Mars Science Laboratory Research Articles

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%.

An immersed interface methodology for simulating supersonic spacecraft parachutes with fluid–structure interaction

The capability of a computational fluid–structure interaction method for simulating thin shell structures with an immersed boundary method and a nonlinear structural dynamics solver is extended in order to simulate supersonic spacecraft parachutes. Methodologies for the representation and motion tracking of thin, sub-grid resolution, thickness Lagrangian geometries in a static Eulerian background mesh are presented in detail. Logical functions for constructing reliable near-wall finite difference operators in the presence of thin geometries and trapped/concave volumes of space are presented. The Darcy–Forchheimer momentum equation is solved as a jump condition at the immersed interface in order to model the porosity of parachute broadcloth. A parallel contact identification and enforcement strategy based on first principles is introduced and validated. The coupled method is then used to simulate wind tunnel experiments conducted to support the Mars Science Laboratory (MSL) mission. In these experiments, a sub-scale MSL disk-gap-band parachute is inflated in a range of Mach numbers and dynamic pressures. The computational method shows good agreement with the experimental data, and where available, other simulation and empirical data, in terms of the opening load magnitude at various Mach numbers and the sustained aerodynamic performance measured by the coefficient of drag. Following quantitative comparison, a qualitative analysis is performed to investigate the effect of freestream Mach number, material porosity, and the bluff upstream payload on the main flow features.

Oxidized and Reduced Sulfur Observed by the Sample Analysis at Mars (SAM) Instrument Suite on the Curiosity Rover Within the Glen Torridon Region at Gale Crater, Mars

AbstractThe Mars Science Laboratory (MSL) Curiosity rover has been assessing the habitability and geologic history of Gale crater, Mars since landing in 2012. One of the primary objectives of the mission was to investigate a clay‐bearing unit identified using orbital spectral data, designated the Glen Torridon (GT) region. This region was of particular interest because of its elevated abundance of clay minerals that may have preserved geochemical evidence of ancient habitable environments. The Curiosity rover explored the GT region for ∼750 sols and analyzed eight drilled samples with the Sample Analysis at Mars (SAM) instrument suite using evolved gas analysis‐mass spectrometry. Evolved sulfur‐bearing gases provided insight about the composition of sulfur‐containing compounds in Martian samples. Evolved gases were analyzed by three methods to understand the oxidation state of sulfur in the samples: (a) SO2 evolution temperature, (b) quadratic discriminant analysis comparing SAM data to SAM‐like laboratory investigations, and (c) sulfur isotope values from evolved 34SO2/32SO2. The results of these three methods were consistent with the majority of sulfur in the GT region being in an oxidized state, but two of the eight samples analyzed by SAM were consistent with the presence of small amounts of reduced sulfur. The oxidized and reduced sulfur could have a variety of sources and represents a nonequilibrium assemblage that could have supported putative ancient chemolithotrophic metabolisms.

From Lake to River: Documenting an Environmental Transition Across the Jura/Knockfarril Hill Members Boundary in the Glen Torridon Region of Gale Crater (Mars).

Between January 2019 and January 2021, the Mars Science Laboratory team explored the Glen Torridon (GT) region in Gale crater (Mars), known for its orbital detection of clay minerals. Mastcam, Mars Hand Lens Imager, and ChemCam data are used in an integrated sedimentological and geochemical study to characterize the Jura member of the upper Murray formation and the Knockfarril Hill member of the overlying Carolyn Shoemaker formation in northern GT. The studied strata show a progressive transition represented by interfingering beds of fine‐grained, recessive mudstones of the Jura member and coarser‐grained, cross‐stratified sandstones attributed to the Knockfarril Hill member. Whereas the former are interpreted as lacustrine deposits, the latter are interpreted as predominantly fluvial deposits. The geochemical composition seen by the ChemCam instrument show K2O‐rich mudstones (∼1–2 wt.%) versus MgO‐rich sandstones (>6 wt.%), relative to the average composition of the underlying Murray formation. We document consistent sedimentary and geochemical data sets showing that low‐energy mudstones of the Jura member are associated with the K‐rich endmember, and that high‐energy cross‐stratified sandstones of the Knockfarril Hill member are associated with the Mg‐rich endmember, regardless of stratigraphic position. The Jura to Knockfarril Hill transition therefore marks a significant paleoenvironmental change, where a long‐lived and comparatively quiescent lacustrine setting progressively changes into a more energetic fluvial setting, as a consequence of shoreline regression due to either increased sediment supply or lake‐level drop.

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.

Spectral Diversity of Rocks and Soils in Mastcam Observations Along the Curiosity Rover's Traverse in Gale Crater, Mars

AbstractThe Mars Science Laboratory Curiosity rover has explored over 400 m of vertical stratigraphy within Gale crater to date. These fluvio‐deltaic, lacustrine, and aeolian strata have been well‐documented by Curiosity's in situ and remote science instruments, including the Mast Camera (Mastcam) pair of multispectral imagers. Mastcam visible to near‐infrared spectra can broadly distinguish between iron phases and oxidation states, and in combination with chemical data from other instruments, Mastcam spectra can help constrain mineralogy, depositional origin, and diagenesis. However, no traverse‐scale analysis of Mastcam multispectral data has yet been performed. We compiled a database of Mastcam spectra from >600 multispectral observations and quantified spectral variations across Curiosity's traverse through Vera Rubin ridge (sols 0–2302). From principal component analysis and an examination of spectral parameters, we identified nine rock spectral classes and five soil spectral classes. Rock classes are dominated by spectral differences attributed to hematite and other oxides (due to variations in grain size, composition, and abundance) and are mostly confined to specific stratigraphic members. Soil classes fall along a mixing line between soil spectra dominated by fine‐grained Fe‐oxides and those dominated by olivine‐bearing sands. By comparing trends in soil versus rock spectra, we find that locally derived sediments are not significantly contributing to the spectra of soils. Rather, varying contributions of dark, mafic sands from the active Bagnold Dune field is the primary spectral characteristic of soils. These spectral classes and their trends with stratigraphy provide a basis for comparison in Curiosity's ongoing exploration of Gale crater.

Detection of Organic Carbon in Mars‐Analog Paleosols With Thermal and Evolved Gas Analysis

AbstractAncient, buried soils, or paleosols, may have been preserved in the geological record on Mars, and are considered high‐priority targets for biosignature investigation. Studies of paleosols on Earth that are similar in composition to putative martian paleosols can provide a reference frame for constraining their organic preservation potential on Mars. However, terrestrial paleosols typically preserve only trace amounts of organic carbon, and determining what carbon is original is complicated by diagenesis and additions of modern carbon. The objectives of this study were (a) to determine whether organic carbon in Mars‐analog paleosols can be detected with thermal and evolved gas analysis, and (b) constrain the age of organic carbon using radiocarbon (14C) dating. Oligocene (33 Ma) paleosols from Oregon were examined with an instrument similar to the Sample Analysis at Mars Evolved Gas Analysis instrument onboard the Mars Science Laboratory Curiosity rover. Trace amounts of organic carbon and fragments of organic molecules were observed in all samples. Total organic carbon (TOC) ranged from 0.002 to 0.032 ± 0.006 wt. %. The near‐surface horizons of paleosols had significantly higher TOC relative to subsurface layers. Radiocarbon dating of four samples revealed an organic carbon age of ∼6,200–14,500 years before present and a fraction modern ranging from 0.16 to 0.46. Modeled abundances of modern carbon in bulk samples ranged from 0.41%–3.1% ± 0.11%, which were consistent with additions of small amounts of modern organic carbon. This work demonstrates that martian paleosols are a potential high priority location for in‐situ biosignature investigation.

The annual cycle of water vapor above gale crater as retrieved by CRISM and compared to ChemCam passive sky spectroscopy

Using spectra returned from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter (MRO), we report atmospheric water vapor column abundances at a spatial resolution of ~ 1 km from observations taken over Gale crater, the landing site of the Mars Science Laboratory (MSL). The observations span a little more than 3 Mars years (MY) from MY 28 at Ls = 116° (October 04, 2006) to MY 31 at Ls = 101° (April 24, 2012). The retrievals were performed using an improved algorithm to correct for the changes in wavelength in the cross-track direction of CRISM images, also known as the “spectral smile”, allowing for a larger fraction of area from each observation to be covered. The water vapor column abundances are retrieved using the strong absorption band of H2O centered at 2600 nm. The seasonal cycle of water vapor above Gale is compared against that from reprocessed and new MSL Curiosity rover ChemCam passive sky observations using updated gas absorption parameters and covering the period between MY 31 at Ls = 291° (March 30, 2013) and MY 35 at Ls = 42° (June 20, 2019). The retrieved annual variation of water vapor from CRISM and ChemCam both display a similar trend with respect to the timing of the maximum and minimum in water abundance, with only minor differences caused by the interannual differences in water vapor and the different retrieval approaches between both instruments, addressing a previously existing discrepancy between ChemCam and CRISM water vapor column abundances.

Pre- and Post-entry, Descent and Landing Assessment of the Martian Atmosphere for the Mars 2020 Rover

This review provides an analysis of activities undertaken by the Mars 2020 Council of Atmospheres (CoA) in support of the entry, descent, and landing (EDL) of the Mars 2020 rover Perseverance in Jezero crater, Mars. The activities of the CoA were designed to evaluate the safety of early-stage landing site candidates and, later, to constrain the range of plausible conditions expected at Jezero crater during the early northern spring season of EDL, following the successful blueprint of similar councils for prior landed Mars missions. The multiyear effort of the CoA involved using a combination of numerical modeling of the local Martian atmosphere with limited-domain mesoscale models and atmospheric reanalysis using data assimilation techniques, along with atmospheric observations from multiple orbiting assets, to generate an atmospheric “forecast” for the day of landing. Here we present an overview of these activities, focusing in greater detail on those elements that depart from prior CoA activities as performed for Mars Phoenix, Mars Science Laboratory, and the InSight lander. Following the successful landing of Perseverance on 2021 February 18, reconstruction and reassessment activities were performed and are presented here, comparing prelanding predictions with actual, as-flown conditions.

Optimizing ExoMars Rover Remote Sensing Multispectral Science: Cross‐Rover Comparison Using Laboratory and Orbital Data

AbstractMultispectral imaging instruments have been core payload components of Mars lander and rover missions for several decades. In order to place into context the future performance of the ExoMars Rosalind Franklin rover, we have carried out a detailed analysis of the spectral performance of three visible and near‐infrared (VNIR) multispectral instruments. We have determined the root mean square error (RMSE) between the expected multispectral sampling of the instruments and high‐resolution spectral reflectance data, using both laboratory spectral libraries and Mars orbital hyperspectral data. ExoMars Panoramic Camera (PanCam) and Mars2020 Perseverance Mastcam‐Z instruments have similar values of RMSE, and are consistently lower than for Mars Science Laboratory Mastcam, across both laboratory and orbital remote sensing data sets. The performance across mineral groups is similar across all instruments, with the lowest RMSE values for hematite, basalt, and basaltic soil. Minerals with broader, or absent, absorption features in these visible wavelengths, such as olivine, saponite, and vermiculite have overall larger RMSE values. Instrument RMSE as a function of filter wavelength and bandwidth suggests that spectral parameters that use shorter wavelengths are likely to perform better. Our simulations of the spectral performance of the PanCam instrument will allow the future use of targeted filter selection during ExoMars 2022 Rosalind Franklin operations on Mars.

Orbital and In-Situ Investigation of Periodic Bedrock Ridges in Glen Torridon, Gale Crater, Mars.

Gale crater, the field site for NASA's Mars Science Laboratory Curiosity rover, contains a diverse and extensive record of aeolian deposition and erosion. This study focuses on a series of regularly spaced, curvilinear, and sometimes branching bedrock ridges that occur within the Glen Torridon region on the lower northwest flank of Aeolis Mons, the central mound within Gale crater. During Curiosity's exploration of Glen Torridon between sols ∼2300–3080, the rover drove through this field of ridges, providing the opportunity for in situ observation of these features. This study uses orbiter and rover data to characterize ridge morphology, spatial distribution, compositional and material properties, and association with other aeolian features in the area. Based on these observations, we find that the Glen Torridon ridges are consistent with an origin as wind‐eroded bedrock ridges, carved during the exhumation of Mount Sharp. Erosional features like the Glen Torridon ridges observed elsewhere on Mars, termed periodic bedrock ridges (PBRs), have been interpreted to form transverse to the dominant wind direction. The size and morphology of the Glen Torridon PBRs are consistent with transverse formative winds, but the orientation of nearby aeolian bedforms and bedrock erosional features raise the possibility of PBR formation by a net northeasterly wind regime. Although several formation models for the Glen Torridon PBRs are still under consideration, and questions persist about the nature of PBR‐forming paleowinds, the presence of PBRs at this site provides important constraints on the depositional and erosional history of Gale crater.

InSight Pressure Data Recalibration, and Its Application to the Study of Long-Term Pressure Changes on Mars.

Observations of the South Polar Residual Cap suggest a possible erosion of the cap, leading to an increase of the global mass of the atmosphere. We test this assumption by making the first comparison between Viking 1 and InSight surface pressure data, which were recorded 40 years apart. Such a comparison also allows us to determine changes in the dynamics of the seasonal ice caps between these two periods. To do so, we first had to recalibrate the InSight pressure data because of their unexpected sensitivity to the sensor temperature. Then, we had to design a procedure to compare distant pressure measurements. We propose two surface pressure interpolation methods at the local and global scale to do the comparison. The comparison of Viking and InSight seasonal surface pressure variations does not show changes larger than ±8 Pa in the CO2 cycle. Such conclusions are supported by an analysis of Mars Science Laboratory (MSL) pressure data. Further comparisons with images of the south seasonal cap taken by the Viking 2 orbiter and MARCI camera do not display significant changes in the dynamics of this cap over a 40 year period. Only a possible larger extension of the North Cap after the global storm of MY 34 is observed, but the physical mechanisms behind this anomaly are not well determined. Finally, the first comparison of MSL and InSight pressure data suggests a pressure deficit at Gale crater during southern summer, possibly resulting from a large presence of dust suspended within the crater.

Crystallinity effects on the vibrational spectral features of saponite: Implications for characterizing variable crystalline phyllosilicates on Mars

X-ray diffraction patterns of Martian mudstones acquired by Chemistry & Mineralogy X-Ray Diffraction (CheMin) aboard Mars Science Laboratory (MSL) suggest that the smectites detected in Gale crater have poor crystallinity. This finding poses an urgent question about the structural ordering of phyllosilicates found globally by Visible/Near-Infrared (VIS-NIR) spectroscopic orbital remote sensing on Mars, linked to their formation conditions. In this study, we synthesized saponite (Nz+x/z[M6][Si8-xAlx]O20(OH)4·nH2O, where M and N correspond to the divalent octahedral cations and the interlayer cations, respectively) with variable crystallinity, which bear structural similarities to the smectite discovered at Gale crater. Synthetic saponite was characterized using Field Emission Scanning Electron Microscopy (FE-SEM), powder X-ray diffraction (XRD), then studied the spectral features of these samples using nuclear magnetic resonance spectroscopy (NMR), Raman spectroscopy, and VIS-NIR reflectance spectroscopy. Our study revealed that the crystallinity of these saponite samples increased (as shown in the FWHM of XRD (060) peak), and is accompanied by (1) improved T-O-T layer stacking along the c axis (specified by the intensity and width of the XRD (001) peak); (2) increased uniformity of the SiO4 unit in tetrahedral sheets (based on the peak widths of Raman spectra and the well-resolved 29Si NMR peaks); (3) improved regularity in the distribution of Mg2+ in octahedral sites and thus the regularity of metal-OH bonds in octahedral sheet (based on the resolution of the NIR 2.2–2.4 μm band and the peak width of the XRD (060,330) peak); and (4) the increased Al in tetrahedral sites and decrease of Al in octahedral sites (the width of 27Al NMR peak), the crystallinity of saponite raised. Based on experimental observations, the first derivative spectra of metal-OH absorptions were proposed as a crystallinity index for smectite on Mars. Our results indicate that different vibration spectroscopy techniques can constrain the structural ordering of smectite on Mars and provide insight into their formation conditions.

PREDICTION OF MARS METEOROLOGICAL VARIABLES USING ARTIFICIAL NEURAL NETWORKS

ABSTRACT Weather forecasting is the task of determining future states of the atmosphere for a given location and time. The techniques to carry out the prediction range from deterministic approaches using complex fluid dynamics models to data-driven approaches using artificial intelligence. While the former is mainly focused on the creation of General Circulation Models, the later are starting to replace them in many situations for Earth’s meteorology and astrophysics. Here, we develop an artificial neural network to perform Mars’ weather forecasting using environmental measurements from the Vikings and Mars Science Laboratory missions. The methodology followed in of this study is a data-driven approach; we make use of computer science expertise which has been long applied to Earth, but not on Mars yet. To do so, we create an artificial neuronal network that predicts the meteorological conditions of the following day using the previous day as input. We show that temperature and pressure are among the most important variables, and that ANN can perform with a 0.5 to 1% accuracy in forecasting diurnal changes in the selected variables. Keywords: ANN, Mars, Weather, Forecast, Curiosity

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.

Diurnal Variability in Aeolian Sediment Transport at Gale Crater, Mars

AbstractA suite of high resolution cameras onboard the Mars Science Laboratory (MSL) Curiosity rover have provided an unparalleled look at active aeolian processes on Mars, including within the first active dune field explored on another planet, the Bagnold Dunes. Here we present results from a subset of MSL's repeat imaging (“change detection”) experiments with temporal resolutions sufficient to probe the diurnal variability in winds within Gale crater. Images reveal that saltation is a near‐daily phenomenon during southern summer, with repeatable diurnal circulation patterns producing steady impact ripple migration toward the west/southwest. Nighttime fluxes are inferred to be ∼four times larger than daytime fluxes, consistent with predictions from the MarsWRF model of multiple periods of enhanced wind between sunset and sunrise. Multiple factors are likely facilitating saltation at this time: (a) time‐averaged nighttime winds have a higher degree of variance (i.e., higher peak friction speeds) than daytime winds, (b) interactions between regional Hadley flows and local, thermally driven slope winds cause increased turbulence at night, and (c) relatively higher atmospheric density produces correspondingly higher shear stresses and decreases critical thresholds. Observations of sand transport at a range of spatiotemporal scales (down to scale of individual particles moving on the timescale of seconds) support the idea that bedform migration is driven by intermittent, low‐flux saltation events when winds fluctuate between canonical impact and fluid thresholds. Yet, whereas gustiness may play a role in initiating transport, saltation is found to be highly predictable on diurnal timescales and is only stochastic on the shortest timescales characteristic of turbulent fluctuations in wind.

Surface energy budget at Curiosity through observations and column modeling

Diurnal ground surface temperatures (Tg) and the five major terms of the surface energy budget (SEB) are displayed from hourly Mars Science Laboratory observations and from column model simulations in four contrasting cases along the Curiosity traverse. Tg and the SEB terms are otherwise well simulated on regolith near the landing spot and on rocky Pahrump Hills, but the residual in observation-based SEB (~downwelling longwave radiation) shows unexplained peaks in the morning and evening and simultaneously model-Tg is too cold. Enhanced or diurnally variable crater dust does not help but diurnally variable soil thermal inertia (suggested by Fourier analysis of observed Tg) reduces both defects at both sites. Sand on the steep Namib dune is instead homogeneous, defects here being reduced by taking into account slope effects. Regolith at the 2018 dust storm site appears inhomogeneous, with the SEB terms and Tg relatively well simulated even in this case of extremely heavy dust load.