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.
Ventifacts, rocks abraded by wind‐borne particles, are found in Gale Crater, Mars. In the eastward drive from “Bradbury Landing” to “Rocknest,” they account for about half of the float and outcrop ...seen by Curiosity's cameras. Many are faceted and exhibit abrasion textures found at a range of scales, from submillimeter lineations to centimeter‐scale facets, scallops, flutes, and grooves. The drive path geometry in the first 100 sols of the mission emphasized the identification of abrasion facets and textures formed by westerly flow. This upwind direction is inconsistent with predictions based on models and the orientation of regional dunes, suggesting that these ventifact features formed from very rare high‐speed winds. The absence of active sand and evidence for deflation in the area indicates that most of the ventifacts are fossil features experiencing little abrasion today.
Key Points
Ventifacts in Gale Crater
May be formed by paleowind
Can see abrasion textures at range of scales
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.
The Desert Research and Technology Studies (D-RATS) field tested two models of human-in-the-loop remote field geology: one based on the Apollo science backroom that integrated tactical and strategic ...decisions, and one that separated tactical and strategic processes as utilized during the Mars Exploration Rovers (MER) and Mars Phoenix Scout missions. The 2010 D-RATS field test was the first attempt at integrating best practices from these two models, to determine how best to maximize science return from future missions.
The Apollo model was utilized in 2008 and 2009 as a way to integrate science into field analog studies; the model allowed for real time communications between the crew on the surface and the scientists in the backroom. This model greatly improved efficiency of field operations and scientific return, but did not allow sufficient time for hypotheses to mature to the point where they could inform operations. The MER/Phoenix model, adapted for the 2010 D-RATS test, divided the responsibilities and processes of tactical science and strategic science. This division provided opportunities to discuss science results in greater detail so that the overall planning of science observations could be iterative rather than static. However, because of the nearly complete separation of the two science teams, there was a great deal of repeated effort as the strategic team had no prior knowledge of the tactical process and the observations that led to certain tactical decisions.
Lessons learned from 2010 D-RATS science operations include: (1) well-trained geologists on the crew and a science backroom with which that crew can interact are both critical components for maximizing science return; (2) sufficient time or another mechanism that increases time available to be spent on science analysis must be built into the system to allow free rein to the scientific process; (3) data flow must be improved so that time is not wasted in repetitive review of acquired datasets; and (4) stable, high-fidelity communication must be available for any science activity where humans are in the loop.
► The D-RATS 2010 field test blended Apollo and MER/Phoenix tactical and strategic processes. ► Geology-trained crew and a science backroom are critical for maximizing science return. ► Sufficient time must be built into the system to allow free rein to the scientific process. ► Data flow must be improved so that time is not wasted in repetitive review of acquired datasets. ► Stable, high-fidelity communication is required for any field science with humans in the loop.
Dawn completes its mission at 4 Vesta Russell, C. T.; Raymond, C. A.; Jaumann, R. ...
Meteoritics & planetary science,
11/2013, Letnik:
48, Številka:
11
Journal Article
Recenzirano
Odprti dostop
The Dawn mission was designed to test our hypothesis about the origin and evolution of the early solar system by visiting the largest differentiated basaltic asteroid, 4 Vesta, believed to be a ...survivor from the earliest times of rocky body formation. Observations from orbit show that Vesta is the parent body of the Howardite, Eucrite, Diogenite meteorites. Vesta has an iron core and a eucritic–diogenitic crust. Its surface is characterized by abundant impact craters but with no evident volcanic features. It has two ancient impact basins in the southern hemisphere that are associated with circum‐planetary troughs. The northern hemisphere is the more heavily cratered and contains the oldest terrains. The surface of Vesta is diverse, with north‐south and east‐west dichotomies in the eucrite‐to‐diogenite ratio. Its surface contains both very bright and very dark material, and its color varies strongly from region to region. Both the mineralogical and the elemental compositions agree with that expected for the HED parent body. Significant OH or H may be present in the upper crust and the presence of pits in “fresh” craters is consistent with the devolatilization of the surface after a collision either brought to or tapped a source of water on Vesta. The presence of dark material on the surface of Vesta suggests efficient transport pathways for organic material, and the mixing of the dark material with the more pristine pyroxene explains the varying albedo across the surface. Vesta has proven to be a reliable witness to the formation of the solar system.
The Murray formation represents fine‐grained sedimentary deposition in lacustrine environments within Gale crater, Mars. Both the overall thickness of the Murray formation and its broad uniformity in ...sedimentary character suggest the potential for a long‐lived, groundwater‐supported lake system. Rock textures were imaged by the Mars Hand Lens Imager camera at the Pahrump Hills location, which represents the lowermost Murray formation. We analyze data from Pahrump Hills to refine earlier estimates of grain size and grain size distribution, as well as to make detailed observations of diagenetic features and modification of primary sedimentological features. These observations and resulting interpretations provide a detailed look at the dynamic behavior of lake systems on Mars. The lower portions of this exposure are characterized by planar laminated, fine‐grained material; the predominant grain size in this region is smaller than that of very fine sand. Diagenetic mineral precipitation is also prominent in these lower layers, evidenced by likely in situ precipitation of lenticular crystals, preferential cementation of laminae in several layers, precipitation of late‐diagenetic crystal clusters, and secondary modification of previously deposited crystals. The upper portions of this locality are coarser‐grained, varicolored, and contain cross‐stratified features. The variation of these features over a relatively thin stratigraphic interval indicates rapid fluctuation in the hydrodynamic behavior of Gale crater lake, similar to that observed in the shallow‐water regions of terrestrial closed basin lakes.
Plain Language Summary
The Murray formation in Gale crater, Mars, is a group of fine‐grained sedimentary rocks that were likely formed in a lake environment, potentially one that was supported by groundwater. We analyzed the many high‐resolution images acquired by the Mars Hand Lens Imager camera at an area called Pahrump Hills to better understand how lakes formed and evolved on Mars. Variation in features such as grain size, mineral precipitation and grain modification reveal a dynamic behavior of the Gale crater lake, similar to that observed in terrestrial closed lake basins.
Key Points
The Murray Formation represents largely lacustrine deposition; pseudomorphic gypsum suggests saline conditions in lower Pahrump Hills
The presence of coarser, detrital sediment in upper Pahrump hills indicates increased freshening associated with fluvial influx
Diagenetic features (preferential cementation, concretions, veins) are variable and indicate multiple alteration episodes
The Mars 2020 Perseverance rover landing site is located within Jezero crater, a
∼
50
km
diameter impact crater interpreted to be a Noachian-aged lake basin inside the western edge of the Isidis ...impact structure. Jezero hosts remnants of a fluvial delta, inlet and outlet valleys, and infill deposits containing diverse carbonate, mafic, and hydrated minerals. Prior to the launch of the Mars 2020 mission, members of the Science Team collaborated to produce a photogeologic map of the Perseverance landing site in Jezero crater. Mapping was performed at a 1:5000 digital map scale using a 25 cm/pixel High Resolution Imaging Science Experiment (HiRISE) orthoimage mosaic base map and a 1 m/pixel HiRISE stereo digital terrain model. Mapped bedrock and surficial units were distinguished by differences in relative brightness, tone, topography, surface texture, and apparent roughness. Mapped bedrock units are generally consistent with those identified in previously published mapping efforts, but this study’s map includes the distribution of surficial deposits and sub-units of the Jezero delta at a higher level of detail than previous studies. This study considers four possible unit correlations to explain the relative age relationships of major units within the map area. Unit correlations include previously published interpretations as well as those that consider more complex interfingering relationships and alternative relative age relationships. The photogeologic map presented here is the foundation for scientific hypothesis development and strategic planning for Perseverance’s exploration of Jezero crater.
A multi‐instrument study of the regolith of Jezero crater floor units by the Perseverance rover has identified three types of regolith: fine‐grained, coarse‐grained, and mixed‐type. Mastcam‐Z, Wide ...Angle Topographic Sensor for Operations and eNgineering, and SuperCam Remote Micro Imager were used to characterize the regolith texture, particle size, and roundedness where possible. Mastcam‐Z multispectral and SuperCam laser‐induced breakdown spectroscopy data were used to constrain the composition of the regolith types. Fine‐grained regolith is found surrounding bedrock and boulders, comprising bedforms, and accumulating on top of rocks in erosional depressions. Spectral and chemical data show it is compositionally consistent with pyroxene and a ferric‐oxide phase. Coarse‐grained regolith consists of 1–2 mm well‐sorted gray grains that are found concentrated around the base of boulders and bedrock, and armoring bedforms. Its chemistry and spectra indicate it is olivine‐bearing, and its spatial distribution and roundedness indicate it has been transported, likely by saltation‐induced creep. Coarse grains share similarities with the olivine grains observed in the Séítah formation bedrock, making that unit a possible source for these grains. Mixed‐type regolith contains fine‐ and coarse‐grained regolith components and larger rock fragments. The rock fragments are texturally and spectrally similar to bedrock within the Máaz and Séítah formations, indicating origins by erosion from those units, although they could also be a lag deposit from erosion of an overlying unit. The fine‐ and coarse‐grained types are compared to their counterparts at other landing sites to inform global, regional, and local inputs to regolith formation within Jezero crater. The regolith characterization presented here informs the regolith sampling efforts underway by Perseverance.
Plain Language Summary
We used multiple instruments on the Perseverance rover to describe three populations of loose sediments found on the floor of Jezero crater by their grain sizes and chemical compositions. The smallest population has grains that are small sand‐sized (80–530 μm) and a mixture of minerals commonly found on Mars, including pyroxene that is present in local rocks and airborne dust found globally. These grains are the easiest to move by wind, so could have distal regional sources as well. Larger gray grains that are 1–2 mm in size and rounded contain olivine. These grains move along the surface, pushed by the impacts of smaller grains that are lifted by the wind. Their size and composition are very similar to olivine grains found in nearby in‐place rocks, indicating that they may have a more local source. Finally, there are larger pieces of rocks that have broken down from the erosion of local in‐place rocks over time and mix with the other types of grains. Loose sediments within the Jezero crater described here can be compared to loose sediments studied at other landing sites on Mars to help understand how Jezero sediments are formed and transported.
Key Points
Textural, spectroscopic, and chemical analyses of regolith in Jezero crater reveal details of fine, coarse, and mixed grain components
Compositional information and physical grain characteristics from those analyses inform transport history and possible source material
Regolith components are compared to their counterparts at other landing sites to inform global versus local inputs to regolith formation
We used MER-derived semi-autonomous rover science operations strategies to determine best practices suitable for remote semi-autonomous lunar rover geology. Two field teams studied two glacial ...moraines as analogs for potential ice-bearing lunar regolith. At each site a Rover Team commanded a human rover to execute observations based on common MER sequences; the resulting data were used to identify and characterize targets of interest. A Tiger Team followed the Rover Team using traditional terrestrial field methods, and the results of the two teams were compared. Narrowly defined goals that can be addressed using cm-scale or coarser resolution may be met sufficiently by the operational strategies adapted from MER survey mode. When reconnaissance is the primary goal, the strategies tested are necessary but not sufficient. Further, there may be a set of optimal observations for such narrowly defined, hypothesis-driven science goals, such that collecting further data would result in diminishing returns. We confirm results of previous tests that indicated systematic observations might improve efficiency during strategic planning, and improve science output during data analysis. This strategy does not markedly improve the rate at which a science team can ingest data to feed back into tactical decision-making. Other methods should be tested to separate the strategic and tactical processes, and to build in time for data analysis.
•We field tested MER-derived rover operations strategies to maximize science return.•Narrowly-defined science goals are addressed sufficiently by the tested strategies.•If reconnaissance is the primary goal, the strategies tested are not sufficient.•There may be a set of observations that optimally meets narrowly-defined goals.
The terrestrial geologist's hand lens is a fundamental tool for identifying and correlating rocks and minerals. We used rover‐inspired methods of remote hand lens–scale data acquisition to conduct ...reconnaissance of a well‐characterized Martian analog field site. The objective was to determine if the current methodologies associated with the use of remote hand lens–scale imagers maximizes science return. Field geologists provided with hand lens–scale images of targets in geologic context could correctly identify many important characteristics of those targets. However, they could not fully confirm or rule out any formation hypothesis using the data provided solely through rover‐driven observational strategies. This was due to (1) a lack of “intermediate‐scale,” or millimeter‐ to centimeter‐scale images providing important contextual information for the targets studied and (2) the limited number of hand lens–scale images that were taken using rover‐driven methodology. We conclude that the benefits of the hand lens as an effective triage tool and discriminator of microtexture are limited using current rover‐driven methodology because the hand lens–type imager is not deployed frequently, and resulting data cannot be used to fully support geochemical observations. We recommend pursuing ways to increase the number of images that can reasonably be acquired at the hand lens scale. In order for hand lens–scale imaging to be fully effective, textural characteristics diagnostic of the nature of a geologic site need to be identifiable at a number of different resolutions; rover microscale observational strategies must include more contextual imaging.
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