Mars Soil Research Articles

Reflectance study of ice and Mars soil simulant associations – I. H2O ice

The reflectance of water ice and dust mixtures depends, amongst other parameters, on how the components are mixed (e.g. intimate mixture, areal mixture or coating). Therefore, when inverting the reflectance spectra measured from planetary surfaces to derive the amount of water ice present at the surface, it is critical to distinguish between different mixing modes of ice and dust. However, the distinction between mixing modes from reflectance spectra remains ambiguous. Here we show how to identify some water ice/soil mixing modes from the study of defined spectral criteria and colour analysis of laboratory mixtures. We have recreated ice and dust mixtures and found that the appearance of frost on a surface increases its reflectance and flattens its spectral slopes, whereas the increasing presence of water ice in intimate mixtures mainly impacts the absorption bands. In particular, we provide laboratory data and a spectral analysis to help interpret ice and soil reflectance spectra from the Martian surface.

CONSERVATION STATUS OF THREE RARE AND ENDEMIC SPECIES FROM TURKEY (Kalidium wagenitzii, Muscari adilii & Verbascum gypsicola)

In this study, we aimed to determine the population size and distribution areas and to re-evaluate IUCN threat categories of Kalidium wagenitzii (Aellen) Freitag & G. Kadereit, Muscari adilii M.B. Güner & H. Duman and Verbascum gypsicola Vural & Aydoğdu, which are endemics of the Central Anatolia region of Turkey. The three species have limited distribution areas and high risk of extinction as a result of human impact. The perennial halophytic species K. wagenitzii was found in 5 localities around Salt Lake (Tuz Gölü) and a total number of 6458 mature individuals were determined. The area of occupancy of the species is 36 km2 and the extent of occurrence is 213 km2. Uncontrolled use of water resources for agricultural purposes is a serious threat factor for the species. Kalidium wagenitzii is listed in EN category according to the IUCN Red List criteria. Muscari adilii prefers marly soils and its habitat type is formed by secondary succession after the destruction of Pinus nigra and oak forests. It is known from 3 localities around Nallıhan-Beypazarı with a population size of 6144 mature individuals. The area of occupancy and the extent of occurrence of the species is 12 km2 and 28 km2, respectively. The pressures on the species are road construction and increase of farmland, afforestation and factory establishment. According to the IUCN Red List criteria, the species is listed in CR category. Verbascum gypsicola is distributed on marly soils. It is known from 3 localities around Nallıhan–Beypazarı and one locality in Sivrihisar-Eskişehir with 2755 mature individuals in total. The area of occupancy of the species is 16 km2 and the extent of occurrence is 269 km2. Overgrazing and expansion of agricultural land, together with factory establishment are the major threats for this species, which is listed as EN in IUCN Red List.

Sulphate soil stabilisation with magnesium binders for road subgrade construction

ABSTRACT This paper analyzes the ability of magnesium oxide-based additives to stabilise a low bearing gypsum marly soil, in order to reach subgrade requirements. This soil was not adequate for stabilisation with lime or cement because of its high sulphate content. Binders considered in this investigation were composed of three reactive Mg products and by products, both with and without ground granulated blast furnace slags (GGBS). They were compared to two cements and an aerial lime as soil stabilisers in a laboratory investigation and a field trial. Laboratory tests showed that Mg products with GGBS reached strength results close and at times even better than those of cement. One of the Mg products was the only additive able to reduce the natural soil swelling. Leaching tests demonstrated the ability of the Mg products to reduce the soil leaching of substances like calcium, magnesium, sulphate and chloride. In field trials two of the Mg products combined with GGBS met the bearing capacity requirements for subgrades, in accordance with the Spanish standard.

Formation of Clay-Rich Layers at The Slip Surface of Slope Instabilities: The Role of Groundwater

Some landslides around the world that have low-angle failure planes show exceptionally poor mechanical properties. In some cases, an extraordinarily pure clay layer has been detected on the rupture surface. In this work, a complex landslide, the so-called Diezma landslide, is investigated in a low- to moderate-relief region of Southeast Spain. In this landslide, movement was concentrated on several surfaces that developed on a centimeter-thick layer of smectite (montmorillonite-beidellite) clay-rich level. Since these clayey levels have a very low permeability, high plasticity, and low friction angle, they control the stability of the entire slide mass. Specifically, the triggering factor of this landslide seems to be linked to the infiltration of water from a karstic aquifer located in the head area. The circulation of water through old failure planes could have promoted the active hydrolysis of marly soils to produce new smectite clay minerals. Here, by using geophysical, mineralogical, and geochemical modelling methods, we reveal that the formation and dissolution of carbonates, sulfates, and clay minerals in the Diezma landslide could explain the elevated concentrations of highly plastic secondary clays in its slip surface. This study may help in the understanding of landslides that show secondary clay layers coinciding to their low-angle failure planes.

Development of martian regolith and bedrock simulants: Potential and limitations of martian regolith as an in-situ resource

The last decade of Martian surface exploration has increased knowledge of the composition and variability of minerals present in the regolith and bedrock. This informs planning for manned missions to Mars for which these surface materials may be an important in-situ resource in agricultural applications. Soil on Mars is known to contain the majority of planet essential nutrients, but many questions of both the benefits (e.g. bioavailability of present nutrients) and limitations (e.g. extent of toxins) of Martian soil as a plant growth medium remain unanswered. It may be necessary to augment Mars soil with other regolith and bedrock materials (e.g. phyllosilicates, carbonates) to produce a medium appropriate for plant growth. A better understanding of the feasibility of using Mars soil as a plant growth medium could be accomplished with methods common to agricultural practices on Earth (e.g. biofertilization) using appropriate regolith and bedrock simulants as a plant growth medium. The study herein discusses the development of five new regolith and bedrock simulants. These simulants are designed to reflect several mineralogical (e.g. phyllosilicate clays) and chemical characteristics of various Mars surface materials that are most relevant to establishing the potential and limitations of these materials as in-situ resources for agricultural applications. The use of simulants provides a test bed for studies examining the potential of Mars' regolith and bedrock in agricultural applications, understanding data gaps surrounding these materials that will need further characterization, and methods to then conduct needed characterization of true Martian-regolith and bedrock in-situ. The simulants discussed herein are analyzed by X-ray diffraction using Reitveld refinement, X-ray fluorescence, V/NIR reflectance spectroscopy, and 57Fe Mössbauer spectroscopy and then compared to equivalent published data available from Mars rover and orbiter missions. The resulting simulants are chemically and mineralogically comparable to Martian regolith and bedrock and reflect data particularly relevant for growing plants on Mars. The developed simulants are relevant for analogue plant growth studies and fertility measurements that may inform hypothesis, habitat design, and mission plans which involve using Martian soil as a plant growth medium.

Organic Matter Preservation in Ancient Soils of Earth and Mars.

The emerging field of astropedology is the study of ancient soils on Earth and other planetary bodies. Examination of the complex factors that control the preservation of organic matter and other biosignatures in ancient soils is a high priority for current and future missions to Mars. Though previously defined by biological activity, an updated definition of soil as planetary surfaces altered in place by biological, chemical or physical processes was adopted in 2017 by the Soil Science Society of America in response to mounting evidence of pedogenic-like features on Mars. Ancient (4.1–3.7 billion year old [Byr]) phyllosilicate-rich surface environments on Mars show evidence of sustained subaerial weathering of sediments with liquid water at circumneutral pH, which is a soil-forming process. The accumulation of buried, fossilized soils, or paleosols, has been widely observed on Earth, and recent investigations suggest paleosol-like features may be widespread across the surface of Mars. However, the complex array of preservation and degradation factors controlling the fate of biosignatures in paleosols remains unexplored. This paper identifies the dominant factors contributing to the preservation and degradation of organic carbon in paleosols through the geological record on Earth, and offers suggestions for prioritizing locations for in situ biosignature detection and Mars Sample Return across a diverse array of potential paleosols and paleoenvironments of early Mars. A compilation of previously published data and original research spanning a diverse suite of paleosols from the Pleistocene (1 Myr) to the Archean (3.7 Byr) show that redox state is the predominant control for the organic matter content of paleosols. Most notably, the chemically reduced surface horizons (layers) of Archean (2.3 Byr) paleosols have organic matter concentrations ranging from 0.014–0.25%. However, clay mineralogy, amorphous phase abundance, diagenetic alteration and sulfur content are all significant factors that influence the preservation of organic carbon. The surface layers of paleosols that formed under chemically reducing conditions with high amounts of iron/magnesium smectites and amorphous colloids should be considered high priority locations for biosignature investigation within subaerial paleoenvironments on Mars.

Swelling properties and lime stabilization of N'Gaous expansive marls, NE Algeria

The interaction of marly soils and buildings in the town of N'Gaous has led to the appearance of deformations and disturbances that have affected many constructions due to the swelling of the underlying soil. In addition, when these soils are used as construction material, embankments, they are extremely problematic. In this article, three sets of samples, from three different locations, were sampled. Their average carbonate content varies from 14% to 33%.The mineralogical and microsctructural characteristics of these soils are studied by X-ray diffraction (XRD), TG/DTA and SEM analysis. These are mainly smectite clays containing kaolinite and other minor constituents. They all have similar structure, laminar texture with an arrangement of clay particles oriented parallel to the bedding and pores of varying size. These soils are very plastic and have a plasticity index ranging from 41.5 to 54.3%. It was found that the swelling pressure before any treatment ranged from 2.3 to 2.7 bars, after treatment the swelling pressure becomes stable with 5% lime, this behavior has a link with the formation of a cementitious phase of calcium silicate hydrate (CSH) type, as revealed by XRD, ATD/TG and analysis and SEM. In terms of results, it was found that the addition of quicklime has clearly reduced the swelling of the tested samples. It was also found that the presence of carbonates with the above mentioned contents in the studied samples (<50%) does not affect negatively the lime treatment of these soils. However, it promotes the stabilization of swelling, which gives encouraging results.

Biosignature Analysis of Mars Soil Analogs from the Atacama Desert: Challenges and Implications for Future Missions to Mars.

The detection of biosignatures on Mars is of outstanding interest in the current field of astrobiology and drives various fields of research, ranging from new sample collection strategies to the development of more sensitive detection techniques. Detailed analysis of the organic content in Mars analog materials collected from extreme environments on Earth improves the current understanding of biosignature preservation and detection under conditions similar to those of Mars. In this article, we examined the biological fingerprint of several locations in the Atacama Desert (Chile), which include different wet and dry, and intermediate to high elevation salt flats (also named salars). Liquid chromatography and multidimensional gas chromatography mass spectrometry measurement techniques were used for the detection and analysis of amino acids extracted from the salt crusts and sediments by using sophisticated extraction procedures. Illumina 16S amplicon sequencing was used for the identification of microbial communities associated with the different sample locations. Although amino acid load and organic carbon and nitrogen quantities were generally low, it was found that most of the samples harbored complex and versatile microbial communities, which were dominated by (extremely) halophilic microorganisms (most notably by species of the Archaeal family Halobacteriaceae). The dominance of salts (i.e., halites and sulfates) in the investigated samples leaves its mark on the composition of the microbial communities but does not appear to hinder the potential of life to flourish since it can clearly adapt to the higher concentrations. Although the Atacama Desert is one of the driest and harshest environments on Earth, it is shown that there are still sub-locations where life is able to maintain a foothold, and, as such, salt flats could be considered as interesting targets for future life exploration missions on Mars.

Assessing effectiveness of thermal treatment and mixing with coarse-grained particles in stabilization of marly soils

Marly soils can show problematic behaviors such as swelling and dispersion when subjected to water. It can cause problems for various civil constructions, including building foundations, water conveyance canals, highways, and airport runways; so appropriate measurements should be taken to stabilize these soils. In this study, two stabilization methods, including thermal treatment and mixing with coarse-grained particles, were utilized to limit swelling of marly soil samples collected from around the Sonqor city and also to improve their strength properties. The results of experimental tests showed that thermal treatment in high temperatures (after 100 °C) led to a decrease and an increase in liquid and plastic limits, respectively, and subsequently plasticity index decreased. However, after 475 °C, the Atterberg limits were almost unchanged. Also, it was found that with increasing heating levels, the swelling potential of the soil samples decreases as free swelling index values of the samples changed from 13.9% (high swelling potential) at 100 °C to 0.89% (low swelling potential) at 500 °C. Based on the experiments, it was observed that by adding 30% of coarse particles to the marly soil samples, engineering properties such as maximum dry density (γdmax), California bearing ratio, and unconfined compressive strength have been improved up to 10%, 59%, and 30%, respectively. Therefore, the stabilized marly soils could be considered as appropriate construction materials.

Using polyacrylamide to control soil splash erosion in rainfalls with variable intensity and duration

Splash erosion is recognized as the first stage in soil erosion process and results from the bombing of the soil surface by rain drops. One of the soil erosion control methods is the use of chemical polymers. The purpose of this study was to investigate the effects of different rates of polyacrylamide - PAM (0, 2, 4 and 6 kg/ha) - on the rate of splash erosion at three rainfall intensities (60, 90 and 120 mm/h) and three rainfall durations (10, 20 and 30 minutes) in laboratory conditions using a FEL3 rainfall simulator and Morgan splash bowls on a marly soil with loam soil texture. In all three intensities, rainfall duration and PAM treatments, the reductions of erosion were significant at 99% level, while their interaction was not statistically significant. The results indicated that 2 kg/ha of PAM did not show any significant difference in splash erosion reduction for all the intensities and durations. Increasing the rate of PAM from 4 kg/ha to 6 kg/ha helped to reduce the splash erosion rate; however, there was not a significant difference between the rates of 4 and 6 kg/ha of PAM in the intensity of 90 and 120 mm/h. Most splash erosion reduction (54%) was obtained for the intensity of 60 mm/h and the duration of 10 min with 6 kg/ha of PAM.

(Invited) Electrochemical Processes for in Situ Resource Utilization

In situ resource utilization (ISRU) is the practice of generating resources when humans are away from Earth. The goals of ISRU include the generation of rocket propellants, building materials, and life sustaining commodities from such resources as the Mars atmosphere, lunar regolith, and even trash. There are many technology options that are currently at different technology readiness levels. This talk will review some of the more mature ISRU technologies and show were electrochemical processes have the potential to be a better option. The generation of oxygen from lunar regolith has been demonstrated using hydrogen and carbothermal reduction processes. Electrolysis of regolith when it is molten or dissolved has the potential for increased yields. Propellant production on Mars can be achieved through capture of carbon dioxide from the Mars atmosphere and water from the Mars soil. The water is split to oxygen and hydrogen, which is used to reduce carbon dioxide to methane, resulting in production of methane and oxygen. The co-electrolysis of carbon dioxide and water can produce methane and oxygen in a single process vessel, reducing the complexity of the overall system. Recent work has shown that this can be done when carbon dioxide is dissolved in an ionic liquid. The same ionic liquid shows a high capacity for carbon dioxide uptake and can be used to collect carbon dioxide. Because ISRU systems are extremely mass constrained, there is a need for gas and water cleanup methods that do not use consumables. Some of the ISRU cleanup challenges and potential solutions, such as electro-dialysis to clean water, will be discussed.

Highway cutting slopes with high rainfall erosion in Morocco: Evaluation of soil losses and erosion control using concrete arches

Highways in northern and northeastern Morocco through mountainous areas generate a series of high cut slopes and embankments. Highway cuttings are generally established in pelitic and marly soils, which are very vulnerable to rainfall erosion. Because of climate change, precipitation is very irregular and often characterized by aggressive showers. This precipitation generates significant soil losses that can compromise the security and durability of highway structures. The Moroccan National Highway Company deploys an important research program and fieldwork to combat the rainfall erosion of cutting slopes. This study concerns the evaluation of soil losses affecting these slopes in the Tangier-Port Tangier Med and Fez-Taza highway sections. It highlights the factors governing soil erosion and proposes a method for the protection of highway cutting slopes by concrete arches. The stability of the cutting slopes several years after the installation of these arches testifies to the efficiency of this protection system.

Crop growth and viability of seeds on Mars and Moon soil simulants

Abstract If humans are going to establish a base on the Moon or on Mars they will have to grow their own crops. An option is to use Lunar and Martian regolith. These regoliths are not available for plant growth experiments, therefore NASA has developed regolith simulants. The major goal of this project was to cultivate and harvest crops on these Mars and Moon simulants. The simulants were mixed with organic matter to mimic the addition of residues from earlier harvests. Ten different crops, garden cress, rocket, tomato, radish, rye, quinoa, spinach, chives, pea and leek were sown in random lines in trays. Nine of the ten species grew well with the exception of spinach. It was possible to harvest edible parts for nine out of ten crops. The total biomass production per tray was highest for the Earth control and Mars soil simulant and differed significantly from Moon soil simulant. The seeds produced by three species were tested for germination (radish, rye and cress). The germination on Moon soil simulant was significantly lower in radish than for the Earth control soil.

Reducing the negative impact of freezing and thawing cycles on marl by means of the electrokinetical injection of calcium chloride

The purpose of this study was to compensate the negative impact of freezing and thawing cycles on marly soil by means of electrokinetical injection of calcium chloride as a remediation method. Therefore, firstly, the effect of concentration of CaCl2 solution, voltage gradient, and electrokinetic remediation time on the marl improvement was assessed. The electrokinetic remediation tests were conducted for nine different testing scenarios. As the improvement verification criteria, the unconfined compressive strength (UCS), electric potential difference, and drainage were measured. After performing the electrokinetic remediation test, three sets of UCS samples were taken from around anode, cathode, and the in-between. Instantly after that, the UCS of the first set was measured so that the improvement effect might be determined. Afterwards, one and four cycles of freezing and thawing were applied to the second and third sets of samples, respectively, and the UCS loss was measured. After four cycles of freeze-thaw, the concentration of 1.1 kg/lit, i.e. 1.1 kg of CaCl2 powder was dissolved in 1 lit of distilled water, and remediation period of 4 days for all locations in the sample, and the voltage gradient of 2 V/cm near anode and 1 V/cm near cathode and the in-between areas resulted into the highest UCS. It should be mentioned that in all test scenarios, the samples after four freeze-thaw cycles still had an acceptable value of UCS, whilst the natural marl samples provided for the study were demolished only under a small load after one freeze-thaw cycle. Micro-structural analysis was also performed based on XRD and SEM methods and it affirmed the occurrence of chemical modification and the change of the particles into flocculated particles and consequently the improvement of marl after electrokinetic remediation.

Natural variation among Arabidopsis thaliana accessions in tolerance to high magnesium supply

High magnesium (Mg2+) in some extreme serpentine soils or semi-arid regions is an important factor affecting crop growth and development. Specific loci that form the genetic framework underlying high Mg2+ homeostasis, however, are not well understood. By using GWA mapping on 388 accessions of Arabidopsis thaliana selected from a worldwide collection and genotyped at approximately 250,00 SNPs, we successfully identified 109 and 74 putative genetic regions associated in nutrient traits under normal (1,000 µM) and high Mg2+ (10,000 µM), respectively. Above 90% SNPs associated with nutrients including Mg2+ and only two SNPs shared between normal and high Mg2+. A single strong peak of SNPs associated with Ca concentration corresponding to candidate gene At1g60420 ARABIDOPSIS NUCLEOREDOXIN (AtNRX1) under high Mg2+ was further determined. Compared with wildtype, mutants of Atnrx1-1 and Atnrx1-2 supplied with high Mg2+ had higher Ca concentrations in the plant, and higher cytosolic Ca2+ concentrations during root elongation, as well as higher fresh weight and lateral-root number. This suggests that AtNRX1 was a critical gene negatively regulating Ca uptake under high Mg2+ conditions. The discovery could help to breed/select crops that can adapt to high-Mg2+ soils such as serpentine soils (high ratio of Mg2+: Ca2+) or Mars soil with high levels of magnesium sulfate.

The Effect of Mars‐Relevant Soil Analogs on the Water Uptake of Magnesium Perchlorate and Implications for the Near‐Surface of Mars

AbstractThe water uptake and release by perchlorate salts have been well studied since the first in situ identification of such salts in the Martian soil by the Phoenix mission in 2008. However, there have been few studies on the effect of the insoluble regolith minerals on the interaction of perchlorate with water vapor. In this work, we investigate the impact of a Mars‐relevant mineral, montmorillonite, and a Mars soil analog, Mojave Mars Simulant (MMS), on the deliquescence (transition from dry crystalline to aqueous via water vapor absorption), ice formation, and efflorescence (transition from aqueous to dry crystalline via loss of water) of pure magnesium perchlorate. We studied mixtures of magnesium perchlorate hexahydrate with either montmorillonite or MMS. Although montmorillonite and MMS are materials that may serve as nuclei for either ice nucleation or salt efflorescence, we find that these soil analogs did not affect the phase transitions of magnesium perchlorate. The salt‐mineral mixture behaved similarly, within estimated uncertainties, to pure magnesium perchlorate in all cases. Experiments were performed in both N2 and CO2 atmospheres, with no detectable difference. We use data from the Mars Science Laboratory Rover Environmental Monitoring Station instrument and the Phoenix Thermal and Electrical Conductivity Probe, as well as modeling of the shallow subsurface, to determine the likelihood of these perchlorate phase transitions occurring at Gale Crater and the northern arctic plains (Vastitas Borealis). We find that aqueous solutions are predicted in the shallow subsurface of the Phoenix landing site, but not predicted at Gale Crater.

UV irradiation of biomarkers adsorbed on minerals under Martian-like conditions: Hints for life detection on Mars

Laboratory simulations of Martian conditions are essential to develop quantitative models for the survival of organic biomarkers for future Mars exploration missions.In this work, we report the results of ultraviolet (UV) irradiation processing of biomarkers adsorbed on minerals under Martian-like conditions. Specifically, we prepared Mars soil analogues by doping forsterite, lizardite, antigorite, labradorite, natrolite, apatite and hematite minerals with organic compounds considered as potential biomarkers of extant terrestrial life such as the nucleotides adenosine monophosphate (AMP) and uridine monophosphate (UMP). We characterized such Mars soil analogues by means of Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and Confocal Raman Imaging Spectroscopy (CRIS), in order to get insights into the specific molecule-mineral interactions and explore the capabilities of different techniques to reveal diagnostic features of these biomarkers. Then, we performed irradiation experiments in the mid-UV spectral region under simulated Martian conditions and under terrestrial ambient conditions for comparison, monitoring the degradation process through DRIFTS.We observed that degradation under Martian-like conditions occurs much slower than in terrestrial ambient conditions. The minerals labradorite and natrolite mainly promote photodegradation of nucleotides, hematite and forsterite exhibit an intermediate degrading effect, while apatite, lizardite and antigorite do not show any significant catalytic effect on the degradation of the target organic species.

ONTOGENETIC STRUCTURE AND TYPES OF CENOPOPULATION OF LASER TRILOBUM (L.) BORKH. (APIACEAE) IN THE MIDDLE VOLGA BASIN

The research of this kind will be in demand for a long time when monitoring natural complexes in connection with the poor study of populations of rare species in nature. The purpose of our study is to study the current state of the cenotic populations of the rare species Laser trilobum (L.) Borkh. (Apiaceae) in the Middle Volga basin. The species is included in the Red Data Book of the Samara Region and some other regions. It is confined to oak forests on limestone and marly soils. Some features of the biology and ecology of the species have been studied in other regions. The natural populations of the species are almost not investigated. We studied the structure of 22 cenopopulations of L. trilobum. In the course of the work, populationbased ontogenetic methods were used. The density of individuals is 5.3–26.1 copies per m2 . In the ontogenesis of L. trilobum, the regenerative, generative periods and eight ontogenetic states are distinguished. Senile individuals are not marked. Fluctuation dynamics of ontogenetic composition is characteristic for populations. The average ontogenetic spectrum for the investigated cenopopulations is a single-vertex left-handed with a predominance of virgin individuals. The estimation of populations was carried out by the criterion of “delta-omega” of L. A. Zhivotovsky (2001). Most of the cenopopulations are young, three are mature, one is transient. A significant number of young plants testify to the high capacity of L. trilobum populations to self-repair and maintain. Populations of the model species in the studied habitats are in a satisfactory state. An increase in the anthropogenic load negatively affects the structure and condition of the cenotic populations.

Retrieval of Compositional End‐Members From Mars Exploration Rover Opportunity Observations in a Soil‐Filled Fracture in Marathon Valley, Endeavour Crater Rim

AbstractThe Opportunity rover investigated a gentle swale on the rim of Endeavour crater called Marathon Valley where a series of bright planar outcrops are cut into polygons by fractures. A wheel scuff performed on one of the soil‐filled fracture zones revealed the presence of three end‐members identified on the basis of Pancam multispectral imaging observations covering ~0.4 to 1 μm: red and dark pebbles, and a bright soil clod. Multiple overlapping Alpha Particle X‐ray Spectrometer (APXS) measurements were collected on three targets within the scuff zone. The field of view of each APXS measurement contained various proportions of the Pancam‐based end‐members. Application of a log maximum likelihood method for retrieving the composition of the end‐members using the 10 APXS measurements shows that the dark pebble end‐member is compositionally similar to average Mars soil, with slightly elevated S and Fe. In contrast, the red pebble end‐member exhibits enrichments in Al and Si and is depleted in Fe and Mg relative to average Mars soil. The soil clod end‐member is enriched in Mg, S, and Ni. Thermodynamic modeling of the soil clod end‐member composition indicates a dominance of sulfate minerals. We hypothesize that acidic fluids in fractures leached and oxidized the basaltic host rock, forming the red pebbles, and then evaporated to leave behind sulfate‐cemented soil.

The Mars Science Laboratory (MSL) Bagnold Dunes Campaign, Phase I: Overview and introduction to the special issue

AbstractThe Bagnold dunes in Gale Crater, Mars, are the first active aeolian dune field explored in situ on another planet. The Curiosity rover visited the Bagnold dune field to understand modern winds, aeolian processes, rates, and structures; to determine dune material composition, provenance, and the extent and type of compositional sorting; and to collect knowledge that informs the interpretation of past aeolian processes that are preserved in the Martian sedimentary rock record. The Curiosity rover conducted a coordinated campaign of activities lasting 4 months, interspersed with other rover activities, and employing all of the rover's science instruments and several engineering capabilities. Described in 13 manuscripts and summarized here, the major findings of the Bagnold Dunes Campaign, Phase I, include the following: the characterization of and explanation for a distinctive, meter‐scale size of sinuous aeolian bedform formed in the high kinetic viscosity regime of Mars' thin atmosphere; articulation and evaluation of a grain splash model that successfully explains the occurrence of saltation even at wind speeds below the fluid threshold; determination of the dune sands' basaltic mineralogy and crystal chemistry in comparison with other soils and sedimentary rocks; and characterization of chemically distinctive volatile reservoirs in sand‐sized versus dust‐sized fractions of Mars soil, including two volatile‐bearing types of amorphous phases.