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It has recently been suggested that clay minerals, which are widespread on the Martian surface, could be the possible source of the basal bright reflections detected by MARSIS at Ultimi Scopuli, instead of briny water. This hypothesis is based on dielectric measurements on a wet Ca‐Montorillonite (STx‐1b) sample conducted at 230 K, which reported permittivity values (apparent permittivity of 39 at 4 MHz) compatible with the median value of 33 retrieved by MARSIS 4 MHz data inversion in the high reflectivity area. These experimental results are, however, incompatible with well‐established dielectric theory and with laboratory measurements on clays, at MARSIS frequency and Martian temperatures, reported in the literature. Here, we replicate the experiment using a setup to precisely control the rate of cooling/warming and the temperature inside and outside the clay sample. We found that the rate of cooling, the position of the temperature sensor and, consequently, the thermal equilibrium between the sample and the sensor play a fundamental role in the reliability of the measurements. Our results indicate that even for a large water content in the clay sample, at 230 K and 4 MHz, the apparent permittivity is only 8.4, dropping to 4.1 at 200 K, ruling out clays as a possible source of the bright reflections detected by MARSIS at the base of the SPLD. Plain Language Summary: The recent discovery of bright basal reflections below the South polar ice cap at Ultimi Scopuli (Mars) by MARSIS has sparked an intense debate on their origin. Because bright radar reflections detected below the ice sheets in Antarctica and Greenland usually indicate the presence of basal water, and based on additional data processing methods, these anomalies were interpreted to be caused by liquid briny water. Recent laboratory measurements questioned this hypothesis and instead suggested that the presence of clay could explain the observed results. According to these measurements, the dielectric properties of wet clay at 230 K (−43°C) mimic the high reflectivity of briny water. Here, we replicate the experiment, making sure to reach thermal equilibrium during each measurement run to guarantee that the temperature is correctly evaluated when the dielectric properties of the sample are measured. This was accomplished using a dedicated setup to precisely control the thermal cycle and to carefully check the internal and external temperatures of the wet clay sample. Our experimental results clearly show that the dielectric properties of clay at 230 K are incompatible with the observed MARSIS anomalies and thus briny water remains the most plausible explanation for the bright basal reflections detected by MARSIS. Key Points: Anomalous bright basal reflections have been detected by MARSIS at Ultimi Scopuli, MarsDielectric measurements of wet clays at low temperature show that they cannot generate strong basal reflectionsReliable measurements of dielectric behavior of planetary analogs require a careful control of the temperature inside the sample [ABSTRACT FROM AUTHOR]

In this contribution, we present a proper extension of the finite-element method based on a variational formulation which is able to take into account the effects of nonconventional materials in the evaluation of the electromagnetic field inside a cavity bounded by both closed and open boundary conditions. As a numerical application, we show how nonconventional materials like, for instance, metamaterials can be used in the design of integrated circuits, in order to reduce the proximity effects among planar transmission lines. Index Terms--Anisotropic media, crosstalk, finite-element method (FEM), microstrip couplers.

Recently, various studies have been carried out in order to address the possible relationships between amplitude attributes of the “first-arrival direct wave” (the so-called “early-time signal,” ETS), propagating at the interface in bistatic ground-penetrating radar (GPR) configurations, and the relevant shallow-soil permittivity parameters (dielectric constant and conductivity). In this frame, ad hoc compared numerical analyses and experimental investigations are extensively developed and discussed here, with the aim of making clearer the distinctive features and the reliability of this technique. The accurate results achieved for the ETS behavior as a function of various GPR system parameters enable us to identify both which are the more revealing signal attributes able to give predictable correlation with the ground permittivity values and the degree of complexity of the functional relationships between ETS amplitude and system parameters. A number of indications and perspectives are, thus, outlined in order to elucidate features, potential and critical aspects of the ETS technique for effective geophysical applications. [ABSTRACT FROM PUBLISHER]

We present the measurements performed with a custom coaxial-cage line designed to determine the complex dielectric permittivity of large samples, made of granular and/or liquid materials. The open structure of the cage facilitates the filling of the line, and allows the uniform compactness of the granular materials having large grain size. The electromagnetic parameters of the samples are retrieved using the line scattering coefficients (S-parameters), measured with a vector network analyzer in the frequency range 1 MHz to 3 GHz. The measurements are carried out on water, ethanol, and glass beads using the Boughriet method, which, for non magnetic materials, optimizes the Nicolson–Ross–Weir algorithm. The results confirm that such a device accurately estimates the material complex permittivity in a wide frequency band. However, at very low frequencies and at frequencies multiple of the line half-wavelength resonances, the accuracy significantly reduces. In particular, the accuracy gets worse for materials with high permittivity and low losses. Nevertheless, for natural geo-materials, usually characterized by appreciable losses, the coaxial-cage line can effectively be used to accurately estimate the material electromagnetic properties in a wide frequency band. [ABSTRACT FROM PUBLISHER]

Geophysical techniques can be effectively applied to produce an image of buried targets in a host medium, through the detection of the 'boundaries' between materials having different values of a specific physical property. Over the last 30 years these methods have been increasingly used to detect the presence of archaeological ruins in the subsurface, thus reducing extensive, destructive, time consuming and expensive excavations. Recently, ground penetrating radar (GPR) has become the most important physical technique in archaeological investigations (allowing for the detection of archaeological targets with both very high vertical and horizontal resolution) and has been successfully applied also to diagnostic purposes in historical buildings and monuments. In this article an overview of the use of radio waves in archaeology is presented, first introducing the main physical concepts of GPR, then presenting some examples of its application to detect ancient buried structures, showing the potential and the limits of such a method. [ABSTRACT FROM AUTHOR]

Two anhydrobiotic strains of the cyanobacterium Chroococcidiopsis, namely CCMEE 029 and CCMEE 171, isolated from the Negev Desert in Israel and from the Dry Valleys in Antarctica, were exposed to salty-ice simulations. The aim of the experiment was to investigate the cyanobacterial capability to survive under sub-freezing temperatures in samples simulating the environment of icy worlds. The two strains were mixed with liquid solutions having sub-eutectic concentration of Na2SO4, MgSO4 and NaCl, then frozen down to different final temperatures (258 K, 233 K and 203 K) in various experimental runs. Both strains survived the exposure to 258 K in NaCl solution, probably as they migrated in the liquid veins between ice grain boundaries. However, they also survived at 258 K in Na2SO4 and MgSO4-salty-ice samples—that is, a temperature well below the eutectic temperature of the solutions, where liquid veins should not exist anymore. Moreover, both strains survived the exposure at 233 K in each salty-ice sample, with CCMEE 171 showing an enhanced survivability, whereas there were no survivors at 203 K. The survival limit at low temperature was further extended when both strains were exposed to 193 K as air-dried cells. The results suggest that vitrification might be a strategy for microbial life forms to survive in potentially habitable icy moons, for example in Europa's icy crust. By entering a dried, frozen state, they could be transported from niches, which became non-habitable to new habitable ones, and possibly return to metabolic activity. [ABSTRACT FROM AUTHOR]

Liquid water was present on the surface of Mars in the distant past; part of that water is now in the ground in the form of permafrost and heat from the molten interior of the planet could cause it to melt at depth. MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) has surveyed the Martian subsurface for more than fifteen years in search for evidence of such water buried at depth. Radar detection of liquid water can be stated as an inverse electromagnetic scattering problem, starting from the echo intensity collected by the antenna. In principle, the electromagnetic problem can be modelled as a normal plane wave that propagates through a three-layered medium made of air, ice and basal material, with the final goal of determining the dielectric permittivity of the basal material. In practice, however, two fundamental aspects make the inversion procedure of this apparent simple model rather challenging: (i) the impossibility to use the absolute value of the echo intensity in the inversion procedure; (ii) the impossibility to use a deterministic approach to retrieve the basal permittivity. In this paper, these issues are faced by assuming a priori information on the ice electromagnetic properties and adopting an inversion probabilistic approach. All the aspects that can affect the estimation of the basal permittivity below the Martian South polar cap are discussed and how detection of the presence of basal liquid water was done is described. [ABSTRACT FROM AUTHOR]

• Bright basal reflections have been detected by MARSIS at Ultimi Scopuli, Mars. • High permittivity contrast between the ice and the basal material is required. • Wet sediments or ponded water have been suggested as the cause of such reflections. • Hydrous minerals and salts are considered as possible alternative to basal water. • Only brines can generate such high dielectric contrast at low basal temperature. Anomalously bright basal reflections detected by MARSIS at Ultimi Scopuli have been interpreted to indicate the presence of water-saturated materials or ponded liquid water at the base of the South Polar Layered Deposits (SPLD). Because conventional models assume basal temperatures (≤200 K) much lower than the melting point of water, this interpretation has been questioned and other explanations for the source of the bright basal reflections have been proposed, involving clay, hydrated salts, and saline ices. Combining previous published data, simulations, and new laboratory measurements, we demonstrate that the dielectric properties of these materials do not generate strong basal reflections at MARSIS frequencies and Martian temperatures. Plausible candidates remain perchlorates and chlorides brines that exhibit a strong dielectric response at much lower temperatures than other materials. This explanation might require that metastability could be maintained for a long period of time on a geological scale. [ABSTRACT FROM AUTHOR]