During Martian solar days 57–100, the Mars Science Laboratory Curiosity rover acquired and processed a solid (sediment) sample and analyzed its mineralogy and geochemistry with the Chemistry and ...Mineralogy and Sample Analysis at Mars instruments. An aeolian deposit—herein referred to as the Rocknest sand shadow—was inferred to represent a global average soil composition and selected for study to facilitate integration of analytical results with observations from earlier missions. During first‐time activities, the Mars Hand Lens Imager (MAHLI) was used to support both science and engineering activities related to sample assessment, collection, and delivery. Here we report on MAHLI activities that directly supported sample analysis and provide MAHLI observations regarding the grain‐scale characteristics of the Rocknest sand shadow. MAHLI imaging confirms that the Rocknest sand shadow is one of a family of bimodal aeolian accumulations on Mars—similar to the coarse‐grained ripples interrogated by the Mars Exploration Rovers Spirit and Opportunity—in which a surface veneer of coarse‐grained sediment stabilizes predominantly fine‐grained sediment of the deposit interior. The similarity in grain size distribution of these geographically disparate deposits support the widespread occurrence of bimodal aeolian transport on Mars. We suggest that preservation of bimodal aeolian deposits may be characteristic of regions of active deflation, where winnowing of the fine‐sediment fraction results in a relatively low sediment load and a preferential increase in the coarse‐grained fraction of the sediment load. The compositional similarity of Martian aeolian deposits supports the potential for global redistribution of fine‐grained components, combined with potential local contributions.
Key Points
Curiosity acquired and examined its first solid sample at the Rocknest sand shadow
MAHLI images were critical in the science investigation of Rocknest materials
MAHLI images played a critical role supporting first‐time engineering activities
We assessed dust coverage on the Mars Science Laboratory Mars Hand Lens Imager (MAHLI) and Alpha Particle X-Ray Spectrometer (APXS) calibration targets from 14 MAHLI images acquired at <100 μm/pixel, ...between Mars Science Laboratory Curiosity rover sols 34 and 2248, in order to place constraints on dust accumulation and removal on two endmember orientations (vertical and horizontal). Dust coverage was estimated by (1) determining reflectance ranges for image pixels covered by dust; (2) using the ratio of calibrated MAHLI red band data to blue band data as a proxy for the concentration of dust on the calibration target; and (3) manually counting dust-covered pixels in representative areas of the MAHLI calibration target. The results of each method are consistent within uncertainties, but the reflectance method provided the most efficient and effective way to measure dust cover on each target. Mean and median dust coverage is ~4.7% and 3.9% for the MAHLI target, 9.4% and 8.9% for the APXS target, and 51.9% and 63.4% for the REMS UV sensor. Maximum dust coverage (during the dust storm) is 49% and 42% for the MAHLI and APXS calibration targets respectively, and 80% for the REMS UV sensor. In modeling dust accumulation and removal, the best fit for the MAHLI and APXS targets is one that assumes 2–4% dust removal per sol and 20–40% efficiency in collection, while for the REMS UV sensor, it is one that assumes near 0 removal and 7% of nominal accumulation. Results indicate that the vertically-mounted MAHLI and APXS targets accumulated less dust overall during the mission than horizontally-mounted hardware such as the REMS UV sensor; this was true even during the 2018 global dust event. In addition, while the vertical orientation did not protect the targets from dust deposition during that event, dust removal following the event was more effective on these targets than on horizontally-mounted hardware. Because conditions cannot be monitored continuously, these studies cannot fully discriminate among the potential causes of this dust removal. However, the results suggest that vertical mounting is a reasonable dust mitigation strategy for hardware for which short-term dust accumulation is not a risk factor.
•Three methods give accurate estimates for martian dust coverage.•Horizontal surfaces are subject to mechanisms that deposit but rarely remove dust.•Vertical surfaces are subject to processes that deposit but also remove dust.•Vertical mounting means less dust accumulation long-term.•Such a configuration does not fully protect hardware from dust.
This paper characterizes the detailed sedimentology of a fluvial sandbody on Mars for the first time and interprets its depositional processes and palaeoenvironmental setting. Despite numerous ...orbital observations of fluvial landforms on the surface of Mars, ground‐based characterization of the sedimentology of such fluvial deposits has not previously been possible. Results from the NASA Mars Science Laboratory Curiosity rover provide an opportunity to reconstruct at fine scale the sedimentary architecture and palaeomorphology of a fluvial environment on Mars. This work describes the grain size, texture and sedimentary facies of the Shaler outcrop, reconstructs the bedding architecture, and analyses cross‐stratification to determine palaeocurrents. On the basis of bedset geometry and inclination, grain‐size distribution and bedform migration direction, this study concludes that the Shaler outcrop probably records the accretion of a fluvial barform. The majority of the outcrop consists of large‐scale trough cross‐bedding of coarse sand and granules. Palaeocurrent analyses and bedform reconstruction indicate that the beds were deposited by bedforms that migrated towards the north‐east, across the surface of a bar that migrated south‐east. Stacked cosets of dune cross‐bedding suggest aggradation of multiple bedforms, which provides evidence for short periods of sustained flow during Shaler deposition. However, local evidence for aeolian reworking and the presence of potential desiccation cracks within the outcrop suggest that fluvial deposition may have been intermittent. The uppermost strata at Shaler are distinct in terms of texture and chemistry and are inferred to record deposition from a different sediment dispersal system with a contrasting provenance. The outcrop as a whole is a testament to the availability of liquid water on the surface of Mars in its early history.
The first four rocks examined by the Mars Science Laboratory Alpha Particle X‐ray Spectrometer indicate that Curiosity landed in a lithologically diverse region of Mars. These rocks, collectively ...dubbed the Bradbury assemblage, were studied along an eastward traverse (sols 46–102). Compositions range from Na‐ and Al‐rich mugearite Jake_Matijevic to Fe‐, Mg‐, and Zn‐rich alkali‐rich basalt/hawaiite Bathurst_Inlet and span nearly the entire range in FeO* and MnO of the data sets from previous Martian missions and Martian meteorites. The Bradbury assemblage is also enriched in K and moderately volatile metals (Zn and Ge). These elements do not correlate with Cl or S, suggesting that they are associated with the rocks themselves and not with salt‐rich coatings. Three out of the four Bradbury rocks plot along a line in elemental variation diagrams, suggesting mixing between Al‐rich and Fe‐rich components. ChemCam analyses give insight to their degree of chemical heterogeneity and grain size. Variations in trace elements detected by ChemCam suggest chemical weathering (Li) and concentration in mineral phases (e.g., Rb and Sr in feldspars). We interpret the Bradbury assemblage to be broadly volcanic and/or volcaniclastic, derived either from near the Gale crater rim and transported by the Peace Vallis fan network, or from a local volcanic source within Gale Crater. High Fe and Fe/Mn in Et_Then likely reflect secondary precipitation of Fe3+ oxides as a cement or rind. The K‐rich signature of the Bradbury assemblage, if igneous in origin, may have formed by small degrees of partial melting of metasomatized mantle.
Key Points
Rocks at the MSL landing site are diverse and alkali‐ and volatile metal‐rich.
Three of the first four rocks studied by APXS form a mixing line in element plots.
The alkali‐rich nature reflects an igneous source affected by metasomatism.
At a Mars analog site in Utah, we tested two science operation methods for data acquisition and decision-making protocols: a scenario where the tactical day is preplanned, but major adjustments may ...still be made before plan delivery; and a scenario in which the sol path must largely be planned before a given tactical planning day and very few adjustments to the plan may be made. The goal was to provide field-tested insight into operations planning for rover missions where science operations must facilitate the efficient choice of sampling locations at a site relevant to searching for habitability and biosignatures. Results of the test indicate that preplanning sol paths did not result in a sol cost savings nor did it improve science return or optimal biologically relevant sample collection. In addition because facies variations in an environment can be subtle and evident only at scales below orbital resolution, acquiring systematic observations is crucial. We also noted that while spectral data provided insight into the chemical components as a whole at this site, they did not provide a guide to targets for which the traverse should be altered. Finally, strategic science planning must include a special effort to account for terrain.
During its first year of operation, the Perseverance rover explored the cratered and fractured floor of Jezero crater on Mars. Here, we report the use of the Scanning Habitability Environments with ...Raman and Luminescence for Organics and Chemicals (SHERLOC) imaging system that includes two high-resolution cameras, the Autofocus and Contextual Imager (ACI) and Wide Angle Topographic Sensor for Operations and eNgineering (WATSON). ACI is a fixed focus gray scale imager with a resolution of 10.1 μm/pixel whereas WATSON is a variable field of view, variable focus imager capable of resolution down to 14 μm/pixel. WATSON is a reflight of the MArs Hand Lens Imager (MAHLI) imager and has similar capabilities. During first-time activities, WATSON was used to support both science and engineering operations related to sample and abrasion patch assessment and sample collection and caching. WATSON also documented the deployment of the Ingenuity helicopter. The Crater Floor Campaign identified two primary rock units, the Máaz formation and the Séítah formation, which have been interpreted as lava flows and an olivine cumulate, respectively. Interpretation of rock textures with WATSON and ACI images was limited to abraded surfaces because unmodified outcrop surfaces (herein termed “natural surfaces”) show high degrees of dust covering, wind abrasion, and coating by secondary mineral products. WATSON and ACI images support the hypothesis that the material of both the Máaz and Séítah formations consists of largely aqueously altered mafic materials with varying igneous origins.
The GHOST field tests are designed to isolate and test science-driven rover operations protocols, to determine best practices. During a recent field test at a potential Mars 2020 landing site analog, ...we tested two Mars Science Laboratory data-acquisition and decision-making methods to assess resulting science return and sample quality: a linear method, where sites of interest are studied in the order encountered, and a “walkabout-first” method, where sites of interest are examined remotely before down-selecting to a subset of sites that are interrogated with more resource-intensive instruments. The walkabout method cost less time and fewer resources, while increasing confidence in interpretations. Contextual data critical to evaluating site geology was acquired earlier than for the linear method, and given a higher priority, which resulted in development of more mature hypotheses earlier in the analysis process. Combined, this saved time and energy in the collection of data with more limited spatial coverage. Based on these results, we suggest that the walkabout method be used where doing so would provide early context and time for the science team to develop hypotheses-critical tests; and that in gathering context, coverage may be more important than higher resolution.
•We tested the effectiveness of two rover science protocols.•We compared the walkabout-first and linear approaches to field work.•Walkabout-first saved time and resources.•Walkabout-first provides context early, raising confidence in interpretations.•Walkabout-first improves the ability to efficiently triage sites of interest.
Resonant inelastic x-ray scattering (RIXS) provides remarkable opportunities to interrogate ultrafast dynamics in liquids. Here we use RIXS to study the fundamentally and practically important ...hydroxyl radical in liquid water, OH(aq). Impulsive ionization of pure liquid water produced a short-lived population of OH(aq), which was probed using femtosecond x-rays from an x-ray free-electron laser. We find that RIXS reveals localized electronic transitions that are masked in the ultraviolet absorption spectrum by strong charge-transfer transitions-thus providing a means to investigate the evolving electronic structure and reactivity of the hydroxyl radical in aqueous and heterogeneous environments. First-principles calculations provide interpretation of the main spectral features.
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