Martian Regolith Simulant Research Articles

Development of an Electrostatic Precipitator to Remove Martian Atmospheric Dust From ISRU Gas Intakes During Planetary Exploration Missions

Manned exploration missions to Mars will need dependable in situ resource utilization (ISRU) for oxygen production. The Martian atmosphere is composed of 95.3% CO2, other gases, and 0.13% O2 at ~ 9 mbar (1% of the Earth's pressure). However, it also contains 2-10- μm dust uploaded by dust devils and high winds. Oxygen extraction requires removal of the dust with little pressure drop (Δp). An electrostatic precipitator (ESP) has lower Δp than a filter, but the low pressure causes an electrical breakdown at electric fields ( ~ 1 kV/cm) ~ 30× lower than on Earth, making implementation challenging. Molecular mean free paths (λ = 4 μm) and ion mobility values (b = 0.008 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V·s) are ~ 100× larger than at Earth's pressure (λ = 44 nm) and (b = 8.4 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> ). The large λ lowers Stokes drag, particularly for smaller particles. Pauthenier field charging dominates for particles with and diffusion charging for d<;2 μm. The low E proportionally decreases both Pauthenier particle charging and the F = qE collection force. This greatly reduces the particle migration velocities (w), e.g., for d = 10 μm, w = 0.01 m/s compared with 0.4 m/s on Earth. However, for small particles (d = 1 μm), this is compensated by diffusion charging and reduced drag ( w = 0.04 m/s on Mars, 0.05 m/s on Earth). The Martian atmosphere was simulated with 95% CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /5% humid air at 9 mbar. Paschen curves were measured, and I- V curves ( I ~ 5 - 300 μA for V ~ 1.3 - 2.3 kV) were obtained for 5-10-cm-diameter wire/rod-cylinder ESPs. Only positive polarity yielded stable uniform corona. Charging of 0.5-1.3-cm-diameter spheres agreed with the Pauthenier theory. A Martian dust simulant collection efficiency test is in progress.

Design and implementation of a particle image velocimetry method for analysis of running gear–soil interaction

Experimental analysis of running gear–soil interaction traditionally focuses on the measurement of forces and torques developed by the running gear. This type of measurement provides useful information about running gear performance but it does not allow for explicit investigation of soil failure behavior. This paper describes a methodology based on particle image velocimetry for analyzing soil motion from a sequence of images. A procedure for systematically identifying experimental and processing settings is presented. Soil motion is analyzed for a rigid wheel traveling on a Mars regolith simulant while operating against a glass wall, thereby imposing plain strain boundary conditions. An off-the-shelf high speed camera is used to collect images of the soil flow. Experimental results show that it is possible to accurately compute soil deformation characteristics without the need of markers. Measured soil velocity fields are used to calculate strain fields.

Developing a Lightweight Martian Soil Simulant for a High-Sinkage Mobility Test

AbstractThe geotechnical properties of Martian soils are critical parameters in predicting and simulating soil behavior with regard to vehicle performance on Mars. In preparation for manned or robotic missions to Mars, surface vehicles must be tested on terrains that represent the mechanical characteristics of the Martian ground. This paper presents the development of a lightweight simulant and its preparation method to emulate the mechanical properties of Martian soil for high sinkage mobility tests. A geotechnical testing program was developed to measure specific gravity, particle size distribution, bulk density, compression indices and shear strength. The simulant can achieve the typical Martian regolith density range, which is approximately 38% of that on earth. This is of particular importance because strength parameters of granular materials, which characterize the plastic behavior of soil samples in sinkage tests, are controlled by the effective confining pressure, which itself is induced by gravity.

Neurotoxic Potential of Lunar and Martian Dust: Influence on Em, Proton Gradient, Active Transport, and Binding of Glutamate in Rat Brain Nerve Terminals

The harmful effects of lunar dust (LD) on directly exposed tissues are documented in the literature, whereas researchers are only recently beginning to consider its effects on indirectly exposed tissues. During inhalation, nano-/microsized particles are efficiently deposited in nasal, tracheobronchial, and alveolar regions and transported to the central nervous system. The neurotoxic potential of LD and martian dust (MD) has not yet been assessed. Glutamate is the main excitatory neurotransmitter involved in most aspects of normal brain function, whereas disturbances in glutamate homeostasis contribute to the pathogenesis of major neurological disorders. The research was focused on the analysis of the effects of LD/MD simulants (JSC-1a/JSC, derived from volcanic ash) on the key characteristics of glutamatergic neurotransmission. The average size of LD and MD particles (even minor fractions) before and after sonication was determined by dynamic light scattering. With the use of radiolabeled l-[(14)C]glutamate, it was shown that there is an increase in l-[(14)C]glutamate binding to isolated rat brain nerve terminals (synaptosomes) in low [Na(+)] media and at low temperature in the presence of LD. MD caused significantly lesser changes under the same conditions, whereas nanoparticles of magnetite had no effect at all. Fluorimetric experiments with potential-sensitive dye rhodamine 6G and pH-sensitive dye acridine orange showed that the potential of the plasma membrane of the nerve terminals and acidification of synaptic vesicles were not altered by LD/MD (and nanoparticles of magnetite). Thus, the unique effect of LD to increase glutamate binding to the nerve terminals was shown. This can have deleterious effects on extracellular glutamate homeostasis in the central nervous system and cause alterations in the ambient level of glutamate, which is extremely important for proper synaptic transmission. During a long-term mission, a combination of constant irritation due to dust particles, inflammation, stress, low gravity and microgravity, radiation, UV, and so on may consequently change the effects of the dust and aggravate neurological consequences.

Water retention of selected microorganisms and Martian soil simulants under close to Martian environmental conditions

Based on the latest knowledge about microorganisms resistant towards extreme conditions on Earth and results of new complex models on the development of the Martian atmosphere we quantitatively examined the water-bearing properties of selected extremophiles and simulated Martian regolith components and their interaction with water vapor under close to Martian environmental conditions. Three different species of microorganisms have been chosen and prepared for our study: Deinococcus geothermalis, Leptothrix sp. OT_B_406, and Xanthoria elegans. Further, two mineral mixtures representing the early and the late Martian surface as well as montmorillonite as a single component of phyllosilicatic minerals, typical for the Noachian period on Mars, were selected. The thermal mass loss of the minerals and bacteria-samples was measured by thermoanalysis. The hydration and dehydration properties were determined under close to Martian environmental conditions by sorption isotherm measurements using a McBain-Bakr quartz spring balance. It was possible to determine the total water content of the materials as well as the reversibly bound water fraction as function of the atmospheres humidity by means of these methods. Our results are important for the evaluation of future space mission outcomes including astrobiological aspects and can support the modeling of the atmosphere/surface interaction by showing the influence on the water inventory of the upper most layer of the Martian surface.

Laboratory analogues of Martian electrostatic discharges

Electrical discharges in Martian analogue materials have previously been generated by agitation of the material in a low-pressure carbon dioxide environment. These results have led to the supposition that lightning is likely on Mars, on the basis that the surface material becomes triboelectrically charged, and the charges are then gravitationally separated in dust storms. We have reproduced one of these experiments and find that triboelectric charging of the Martian regolith simulant by the walls of the vessel used can adequately explain all the effects observed. Our results indicate that unless special care is taken to avoid wall effects, the electrostatic properties of a laboratory system cannot be extrapolated to the Martian environment. We also note that charging of the outside of the vessel used can generate transients within the vessel which could be mistaken for electrical discharge signals, unless accompanied by optical emissions.

Extraction of polar and nonpolar biomarkers from the martian soil using aqueous surfactant solutions

The Life Marker Chip is being designed to detect the chemical evidence of life in the martian soil. It will use an aqueous surfactant solution to extract polar and nonpolar biomarkers from the martian soil and to transport them into an antibody-based detector for characterisation. Currently, a solution of 1.5gl−1 polysorbate 80 in 20:80 (vol:vol) methanol:water is being considered and appears to be suitable. Here, we have investigated the ability of a range of other surfactant solutions to extract a suite of eight standards spiked on the surfaces of the martian soil simulant JSC Mars-1 and tested the compatibility of the best two surfactants with a representative antibody assay for the detection of pyrene. The results show that using 20:80 (vol:vol) methanol:water as the solvent leads to increased recoveries of standards than using water alone. The poloxamer surfactants Pluronic® F-68 and Pluronic® F-108 are not effective at extracting the standards from JSC Mars-1 at any of the concentrations tested here. The fluorosurfactant Zonyl® FS-300 is able to extract the standards, but not as efficiently as polysorbate 80 solutions. Most successful of the alternative surfactants was the polysiloxane poly[dimethylsiloxane-co-[3-(2-(2-hydroxyethoxy)ethoxy)propyl]methylsiloxane] (PDMSHEPMS) which is able to extract the standards from JSC Mars-1 with an efficiency approximately equal to that of polysorbate 80 solutions of the same concentration. Enhanced recovery of the standards using polysorbate 80 and PDMSHEPMS solutions can be achieved by increasing the concentration of surfactant, from 1.5gl−1 to 10gl−1, leading to an increase in the recovery of standards of about 50%. Polysorbate 80 at concentrations of 1.5gl−1 and 10gl−1 and Zonyl® FS-300 and PDMSHEPMS (both at a concentration of 10gl−1) are also compatible with the representative pyrene antibody assay.

Characterisation of martian soil simulants for the ExoMars rover testbed

The European Space Agency (ESA) ExoMars mission involves landing a rover on the surface of Mars on an exobiology mission to extend the search for life. The locomotion capabilities of the ExoMars rover will enable it to use its scientific instruments in a wide variety of locations. Before it is sent to Mars, this locomotion system must be tested and its performance limitations understood. To test the locomotion performance of the ExoMars rover, three martian regolith simulants were selected: a fine dust analogue, a fine Aeolian sand analogue, and a coarse sand analogue. To predict the performance of the ExoMars rover locomotion system in these three regolith simulants, it is necessary to measure some fundamental macroscopic properties of the materials: cohesion, friction angle, and various bearing capacity constants. This paper presents the tests conducted to determine these properties. During these tests, emphasis was placed on preparing the regolith simulants at different levels of density in order to evaluate its impact on the value of the parameters in particular. It was shown that compaction can influence the Bekker coefficients of pressure-sinkage. The shear properties are consistent with the critical state model at normal stresses similar to those of the ExoMars rover in all but one of the simulants, which showed behaviour more consistent with transitional soil behaviour. It is necessary to give due consideration to these variations to ensure a robust test regime is developed when testing the tractive ability of the ExoMars mobility system.

Self-propagating high-temperature reactions for the fabrication of Lunar and Martian physical assets

The development of a new process potentially useful for future manned Lunar and/or Martian space missions in the framework of the so-called ISRU (In-Situ Resource Utilization) and ISFR (In-Situ Fabrication and Repair) concepts is described and discussed in this work. This process involves the fabrication of physical assets by self-propagating high temperature synthesis (SHS) for construction applications in Lunar and Martian environments starting from different Lunar or Martian regolith simulants and aluminum, as reducing agent. In addition, although Moon and Mars already contain ilmenite (FeTiO 3) and iron oxides, respectively, the latter ones are also added to the initial mixtures to promote suitable SHS reactions. A complete scheme for the fabrication of physical assets to be used as protection against solar rays, solar wind and meteoroids, where all required stages are indicated, is finally proposed in the framework of a recently filed patent.

New Solvents for Space Missions: Utility for Life Detection Instruments and Notable Terrestrial Applications

Instruments designed to test for signs of life on Mars must have operational simplicity and efficiency. One example is the Life Marker Chip being developed to fly on the forthcoming European Space Agency ExoMars mission. Target organic compounds include both polar and non polar molecules and, prior to our patented discovery, no solvent had been tested which effectively extracted both types of molecule in a fashion which was compatible with antibodybased detectors. We have compared the extraction efficiency of water-based solvents alongside conventional organic solvents to determine their suitability for extracting organic mixtures on space missions. Using a range of hydrocarbon standards and a Mars regolith simulant (JSC Mars-1) we have concluded that a water-methanol mix with 1.5 to 2.5 g/L of polysorbate 80 represents the most suitable solvent with extraction efficiencies that can achieve up to approximately 30% of that using conventional organic solvents (assuming 100% efficiency with 93:7 (vol:vol) dichloromethane:methanol mixtures). The surfactant solution will also provide solutions to terrestrial problems, one of which is explored in the patented work. Keywords: Life detection, organic compounds, extraction, Life Marker Chip, ExoMars, surfactants, Polysorbate, sonication, gas chromatograph, Spin-offs, polyoxyethylene

Analysis of carbonaceous biomarkers with the Mars Organic Analyzer microchip capillary electrophoresis system: Aldehydes and ketones

A microchip CE method is developed for the analysis of two oxidized forms of carbon, aldehydes and ketones, with the Mars Organic Analyzer (MOA). Fluorescent derivitization is achieved in ∼ 15 min by hydrazone formation with Cascade Blue hydrazide in 30 mM borate pH 5-6. The microchip CE separation and analysis method is optimized via separation in 30 mM borate buffer, pH 9.5, at 20°C. A carbonyl standard consisting of ten aldehydes and ketones found in extraterrestrial matter is successfully separated; the resulting LOD depends on the reactivity of the compound and range from 70 pM for formaldehyde to 2 μM for benzophenone. To explore the utility of this method for analyzing complex samples, analyses of several fermented beverages are conducted, identifying ten aldehydes and ketones ranging from 30 nM to 5 mM. A Martian regolith simulant sample, consisting of a basalt matrix spiked with soluble ions and acetone, is designed and analyzed, but acetone is found to have a limited detectable lifetime under simulant Martian conditions. This work establishes the capability of the MOA for studying aldehydes and ketones, a critical class of oxidized organic molecules of interest in planetary and in terrestrial environmental and health studies.

Self-Propagating High-Temperature Synthesis Reactions for ISRU and ISFR Applications

&lt;p&gt;In the framework of ISRU (In-Situ Resource Utilization) and ISFR (In-Situ Fabrication and Repair) applications, a novel recently patented process based on the occurrence of Self-propagating High temperature Synthesis (SHS) reactions potentially exploitable for the in-situ fabrication of construction materials in Lunar and Martian environments is described in this work. Specifically, the SHS process involves thermite reactions type between Lunar or Martian regolith simulants and aluminum as reducing agent. To overcome the fact that the original content of ilmenite (FeTiO&lt;sub&gt;3&lt;/sub&gt;) and ferric oxide (Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;) on Moon and Mars soils, respectively, is not enough to make the SHS process possible, suitable amounts of these species have to be added to the starting mixtures. The dependence of the most important processing parameters, particularly the composition of the starting mixture, evacuation level, and gravity conditions, on SHS process behaviour and product characteristics is specifically examined for the case of Lunar regolith. All the obtained findings allows us to conclude that the optimized results obtained under terrestrial conditions are valid for in-situ applications in Lunar environment. In particular, parabolic flight experiments evidenced that neither SHS process dynamics nor product characteristics are significantly influenced in both Lunar and Martian systems when passing from Earth to low gravity conditions. Finally, the complete scheme involving all stages required for the fabrication of physical assets to be used as protection against solar rays, solar wind and meteoroids, etc., is reported.&lt;/p&gt;

Methane adsorption on a martian soil analog: An abiogenic explanation for methane variability in the martian atmosphere

Recent observations suggest methane in the martian atmosphere is variable on short spatial and temporal scales. However, to explain the variability by loss reactions requires production rates much larger than expected. Here, we report results of laboratory studies of methane adsorption onto JSC-Mars-1, a martian soil simulant, and suggest that this process could explain the observations. Uptake coefficient ( γ) values were measured as a function of temperature using a high-vacuum Knudsen cell able to simulate martian temperature and pressure conditions. Values of γ were measured from 115 to 135 K, and the data were extrapolated to higher temperatures with more relevance to Mars. Adsorptive uptake was found to increase at lower temperatures and larger methane partial pressures. Although only sub-monolayer methane surface coverage is likely to exist under martian conditions, a very large mineral surface area is available for adsorption as atmospheric methane can diffuse meters into the regolith. As a result, significant methane may be temporarily lost to the regolith on a seasonal time scale. As this weak adsorption is fully reversible, methane will be re-released into the atmosphere when surface and subsurface temperatures rise and so no net loss of methane occurs. Heterogeneous interaction of methane with martian soil grains is the only process proposed thus far which contains both rapid methane loss and rapid methane production mechanisms and is thus fully consistent with the reported variability of methane on Mars.

Particle transport and distribution on the Mars Science Laboratory mission: Effects of triboelectric charging

We report on the nature of fine particle (<150 μm) transport under simulated martian conditions, in order to better understand the Mars Science Laboratory’s (MSL) sample acquisition, processing and handling subsystem (SA/SPaH). We find that triboelectric charging due to particle movement may have to be controlled in order for successful transport of fines that are created within the drill, processed through the Collection and Handling for In situ Martian Rock Analysis (CHIMRA) sample handing system, and delivered to the Sample Analysis at Mars (SAM) and Chemistry and Mineralogy (CheMin) instruments. These fines will be transferred from the surface material to the portioner, a 3 mm diameter, 8 mm deep distribution center where they will drop ∼2 cm to the instrument inlet funnels. In our experiments, movement of different material including terrestrial analogs and martian soil simulants (Mars Mojave Simulant – MMS) resulted in 1–7 nanocoulombs of charge to build up for several different experimental configurations. When this charging phenomenon occurs, several different results are observed including particle clumping, adherence of material on conductive surfaces, or electrostatic repulsion, which causes like-charged particles to move away from each other. This electrostatic repulsion can sort samples based upon differing size fractions, while adhesion causes particles of different sizes to bind into clods. Identifying these electrostatic effects can help us understand potential bias in the analytical instruments and to define the best operational protocols to collect samples on the surface of Mars.

Particle‐size dependent bipolar charging of Martian regolith simulant

The intense dust devils and dust storms on Mars are believed to generate large electrostatic fields that significantly alter geophysical and geochemical processes on the planet. The existence of such fields must be related to a mechanism by which charged dust separates by polarity; it has been widely hypothesized that this separation originates from a particle‐size dependence of the charge polarity, but this effect has never been demonstrated. To address this issue, we carry out experiments on the triboelectric charging of Martian regolith simulant (JSC‐1 Mars), using a fluid flow apparatus wherein only particle‐particle interactions occur, as is the case in Martian dust events. Our experiments show direct evidence that smaller particles tend to charge negatively and larger particles tend to charge positively, which provides a mechanism for the charge separation that creates electric fields in Martian dust events.

Cyanobacteria for Space Agriculture on Mars

The growth of terrestrial cyanobacterium, Nostoc sp., on the Martian Regolith Simulant (MRS) and its vacuum tolerance were examined in relevance of our challenges to inhabit Mars. The viability of the cyanobacteria was evaluated by microscopic observation after staining by fluorescein diacetate (FDA). The general terrestrial cyanobacterial lump collected from the ground showed a significantly high tolerance against exposure to high vacuum environment for more than one year. To elucidate its high tolerance function scientifically, Nostoc sp. HK-01 was used as another material for this study. After two weeks exposure to high vacuum environment (10-5 Pa), Nostoc sp. HK-01 start to grow again in a liquid culture medium. The A'MED (Arai's Mars Ecosystem Dome) is designed to be installed on Mars for agricultural production. A'MED was found useful to conduct our study. Nostoc sp. HK-01 grew for over 140 days, and chlorophyll synthesis was normal on the MRS. These results verify the possible adaptation of cyanobacteria, and growth under the low atmospheric pressure environment on Mars.

Ejecta from impacts at 0.2–2.3 m/s in low gravity

Collisions between planetary ring particles and in some protoplanetary disk environments occur at speeds below 10 m/s. The particles involved in these low-velocity collisions have negligible gravity and may be made of or coated with smaller dust grains and aggregates. We undertook microgravity impact experiments to better understand the dissipation of energy and production of ejecta in these collisions. Here we report the results of impact experiments of solid projectiles into beds of granular material at impact velocities from 0.2 to 2.3 m/s performed under near-weightless conditions on the NASA KC-135 Weightless Wonder V. Impactors of various densities and radii of 1 and 2 cm were launched into targets of quartz sand, JSC-1 lunar regolith simulant, and JSC-Mars-1 martian regolith simulant. Most impacts were at normal or near-normal incidence angles, though some impacts were at oblique angles. Oblique impacts led to much higher ejection velocities and ejecta masses than normal impacts. For normal incidence impacts, characteristic ejecta velocities increase with impactor kinetic energy, KE, as approximately KE 0.5. Ejecta masses could not be measured accurately due to the nature of the experiment, but qualitatively also increased with impactor kinetic energy. Some experiments were near the threshold velocity of 0.2 m/s identified in previous microgravity impact experiments as the minimum velocity needed to produce ejecta [Colwell, J.E., 2003. Icarus 164, 188–196], and the experimental scatter is large at these low speeds in the airplane experiment. A more precise exploration of the transition from low-ejecta-mass impacts to high-ejecta-mass impacts requires a longer and smoother period of reduced gravity. Coefficient of restitution measurements are not possible due to the varying acceleration of the airplane throughout the experiment.

Growth of terrestrial cyanobacterium, Nostoc sp., on Martian Regolith Simulant and its vacuum tolerance

The growth of terrestrial cyanobacterium, Nostoc sp., on the Martian Regolith Simulant (MRS) and its vacuum tolerance were studied as one of our challenges in this century to inhabit Mars. The viability of the tested cyanobacteria was evaluated by microscopic observation after staining by fluorescein diacetate (FDA). The general terrestrial cyanobacterial lump collected from the ground showed a significantly high tolerance to a high vacuum environment (10-5 Pa) for over one year. To scientifically elucidate its high tolerance function, Nostoc sp. HK-01 was used as another suitable scientific material for this study. After exposure to the high vacuum environment (10-5 Pa) for two weeks, Nostoc sp. HK-01 began to grow again. Some of it was also re-incubated again with a liquid culture medium. The A'MED (Arai's Mars Ecosystem Dome) is designed to be installed on Mars for agricultural production. A'MED was useful to conduct our study. We performed the fundamental experiment using the MRS. Nostoc sp. HK-01 was found to grow for over 140 days along with having the normal function of chlorophyll synthesis on the MRS. These results show the possibility that cyanobacteria could adapt to the MRS, and grow under the low pressure environment expected on Mars.

Toxicity of Lunar and Martian Dust Simulants to Alveolar Macrophages Isolated from Human Volunteers

NASA is planning to build a habitat on the Moon and use the Moon as a stepping stone to Mars. JSC-1, an Arizona volcanic ash that has mineral properties similar to those of lunar soil, is used to produce lunar environments for instrument and equipment testing. NASA is concerned about potential health risks to workers exposed to these fine dusts in test facilities. The potential toxicity of JSC-1 lunar soil simulant and a Martian soil simulant (JSC-Mars-1, a Hawaiian volcanic ash) was evaluated using human alveolar macrophages (HAM) isolated from volunteers; titanium dioxide and quartz were used as reference dusts. This investigation is a prerequisite to studies of actual lunar dust. HAM were treated in vitro with these test dusts for 24 h; assays of cell viability and apoptosis showed that JSC-1 and TiO2 were comparable, and more toxic than saline control but less toxic than quartz. HAM treated with JSC-1 or JSC-Mars 1 showed a dose-dependent increase in cytotoxicity. To elucidate the mechanism by which these dusts induce apoptosis, we investigated the involvement of scavenger receptors (SR). Pretreatment of cells with polyinosinic acid, an SR blocker, significantly inhibited both apoptosis and necrosis. These results suggest HAM cytotoxicity may be initiated by interaction of the dust particles with SR. Besides being cytotoxic, silica is known to induce shifting of HAM phenotypes to an immune active status. The immunomodulatory effect of the dust simulants was investigated. Treatment of HAM with either simulant caused preferential damage to the suppressor macrophage subpopulation, leading to a net increase in the ratio of activator (RFD1+) to suppressor (RFD1+7+) macrophages, an effect similar to that of treatment with silica. It is recommended that appropriate precautions be used to minimize exposure to these fine dusts in large-scale engineering applications.

AFM investigation of Martian soil simulants on micromachined Si substrates

The micro and nanostructures of Martian soil simulants with particles in the micrometre-size range have been studied using a combination of optical and atomic force microscopy (AFM) in preparation for the 2007 NASA Phoenix Mars Lander mission. The operation of an atomic force microscope on samples of micrometre-sized soil particles is a poorly investigated area where the unwanted interaction between the scanning tip and loose particles results in poor image quality and tip contamination by the sample. In order to mitigate these effects, etched silicon substrates with a variety of features have been used to facilitate the sorting and gripping of particles. From these experiments, a number of patterns were identified that were particularly good at isolating and immobilizing particles for AFM imaging. This data was used to guide the design of micromachined substrates for the Phoenix AFM. Both individual particles as well as aggregates were successfully imaged, and information on sizes, shapes and surface morphologies were obtained. This study highlights both the strengths and weaknesses of AFM for the potential in situ investigation of Martian soil and dust. Also presented are more general findings of the limiting operational constraints that exist when attempting the AFM of high aspect ratio particles with current technology. The performance of the final designs of the substrates incorporated on Phoenix will be described in a later paper.