Mars Science Laboratory Rover Research Articles

Observed Correlation Between Local Topography and Passive Neutron Measurements From the Dynamic Albedo of Neutrons (DAN) Instrument on the Mars Science Laboratory (MSL) Rover

AbstractThe Dynamic Albedo of Neutrons (DAN) instrument on the Mars Science Laboratory Curiosity rover primarily measures neutrons that have undergone interactions with rocks and materials in the rover's local environment. As the rover ascends Aeolis Mons, it may encounter more extreme local topography (e.g., cliffs, gullies, canyons). We present three parts of the rover's traverse in which local topography, expressed as the average local relief relative to the rover, is moderately to strongly correlated with an increase in passive thermal neutron count rates. These increases in count rates are consistent with results from radiation transport models of the instrument's performance near simulated topographic features. Additional DAN measurements in areas of high average local relief (>0.25 m) within 5 m of the instrument could bolster this correlation. DAN's sensitivity to topography in its passive mode could be utilized as a new measurement capability and has implications for the operation of future landed missions carrying neutron spectrometers (e.g., VIPER, MoonRanger, Lunar‐VISE).

Gypsum on Mars: A Detailed View at Gale Crater

Gypsum is a common mineral at Gale crater on Mars, currently being explored by the Mars Science Laboratory (MSL) rover, Curiosity. In this paper, we summarize the associations of gypsum with other sulfate minerals (bassanite, anhydrite, jarosite, starkeyite, and kieserite) from the lowest levels of the crater’s northern moat zone (Aeolis Palus) up through ~0.8 km of the stratigraphic section in the lower slopes of the sedimentary mound developed around the central peak, Aeolis Mons (informally, Mount Sharp). The analysis is based on results from the CheMin X-ray diffraction instrument on Curiosity, supplemented with information from the rover’s versatile instrument suite. Gypsum does not occur with the same frequency as less hydrous Ca-sulfates, likely, in most cases, because of its dehydration to bassanite and possibly to anhydrite. All three of these Ca-sulfate phases often occur together and, along with other sulfates, in mixed assemblages that are evidence of limited equilibration on a cold, dry planet. In almost all samples, at least one of the Ca-sulfate minerals is present, except for a very limited interval where jarosite is the major sulfate mineral, with the implication of more acidic groundwater at a much later time in Gale crater’s history. Although observations from orbit reveal a sulfate-rich surface, currently active dark basaltic dunes at Gale crater have only small amounts of a single sulfate mineral, anhydrite. Gale crater has provided the most complete mineralogical analysis of a site on Mars so far, but the data in hand show that Gale crater mineralogy is not a blueprint with planet-wide application. The concurrent study of Jezero crater by the Mars 2020 mission and comparisons to what is believed to be the most extensive deposit of gypsum on Mars, in the dune fields at the north polar ice cap, show significant diversity. Unraveling the stories of gypsum and other sulfates on Mars is just beginning.

Experimental Scattering Matrices of Martian Dust Aerosols with Narrow Particle-size Distributions

We present experimental scattering matrices of the JSC Mars-1, MMS-2, and MGS-1 simulants at 488 and 640 nm. The analogs were processed so that narrow size distributions representative of Martian dust aerosols during different dust cycles were obtained. We find that the forward peak of the phase function depends on particle size as it becomes narrower with increasing size, whereas the side- and backscattering directions depend on both composition and size so that increasing size and decreasing absorption produce a flatter curve. The position and maximum of the degree of linear polarization varies based on particle size and composition, and the negative polarization branch is more prominent for wavelength-scale particles diminishing with increasing size. The linear depolarization is strongly affected by size and composition. Finally, we compare sky-brightness curves measured by the Navcam and Hazcam engineering cameras on board the Mars Science Laboratory rover to the measured phase functions. The observations show a narrower peak at the forward direction and a flatter curve toward the side- and backscattering directions with an increasing dust load in the atmosphere, similar to what can be seen for the measured phase functions of the analogs with increasing particle size. In the case of the analogs, the flattening of the curve can be caused by an increase in multiple scattering within a particle by wavelength-scale surface roughness and/or internal inclusions. For the observed sky brightnesses, particle aggregation and multiple scattering among particles in denser dust conditions play a major role.

Expanded Insights into Martian Mineralogy: Updated Analysis of Gale Crater’s Mineral Composition via CheMin Crystal Chemical Investigations

This study presents mineral composition estimates of rock and sediment samples analyzed with the CheMin X-ray diffraction instrument on board the NASA Mars Science Laboratory rover, Curiosity, in Gale crater, Mars. Mineral composition is estimated using crystal-chemically derived algorithms applied to X-ray diffraction data, specifically unit-cell parameters. The mineral groups characterized include those found in major abundance by the CheMin instrument (i.e., feldspar, olivine, pyroxene, and spinel oxide). In addition to estimating the composition of the major mineral phases observed in Gale crater, we place their compositions in a stratigraphic context and provide a comparison to that of martian meteorites. This work provides expanded insights into the mineralogy and chemistry of the martian surface.

The Chemistry and Mineralogy (CheMin) X-ray Diffractometer on the MSL Curiosity Rover: A Decade of Mineralogy from Gale Crater, Mars

For more than a decade, the CheMin X-ray diffraction instrument on the Mars Science Laboratory rover, Curiosity, has been returning definitive and quantitative mineralogical and mineral–chemistry data from ~3.5-billion-year-old (Ga) sediments in Gale crater, Mars. To date, 40 drilled rock samples and three scooped soil samples have been analyzed during the rover’s 30+ km transit. These samples document the mineralogy of over 800 m of flat-lying fluvial, lacustrine, and aeolian sedimentary rocks that comprise the lower strata of the central mound of Gale crater (Aeolis Mons, informally known as Mt. Sharp) and the surrounding plains (Aeolis Palus, informally known as the Bradbury Rise). The principal mineralogy of the sedimentary rocks is of basaltic composition, with evidence of post-depositional diagenetic overprinting. The rocks in many cases preserve much of their primary mineralogy and sedimentary features, suggesting that they were never strongly heated or deformed. Using aeolian soil composition as a proxy for the composition of the deposited and lithified sediment, it appears that, in many cases, the diagenetic changes observed are principally isochemical. Exceptions to this trend include secondary nodules, calcium sulfate veining, and rare Si-rich alteration halos. A surprising and yet poorly understood observation is that nearly all of the ~3.5 Ga sedimentary rocks analyzed to date contain 15–70 wt.% of X-ray amorphous material. Overall, this >800 m section of sedimentary rock explored in lower Mt. Sharp documents a perennial shallow lake environment grading upward into alternating lacustrine/fluvial and aeolian environments, many of which would have been habitable to microbial life.

A decade of quantitative mineralogy on Mars: results from the CheMin X-ray diffractometer on the Mars Science Laboratory rover Curiosity

A decade of quantitative mineralogy on Mars: results from the CheMin X-ray diffractometer on the Mars Science Laboratory rover Curiosity

Results from the Radiation Assessment Detector on the International Space Station: Part 1, the Charged Particle Detector

We report the results of the first six years of measurements of the energetic particle radiation environment on the International Space Station (ISS) with the Radiation Assessment Detector (ISS-RAD), spanning the period from February 2016 to February 2022. The first RAD was designed and built for MSL, the Mars Science Laboratory rover, also known as Curiosity; it has been operating on Mars since 2012 and is referred to here as MSL-RAD. ISS-RAD combines two sensor heads, one nearly identical to the single MSL-RAD sensor head, the other with greatly enhanced sensitivity to fast neutrons. These two sensor heads are referred to as the Charged Particle Detector (CPD) and Fast Neutron Detector (FND), respectively. Despite its name, the CPD is also capable of measuring high-energy neutrons and γ-rays, as is MSL-RAD. ISS-RAD was flown to the ISS in December 2015 and was deployed in February 2016, initially in the USLab module. RAD was used as a survey instrument from January 2017 through May 2020, when the instrument was positioned in the USLab and set to a zenith-pointing orientation. The energetic particle environment on the ISS is complex and varies on short time scales owing to the orbit, which has a 51.6∘ inclination with respect to the equator and has had an altitude in the 400–440 km range in this time period. The ISS moves continuously through the geomagnetic field, the strength of which varies with latitude, longitude, and altitude. The orbit passes through the South Atlantic Anomaly (SAA) several times a day, where magnetically trapped protons and electrons produce large but transient increases in observed fluxes and absorbed dose rates. The environment inside the ISS is affected by the solar cycle, altitude, and the local shielding, which varies between different ISS modules. We report results for charged particle absorbed dose and dose equivalent rates in various positions in the ISS. In an accompanying paper, we report similar results for neutron dose equivalent rates obtained with the ISS-RAD Fast Neutron Detector.

Multivariate Variance-Based Genetic Ensemble Learning for Satellite Anomaly Detection

Proactive diagnosis of spacecraft issues and response to conceivable hazards has attracted considerable interest. Hidden anomalies in satellites can cause overall system degradation. In multivariate time series anomaly detection (AD), several sensors report to a fusion center at each timestamp. Each of these sensors measures a specific feature of the satellites. In this paper, we first leverage the eigenvalues of covariance metrics of a multivariate time series to determine the anomaly score at each timestamp. Then, the anomaly scores are fed to various machine learning models. After that, we employ a Multivariate Variance-based Genetic Ensemble (MVVGE) learning method to ensemble the results of several models based on their corresponding performance. More specifically, we ensemble different Neural Network (NN), Random Forest (RF), and Linear Regression (LR) models based on their associated variance to catch the anomalies of three datasets, i.e., two satellite datasets: i) Soil Moisture Active Passive (SMAP), ii) Mars Science Laboratory rover (MSL), and Server Machine Dataset (SMD). Given that establishing the model confidence region is the bottleneck of our approach, we use an approximated version of the Bayesian NNs (BNN)s for acquiring confidence intervals of NN-based models. For RF and LR confidence intervals, we use an empirical method and bootstrapping, respectively. Simulation results confirm the superiority of our proposed approach compared to other methods.

Hydration of a Clay‐Rich Unit on Mars, Comparison of Orbital Data to Rover Data

AbstractGlen Torridon (GT) is a geomorphic feature of Aeolis Mons (informally Mt. Sharp) in Gale crater, Mars, variably covered by local regolith and wind‐blown basaltic sands. The Mars Reconnaissance Orbiter's Compact Imaging Spectrometer for Mars (CRISM) detected clay minerals in GT, making GT a target of investigation by the Mars Science Laboratory (MSL) rover, Curiosity, which confirmed a large abundance of clays. The MSL Dynamic Albedo of Neutrons (DAN) instrument observed enrichments in bulk subsurface (<50 cm) hydration along the rover traverse compared to lower stratigraphic sections of Mt. Sharp. Here, we investigate the relationship between the CRISM 3 µm hydration index and DAN results, taking into consideration the different spatial scales and effective depths of these two instruments. We show that the elevated hydration observed by CRISM in one area of GT corresponds to elevated DAN‐derived hydration, while the lower CRISM hydration in another area of GT does not correspond to a significantly lower DAN‐derived hydration. We find that CRISM measured lower hydration in areas with good bedrock exposure or sand cover, while DAN bulk hydration is relatively insensitive to these characteristics. DAN active neutron results also show that the stratigraphically higher section of GT has significantly higher neutron absorption, which could be due to Fe‐ and Mn‐rich diagenetic features. Additionally, DAN results show that GT is enriched in hydrogen with respect to other, less clay‐rich units observed throughout the traverse, suggesting that subsurface clay minerals could be a significant reservoir for the hydration measured by DAN in GT.

The Curiosity Rover's Exploration of Glen Torridon, Gale Crater, Mars: An Overview of the Campaign and Scientific Results.

The Mars Science Laboratory rover, Curiosity, explored the clay mineral-bearing Glen Torridon region for 1 Martian year between January 2019 and January 2021, including a short campaign onto the Greenheugh pediment. The Glen Torridon campaign sought to characterize the geology of the area, seek evidence of habitable environments, and document the onset of a potentially global climatic transition during the Hesperian era. Curiosity roved 5km in total throughout Glen Torridon, from the Vera Rubin ridge to the northern margin of the Greenheugh pediment. Curiosity acquired samples from 11 drill holes during this campaign and conducted the first Martian thermochemolytic-based organics detection experiment with the Sample Analysis at Mars instrument suite. The lowest elevations within Glen Torridon represent a continuation of lacustrine Murray formation deposits, but overlying widespread cross bedded sandstones indicate an interval of more energetic fluvial environments and prompted the definition of a new stratigraphic formation in the Mount Sharp group called the Carolyn Shoemaker formation. Glen Torridon hosts abundant phyllosilicates yet remains compositionally and mineralogically comparable to the rest of the Mount Sharp group. Glen Torridon samples have a great diversity and abundance of sulfur-bearing organic molecules, which are consistent with the presence of ancient refractory organic matter. The Glen Torridon region experienced heterogeneous diagenesis, with the most striking alteration occurring just below the Siccar Point unconformity at the Greenheugh pediment. Results from the pediment campaign show that the capping sandstone formed within the Stimson Hesperian aeolian sand sea that experienced seasonal variations in wind direction.

A free and open-source solution for Rietveld refinement of XRD data from the CheMin instrument onboard the Mars rover Curiosity

The Rietveld refinement software Profex is an open-source and platform-independent solution for the processing of powder X-ray diffraction datasets. It is based on the BGMN refinement kernel and uses a description of the diffractometer configuration to determine the instrument-related peak profile. In this article we present a Profex configuration file for the Chemistry and Mineralogy (CheMin) X-ray diffractometer (XRD), which is on-board the Mars Science Laboratory rover Curiosity . For the past decade, Curiosity has been on a mission on Mars to find out whether the planet was once habitable for microbial life. The CheMin XRD determines the mineralogical phases and abundances of Martian soil and rocks in Gale Crater, Mars. Since its arrival on Mars in 2012, Curiosity has analyzed powdered soil and rock samples with the CheMin instrument and transmitting the raw XRD data acquired back to Earth. Adaptations of Profex to work seamlessly with CheMin XRD datasets involved creating a new configuration file for the CheMin instrument, as well as adding the Mars Mineral Compendium, a compilation of structural models specifically selected for the analysis of Mars sedimentary soil and rock samples, to Profex . Using example refinements, we demonstrate that this software solution is well suited for quantitative analysis of CheMin XRD datasets. • CheMin was sent to Mars on-board the Rover Curiosity to analyze Martian rock and soil samples by XRD. • Profex is a software for the processing of XRD datasets by Rietveld refinement. • We adapted Profex for the refinement of CheMin XRD datasets. • Successful phase identification and quantification with Profex was demonstrated. • Profex is open-source software and runs on all major operating systems.

Elemental composition of manganese- and phosphorus-rich nodules in the Knockfarril Hill member, Gale crater, Mars

The Mars Science Laboratory rover Curiosity encountered nodules rich in manganese and phosphorus while exploring the Knockfarril Hill member of Gale crater on Mars. Deconvolution of X-ray spectroscopy data acquired by the Alpha Particle X-ray Spectrometer (APXS) at the spectral level indicate P2O5 concentrations possibly in excess of 18 wt% and MnO exceeding 8 wt%. The nodules occur intermittently in ∼mm-thick layers concordant with the sedimentary laminae, extending up to ∼10 cm laterally. Calcium sulfate associated with the nodules is interpreted as having precipitated from fluid that infiltrated between the nodule-bearing bedding planes in a separate and subsequent fluid event. Though the Mn- and P-bearing phase(s) was(were) not definitively identified by X-ray diffraction, evolved gas analyses show that the oxidation state of Mn is most likely 2+.

Mars Science Laboratory CheMin Data From the Glen Torridon Region and the Significance of Lake‐Groundwater Interactions in Interpreting Mineralogy and Sedimentary History

AbstractThe Glen Torridon (GT) region in Gale crater, Mars is a region with strong clay mineral signatures inferred from orbital spectroscopy. The CheMin X‐ray diffraction (XRD) instrument onboard the Mars Science Laboratory rover, Curiosity, measured some of the highest clay mineral abundances to date within GT, complementing the orbital detections. GT may also be unique because in the XRD patterns of some samples, CheMin identified new phases, including: (a) Fe‐carbonates, and (b) a phase with a novel peak at 9.2 Å. Fe‐carbonates have been previously suggested from other instruments onboard, but this is the first definitive reporting by CheMin of Fe‐carbonate. This new phase with a 9.2 Å reflection has never been observed in Gale crater and may be a new mineral for Mars, but discrete identification still remains enigmatic because no single phase on Earth is able to account for all of the GT mineralogical, geochemical, and sedimentological constraints. Here, we modeled XRD profiles and propose an interstratified clay mineral, specifically greenalite‐minnesotaite, as a reasonable candidate. The coexistence of Fe‐carbonate and Fe‐rich clay minerals in the GT samples supports a conceptual model of a lacustrine groundwater mixing environment. Groundwater interaction with percolating lake waters in the sediments is common in terrestrial lacustrine settings, and the diffusion of two distinct water bodies within the subsurface can create a geochemical gradient and unique mineral front in the sediments. Ultimately, the proximity to this mixing zone may have controlled the secondary minerals preserved in sedimentary rocks exposed in GT.

Chicxulub-like Gale impact into an ocean/land interface on Mars: An explanation for the formation of Mount Sharp

A geologic investigation of Gale Crater and surrounding terrain was conducted combining orbital data with reported in situ information collected through the Mars Science Laboratory (MSL Curiosity) rover cameras to better explain the anomalous features in and nearby Gale Crater with the primary focus being the formational history of Aeolis Mons, informally named Mount Sharp. Features identified through the orbital- and field-based data collectively can be best explained by an impact into the dichotomy boundary, with the northern half of the target environment being an ocean and water-enriched ignimbrite and the southern half being crustal basement/protolith of Terra Cimmeria (part ocean and part land). Such a spatial association, together with the released impact energy of the resulting ∼154 km-diameter Gale Crater, is similar to the Chicxulub impact crater on Earth in which case the target material being both ocean water and continental crust (i.e., continental shelf underlain by granite-composing continental crust) and the planetary environmental and life conditions being highly altered. This paper presents a working hypothesis, backed by orbital and ground data available thus far, for spatio-temporal events that may have transpired during impact and post-impact to the present. This proposed sequence of events and other working hypotheses will be tested by the ongoing MSL Curiosity investigation as the rover traverses up Mount Sharp.

Active Ground Patterns Near Mars' Equator in the Glen Torridon Region of Gale Crater

AbstractOn Mars, near the equator, much of the terrain in Gale Crater consists of bedrock outcrops separated by relatively smooth, uniform regolith surfaces. In scattered sites, however, distinct patterns—in the form and texture of the ground surface—contrast sharply with the typical terrain and with eolian bedforms. This paper focuses on these diverse, intriguing ground patterns. They include ∼1 to >10 m‐long linear disruptions of uniform regolith surfaces, alignments, and other arrangements of similar‐sized rock fragments and shallow, ∼0.1 m‐wide sandy troughs 1–10 m in length. Similar features were recognized early in the Mars Science Laboratory (MSL) mission, but they received only limited attention until Curiosity, the MSL rover, encountered striking examples in the Glen Torridon region. Herein, the ground patterns are illustrated with rover images. Potential mechanisms are briefly discussed in the context of the bedrock composition and atmospheric conditions documented by Curiosity. The evidence suggests that the patterns are active forms of spontaneous granular organization. It leads to the hypothesis that the patterns arise and develop from miniscule, inferred cyclic expansion and contraction of the bedrock and regolith, likely driven by oscillating transfers of energy and moisture between the atmosphere and the terrain. The hypothesis has significant implications for studies of contemporary processes on Mars on both sides of the atmosphere‐lithosphere interface. The ground patterns, as well as ripples and dunes formed by the wind, constitute remarkable extra‐terrestrial examples of granular self‐organization, complex phenomena well known in diverse systems on Earth.

Highly Accurate Visual Method of Mars Terrain Classification for Rovers Based on Novel Image Features.

It is important for Mars exploration rovers to achieve autonomous and safe mobility over rough terrain. Terrain classification can help rovers to select a safe terrain to traverse and avoid sinking and/or damaging the vehicle. Mars terrains are often classified using visual methods. However, the accuracy of terrain classification has been less than 90% in read operations. A high-accuracy vision-based method for Mars terrain classification is presented in this paper. By analyzing Mars terrain characteristics, novel image features, including multiscale gray gradient-grade features, multiscale edges strength-grade features, multiscale frequency-domain mean amplitude features, multiscale spectrum symmetry features, and multiscale spectrum amplitude-moment features, are proposed that are specifically targeted for terrain classification. Three classifiers, K-nearest neighbor (KNN), support vector machine (SVM), and random forests (RF), are adopted to classify the terrain using the proposed features. The Mars image dataset MSLNet that was collected by the Mars Science Laboratory (MSL, Curiosity) rover is used to conduct terrain classification experiments. The resolution of Mars images in the dataset is 256 × 256. Experimental results indicate that the RF classifies Mars terrain at the highest level of accuracy of 94.66%.

A primordial atmospheric origin of hydrospheric deuterium enrichment on Mars

The deuterium-to-hydrogen (D/H or 2H/1H) ratio of Martian atmospheric water (∼6× standard mean ocean water, SMOW) is higher than that of known sources, requiring planetary enrichment. A recent measurement by NASA's Mars Science Laboratory rover Curiosity of Hesperian-era (>3 Ga) clays yields a D/H ratio ∼3×SMOW, demonstrating that most of the enrichment occurs early in Mars's history, reinforcing the conclusions of Martian meteorite studies. As on Venus, Mars's D/H enrichment is widely thought to reflect preferential loss to space of 1H (protium) relative to 2H (deuterium), but both the cause and the global environmental context of large and early hydrogen losses remain to be determined. Here, we apply a recent model of primordial atmosphere evolution to Mars, link the magma ocean of the accretion epoch with a subsequent water-ocean epoch, and calculate the behavior of deuterium for comparison with the observed record. In contrast to earlier works that consider Martian D/H fractionation in atmospheres in which hydrogen reservoirs are present exclusively as H2O or H2, here we consider 2-component (H2O-H2) outgassed atmospheres in which both condensing (H2O) and escaping (H2) components – and their interaction – are explicitly calculated. We find that a ≈2-3× hydrospheric deuterium-enrichment is produced rapidly if the Martian magma ocean is chemically reducing at last equilibration with the primordial atmosphere, making H2 and CO the initially dominant species, with minor abundances of H2O and CO2. Reducing gases – in particular H2 – can cause substantial greenhouse warming and prevent a water ocean from freezing immediately after the magma ocean epoch. We find that greenhouse warming due to plausible H2 inventories (pH=21−102 bars) yields surface temperatures high enough (T=s290−560 K) to stabilize a water ocean and produce an early hydrological cycle through which surface water can be circulated. Moreover, the pressure-temperature conditions are high enough to produce ocean-atmosphere H2O-H2 isotopic equilibrium through gas-phase deuterium exchange such that surface H2O strongly concentrates deuterium relative to H2, which preferentially takes up protium and escapes from the primordial atmosphere. The efficient physical separation of deuterium-rich (H2O) and deuterium-poor (H2) species via condensation permits equilibrium isotopic partitioning and early atmospheric escape to be recorded in modern crustal reservoirs. The proposed scenario of primordial H2-CO-rich outgassing and escape suggests significant durations (>Myr) of chemical conditions on the Martian surface conducive to prebiotic chemistry immediately following magma ocean crystallization.

The Aeolian Environment in Glen Torridon, Gale Crater, Mars

AbstractThe Mars Science Laboratory (MSL) rover spent a full martian year exploring the phyllosilicate‐bearing Glen Torridon trough on the flank of Aeolis Mons in Gale crater, enabling in‐depth assessment of aeolian processes. MSL encountered erosional and depositional features recording a long aeolian history. The trough has served as a long‐term conduit for sand transport, probably involving many cycles of sand accumulation and deflation. Rock abrasion textures indicate sand‐driving winds blowing W‐SW (opposite of abrasion textures on the Greenheugh Pediment above the trough floor). Indurated megaripple surfaces with 2–5 mm grains contrast with seasonally active ripples having finer maximum grain sizes, indicating more vigorous saltation in the past. Active ripples display a broad continuum of wavelengths, as well as coarser grains at crests than troughs, consistent with origins as impact ripples. Orientations of a wind streak extending from a large ripple field, and sandy wind tails behind obstacles, indicate sand is driven W‐SW in the current era, approximately along the trough axis. Erosion of drill tailings piles was strongly seasonal, enhanced during late spring and early summer (perihelion). Climate modeling suggests W‐SW sand transport can be attributed to seasonal enhancement of nighttime regional winds entering Gale crater from the N, combined with local katabatic winds flowing down the slopes of Aeolis Mons. However, it is unclear whether sand transport at Glen Torridon is primarily from these wind components combining and acting simultaneously, or occurring in serial at different times of night; field evidence supports both possibilities.

Reconstruction of pH, redox condition, and concentrations of major components in ancient liquid water from the Karasburg member, Murray formation, Gale Crater, Mars

Mars once possessed liquid water on its surface. In investigations of aqueous conditions on early Mars, the Mars Science Laboratory rover Curiosity has provided mineralogical and geochemical data from lacustrine sediments of Gale Crater, site of a former lake. Recently, the top-down method for quantitative reconstruction of the chemical parameters of ancient pore water, based on exchangeable cation compositions in smectite and secondary minerals, was developed and applied to the Yellowknife Bay sediments in Gale Crater. Here we report the application of this method to lacustrine sediment from the Quela drill site in Gale Crater, in the Karasburg member of the Murray formation. The results show that the final pore water to interact with the sediments had the following chemistry: pH = 3.6–5.6, Eh > 0.22 V, molality of Na ({Na}) = 0.14–2.2 mol/kg, {K} = 0.0080–0.31 mol/kg, {Ca} = 0.021–0.21 mol/kg, {Mg} < 0.14 mol/kg, {Fe(II)} < 0.063 mol/kg, {Cl} = 0.096–2.6 mol/kg and {SO4} = 0.048–0.33 mol/kg. At two adjacent drill sites (Marimba and Sebina), the comparable mineral assemblages and smectite interlayer compositions imply that they have water chemistry similar to that of the Quela sediment. The inferred pore water was undersaturated with respect to halite by an order of magnitude, although the sediment contains halite. This suggests that the final water in the Quela sediment disappeared by freezing and sublimation rather than evaporation. One interpretation of the high Na and Cl concentrations of the final pore water at Quela is that the sediment was deposited in an arid climate at around 3.5 Ga. The high salinity of the final pore water at Quela relative to that at Yellowknife Bay suggests that climate may have shifted from semi-arid when the Yellowknife Bay formation was deposited to arid when the Karasburg member was deposited. Alternatively, the high salinity at Quela suggests that the post-depositional fluids at 2–3 Ga was enriched in Na. In contrast to low Na in the post-depositional fluids in the underlying Yellowknife Bay, the high salinity of the post-depositional fluids of the Quela suggests different origin and/or timing of the re-wetting events between these two sites. The acidic pH and high Eh suggest that the Quela sediment was intensively affected by oxidizing and acidic post-depositional fluids. The pH of the final pore water would not have allowed the preservation of Ca and Mg carbonates under attainable CO2 partial pressures, which is consistent with the scenario of carbonate dissolution by acidic post-depositional fluids on Mars.

Characteristics of convective vortices and dust devils at gale crater on Mars during MY33

Convective vortices that are dust laden (dust devils), are believed to be an efficient mechanism for particle entrainment in the Martian atmosphere. Such vortices can be identified in-situ by landers or rovers by the reduced surface pressure when they pass by the instrument. We analyse data from the Rover Environmental Monitoring Station (REMS) on-board the Mars Science Laboratory (MSL) rover Curiosity during mission sols 1019 to 1686 (corresponding to Martian Year (MY) 33). We identified 611 short pressure drops that likely indicate the passage of convective vortices in vicinity of the rover. The cumulative power-law analysis of the detected pressure drops suggests a low abundance of stronger pressure drop events at the MSL site as compared to the Pathfinder and Phoenix sites. The reason for this can be attributed to the smaller boundary layer height at Gale crater. The power-law slope is smaller for MY 33 as compared to previous years, suggesting that the dust devil activity also increased inside the Gale crater with the progressing year. Among all vortices detected, 63 vortices (∼10%) also show a simultaneous drop in ultraviolet intensity, which signifies obscuration of sunlight by the dust-laden vortices. A seasonal study for dust devils occurrences based on UV flux data shows an increase in their frequency during the local southern summer season. A majority of our estimated tangential wind velocities are well below the Martian dust lifting threshold. This indicates that either the vortices passed far from the measuring instrument or that the threshold being used is higher than the actual threshold on Mars.