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Article

WNMS: A New Basaltic Simulant of Mars Regolith

by
Abdur Rahim
1,*,
Umair Majeed
2,
Muhammad Irfan Zubair
3 and
Muhammad Shahzad
4
1
Department of Transportation Engineering and Management, University of Engineering & Technology, Lahore 54890, Pakistan
2
Geological Survey of Pakistan, Karachi 75290, Pakistan
3
Geological Survey of Pakistan, Lahore 54782, Pakistan
4
Department of Mining Engineering, University of Engineering & Technology, Lahore 54890, Pakistan
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(18), 13372; https://doi.org/10.3390/su151813372
Submission received: 28 May 2023 / Revised: 30 August 2023 / Accepted: 4 September 2023 / Published: 6 September 2023
Browse Figures
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Abstract

:
The use of planetary regolith can be explored via the utilization of simulants. The existing Martian simulants have differences due to varying source materials and design parameters. Additional simulants are needed because the few available simulants do not replicate the compositional diversity of Martian regolith. This study discusses the development of a low-cost construction simulant of Mars. The area of Winder Nai in Pakistan was selected for field sampling of basalt because of local availability and easy access. The dust was produced from rock samples through mechanical crushing and grinding. The physical properties, composition, mineralogy, and surface morphology were evaluated via geotechnical tests, Energy Dispersive X-ray (EDX) spectroscopy, X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM), respectively. The designed simulant has a well-graded particle size distribution with a particle density and bulk density of 2.58 g/cm3 and 1.16 g/cm3, respectively. The elemental composition of Winder Nai Mars Simulant (WNMS) is within ±5 wt% of the Rocknest and the average Martian regolith composition except for SO3. For SiO2, Al2O3, and Fe2O3, WNMS has a good match with the Martian regolith. The content of CaO and TiO2 in WNMS is higher than, and content of MgO is lower than, the average Martian values. The rock can be classified as basalt based on the Total Alkali Silica (TAS) diagram. XRD spectrum indicates the occurrence of plagioclase and pyroxene as the main signature minerals of basalt. The particle morphology of WNMS is angular to subangular, and the simulant indicates the presence of 3.8 wt% highly paramagnetic particles. The volatile loss is 0.25 wt% at 100 °C, 1.73 wt% at 500 °C, and 3.05 wt% at 950 °C. The composition of WNMS, basaltic mineralogy, morphology, magnetic properties, and volatile content are comparable with MMS-2 and a few other simulants.

1. Introduction

The regolith of Mars is being widely studied not only for landing and rover operations, but also for habitation purposes. It can directly be used as a construction material in its compacted form and in various types of concretes [1]. It provides an excellent shield against harmful cosmic rays [2]. The properties of regolith are imitated using laboratory-developed simulants. These simulants are specifically designed to match specific properties of a range of planetary bodies [3]. The properties include magnetic, optic, and geotechnical properties (such as density and particle size distribution), etc.
The observations from telescopes, orbiters, landers, rovers, and meteorites have helped us to understand the composition, conditions, and properties of the regolith [4]. Extensive data are available from different Mars missions, including the Viking 1, Viking 2, Pathfinder, Sojourner, Spirit, Opportunity, Phoenix, Curiosity, InSight, and Mars 2020 (Perseverance, Ingenuity) missions. The devices of these missions, such as the Mars Hand Lens Imager (MAHLI) of the Curiosity rover and the Wide Angle Topographic Sensor for Operations and eNgineering (WATSON) imager of the Perseverance rover, can image the regolith to micron scale.
The data are available for several locations, including Vastitas Borealis, Meridiani Planum, Chryse Planitia, Utopia Planitia, Ares Vallis, Elysium Planitia, Gusev crater, Gale crater, Jezero crater, etc. [5]. The Martian regolith properties at different locations are used to select the terrestrial rock and volcanic ash composition to closely match the desired properties [6].
Basalt is an igneous rock that is abundantly available on the surface crust of the Earth’s Moon, Mars, and Venus [7]. It is an extrusive volcanic rock, and its color varies from dark grey to black. It contains minerals such as feldspar, pyroxene, olivine, etc. The evidence for the abundant presence of basalt on planetary bodies is supported by studies on Mars meteorites, in situ experiments, and lunar mares (dark regions) basalt samples collected from Apollo missions [4,8,9,10].
Vaughan et al. [11] reported that the regolith at the Octavia E. Butler landing site indicates the presence of pyroxene and ferric oxide bearing phase in fine grains and olivine in the coarser grains. Cardarelli et al. [12] classified the regolith at the Jezero crater floor into three classes: (a) coarse, dark sand grains, (b) fine, redder grains, and (c) pebble-to-cobble rock fragments. These classes are defined by their size, shape, and color. Cousin et al. [13] compared the regolith at the Jezero and Gale craters. For Jezero, they observed the difference between the composition of fine/medium-size fractions (more enriched in Al2O3, CaO, and alkali) and coarse-grained fractions (more enriched in FeO and MgO with low SiO2). The coarse fraction is more enriched in olivine and pyroxene. Jezero has lower levels of S and higher levels of MgO compared to Gale. Moreover, it has more coarse grains compared to Gale, and there is a compositional similarity between the fine-grained fractions of both craters.
Currently, several simulants exist for lunar and Mars exploration. The Martian simulants include JSC Mars-1 [14], MMS-1, 2, Salten Skov I [15], ES-1, 2, 3, CWRU1 [16], JMSS-1 [17], UC Mars simulant [18], Y-Mars [19], MGS-1 [6] (Cannon et al., 2019), OUCM/EB/HR/SR-1/2 [20], JSC-RN [21], NEU Mars-1 [22], HIT-M-1 [23], JEZ-1 [24], and JMDS-1 [25]. A comparison of some of the simulants is given by Karl et al. [26].
There are compositional and mineralogical differences in simulants due to the absence of return samples, differences in the source material, and a change in design philosophy to develop these simulants. For example, JSC Mars-1 is made from altered volcanic ash from a Hawaiian cinder cone to match the reflectance spectra of the brighter region of Mars. Furthermore, it is a clay-like coarser hygroscopic simulant exhibiting weight loss on drying [27]. Another widely used simulant, MMS, is derived from Saddleback Mountain in the Mojave Desert (California, US); although it is hygroscopically inert, it is devoid of perchlorate. MGS-1 was developed through the mixing of pure minerals. This simulant also does not include perchlorate. However, the design philosophy allows addition for it. MGS-1 is claimed to be the highest-fidelity Mars simulant [6,28]. There are also commercial simulants such as MMS-2 (of Martian Garden). This has been criticized for its source and highly processed nature.
Nørnberg et al. [15] developed a magnetic dust analog named ‘Salten Skov I’ using fine-grained magnetic iron oxide from Denmark. According to the authors, it is a good analog due to its grain size, magnetic properties, optical reflectance, etc. ES-X was developed by the European Space Agency (ESA) to test the locomotion performance of the ExoMars rover [29]. Zeng et al. [17] developed a simulant called the Jining Martian Soil Simulant (JMSS-1), while also adding magnetite and hematite during the mechanical crushing of basalt. The addition of magnetite and hematite increased the iron oxide (Fe2O3) content from 11 wt% (percent by weight) to 16 wt%. However, according to the research, the addition of iron oxides to basalt has possibly contributed to the higher bulk density of JMSS-1.
There are two approaches for developing a simulant: firstly, building the simulant from individual minerals, and secondly, selecting rock, rock dust, or volcanic ash [6,17]. In the first approach, relatively pure mineral chemistries can be added to produce the simulant. However, this approach is expensive and requires more control for production. The second approach is simple, easy, and produces an inexpensive simulant. Its design philosophy can be summarized as follows: identifying the target properties, selecting the appropriate basalt source, acquiring the rock dust, or crushing the rock, evaluation of physical, chemical, and mineralogical properties, and determination of particle size and morphology. These properties are matched with regolith, and additional minerals or compounds can be added to the simulant.
Scott et al. [18] highlighted the need to develop a variety of simulants because a single simulant cannot replicate the entire Martian surface. This is due to the considerable difference in composition and mineralogy of the regolith of Mars. Furthermore, most simulants are either unavailable, expensive, and difficult to procure, or address specific needs of research projects.
The focus of this study is the development of a low-cost and locally available Mars regolith simulant. The objectives of this research are to identify available basalt sources in Pakistan, evaluate rock for its suitability as a simulant, and preparation of the simulant. In total, 50 Kg of rock samples was collected, and the simulant was produced for research activities.

2. Design Approach

A design approach was established to develop the simulant and compare its properties with different simulants and Mars regolith (Figure 1). A basalt source in Pakistan was selected for field sampling. The collected rock pieces were acquired in the laboratory. The dust sample preparation techniques involved cyclic operations of comminution, mixing, and division to produce analytical samples for the determination of chemical composition, mineralogy, and particle morphology.
The geotechnical properties were measured including bulk density, particle density, and particle size distribution. In case of insufficient particle size distribution, the rock dust was further processed for size reduction. The chemical composition and mineralogy of rock dust were evaluated via Energy Dispersive X-ray spectroscopy (EDX) with Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD), respectively. The properties were compared with different simulants and with the values of Mars regolith. The surface morphology was analyzed via Scanning Electron Microscopy (SEM). In cases of unsatisfactory properties, the relevant steps were repeated.

3. Basalt Source and Sampling

The sampling site is located to the east of Winder city, accessible via national highway N-25. The samples were collected by geologists from the outcrop of the Parh group in Jhakkar dhoro, Winder Nai. The geographical coordinates of the sampling site are 25°22′49.62″ N and 66°55′15.70″ E (Figure 2). Parh group volcanics were first described by Vredenburg [30], who related them to the Deccan Traps of India. These volcanic rocks were recognized as the irregularly interlayered heterogeneous assemblage of volcanic and sedimentary rocks in the upper part of the Cretaceous sequence and classified as basalts [31,32,33].
The volcanic rocks of the Parh Group are located extensively throughout the province of Balochistan in Pakistan. However, in the selected sampling site it is present in the form of scattered alluvium/vegetation-covered outcrops exposed in the nala cuttings (Figure 3). The red dotted lines indicate the basalt body. The rock chip samples were collected randomly from multiple locations from a single exposure in nala cutting with the help of a sledgehammer. In this study, the scope of work was limited to geological field work for sample collection from desired outcrop rather than detailed geological mapping. In the laboratory, rock dust of approximately 150 µm particle size was prepared from these rock pieces. The analytical sample was oven-dried prior to analysis. The sample was analyzed for its chemical composition by Energy Dispersive X-ray spectroscopy (EDX), mineralogical composition by X-ray Diffraction (XRD) and particle morphology by Scanning Electron Microscopy (SEM). Based on the Total Alkali Silica (TAS) diagram, the sample was classified as basalt. The scope of this work was to collect rock samples from the desired outcrop/unit rather than detailed mapping or extensive geological work.

4. Production of Rock Dust

An attempt was made to achieve approximate 150 µm particle size distribution. The overall process was selected to represent physical weathering. The rock dust was produced by crushing/grinding, mixing, and division in a cyclic manner to ensure the representativeness of the gross sample. The large lumps were first hammered to reduce their size to approximately 6 inches (152.4 mm). Primary crushing was carried out in a laboratory single-toggle jaw crusher, which breaks particles by compression. It consists of two jaws or plates making an acute angle with each other; one of them is moveable in to-and-fro motion with rpm in the range of 325–375. It can accept feed up to a size of 6 inches (152.4 mm) feed opening size and reduce it down to a discharge opening size of less than 1.25 inches (31.75 mm).
The crushed product from the jaw crusher was subjected to secondary crushing by a laboratory roll crusher. This crusher is made up of two rolls rotating towards each other at 250–300 rpm. It also breaks particles by compression. It was set to accept feed particles up to 1.25 inches (31.75 mm) and produce product particles less than ¼ inch (6.35 mm) in size.
Due to the low reduction ratio in secondary crushing and a maximum feed size limit of 5 mm for grinding machines, tertiary crushing (third stage) was included in the particle size reduction process. Tertiary crushing was performed by reducing the distance between the rolls down to 1/16 inch (1.59 mm). After each stage of crushing, the crushed product was thoroughly mixed and divided into two parts: one was reserved, and the other was subject to further processing. The same procedures were used for grinding products, leading to an ultimate particle target size of less than 150 μm. For grinding, the ball mill was used in two stages: coarse grinding and fine grinding. In coarse grinding, balls with a size of 2 inches (50.8 mm) were used, while in fine grinding, 1 inch (25.4 mm) sized balls were utilized. The volume of balls was kept at around 40% of the mill volume in both cases.
The dust produced after this process was referred to as Winder Nai Mars Simulant (WNMS). Figure 4A shows the potential simulant in comparison with MMS-2 and Mars regolith at three different locations of the Curiosity rover. Panel A contains the combined image of MMS-2 and WNMS. Figure 4B shows the rock dust at the edge of a drill hole completed by the Curiosity on Mount Sharp. Figure 4C also shows a 1.6 cm dia shallow drill hole to collect powdered sample material from the interior of the rock. In Figure 4D, a close-up view of the sands in the Rocknest wind drift is shown.

5. Test Methods

The physical and chemical properties, mineralogy, and surface morphology were measured for WNMS produced from the mechanical crushing of basalt.

5.1. Geotechnical Tests

The geotechnical tests included bulk density, particle density, and particle size distribution (PSD). These tests were performed according to American Society for Testing and Materials (ASTM) standards. The bulk density of the simulant was calculated as per ASTM D7263-21 [35]. It was calculated by dividing the mass of the bulk solid quantity (in natural condition) by its total volume.
The particle density (or specific gravity) of the rock dust was calculated by the pycnometer method according to ASTM D854-14 [36]. In this test, the weight of the clean and empty pycnometer was recorded to the nearest 0.01 g as W1. The sample was oven-dried at 110 °C to a constant mass. The sample was then added to the pycnometer and weight was measured as W2. Afterward, distilled water was added to half of the depth of the main body of the pycnometer and agitated to form a slurry. A partial vacuum was applied to remove entrapped air. Later, the pycnometer was filled with distilled water up to the calibration mark. After wiping, its weight was recorded as W3. Also, the weight of the pycnometer only filled with water was measured as W4. The specific gravity was calculated as a ratio of the mass of dust in the pycnometer with the equivalent mass of water replaced by the dust, as shown in the following equation.
G s = W 2 − W 1 W 4 − W 1 − W 3 − W 2
The particle size distribution (gradation) was evaluated via hydrometer analysis according to ASTM D7928-21e1 [37]. The hydrometer analysis is used to calculate the particle size based on the settling particles in the liquid suspension. In this test, a hydrometer measures the fluid density and number of suspended particles at different time intervals. The readings help to calculate the distribution of mass as a function of the particle size. The results are presented in the form of a gradation curve.

5.2. Energy Dispersive X-ray (EDX) Spectroscopy

The elemental composition of rock was measured by scanning the specimen at the microscale with Energy dispersive X-ray spectroscopy (EDX) system attached to Scanning Electron Microscope (SEM). The SEM-EDX system was able to detect elements from Boron (5B) to Uranium (92U). In this analysis, SEM was JSM5910 (JEOL Limited, Japan) and EDX was INCA200 (Oxford Instruments, UK). The different peaks were identified in EDX spectra obtained by five punctual scans with electron beams through accelerating voltages of 15.17 kV at different locations within the sample. The measured peak intensities were converted to weight percentages by the software and the average composition was computed.

5.3. X-ray Diffraction (XRD)

The rock mineralogy of WNMS was measured through X-ray diffraction (XRD). A Bruker D8 Advance Diffractometer was used to record the X-ray diffraction pattern with Cu Kα radiation of wavelength 1.5406 Å. The other equipment parameters included tube current and voltage as 40 mA and 40 kV, respectively. The slow scan was used to analyze the crystal structure of the minerals with a diffraction angle (2θ) from 10° to 80° [38]. A step size of 0.02° was used for 3468 steps with a total time per step as 67.2 s. The intensities and diffraction angles (2θ) values were plotted [39] and after initial smoothening, the base was subtracted in OriginPro (version 2023b). The spectrum was then analyzed in Profex for phase matching and Rietveld refinement [40].

5.4. Scanning Electron Microscopy (SEM)

The particle shape and surface morphology of MMS-2 and WNMS simulants were determined via the Nova NanoSEM 450 Field-Emission Scanning Electron Microscope (FE SEM) of FEI (US) at a magnification level of 10,000×. The SEM images of dust particles passing through the ASTM sieve 200 were acquired with a working distance (WD) of 5.4 mm at a horizontal field width (HFW) of 20.7 μm. The particle shape in SEM images was determined as per the findings of Powers [41].

5.5. Magnetic and Volatile Content

The presence of different Fe oxide minerals in basalt contributes to its strong magnetic signatures. A magnetic separation test was performed on a wet low-intensity drum-type magnetic separator (WLIMS) to separate highly paramagnetic (ferromagnetic particles, i.e., magnetite) from diamagnetic materials. This magnetic separator has a drum that rotates at 50 rpm. The drum contains a permanent magnet with a maximum magnetic intensity of 1600 Gauss (0.16 T). The position of the magnet inside the drum is variable. The feed, having a particle size of less than 32 mesh (1 mm), was thoroughly mixed in a drum mixer to form slurry feed, having a solids percentage of around 10%. After the experiment, particles in both concentrate and tailings were allowed to settle. The clear water was cautiously decanted followed by drying the products in the oven and their weights were measured.
The volatile contents of WNMS and MMS-2 were measured at 125 °C, 250 °C, 500 °C, 750 °C, and 950 °C. For this purpose, a total of 10 crucibles with a 30 mL capacity each were washed and then dried in an oven at 110 °C. For each material, 5 crucibles were used, and the empty weight of the crucibles (A) was recorded. A sample of 1 g ± 0.02 g was poured into each crucible and its weight with the sample was measured (B). The crucibles were placed into an electric muffle furnace. The temperature at each stage was maintained for one hour. One crucible of both WNMS and MMS-2 at each stage was taken out into the desiccator and its weight (C) was measured after cooling. The volatile matter (VM) was calculated by dividing the weight of the furnace-dried sample by the unheated sample expressed as percentage i.e., (B − C)/(B − A) × 100.

6. Result and Discussion

6.1. Density and Particle Size Distribution

The particle density was found to be 2.58 g/cm3 and the bulk density was 1.16 g/cm3. In comparison, JSC Mars 1 had values of 1.91 ± 0.02 g/cm3 and 0.87–1.07 g/cm3, respectively. A comparison of the bulk density of JMSS-1 (1.45 g/cm3) with different simulants and landing sites is summarized by Zeng et al. [17]. According to Allen et al. [14], the drift material of the Viking 1 landing site has a bulk density of 1.2 ± 0.2 g/cm3, while blocky material has a value of 1.6 ± 0.4 g/cm3. Golombek et al. [42] computed the bulk densities at five landing sites on Mars for different types of regolith. The values in gm/cm3 were 1.0–1.3 (drift), 1.1–1.3 (sand) 1.1–1.6 (crusty to cloddy soil), blocky indurated soil (1.2–2.0) and dense float volcanic rock (2.6–2.8). The bulk density of WNMS is comparable with the Martian regolith.
Figure 5 shows the comparison of the particle size distribution of MMS-2 and WNMS for particles passing through ASTM sieve 200. The Winder Nai Mars Simulant (WNMS) shows a more well-graded particle size distribution. It also indicates no further requirement for the crushing of basalt dust. The liquid limit test indicated the cohesionless character of WNMS.

6.2. Chemical Composition

Table 1 compares the elemental composition of WNMS with different simulants and composition at Rocknest and average Martian regolith values. The chemical composition of WNMS is measured through semi-quantitative EDX technique. The results show that the elemental composition of WNMS is within ±5 wt% composition of the Rocknest, as well as the average Martian regolith composition for all the elements except SO3. In comparison, MSG-1 has values within 4 wt% of Rocknest (target) chemistry, except for SiO2 and MgO [6]. As MGS-1 is a mineralogical standard, according to the authors, it is difficult to obtain terrestrial minerals with appropriate crystal chemistry for Mars. For other simulants, variation is observed for MgO, although values are within the range of target chemistry ±5 wt% of Martian values. Similarly, all simulants of Ramkissoon et al. [20], on the whole, have values within ±5 wt%, corresponding to diverse Martian surface environments (such as sulfur-rich and hematite-rich regolith).
In terms of SiO2, Al2O3, Fe2O3, WNMS, and MMS-2 have a good match to the Martian regolith values compared to JSC Mars-1, MSG-1, and JMSS-1. CaO content is higher in WNMS and lower in MSG-1 in comparison to other simulants and regolith. Similarly, the TiO2 content of WNMS and JSC Mars-1 is higher and K2O is relatively higher in JMSS-1. The values can further be compared with data from different locations, as reported in various studies [20,43,44].
In Table 1, only MMS-2 and MSG-1 indicate the presence of SO3 among all simulants. Also, according to Cannon et al. [6], most of the simulants reported in the literature do not indicate the presence of SO3. However, Martian regolith contains approximately 6 wt% of SO3. This indicates that the lower SO3 content in already developed simulants is a concern. For the simulant utilized for construction purposes, the difference in SO3 content would not affect sulfur concrete, reported to be the most suitable concrete for Mars. However, increased SO3 content can affect the properties of ordinary Portland cement concrete. In addition to this, MgO content can also affect the properties of cement concrete. According to Zayed et al. [45], the presence of both SiO3 and MgO in cement would affect its performance in concrete.
Based on the Total Alkali Silica (TAS) diagram in Figure 6, the rock can be classified as basalt. Moreover, according to classification of Irvine and Baragar [46], the basalt is tholeiitic basalt, and it belongs to the category of subalkaline rocks. Mangold et al. [47] also used the TAS diagram to classify different regolith values. They reported the results of six conglomerates analyzed via the Alpha Particle X-ray Spectrometer and 40 analyzed by the ChemCam of the Curiosity rover. The classification mainly ranged from basalt to basaltic andesite, and had an average basalt crust composition. The overall results show an acceptable composition of simulants within ±5 wt% of the Rocknest, as well as the average Martian regolith values. Moreover, the rock type is representative of the average Martian crust.
Table 1. Comparison of the elemental composition with different simulants and Mars regolith.
Table 1. Comparison of the elemental composition with different simulants and Mars regolith.
OxidesWNMS (%)MMS-2 *JSC Mars-1 [14]MSG-1 [6]JMSS-1 [17]Rocknest
[21]		Avg Martian Value [48]
SiO247.6243.8043.5050.8049.28 42.9745.41
Al2O312.1513.0723.308.9013.64 9.379.71
Fe2O318.8818.3715.6013.3016.00 19.1816.73
CaO11.417.986.203.707.56 7.266.37
TiO23.310.833.800.301.78 1.190.90
K2O0.370.370.600.301.020.490.44
SO3-6.11-2.10-5.476.16
MnO-0.130.300.100.14 0.420.33
Cr2O3-0.04-0.10-0.490.36
P2O5-0.130.900.400.30 0.950.83
MgO4.146.663.4016.706.35 8.698.35
Na2O2.142.512.403.402.92 2.702.73
Cl-----0.690.68
Total100.02100.00100.00100.1098.99 **99.8799.00
* https://www.themartiangarden.com/tech-specs (accessed on 20 April 2023). Note: Iron oxide is reported here as Fe2O3 and ** LOI is omitted.

6.3. Mineralogy

WNMS was analyzed using X-ray diffraction (XRD) to examine the signature minerals of basalt. The XRD spectrum is shown in Figure 7, and the summary of results and Rietveld refinement parameters are presented in Table 2. The results show the presence of essential basalt minerals, including plagioclase as oligoclase (46.18%) and pyroxene as augite (43.20%). The other minerals found include calcite (3.84%), ilmenite (2.63%), biotite (2.63%), magnetite (0.82%), olivine (0.35%), and hematite (0.33%). The tholeiitic basalts have no olivine or nominal value of olivine in its composition. The presence of calcite in basalt is atypical, and it indicates some degree of environmental alteration. The iron oxide minerals including magnetite (Fe3O4) and traces of ilmenite (FeTiO3) and hematite (Fe2O3) have a total content of 3.78%. The Chi-squared (X2) and Goodness of Fit (GoF) are 1.27 and 1.13, respectively. These refinement parameters indicate a successful convergence of the Rietveld refinement.
The regolith at Rocknest includes minerals in terms of wt% as: plagioclase (40.7%), pyroxene (30.4%), olivine (20.5%), magnetite (2.5%), anhydrite (1.6%), hematite (1.4%), ilmenite (1.3%), and quartz (1.3%) [6,44]. Moreover, in the regolith of Mars, olivine is not as prevalent compared to plagioclase and pyroxene [49]. The magnetite/titanomagnetite gives magnetic character to the Martian regolith [50]. The level of magnetite is between 1 and 7 wt% for the Martian regolith, as estimated by Viking and Pathfinder missions.
For construction purposes, the nature of aggregate can affect the Alkali Silica Reaction (SAR) in cement concrete [18]. This, as a result, can affect the durability of concrete. For Martian concrete made with sulfur, this is not a problem due to the mechanical bond and more compacted nature of concrete [51]. The designed simulant reasonably reflects the essential mineralogy needed for a basaltic regolith simulant.
Furthermore, a scan in the low 2θ range (0–10°) can be useful to detect the presence of phyllosilicates such as biotite. This work has limitations in the study of degree of rock alteration and miner phases through petrography; therefore, a thin-section petrography is further recommended.

6.4. Particle Morphology

Figure 8 shows SEM images of MMS-2 and WNMS at a magnification level of 10,000×. The WNMS particles are finer, less-processed, and granoulous in nature as compared to MMS-2 (Martian Garden), while both simulants contain angular to subangular particles. According to Powers [41] classification, both simulants can be classified as angular. WNMS has some surface texture and elongated particles. SEM also indicates the less-cohesive nature of the particles of WNMS. In comparison, the particles in JMSS-1 are also angular to subangular [17]. Also, Scott et al. [18] reported angular, very angular, and fewer sub-angular shape particles for their simulant. The angular shape results from the mechanical crushing of the rocks to produce simulants.
There is an absence of SEM analysis in the Mars regolith; however, images captured by the Mars Hand Lens Imager on Nasa’s Curiosity rover indicate the presence of spherical particles with more fine dust. This is due to aeolian weathering, most probably in the absence of water. The mechanical crushing of rock produces angular particles, and this remains a challenge with most of the simulants. The results show that WNMS can be used as a simulant so far as particle morphology is concerned.

6.5. Magnetic Properties and Volatile Content

The results of the low-intensity drum-type magnetic separator indicate a presence of 3.8 wt% magnetic content. In comparison, MMS-2 has a 3.1 wt% magnetic content. The wet process was preferred because, in a handheld magnet experiment and dry magnetic separator, a large number of fines adhered to the magnetic surface. A handheld approach was used by Allen et al. [14] for JSC Mars-1 and lifted approximately 25 wt% magnetic content and fines. The work also reports the magnetic content of 1–7% lifted by magnetic arrays of Viking and Pathfinder. There is a further need to investigate the magnetic phase of WNMS.
The use of regolith as a construction material has shown to have excellent radiation shielding properties. The higher amount of magnetite as an aggregate or as an additive in cement will increase the thermal conductivity of concrete and radiation shielding properties. The magnetite variation among simulants is less likely to cause any substantial difference.
Figure 9 shows the volatile content for WNMS and MMS-2. The results show the presence of volatiles in both simulants. On average, MMS-2 has more volatile content at different temperatures. The loss of water measured at 125 °C shows an increased value for MMS-2. The higher water escape rate in the MMS-2 sample may be attributed to its hygroscopic properties and the timing of procurement, as the MMS-2 was obtained in 2019 and the WNMS was relatively fresh. Moreover, WNMS is more well-graded, as indicated by the hydrometer analysis (Figure 5) and SEM analysis (Figure 8). Also, the MMS-2 particles seem to be more processed and angular in comparison with WNMS. All these factors might have increased the loss of water.
The volatile loss of WNMS is 0.25 wt% at 125 °C, 1.73 wt% at 500 °C and 3.05 wt% at 950 °C, while MMS-2 shows a volatile loss of 2.43 wt% at 125 °C, 4.78 wt% at 500 °C, and 6.89 wt% at 950 °C. In comparison, JMSS-1 has a water loss of 1.49 wt% and 4.7 wt% at 100 °C and 500 °C, respectively. For MSG-1, a loss of 3.9% was observed from 30 °C to 500 °C. In contrast, JSC Mars-1 has a loss of 7.8 wt% at 100 °C and 21.1 wt% at 600 °C. MMS lost 1.7 wt% of water at 100 °C, and 7.2 wt% at 500 °C [6,14,17,27]. This loss can be due to several volatile species, including water. There is a need to further evaluate these volatile components. In comparison to the Mars regolith, WNMS released 1.73 wt% at 500 °C, while dry regolith by Viking experiments released 0.1 to 1.0 wt% volatiles for samples heated up to 500 °C [27].

7. Conclusions and Recommendations

The Martian regolith is being widely studied for exploration and habitation purposes. Basalt is abundantly available on Mars and is the main ingredient of the simulants. In this research, the basalt source in Pakistan was identified, and a simulant was produced after acquiring field samples. The following conclusions are drawn from this study:
  • The area of Winder Nai in Pakistan is suitable due to its availability and ease of access. The particle density and bulk density of the simulant are 2.58 g/cm3 and 1.16 g/cm3, respectively. The WNMS shows a well-graded particle size distribution. It also shows the presence of angular to subangular fine and granoulous particles with some surface texture.
  • The elemental composition of WNMS is within ±5 wt% of the elemental composition at Rocknest and average Martian regolith values with the exception of SO3.
  • SiO2, Al2O3, and Fe2O3 for WNMS and MMS-2 have a good match to the Martian regolith values compared to JSC Mars-1, MSG-1, and JMSS-1. The content of CaO and TiO2 in WNMS is higher compared to that of the regolith. However, the values are within acceptable limits. The SO3 content in most of the simulants is lower than the Martian regolith. The difference in MgO and SO3 content would not affect sulfur concrete, generally reported to be the most suitable concrete for Mars.
  • Based on the Total Alkali Silica (TAS) diagram, the rock can be classified as basalt.
  • XRD spectrum indicates peaks corresponding to basalt, indicating plagioclase (46.18%) and pyroxene (43.20%). The total iron oxide minerals have a total content of 3.78%.
  • WNMS shows good magnetic properties with the presence of 3.8 wt% highly paramagnetic magnetic content. In comparison, MMS-2 has a 3.1 wt% magnetic content. The volatile loss of WNMS is 0.25 wt% at 125 °C, 1.73 wt% at 500 °C and 3.05 wt% at 950 °C. These values are higher than the regolith values and lower than those for JSC Mars-1 and MMS-2, JMSS-1, and MSG-1.
  • There is a further need to study the petrography through a thin section of rock for the degree of rock alteration and minor phases. It is also recommended that the hygroscopic properties, phase of magnetic particles, and nature of volatile loss at different temperatures be further investigated. Similar endeavors will help researchers in multidisciplinary fields of low-developed and developing countries to play their role in planetary research.

Author Contributions

Conceptualization, A.R.; Methodology, A.R., U.M. and M.S.; Validation, M.I.Z.; Formal analysis, A.R.; Investigation, A.R. and M.S.; Resources, U.M. and M.I.Z.; Data curation, M.I.Z.; Writing—original draft, A.R.; Writing—review & editing, U.M. and M.S.; Visualization, U.M.; Project administration, M.I.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are contained within the article.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Characterization of basalt and production of Winder Nai Mars Simulant (WNMS).
Figure 1. Characterization of basalt and production of Winder Nai Mars Simulant (WNMS).
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Figure 2. Geological map of the study area with marked sampling site (after [34]).
Figure 2. Geological map of the study area with marked sampling site (after [34]).
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Figure 3. Field photograph showing the exposure of basalt in nala cutting/sample collection site.
Figure 3. Field photograph showing the exposure of basalt in nala cutting/sample collection site.
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Figure 4. (A) WNMS and MMS-2, (B) regolith at Rocknest (Sol 3624), (C) borehole in Windjana (Sol 615), (D) sand grains less than 150 microns (Sol 73).
Figure 4. (A) WNMS and MMS-2, (B) regolith at Rocknest (Sol 3624), (C) borehole in Windjana (Sol 615), (D) sand grains less than 150 microns (Sol 73).
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Figure 5. Particle size distribution of MMS-2 and WNMS based on hydrometer analysis.
Figure 5. Particle size distribution of MMS-2 and WNMS based on hydrometer analysis.
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Figure 6. Total Alkali Silica (TAS) diagram of different simulants and Mars regolith.
Figure 6. Total Alkali Silica (TAS) diagram of different simulants and Mars regolith.
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Figure 7. XRD spectrum for basalt minerals in WNMS.
Figure 7. XRD spectrum for basalt minerals in WNMS.
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Figure 8. Scanning Electron Microscopic images of MMS-2 and WNMS.
Figure 8. Scanning Electron Microscopic images of MMS-2 and WNMS.
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Figure 9. Volatile content of WNMS and MMS-2.
Figure 9. Volatile content of WNMS and MMS-2.
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Table 2. Mineralogical composition through XRD.
Table 2. Mineralogical composition through XRD.
ParameterValue (%)Estimated SD
Plagioclase46.180.009
Pyroxene43.200.009
Calcite3.840.004
Ilmenite2.630.003
Biotite2.630.004
Magnetite0.820.002
Olivine0.350.003
Hematite0.330.001
Statistics
Rwp48.91
Rexp43.45
X21.27
GoF1.13
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Rahim, A.; Majeed, U.; Zubair, M.I.; Shahzad, M. WNMS: A New Basaltic Simulant of Mars Regolith. Sustainability 2023, 15, 13372. https://doi.org/10.3390/su151813372

AMA Style

Rahim A, Majeed U, Zubair MI, Shahzad M. WNMS: A New Basaltic Simulant of Mars Regolith. Sustainability. 2023; 15(18):13372. https://doi.org/10.3390/su151813372

Chicago/Turabian Style

Rahim, Abdur, Umair Majeed, Muhammad Irfan Zubair, and Muhammad Shahzad. 2023. "WNMS: A New Basaltic Simulant of Mars Regolith" Sustainability 15, no. 18: 13372. https://doi.org/10.3390/su151813372

APA Style

Rahim, A., Majeed, U., Zubair, M. I., & Shahzad, M. (2023). WNMS: A New Basaltic Simulant of Mars Regolith. Sustainability, 15(18), 13372. https://doi.org/10.3390/su151813372

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