Revealing a Record of Climate Change in the Cavi Unit With SHARAD

“…We then translated the bulk relative permittivity ε ′ cavi to composition assuming a three‐component mixture of basalt ( ε ′ basalt = 8.8; Nunes & Phillips, 2006), gypsum ( ε ′ gypsum = 6.6; derived from Heggy et al, 2001; see supporting information S3), and water ice ( ε ′ ice = 3.1; Brouet et al, 2016; Heggy et al, 2008; Mattei et al, 2014). These correspond to the three major components detected within cavi by previous studies, as discussed above.…”

Islands of ice on Mars and Pluto

“…When a value of ε' is inferred, it is compared to values of ε' of relevant Martian materials. For pure water ice, we assume that the value of ε' is 3.15 (Brouet et al, ; Matsuoka et al, ). The value of ε' for solid basalt is dependent on material properties such as vesicularity, bulk density, and mineralogy (e.g., Campbell & Ulrichs, ; Pettinelli et al, ) but is consistently greater than that of water ice; we assume a nominal value of 7.54 (Rust et al, ).…”