The Meridiani Planum region on Mars has extensive sulfate-rich sedimentary deposits (∼20 wt% SO42−) that are hypothesized to have formed from regional groundwater upwelling that led to the ...precipitation of secondary Fe-, Mg-, Ca-sulfate minerals and cementation of basaltic sediments. However, the primary source of sulfur (S) for these abundant secondary sulfate minerals is unclear. Therefore, in this study the contributions of volcanic S via surface water and groundwater were investigated in the terrestrial basaltic analogs of Hawaii and Iceland to determine the importance of active volcanism and climate on S cycling as well as the resulting timescale of aqueous activity in the Meridiani Planum region. SO42− fluxes (contributions) were calculated in metric tons/yr using historical data from online repositories and normalized to the catchment area to determine the SO42− load in metric tons/yr/km2. Our results show that the SO42− load is greatly affected by climate, typically ranging from ∼7.3 to 170 metric tons/yr/km2 under wetter conditions and ∼ 2.6 to 43 metric tons/yr/km2 under dry conditions. Active S degassing and accompanying S-rich mineralization from current hydrothermal activity greatly increased the SO42− loads (∼2.8 to 170 metric tons/yr/km2) compared to non-active catchments (2.6 to 13 metric tons/yr/km2). Younger basaltic bedrock with greater permeability and groundwater-rock interactions was also found to be important, resulting in higher SO42− loads (∼26 to 170 metric tons/yr/km2) compared to older, less permeable catchments (∼2.6 to 12 metric tons/yr/km2). Based on these terrestrial SO42− loads in Hawaii and Iceland, we calculated a range of possible loads and timescales of SO42− transport in Meridiani Planum under variable environmental conditions. Results show that the smallest SO42− loads and longest timescales would occur in Meridiani under dry, non-volcanically active conditions, typically requiring ∼16 to 65 Ma of an active aqueous system, as in the older catchments of Hawaii and Iceland. Conversely, the largest SO42− fluxes and shortest timescales would occur under wet, volcanically active conditions, requiring ∼1.0 to 6.9 Ma, as in the younger catchments of Hawaii and Iceland. Our results suggest that moderately wet conditions with some active hydrothermal S input would be needed to transport and deposit the equivalent mass of SO42− currently present in the sulfate-rich deposits of Meridiani Planum.
•Aqueous processes on basaltic terrains contribute significant amounts of SO42−.•Climate controls aqueous SO42− contributions from volcanic sources.•Larger SO42− fluxes accompany groundwater flows.•Possible timescales of water activity in Meridiani Planum range from ∼16 to 65 Ma.
Mars was warmer and wetter during the early to middle Noachian, before a hydrologic and climatic transition in the late Noachian led to a decrease in erosion rates, a change in valley network ...morphology, and a geochemical shift from phyllosilicate to sulfate formation that culminated in the formation of widespread sulfate‐rich sedimentary deposits in Meridiani Planum and the surrounding Arabia Terra region. This secular evolution was overprinted by episodic and periodic variability, as recorded in the fluvial record, sedimentary layering, and erosional discontinuities. We investigate the temporal evolution of Martian groundwater hydrology during the Noachian and early Hesperian epochs using global‐scale hydrological models. The results suggest that the more active hydrological cycle in the Noachian was a result of a greater total water inventory, causing a saturated near‐surface and high precipitation rates. The late Noachian hydrologic, climatic, and geochemical transition can be explained by a fundamental shift in the hydrological regime driven by a net loss of water due to impact and solar wind erosion of the atmosphere. Following this transition, the water table retreated deep beneath the surface, except in isolated regions of focused groundwater upwelling and evaporation, producing the playa evaporites in Meridiani Planum and Arabia Terra. This long‐term evolution was modulated by shorter‐term climate forcing in the form of periodic and chaotic variations in the orbital parameters of Mars, resulting in changes in the volume of water sequestered in the polar caps and cryosphere. This shorter‐term forcing can explain the observed periodic and bundled sedimentary layering, erosional unconformities, and evidence for a fluctuating water table at Meridiani Planum.
Water Activity and the Challenge for Life on Early Mars Tosca, Nicholas J; Knoll, Andrew H; McLennan, Scott M
Science (American Association for the Advancement of Science),
05/2008, Letnik:
320, Številka:
5880
Journal Article
Recenzirano
In situ and orbital exploration of the martian surface has shown that acidic, saline liquid water was intermittently available on ancient Mars. The habitability of these waters depends critically on ...water activity (Formula: see text), a thermodynamic measure of salinity, which, for terrestrial organisms, has sharply defined limits. Using constraints on fluid chemistry and saline mineralogy based on martian data, we calculated the maximum Formula: see text for Meridiani Planum and other environments where salts precipitated from martian brines. Our calculations indicate that the salinity of well-documented surface waters often exceeded levels tolerated by known terrestrial organisms.
The Opportunity Rover has been exploring Meridiani Planum; concurrently, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) has been collecting orbital hyperspectral data. Herein, both ...surface and orbital data are used to characterize surface properties at the Opportunity traverse region around Victoria crater. Results agree with previous studies, which used Opportunity's Panoramic Camera (Pancam) data, and the current study extends estimates of the Hapke single‐particle‐scattering albedo and asymmetry parameter to a greater spatial and spectral range. Results are useful for determining boundaries between surface units that otherwise look relatively uniform spectrally. This work also provides photometric functions essential for converting spectra to a single viewing geometry to yield more accurate spectral comparisons. Retrieved single‐scattering albedos range from 0.42 to 0.57 (0.5663–2.2715 micrometers) and retrieved asymmetry parameters range from −0.27 to −0.17 (moderately backscattering). Surfaces become more backscattering with increasing wavelength above 1 µm. The majority of Victoria crater's ejecta apron is more backscattering than surrounding regions, indicating a change in physical properties. Images taken when the rover traversed this unit show a cover of basaltic soil with superposed millimeter‐scale hematitic spherules. Wind streaks on the apron appear smooth (low backscatter) because basaltic sands have partly buried spherules, lessening millimeter‐scale roughness. CRISM‐derived scattering parameters also show that bedrock‐dominated surfaces are less backscattering than soil‐covered surfaces, largely due to lower areal abundance of spherules. The ability to analyze surface unit spherule cover is important because it relates to a wetter period during which spherules formed in Meridiani.
Key Points
In situ & orbital data are used to characterize surfaces at Meridiani Planum
Scattering at Meridiani is affected by spherule size, abundance, & burial depth
Orbital photometric data linked with sub‐pixel‐scale surface roughness
Impure reworked evaporitic sandstones, preserved on Meridiani Planum, Mars, are mixtures of roughly equal amounts of altered siliciclastic debris, of basaltic provenance (40
±
10% by mass), and ...chemical constituents, dominated by evaporitic minerals (jarosite, Mg-, Ca-sulfates
±
chlorides
±
Fe-, Na-sulfates), hematite and possibly secondary silica (60
±
10%). These chemical constituents and their relative abundances are not an equilibrium evaporite assemblage and to a substantial degree have been reworked by aeolian and subaqueous transport. Ultimately they formed by evaporation of acidic waters derived from interaction with olivine-bearing basalts and subsequent diagenetic alteration. The rocks experienced an extended diagenetic history, with at least two and up to four distinct episodes of cementation, including stratigraphically restricted zones of recrystallization and secondary porosity, non-randomly distributed, highly spherical millimeter-scale hematitic concretions, millimeter-scale crystal molds, interpreted to have resulted from dissolution of a highly soluble evaporite mineral, elongate to sheet-like vugs and evidence for minor synsedimentary deformation (convolute and contorted bedding, possible teepee structures or salt ridge features). Other features that may be diagenetic, but more likely are associated with relatively recent meteorite impact, are meter-scale fracture patterns, veins and polygonal fractures on rock surfaces that cut across bedding. Crystallization of minerals that originally filled the molds, early cement and sediment deformation occurred syndepositionally or during early diagenesis. All other diagenetic features are consistent with formation during later diagenesis in the phreatic (fluid saturated) zone or capillary fringe of a groundwater table under near isotropic hydrological conditions such as those expected during periodic groundwater recharge. Textural evidence suggests that rapidly formed hematitic concretions post-date the primary mineral now represented by crystal molds and early pore-filling cements but pre-date secondary moldic and vug porosity. The second generation of cements followed formation of secondary porosity. This paragenetic sequence is consistent with an extended history of syndepositional through post-depositional diagenesis in the presence of a slowly fluctuating, chemically evolving, but persistently high ionic strength groundwater system.
This paper is the third paper of a series that provides the modal mineralogy of the Martian surface (M3 project) at the global scale using near-infrared hyperspectral imagery. Numerous locations at ...the surface of Mars have previously been identified to harbor hydrated minerals which offer unique insights on the past water activity at the red planet. A radiative transfer model has been used to reproduce the spectra of these locations, based on the OMEGA instrument (Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité). Here we present the methodology applied to derive the hydrated quantitative composition and the first global compositional maps of hydrated minerals at Mars. Millions of spectra have been modelled to extract the modal composition of the hydrated locations, excluding sulfate-rich units. The lithology is summarized with 11 compositional maps of hydrated minerals at global scale at a sub-kilometer resolution. The hydrated mineralogy is dominated by an end-member of Fe-hydroxide, Fe- and Al-phyllosilicates and Fe/Mg micas which have on average an abundance >6 vol% and are spread globally on the identified regions. Locally, spots with high abundance (>20 vol%) of Al-smectite and Chlorite are also identified. The abundance of hydrated minerals is highest in Marwth Vallis, Nili Fossae and Meridiani Planum. However, the primary minerals almost always account for more than 50% of the composition. The modelling offers an opportunity to do local analysis of prospective landing sites and prepare for the upcoming landed missions. In the landing site for the ExoMars2022 and Mars2020 rovers, the obtained composition is in agreement with the expected detected mineralogy which demonstrates the robustness of the model and also offers a representation of the compositional variability. These global maps open the way to follow-up studies that will provide an in-depth characterization of the compositional gradients in local settings. Additionally, these compositional maps can 1) be used to calculate the water content namely potential amount of water stored within the quantified minerals and 2) provide information about the ISRU potential.
•We present global abundance maps of hydrated silicates on Mars at high resolution•We describe in detail the radiative transfer model and its associated uncertainties•We provide a description and analysis of the mineralogical assemblages•We emphasize on local analyses of targeted landing sites for rover missions
Sedimentary rocks at Eagle crater in Meridiani Planum are composed of fine-grained siliciclastic materials derived from weathering of basaltic rocks, sulfate minerals (including magnesium sulfate and ...jarosite) that constitute several tens of percent of the rock by weight, and hematite. Cross-stratification observed in rock outcrops indicates eolian and aqueous transport. Diagenetic features include hematite-rich concretions and crystal-mold vugs. We interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history. The environmental conditions that they record include episodic inundation by shallow surface water, evaporation, and desiccation. The geologic record at Meridiani Planum suggests that conditions were suitable for biological activity for a period of time in martian history.
This short essay discusses the recent view put forward by some authors according to which there was no per capita income gap between the North and the South of Italy at the time of Unification and ...therefore economic dualism was born after unification. Three are the arguments developed: first, the soundness of the new numerical estimates of the income gap is disputed, on various grounds; second the relevance of per capita income in the pre- modernization period as an indicator of likelihood of progress is considered very limited. There are other more important indicators to look at: commerce, transports, manufactured goods, finance and, above all, literacy. The third argument is connected to a recent research on the fiscal reforms enacted immediately after unification, which did not produce a levelling of per capita tax payments between North and South. The conclusion reached is that the revision has not proved that the North-South economic and social gap was born after unification.
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