Spherical Fe-oxide concretions have been recognized in both terrestrial and Martian strata and are thought to record a variety of past environmental and alteration conditions. This paper presents a ...comprehensive review of the occurrence and elemental composition of spherical Fe-oxide concretions on Earth and Mars and their proposed mechanisms of formation. On the basis of geological evidence from Utah and Mongolia, Fe-oxide concretions are considered to form by pH-buffering reactions between Fe-rich acidic water and precursor calcite concretions. By comparing the characteristics of hematite spherules in Meridiani Planum and spherical nodules in Gale Crater, we propose that Martian concretions may also have been formed by interaction between pre-existing carbonates and sulfuric acidic water that infiltrated the rocks early in Martian history. The abundant hematite spherules in Meridiani Planum and spherical nodules in Gale Crater can be considered as relicts of the widespread deposition of carbonate that occurred during the late Noachian-early Hesperian (c. 3.8 to 3.7 Ga) and its dissolution during the late Hesperian (c. 3.5 to 3.2 Ga).
The mineralogical and elemental compositions of the martian soil are indicators of chemical and physical weathering processes. Using data from the Mars Exploration Rovers, we show that bright dust ...deposits on opposite sides of the planet are part of a global unit and not dominated by the composition of local rocks. Dark soil deposits at both sites have similar basaltic mineralogies, and could reflect either a global component or the general similarity in the compositions of the rocks from which they were derived. Increased levels of bromine are consistent with mobilization of soluble salts by thin films of liquid water, but the presence of olivine in analysed soil samples indicates that the extent of aqueous alteration of soils has been limited. Nickel abundances are enhanced at the immediate surface and indicate that the upper few millimetres of soil could contain up to one per cent meteoritic material.
Observations of fresh impact craters by the Opportunity rover and in high‐resolution orbital images constrain the latest phase of granule ripple migration at Meridiani Planum to have occurred between ...∼50 ka and ∼200 ka. Opportunity explored the fresh Resolution crater cluster and Concepción crater that are superposed on and thus younger than the ripples. These fresh craters have small dark pebbles scattered across their surfaces, which are most likely fragments of the impactor, suggesting that the dark pebbles and cobbles observed by Opportunity at Meridiani Planum are a lag of impactor‐derived material (either meteoritic or secondary impactors from elsewhere on Mars). Two larger, fresh‐rayed craters in Meridiani Planum bracket ripple migration; secondaries from Ada crater are clearly superposed on and secondaries from an unnamed 0.84 km diameter crater have been modified and overprinted by the ripples. Three methods were used to estimate the age of these craters and thus when the latest phase of ripple migration occurred. The inactivity of the ripples over the past ∼50 ka at Meridiani is also consistent with other evidence for the stability of the ripples, the lack of observed eolian bed forms in craters that formed in the past 20 years, and little evidence for much dune motion in the past 30 yr on Mars. Observations of crater morphology and their interaction with the ripples allow the development of a general time scale for craters in Meridiani Planum over the past million years.
Tectonic Implications of Mars Crustal Magnetism Connerney, J. E. P.; Acuña, M. H.; Ness, N. F. ...
Proceedings of the National Academy of Sciences - PNAS,
10/2005, Letnik:
102, Številka:
42
Journal Article
Recenzirano
Odprti dostop
Mars currently has no global magnetic field of internal origin but must have had one in the past when the crust acquired intense magnetization, presumably by cooling in the presence of an Earth-like ...magnetic field (thermoremanent magnetization). A new map of the magnetic field of Mars, compiled by using measurements acquired at an ≈400-km mapping altitude by the Mars Global Surveyor spacecraft, is presented here. The increased spatial resolution and sensitivity of this map provide new insight into the origin and evolution of the Mars crust. Variations in the crustal magnetic field appear in association with major faults, some previously identified in imagery and topography (Cerberus Rupes and Valles Marineris). Two parallel great faults are identified in Terra Meridiani by offset magnetic field contours. They appear similar to transform faults that occur in oceanic crust on Earth, and support the notion that the Mars crust formed during an early era of plate tectonics.
The Mars Exploration Rover Opportunity touched down at Meridiani Planum in January 2004 and since then has been conducting observations with the Athena science payload. The rover has traversed more ...than 5 km, carrying out the first outcrop‐scale investigation of sedimentary rocks on Mars. The rocks of Meridiani Planum are sandstones formed by eolian and aqueous reworking of sand grains that are composed of mixed fine‐grained siliciclastics and sulfates. The siliciclastic fraction was produced by chemical alteration of a precursor basalt. The sulfates are dominantly Mg‐sulfates and also include Ca‐sulfates and jarosite. The stratigraphic section observed to date is dominated by eolian bedforms, with subaqueous current ripples exposed near the top of the section. After deposition, interaction with groundwater produced a range of diagenetic features, notably the hematite‐rich concretions known as “blueberries.” The bedrock at Meridiani is highly friable and has undergone substantial erosion by wind‐transported basaltic sand. This sand, along with concretions and concretion fragments eroded from the rock, makes up a soil cover that thinly and discontinuously buries the bedrock. The soil surface exhibits both ancient and active wind ripples that record past and present wind directions. Loose rocks on the soil surface are rare and include both impact ejecta and meteorites. While Opportunity's results show that liquid water was once present at Meridiani Planum below and occasionally at the surface, the environmental conditions recorded were dominantly arid, acidic, and oxidizing and would have posed some significant challenges to the origin of life.
Phyllosilicates have been identified on the Martian surface from orbit, and are hypothesized to have formed under wet, non‐acidic conditions early in the planet's history. Exposures of these minerals ...have not yet been examined by a landed mission. Using Mars Reconnaissance Orbiter data, we report the detection of phyllosilicate‐bearing outcrops that may be accessible by the Mars Exploration Rover Opportunity currently exploring Meridiani Planum. The phyllosilicates are associated with layered, polygonally fractured rocks exposed in the rim of the 20 km diameter crater Endeavour. These rocks may have formed via regional or global‐scale processes of aqueous alteration that predated the period of acid sulfate formation recorded in the rocks that Opportunity has studied to date. Detailed characterization by Opportunity could better constrain the conditions under which these phyllosilicates formed. Hydrated sulfates are also detected from orbit in the plains adjacent to Endeavour's rim, providing the first opportunity for ground truth of these detections.
The martian surface is a natural laboratory for testing our understanding of the physics of aeolian (wind-related) processes in an environment different from that of Earth. Martian surface markings ...and atmospheric opacity are time-variable, indicating that fine particles at the surface are mobilized regularly by wind. Regolith (unconsolidated surface material) at the Mars Exploration Rover Opportunity's landing site has been affected greatly by wind, which has created and reoriented bedforms, sorted grains, and eroded bedrock. Aeolian features here preserve a unique record of changing wind direction and wind strength. Here we present an in situ examination of a martian bright wind streak, which provides evidence consistent with a previously proposed formational model for such features. We also show that a widely used criterion for distinguishing between aeolian saltation- and suspension-dominated grain behaviour is different on Mars, and that estimated wind friction speeds between 2 and 3 m s-1, most recently from the northwest, are associated with recent global dust storms, providing ground truth for climate model predictions.
The Miniature Thermal Emission Spectrometer (Mini-TES) on Opportunity investigated the mineral abundances and compositions of outcrops, rocks, and soils at Meridiani Planum. Coarse crystalline ...hematite and olivine-rich basaltic sands were observed as predicted from orbital TES spectroscopy. Outcrops of aqueous origin are composed of 15 to 35% by volume magnesium and calcium sulfates a high-silica component modeled as a combination of glass, feldspar, and sheet silicates (~20 to 30%), and hematite; only minor jarosite is identified in Mini-TES spectra. Mini-TES spectra show only a hematite signature in the millimeter-sized spherules. Basaltic materials have more plagioclase than pyroxene, contain olivine, and are similar in inferred mineral composition to basalt mapped from orbit. Bounce rock is dominated by clinopyroxene and is close in inferred mineral composition to the basaltic martian meteorites. Bright wind streak material matches global dust. Waterlain rocks covered by unaltered basaltic sands suggest a change from an aqueous environment to one dominated by physical weathering.
The present article proposes an approach to analyze the photometric properties of the surface materials from multi‐angle observations acquired by the Compact Reconnaissance Imaging Spectrometer for ...Mars (CRISM) on‐board the Mars Reconnaissance Orbiter. We estimate photometric parameters using Hapke's model in a Bayesian inversion framework. This work also represents a validation of the atmospheric correction provided by the Multi‐angle Approach for Retrieval of Surface Reflectance from CRISM Observations (MARS‐ReCO) proposed in the companion article. The latter algorithm retrieves photometric curves of surface materials in reflectance units after removing the aerosol contribution. This validation is done by comparing the estimated photometric parameters to those obtained from in situ measurements by Panoramic Camera instrument at the Mars Exploration Rover (MER) Spirit and MER Opportunity landing sites. Consistent photometric parameters with those from in situ measurements are found, demonstrating that MARS‐ReCO gives access to accurate surface reflectance. Moreover, the assumption of a non‐Lambertian surface as included in MARS‐ReCO is shown to be significantly more precise to estimate surface photometric properties from space in comparison to methods based on a Lambertian surface assumption. In the future, the presented method will allow us to map from orbit the surface bidirectional reflectance and the related photometric parameters in order to characterize the Martian surface.
Key PointsThe surface photometric properties were estimated from CRISM multi‐angle imagesValidation of atmospheric correction provided by MARS‐ReCOConsistency with in situ photometric parameters
•A clay-bearing layer is detected within the sulfate-rich deposits of Meridiani Planum.•Landscape formation such as karst emplacement seems mineralogy-driven.•The regional mineralogy and geology is ...best explained by surficial and groundwater processes.
The area of Meridiani Planum on Mars became of particular interest after the detection of coarse-grained, gray hematite, which led to the choice of this region as final landing site for the Mars Exploration Rover Opportunity. Multiple additional minerals have since been detected in the region, both from orbit and in situ. The present paper reassesses in detail the mineralogy and geomorphology of the area (between 3.5°S to 6.5°N latitude and 8.0°W to 8.0°E longitude) using visible and near-infrared hyperspectral data, merged with high spatial resolution images into a Geographic Information System. Fe/Mg-rich phyllosilicates, as well as several types of sulfates are identified within the kilometer of sedimentary deposits constituting the etched terrains and the overlying hematite-rich plains. The mineralogical stratigraphy of the etched terrains is characterized by a sulfate-rich unit, enriched in Fe/Mg-rich clays in its uppermost part. This clay-rich horizon is capped by another sulfate-rich unit, of different composition, associated with hematite detections and constituting the material of the hematite plains unit. The clay-bearing unit, which directly underlies the hematite plains, may be exposed in the rim of Endeavour Crater and could correspond to the material that is currently being analyzed by Opportunity. Diverse landforms including karsts and pan features are observed at the surface of the hydrated etched terrains and indicate past surface water and potential groundwater aquifers. Our analysis reveals that both surficial water and groundwater processes are required to explain the diversity of morphologies and mineralogies observed in the area. Although orbital detections are consistent with the hematite and sulfate detections made in situ by Opportunity in the hematite plains, they also show the presence of a clay-rich horizon at depth, overlying another, thicker, possibly chemically distinct, sulfate-rich unit within the etched terrains. Therefore we conclude that the very acidic conditions that prevailed during the formation of the topmost sulfate-rich unit, as observed in Meridiani Planum and in the hematite plains by the rover Opportunity, are not representative of the entire history of the etched terrains. In contrast, most hydrated minerals in Meridiani Planum likely formed at more neutral pH, at the beginning of the Hesperian. The overall sulfate/clay/sulfate sequence is similar to the one observed in Gale Crater, the landing site of the Mars Science Laboratory rover.
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