Shaler: in situ analysis of a fluvial sedimentary deposit on Mars     

《Sedimentology》2018,65(1):96-122

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.  相似文献   

A  3.5 Ga record of water-limited, acidic weathering conditions on Mars     

Joel A. Hurowitz  Scott M. McLennan 《Earth and Planetary Science Letters》2007,260(3-4):432-443

The secondary mineral budget on Earth is dominated by clay minerals, Al-hydroxides, and Fe-oxides, which are formed under the moderate pH, high water-to-rock ratio conditions typical of Earth's near-surface environment. In contrast, geochemical analyses of rocks and soils from landed missions to Mars indicate that secondary mineralogy is dominated by Mg (± Fe, Ca)-sulfates and Fe-oxides. This discrepancy can be explained as resulting from differences in the chemical weathering environment of Earth and Mars. We suggest that chemical weathering processes on Mars are dominated by: (1) a low-pH, sulfuric acid-rich environment in which the stoichiometric dissolution of labile mineral phases such as olivine and apatite (± Fe–Ti oxides) is promoted; and (2) relatively low water-to-rock ratio, such that other silicate phases with slower dissolution rates (e.g., plagioclase, pyroxene) do not contribute substantially to the secondary mineral budget at the Martian surface. Under these conditions, Al-mobilization is limited, and the formation of significant Al-bearing secondary phases (e.g., clays, Al-hydroxides, Al-sulfates) is inhibited. The antiquity of rock samples analyzed in-situ on Mars suggest that water-limited acidic weathering conditions have more than likely been the defining characteristic of the Martian aqueous environment for billions of years.  相似文献   

Investigating the ancient Martian magnetic field using microwaves   总被引：1，自引：0，他引：1  

John Shaw  Mimi J. Hill  Steven J. Openshaw 《Earth and Planetary Science Letters》2001,190(3-4):103-109

The new microwave palaeointensity technique has been used to investigate samples from the Martian meteorite Nakhla. This technique is a promising new way to obtain absolute palaeointensity information regarding the ancient Martian magnetic field as recorded by the Martian meteorites. Assuming that a part of the magnetic remanence is of thermal origin and originating on Mars the two samples studied yield estimates of 4 μT for the Martian magnetic field at 1.35 Ga.  相似文献   

Solar ultraviolet transfer in the Martian atmosphere: biological and geological implications     

C Córdoba-Jabonero  L.M LaraA.M Mancho  A MárquezR Rodrigo 《Planetary and Space Science》2003,51(6):399-410

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Mapping of Ozone and Water in the Atmosphere of Mars near the 1997 Aphelion     

Robert E. NovakMichael J. Mumma  Michael A. DiSanti  Neil Dello Russo  Karen Magee-Sauer 《Icarus》2002,158(1):14-23

We present absolute abundances and latitudinal variations of ozone and water in the atmosphere of Mars during its late northern spring (L_s=67.3°) shortly before aphelion. Long-slit maps of the a¹Δ_g state of molecular oxygen (O₂) and HDO, an isotopic form of water, were acquired on UT January 21.6 1997 using a high-resolution infrared spectrometer (CSHELL) at the NASA Infrared Telescope Facility. O₂(a¹Δ_g) is produced by ozone photolysis, and the ensuing dayglow emission at 1.27 μm is used as a tracer for ozone. Retrieved vertical column densities for ozone above ∼20 km ranged between 1.5 and 2.8 μm-atm at mid- to low latitudes (30°S-60°N) and decreased outside that region. A significant decrease in ozone density is seen near 30°N (close to the subsolar latitude of 23.5°N). The rotational temperatures retrieved from O₂(a-X) emissions show a mean of 172±2.5 K, confirming that the sensed ozone lies in the middle atmosphere (∼24 km). The ν₁ fundamental band of HDO near 3.67 μm was used as a proxy for H₂O. The retrieved vertical column abundance of water varies from 3 precipitable microns (pr-μm) at ∼30°S to 24 pr-μm at ∼60°N. We compare these results with current photochemical models and with measurements obtained by other methods.  相似文献   

Strength of Faults on Mars from MOLA Topography     

David N. BarnettFrancis Nimmo 《Icarus》2002,157(1):34-42

The stresses which must be maintained on faults bounding the rift topography at Tempe Fossae—the “North Tempe Rift” (NTR)—and Valles Marineris (VM) on Mars are estimated, using a simple elastic model and topographic data from the Mars Orbiter Laser Altimeter (MOLA). The absence of rift-flank uplift at the NTR is consistent with an elastic thickness, T_e, of 20 km or greater at the time of rift formation. The maximum resolved shear stresses on bounding faults due to this topography do not therefore exceed 20 MPa, similar to the inferred strength of terrestrial faults. Elastic thickness estimates at VM are mostly around 50 km or greater. Therefore, for canyon widths of ∼400 km, the bounding faults of VM, if present, must be able to withstand stresses of up to approximately 100 MPa. However, if the fault-controlled sections of the canyons do not exceed 150 km in width, as suggested by geomorphological analysis, the fault strength required is only 20 MPa. Although the maximum resolved shear stresses required to support the topography at VM may need to be greater than the stresses which terrestrial faults can support, at least some faults on Mars are no stronger than similar features on Earth. This observation is consistent with the existence of liquid water in the shallow subsurface of Mars at the time the faults were active. On Venus, plate tectonics is probably prevented by the frictional resistance to motion across strong faults. On Mars, it is more likely that the large thickness of the elastic layer of the lithosphere and the possible positive buoyancy of the crust are responsible for the observed lack of plate tectonics.  相似文献   

The complex refractive index of limestone particles: an extension to the FIR range for Mars applications     

V Orofino  A BlancoS Fonti  A.C MarraN Polimeno 《Planetary and Space Science》2002,50(9):839-847

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CO₂ Snow on Mars and Early Earth: Experimental Constraints     

David L. GlandorfAnthony Colaprete  Margaret A. TolbertOwen B. Toon 《Icarus》2002,160(1):66-72

Greenhouse warming due to carbon dioxide atmospheres may be responsible for maintaining the early Earth's surface temperature above freezing and may even have allowed for liquid water on early Mars. However, the high levels of CO₂ required for such warming should have also resulted in the formation of CO₂ clouds. These clouds, depending on their particle size, could lead to either warming or cooling. The particle size in turn is determined by the nucleation and growth conditions. Here we present laboratory studies of the nucleation and growth of carbon dioxide on water ice under martian atmospheric conditions. We find that a critical saturation, S=1.34, is required for nucleation, corresponding to a contact parameter between solid water and solid carbon dioxide of m=0.95. We also find that after nucleation occurs, growth of CO₂ is very rapid, and we report the growth rates at a number of supersaturations. Because growth would be expected to continue until the CO₂ pressure is lowered to its vapor pressure, we expect particles larger than those being currently suggested for the present and past martian atmospheres. Using this information in a microphysical model described in a companion paper, we find that CO₂ clouds are best described as “snow,” having a relatively small number of large particles.  相似文献   

An Origin for the Linear Magnetic Anomalies on Mars through Accretion of Terranes: Implications for Dynamo Timing     

Alberto G. FairénJavier Ruiz  Francisco Anguita 《Icarus》2002,160(1):220-223

The proposed existence of magnetic lineations in the Terra Cimmeria and Terra Sirenum regions of Mars was initially explained by Earth-like sea-floor spreading. Here we argue instead that these lineations could have been formed at a convergent plate margin through collision and accretion of terranes. A similar process produced banded magnetic anomalies, similar in geometry and even in size to those in Earth's North American Cordillera. Because only sparse and generally weak anomalies have been detected in the martian northern lowlands, which could constitute an analog to the terrestrial oceanic crust, it is possible that the magnetic field stopped its activity while crustal recycling was still active in Mars.  相似文献   

Spectral scaling in Mars topography: effect of craters     

Vladimir Nikora  Derek Goring 《Acta Geophysica》2006,54(1):102-112

Extensive computer simulations aimed at testing a hypothesis that impact craters may explain the scaling behaviour of surface spectra are presented. The simulations show that indeed crater effects alone may explain the spectral scaling of Mars’ topography revealed from MOLA data. The range of the scaling exponents obtained for a wide range of simulation parameters does not exceed the limits observed for Mars. The simulations suggest that the shape of large craters is the key factor leading to the two scaling ranges in the surface spectra. Particular values of the scaling exponents may additionally depend on the depth-diameter relationship and the crater size distribution.  相似文献