Regolith Analogues Research Articles

The effectiveness of microwave heating as an ISRU extraction technique on different arrangements of icy lunar regolith.

The lunar poles potentially contain vast quantities of water ice. The water ice is of interest due to its capability to answer scientific questions regarding the Solar System’s water reservoir and its potential as a usable space resource for the creation of a sustainable cislunar economy. The lunar polar water ice exists in extremely harsh conditions under vacuum at temperatures as low as 40 K. Therefore, finding the most effective technique for extracting this water ice is an important aspect of ascertaining the suitability of lunar water as an economically viable space resource. Based on previous work, this study investigates the impact of the different possible arrangements of icy regolith in the lunar polar environment on the suitability of microwave heating as a water extraction technique. Three arrangements of icy regolith analogues were created: permafrost, fine granular, and coarse granular. The samples were created to a mass of 40 g, using the lunar highlands simulant LHS-1, and a target water content of 5 wt. %. The samples were processed in a microwave heating unit using 250 W, 2.45 GHz microwave energy for 60 min. The quantity of water extracted was determined by measuring the sample mass change in real-time during microwave heating and the sample mass before and after heating. The permafrost, fine granular, and coarse granular samples had extraction ratios of 92 %, 83 %, and 97 %, respectively. Possible explanations for the observed variations seen in the mass loss profiles of the respective samples are provided, including explanations for the differences between samples of varying ice morphology (permafrost and granular) and the differences between samples with varying ice surface areas (fine and coarse granular). While differences were observed, microwave heating effectively extracted water in all the samples and remains an effective ISRU technique for extracting water from icy lunar regolith. Differences in the water extraction of different icy regolith could be useful in determining the arrangement of ice in buried samples.

Selective laser melting of partially amorphous regolith analog for ISRU lunar applications

As the idea of crewed outposts on the Moon gains momentum, In-Situ Resource Utilization (ISRU) technologies tend to become imperative to fulfill astronauts' needs. This article explores a way to use the lunar regolith as a source material for the additive manufacturing of complex objects, based on the selective laser melting (SLM) technique. A lunar regolith analog, Basalt of Pic d’Ysson (BPY), is used as a starting point for this study, to investigate the now demonstrated impact of amorphous analog content in the powder bed, substrate type, and post-SLM annealing treatments on the mechanical properties of 3D-printed objects. Improvements to the manufacturing and sample extraction stages are proposed to systematically reproduce the high compressive strength values obtained, thus contributing to the robustness and reliability of the process.

Laboratory VIS–NIR reflectance measurements of heated Vesta regolith analogs: Unraveling the spectral properties of the pitted impact deposits on Vesta

AbstractPitted impact deposits on Vesta show higher reflectance and pyroxene absorption band strengths compared to their immediate surroundings and other typical Vestan materials. We investigated whether heating to different temperatures for different durations of Vestan regolith analog materials can reproduce these spectral characteristics using mixtures of HEDs, the carbonaceous chondrite Murchison, and terrestrial analogs. We find no consistent spectral trend due merely to temperature increases, but observed that the interiors of many heated samples show both higher reflectance and pyroxene band I strength than their heated surfaces. With electron probe microanalysis, we additionally observe the formation of hematite, which could account for the higher reflectance. The presence of hematite indicates oxidation occurring in the sample interiors. In combination with heat, this might cause the increase of pyroxene band strengths through migration of iron cations. The effect grows larger with increasing temperature and duration, although temperature appears to play the more dominant role. A higher proportion of Murchison or the terrestrial carbonaceous chondrite analog within our mixtures also appears to facilitate the onset of oxidation. Our observations suggest that both the introduction of exogenic material on Vesta as well as the heating from impacts were necessary to enable the process (possibly oxidation) causing the observed spectral changes.

Optical polarization studies of latex beads in aqueous solution: An analog for radar scattering in icy regolith

This study presents low phase angle 0°–5° measurements of polarimetric properties of icy planetary regolith analog materials acquired using the custom-built Multi-Axis- Goniometer-Instrument (MAGI). We present same sense (SC), and opposite sense (OC) backscatter circular polarization coefficients, circular polarization ratio (CPR), and degree linear polarization (DLP) of spherical latex (non-dye) beads of varying sizes and volume concentrations (v/v) in aqueous solutions (λ=0.8μm) in water. We also present measurements of alumina powder in air at λ=1.064μm. Measurements showed that at a low incidence angle (i=0°), backscatter is dominated by surface specular single-bounce scattering, that hides other scattering processes. At high (i=15°) incidence angle, surface single-bounce surface scattering becomes negligible, allowing for the detection of diffuse, dihedral (multiple bounces) scattering. We find that classical Mie alumina particles (2.1μm,4.0μm) enhance subsurface scattering due to a larger void space relative to larger Mie particles (30μm), that cause the radar signal to scatter forward off small imperfections, maintaining the polarization properties of the signal and generating high >1CPR. Latex beads, representing impurities, demonstrate the impact of isotropic and anisotropic scattering on radar signatures. This study also found that the scattering medium’s anisotropy correlates to the size of the beads, while the void space of the medium inversely correlates with the bead size and the volume concentration (v/v) of the beads. Rayleigh beads, due to isotropic scattering from the reduced scattering cross-section and higher transparency relative to larger impurities, generate subsurface single bounce scattering from the sample platform, producing OC≫SC and a low (<0.5)CPR across all v/v. Rayleigh impurities in transparent water-ice simulate single bounce scattering from underlying layers. Conversely, classical and large Mie beads generate anisotropic scattering that intensifies scattering in the forward direction with high CPR, inversely proportional to the volume concentration. This study aids in interpreting radar observations of icy bodies in the solar system, providing insights into the interplay between radar waves and icy regolith compositions.

Synchrotron x‐ray diffraction for sealed Mars Sample Return sample tubes

AbstractThe joint NASA‐ESA Mars sample return campaign aims to return up to 31 sample tubes containing drilled sedimentary and igneous cores and regolith. The titanium alloy tubes will initially still be sealed when they are retrieved. Several types of measurement will be carried out on sealed samples in the pre‐basic characterization phase of scientific investigation. We show that powder x‐ray diffraction (XRD) analysis can be successfully carried out on sealed samples using an x‐ray source at the I12 beamline of Diamond Light Source synchrotron. Our experiment used an analog sample tube and a Martian regolith analog (Icelandic basaltic sand). The titanium walls of the tube analog give strong but few diffraction peaks, making identification of the major constituent mineral phases feasible. A more significant constraint on quantification of mineral phase abundances by this XRD technique is likely to be the grain size of the sample. This technique opens up the possibility of initial mineralogical analysis of samples returned from Jezero crater without opening the sample tubes and the potential changes to the sample that entails.

Sensitivity Analysis of the DEM Model Numerical Parameters on the Value of the Angle of Repose of Lunar Regolith Analogs

Abstract The discrete element method (DEM) is a numerical technique used in many areas of modern science to describe the behavior of bulk materials. Terramechanics of planetary soil analogs for in situ resource utilization activities is a research field where the use of DEM appears to be beneficial. Indeed, the close-to-physics modeling approach of DEM allows the researcher to gain much insight into the mechanical behavior of the regolith when it interacts with external devices in conditions that are hard to test experimentally. Nevertheless, DEM models are very difficult to calibrate due to their high complexity. In this paper, we study the influence of fundamental model parameters on specific simulation outcomes. We provide qualitative and quantitative assessments of the influence of DEM model parameters on the simulated repose angle and computational time. These results help to understand the behavior of the numerical model and are useful in the model calibration process.

A review on the preparation techniques and geotechnical behaviour of icy lunar regolith simulants

This review provides an in-depth analysis of the methods used to produce icy regolith simulants with a focus on the Moon. Current knowledge of the form and morphology of ice on the Moon is limited, yet a wide range of studies have used ice and regolith analogues to simulate the icy material in lunar cold traps. The physical properties of ice on the Moon may vary significantly depending on its form as either an amorphous or crystalline solid, as well as its physical texture with lunar regolith. As a result, the choice of a particular preparation technique used to create an icy regolith simulant may directly impact the results of a study. It is found that sample preparation techniques can be broadly classified based on the mechanism of ice formation, proposed as either the freezing of liquid to solid, direct deposition (desublimation) of vapor to solid, or the comminution of large blocks to smaller fragments. Secondary growth structures including re-cementation, vapor re-deposition or ductile deformation of ice can also be achieved by post-processing techniques like thermal or pressure-induced metamorphism of the ice. Differences in the form and morphology of icy regolith is also found to significantly influence geotechnical behaviour to a greater extent than changes in ice content, bulk density or temperature. Specifically, vapor-deposited and amorphous ices which best simulate the formation conditions of ice on the Moon are the weakest, whilst ice-cemented ’mud-pies’ which are commonly produced by gradually freezing simulant mixtures containing liquid water, which is not stable on the Moon, can be orders of magnitude stronger. The limitations of current simulants are highlighted, and several opportunities to combine or improve existing techniques are provided. In conclusion, further study using techniques that involve comminution and deposition of ice in the absence of the liquid phase of water are recommended to better emulate the formation and weathering pathways of icy regolith on the Moon, and ultimately its physical properties.

Dynamic Mechanical Analysis Test for Evaluating Loose Sands on a Wide Strain Range—Application to the InSight Mission on Mars

Abstract The dynamic properties of loose sands under low stresses are an unexplored topic in soil dynamics because these soil conditions are uncommon in most geotechnical structures on Earth. However, low densities and low-stress conditions prevail on other planets, like, for instance, the surface of Mars, for which particular attention is presently given through the InSight NASA mission. This work presents a new procedure for measuring the dynamic properties of loose sand under low stress by using the dynamical mechanical analysis (DMA) tester, a technique commonly used in asphalt engineering but not in geotechnical engineering. Compared to traditional geotechnical methods (resonant column and cyclic triaxial tests), DMA investigates a broader range of strains using a single apparatus. In this work, we assess the dynamical properties of loose fine sand Dr ≈ 0.2, considered a possible Mars regolith analog, by varying the input strain from γ = 10−6 to γ = 10−2 while applying confining pressures from σ3 = 3 kPa to σ3 = 30 kPa. The results validate the proposed procedure, showing an increment of the shear modulus as the confining pressure increases. Furthermore, they highlight DMA’s advantages for studying the dynamic properties of granular soils under low stress and strain.

Spectroscopic investigations of fungal biomarkers after exposure to heavy ion irradiation

The main objective of the ongoing and future space exploration missions is the search for traces of extant or extinct life (biomarkers) on Mars. One of the main limiting factors on the survival of Earth-like life is the presence of harmful space radiation, that could damage or modify also biomolecules, therefore understanding the effects of radiation on terrestrial biomolecules stability and detectability is of utmost importance. Which terrestrial molecules could be preserved in a Martian radiation scenario? Here, we investigated the potential endurance of fungal biomolecules, by exposing de-hydrated colonies of the Antarctic cryptoendolithic black fungus Cryomyces antarcticus mixed with Antarctic sandstone and with two Martian regolith analogues to increasing doses (0, 250 and 1000 Gy) of accelerated ions, namely iron (Fe), argon (Ar) and helium (He) ions. We analyzed the feasibility to detect fungal compounds with Raman and Infrared spectroscopies after exposure to these space-relevant radiations.

Dry-Adhesive Microstructures for Material Handling of Additively Manufactured and Deep-Rolled Metal Surfaces with Reference to Mars.

Once on Mars, maintenance and repair will be crucial for humans as supply chains including Earth and Mars will be very complex. Consequently, the raw material available on Mars must be processed and used. Factors such as the energy available for material production play just as important a role as the quality of the material that can be produced and the quality of its surface. To develop and technically implement a process chain that meets the challenge of producing spare parts from oxygen-reduced Mars regolith, this paper addresses the issue of low-energy handling. Expected statistically distributed high roughnesses of sintered regolith analogs are approximated in this work by parameter variation in the PBF-LB/M process. For low-energy handling, a dry-adhesive microstructure is used. Investigations are carried out to determine the extent to which the rough surface resulting from the manufacturing process can be smoothed by deep-rolling in such a way that the microstructure adheres and enables samples to be transported. For the investigated AlSi10Mg samples (12 mm × 12 mm × 10 mm), the surface roughness varies in a wide range from Sa 7.7 µm to Sa 64 µm after the additive manufacturing process, and pull-off stresses of up to 6.99 N/cm2 could be realized after deep-rolling. This represents an increase in pull-off stresses by a factor of 392.94 compared to the pull-off stresses before deep-rolling, enabling the handling of even larger specimens. It is noteworthy that specimens with roughness values that were previously difficult to handle can be treated post-deep-rolling, indicating a potential influence of additional variables that describe roughness or ripples and are associated with the adhesion effect of the microstructure of the dry adhesive.

Organic detection in the near-infrared spectral Phobos regolith laboratory analogue in preparation for the Martian Moon eXploration mission

Context.The Martian Moon eXploration mission (MMX) of the Japanese space agency (JAXA) is scheduled to take off in September 2024 to explore Phobos and Deimos – the two martian moons – by in situ observations, but also by a sampling and returning regolith samples to Earth. The origins of Phobos and Deimos are still unknown and their understanding is one of the main goals of the MMX mission. In one scenario, Phobos could be a captured asteroid, as the Phobos spectrum is similar to dark D-type asteroids.Aims.For the present work, we considered the hypothesis of Phobos being a captured D-type asteroid, and we investigated the detectability of organics on Phobos using laboratory spectral analogues.Methods.We synthesised a near-infrared spectral analogue of Phobos composed of olivine (77 vol.%, 50–125 µm), hyperfine anthracite (20 vol.%, &lt;1 µm), and organic tholins (3 vol.%, ~400 nm) by measuring the reflectance spectrum from 0.4 to 4.75 µm with the SHADOWS spectrogonio-radiometre developped at IPAG. The best spectral match for a Phobos regolith analogue was chosen based on its reflectance level and spectral slope similarities to Phobos’ observed spectrum. Several samples were then prepared by adding a different volume content of organic matter (Titan tholins). We monitored the 3 µm band attributed toN-Hbands stretching modes absorption due to the amine function in the tholins, so as to assess the detectability of the NH-rich organics on Phobos.Results.We have demonstrated that the organic compounds become detectable for more than 5 vol.% in the mixture. We further studied the observation geometry effects on the absorption band depth and found no significant effect except at large phase angles (&gt;80º). These results will be useful to interpret the data of the MMX Infrared Spectrometer (MIRS) onboard the MMX spacecraft, which will measure the spectral reflectance of Phobos from 0.9 to 3.6 µm.

Determination of Broadband Complex EM Parameters of Powdered Materials: 1. MCMC‐Based Two‐Port Transmission Line Measurements

AbstractWe propose a Bayesian Markov Chain Monte Carlo parameter estimation technique to determine frequency‐dependent complex dielectric permittivity and permeability of powdered planetary regolith analog materials from coaxial transmission line measurements. The technique uses either a flat (non‐dispersive) or a generalized dielectric response model to simultaneously determine the complex permittivity and permeability from measured scattering parameters. By exploring the parameter space, the technique reduces the dependence on good initial model parameters required by typical optimization methods. The technique can be used with either two‐port measurements or shorted measurements, where an additional one‐port shorted sample is measured. We find the technique is able to accurately determine electromagnetic parameters of low‐loss, high dielectric, and magnetic materials. The technique is also robust to half‐wavelength resonances in the sample as well as the presence of higher order modes.

Determination of Broadband Complex EM Parameters of Powdered Materials: 2. Ilmenite‐Bearing Lunar Analogue Materials

AbstractWe present systematic measurements of the frequency‐dependent complex dielectric permittivity of lunar regolith analogue samples with increasing amounts of the mineral ilmenite along with Bayesian model fits using a one‐pole Cole‐Cole model. We use these results to calculate a lower bound for the attenuation of radar signals in dB/m based on ilmenite content. We compare our measurement results with previous efforts to use Earth‐based radar maps to calculate the effect of ilmenite on radar attenuation and find that they are in agreement. We also revisit the ilmenite‐dependent loss tangent relationships of Carrier III et al. (1991) and demonstrate the significant frequency‐dependent effect of ilmenite content on signal attenuation as well as the effect of minor variations in loss tangent for depth‐to‐feature determinations. The results presented here are the first systematic laboratory measurements investigating the effect of ilmenite on radar attenuation and show future promise for the application of dielectric spectroscopy, or the identification of materials based on their electromagnetic properties in the radar and microwave range.

Experimental Research of Veles Planetary Rover Performing Simple Construction Tasks

The paper is concerned with the problem of experimental research of Veles planetary rover performing simple construction tasks. The current state of the art in planetary rovers and their research in construction tasks are discussed. The Veles rover solution designed for construction tasks and experimental testbed are described. The experimental testbed included a test room with Moon regolith analogue. Experimental research concerning rover mobility and manipulation tasks were carried out. Experimental research consisted of various scenarios,, including clearing an area that removes boulders and levelling the soil. The complementary scenario for the area preparation was to exchange the tools of the manipulator. In this case, the gripper and the shovel were used as end-effectors for moving objects, both structured or in the form of regolith. Results of selected experimental research are presented and discussed. Finally, directions of future works of the rover are pointed out.

Biosignature stability in space enables their use for life detection on Mars.

Two rover missions to Mars aim to detect biomolecules as a sign of extinct or extant life with, among other instruments, Raman spectrometers. However, there are many unknowns about the stability of Raman-detectable biomolecules in the martian environment, clouding the interpretation of the results. To quantify Raman-detectable biomolecule stability, we exposed seven biomolecules for 469 days to a simulated martian environment outside the International Space Station. Ultraviolet radiation (UVR) strongly changed the Raman spectra signals, but only minor change was observed when samples were shielded from UVR. These findings provide support for Mars mission operations searching for biosignatures in the subsurface. This experiment demonstrates the detectability of biomolecules by Raman spectroscopy in Mars regolith analogs after space exposure and lays the groundwork for a consolidated space-proven database of spectroscopy biosignatures in targeted environments.

Thermal conductivity of planetary regoliths: The effects of grain-size distribution

The thermal properties of a planet's regolith are of primary importance in solar system exploration. Thermal conductivity and the related parameter thermal inertia are often used to decipher the regolith's structure, grain size, and areal distribution. In this work we utilize a guarded-heat-flow apparatus to measure the thermal conductivity of mono-dispersed and bimodal size populations of regolith analogs (borosilicate-glass beads and terrestrial soils) under a range of interstitial gas pressures from 10−5 to 103 mb, at 20 °C. From these measurements we further develop a physically based analytical model for use as a predictive tool for planetary research.While our results for mono-dispersed grains agree well with previous studies, our findings for bimodal grain-size mixtures do not. Our results demonstrate that the functional dependence of thermal conductivity on interstitial gas pressure closely follows that of the fine-grained component of the mixture, but uniformly offset to higher conductivity values depending only on the volume fraction of the coarse component. The grain size of the coarse fraction plays no role. The reason for the difference with previous studies appears to be related to limitations with the transient-heated-wire method in previous work. Our results suggest that, on Mars, large quantities of coarse grain material, such as sand or cobbles, could be hidden in regional dust deposits. Additionally, variations in the thermal properties of aeolian dune fields may result from differences between age-related dust infiltration and self-cleansing sand migration, rather than any real differences in local grain size. On Earth, at high gas pressures, grain size mixtures result in higher thermal conductivity than any component alone, consistent with field observations.

Metabolomic Profile of the Fungus Cryomyces antarcticus Under Simulated Martian and Space Conditions as Support for Life-Detection Missions on Mars.

The identification of traces of life beyond Earth (e.g., Mars, icy moons) is a challenging task because terrestrial chemical-based molecules may be destroyed by the harsh conditions experienced on extraterrestrial planetary surfaces. For this reason, studying the effects on biomolecules of extremophilic microorganisms through astrobiological ground-based space simulation experiments is significant to support the interpretation of the data that will be gained and collected during the ongoing and future space exploration missions. Here, the stability of the biomolecules of the cryptoendolithic black fungus Cryomyces antarcticus, grown on two Martian regolith analogues and on Antarctic sandstone, were analysed through a metabolomic approach, after its exposure to Science Verification Tests (SVTs) performed in the frame of the European Space Agency (ESA) Biology and Mars Experiment (BIOMEX) project. These tests are building a set of ground-based experiments performed before the space exposure aboard the International Space Station (ISS). The analysis aimed to investigate the effects of different mineral mixtures on fungal colonies and the stability of the biomolecules synthetised by the fungus under simulated Martian and space conditions. The identification of a specific group of molecules showing good stability after the treatments allow the creation of a molecular database that should support the analysis of future data sets that will be collected in the ongoing and next space exploration missions.

Investigation of fungal biomolecules after Low Earth Orbit exposure: a testbed for the next Moon missions.

SummaryThe Moon is characterized by extremely harsh conditions due to ultraviolet irradiation, wide temperature extremes, vacuum resulting from the absence of an atmosphere and high ionizing radiation. Therefore, its surface may provide a unique platform to investigate the effects of such conditions. For lunar exploration with the Lunar Gateway platform, exposure experiments in Low Earth Orbit are useful testbeds to prepare for lunar space experiments and to understand how and if potential biomarkers are influenced by extra‐terrestrial conditions. During the BIOMEX (BIOlogy and Mars EXperiment) project, dried colonies of the fungus Cryomyces antarcticus grown on Lunar Regolith Analogue (LRA) were exposed to space conditions for 16 months aboard the EXPOSE‐R2 payload outside the International Space Station. In this study, we investigated the stability/degradation of fungal biomarkers in LRA after exposure to (i) simulated space and (ii) real space conditions, using Raman spectroscopy, gas chromatography–mass spectrometry and DNA amplification. The results demonstrated that fungal biomarkers were detectable after 16 months of real space exposure. This work will contribute to the interpretation of data from future biological experiments in the Cislunar orbit with the Lunar Gateway platform and/or on the lunar surface, in preparation for the next step of human exploration.

CaSSIS color and multi-angular observations of Martian slope streaks

Slope streaks are albedo features that form frequently on equatorial Martian slopes. Most slope streaks are dark relative to surrounding terrains, a minor fraction is bright, and there are rare transitioning streaks that exhibit a contrast reversal partway downslope. Their formation mechanisms and physical surface properties are not well understood. New observations acquired by the Colour and Stereo Surface Imaging System (CaSSIS) on board ESA's ExoMars Trace Gas Orbiter (TGO) provide insights into slope streaks' surface microstructure, roughness and particle size ranges. Using multiple phase angle observations, we show that dark slope streaks are substantially rougher and possibly more porous than their bright counterparts, which are likely composed of more compact regolith. Color data acquired in the four wavelength bands suggest that dark streaks are spectrally similar to bright streaks but are composed of larger particles. The comparison of our orbital results to the laboratory measurements of Martian regolith analogs indicates that particles within dark slope streaks may be up to a factor of four larger than the granular material of the surrounding terrains. At one study site in Arabia Terra, using complementary imagery from other orbiters, we identify a case where dark slope streaks turned fully bright in a twenty-year period. These and CaSSIS observations suggest that bright slope streaks are old dark slope streaks, likely formed by deposition of dust or decomposition of surface aggregates into smaller particles.

The Detectability Limit of Organic Molecules Within Mars South Polar Laboratory Analogs

AbstractA series of laboratory experiments was carried out in order to generate a diagnostic spectrum for polycyclic aromatic hydrocarbons (PAHs) of astrobiological interest in the context of the Martian South Polar Residual Cap (SPRC), to establish PAH spectral features more easily detectable in CO2 ice (mixed with small amounts of H2O ice) than the previously reported absorption feature at 3.29 µm in order to constrain their detectability limit. There is currently no existing literature on PAH detection within SPRC features, making this work novel and impactful given the recent discovery of a possible subglacial lake beneath the Martian South Pole. Although they have been detected in Martian meteorites, PAHs have not been detected yet on Mars, possibly due to the deleterious effects of ultraviolet radiation on the surface of the planet. SPRC features may provide protection to fragile molecules, and this work seeks to provide laboratory data to improve interpretation of orbital remote sensing spectroscopic imaging data. We also ascertain the effect of CO2 ice sublimation on organic spectra, as well as provide PAH reference spectra in mixtures relevant to Mars. A detectability limit of ∼0.04% has been recorded for observing PAHs in CO2 ice using laboratory instrument parameters emulating those of the Compact Reconnaissance Imaging Spectrometer for Mars, with new spectral slope features revealed between 0.7 and 1.1 µm, and absorption features at 1.14 and most sensitively, at 1.685 µm. Mars regolith analog mixed with a concentration of 1.5% PAHs resulted in no discernible organic spectral features. These detectability limits measured in the laboratory are discussed and extrapolated to the effective conditions on the Mars South Polar Cap in terms of dust and water ice abundance and CO2 ice grain size for both the main perennial cap and the H2O ice‐dust sublimation lag deposit.