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1.
Alberto G. Fairén 《Icarus》2010,208(1):165-48
Water on Mars has been explained by invoking controversial and mutually exclusive solutions based on warming the atmosphere with greenhouse gases (the “warm and wet” Mars) or on local thermal energy sources acting in a global freezing climate (the “cold and dry” Mars). Both have critical limitations and none has been definitively accepted as a compelling explanation for the presence of liquid water on Mars. Here is considered the hypothesis that cold, saline and acidic liquid solutions have been stable on the sub-zero surface of Mars for relatively extended periods of time, completing a hydrogeological cycle in a water-enriched but cold planet. Computer simulations have been developed to analyze the evaporation processes of a hypothetical martian fluid with a composition resulting from the acid weathering of basalt. This model is based on orbiter- and lander-observed surface mineralogy of Mars, and is consistent with the sequence and time of deposition of the different mineralogical units. The hydrological cycle would have been active only in periods of dense atmosphere, as having a minimum atmospheric pressure is essential for water to flow, and relatively high temperatures (over ∼245 K) are required to trigger evaporation and snowfall; minor episodes of limited liquid water on the surface could have occurred at lower temperatures (over ∼225 K). During times with a thin atmosphere and even lesser temperatures (under ∼225 K), only transient liquid water can potentially exist on most of the martian surface. Assuming that surface temperatures have always been maintained below 273 K, Mars can be considered a “cold and wet” planet for a substantial part of its geological history.  相似文献   

2.
Three decades of slope streak activity on Mars   总被引：1，自引：0，他引：1  
Slope streaks are surficial mass movements that are abundant in the dust-covered regions of Mars. Targeting of slope streaks seen in Viking images with the Mars Orbiter Camera provides observations of slope streak dust activity over two to three decades. In all study areas, new and persisting dark slope streaks are observed. Slope streaks disappeared in one area, with persisting streaks nearby. New slope streaks are found to be systematically darker than persisting streaks, which indicates gradual fading. Far more slope streaks formed at the study sites than have faded from visibility. The rate of formation at the study sites was 0.03 new slope streaks per existing streak per Mars year. Bright slope streaks do not presently form in sudden events as dark slope streaks do. Instead, bright streaks might form from old dark slope streaks, perhaps transitioning through a partially faded stage.  相似文献   

3.
Gullies are extremely young erosional/depositional systems on Mars that have been carved by an agent that was likely to have been comprised in part by liquid water [Malin, M.C., Edgett, K.S., 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330-2335; McEwen, A.S. et al., 2007. A closer look at water-related geologic activity on Mars. Science 317, 1706-1709]. The strong latitude and orientation dependencies that have been documented for gullies require (1) a volatile near the surface, and (2) that insolation is an important factor for forming gullies. These constraints have led to two categories of interpretations for the source of the volatiles: (1) liquid water at depth beneath the melting isotherm that erupts suddenly (“groundwater”), and (2) ice at the surface or within the uppermost layer of soil that melts during optimal insolation conditions (“surface/near-surface melting”). In this contribution we synthesize global, hemispheric, regional and local studies of gullies across Mars and outline the criteria that must be met by any successful explanation for the formation of gullies. We further document trends in both hemispheres that emphasize the importance of top-down melting of recent ice-rich deposits and the cold-trapping of atmospherically-derived H2O frost/snow as important components in the formation of gullies. This provides context for the incorporation of high-resolution multi-spectral and hyper-spectral data from the Mars Reconnaissance Orbiter that show that (1) cold-trapping of seasonal H2O frost occurs at the alcove/channel-level on contemporary Mars; (2) gullies are episodically active systems; (3) gullies preferentially form in the presence of deposits plausibly interpreted as remnants of the Late Amazonian emplacement of ice-rich material; and (4) gully channels frequently emanate from the crest of alcoves instead of the base, showing that alcove generation is not necessarily a product of undermining and collapse at these locations, a prediction of the groundwater model. We interpret these various lines of evidence to mean that the majority of gullies on Mars are explained by the episodic melting of atmospherically emplaced snow/ice under spin-axis/orbital conditions characteristic of the last several Myr.  相似文献   

4.
Slope streaks are a form of gravity-driven mass-movements that frequently occur on Mars today. The cause of slope streak formation remains unclear; both, dry and wet processes have been suggested. Here, we observationally constrain the time of the year during which slope streaks form. Imagery from four Mars-orbiting cameras is mined to identify locations that have been imaged repeatedly, and the overlapping images are surveyed for streak activity. A search algorithm automatically finds the locations on the surface that have been imaged most often based on a graph representation. Dark slope streaks are found to form sporadically throughout the Mars year. At one study site in the Olympus Mons Aureole, observations constrain slope streak formation to at least five distinct time intervals within a single Mars year. New slope streaks form spatially isolated or in small groups within a few kilometers of one another. The observations suggest that slope streak triggering is unrelated to season and not caused by any large regional events. Most slope streaks are caused by sporadic events of small spatial extent.  相似文献   

5.
Recent gully deposits on Mars have been attributed to both wet and dry mass wasting processes. In this paper frosted granular flow (FGF) is presented as a new hypothesis for recent mass wasting activity in martian gullies. FGF is a rare type of granular flow observed on a talus slope in the Province of Québec, Canada [Hétu, B., van Steijn, H., Vandelac, P., 1994. Géogr. Phys. Quat. 48, 3-22]. Frost reduces dynamic inter-particle friction, enabling flows to mobilize onto relatively low slope gradients (25-30°) compared to those involving dry granular flow of the same material (35-41°). Resulting erosional and depositional features include straight to sinuous channels, levees and digitate to branching arrangements of terminal deposits. Similar features are commonly found in association with geologically-young gully systems on Mars. Based on terrestrial observations of FGF processes the minimum criteria required for their occurrence on Mars include: (i) readily mobilized, unconsolidated sediment at the surface; (ii) an upper slope gradient at or near the angle of repose; (iii) frost accumulation at the surface; and (iv) triggering by rock fall. All four conditions appear to be met in many areas on present-day Mars though triggering mechanisms may vary. Compared to terrestrial FGFs, which are lubricated by thin liquid films at inter-particle contacts, those occurring on Mars are more likely lubricated by vaporization of CO2 and small amounts of H2O frost that becomes incorporated in the translating mass. Some recent mass wasting activity in martian gullies, therefore, could be interpreted as the product of FGF.  相似文献   

6.
Mars General Circulation Model (GCM) simulations are presented to illustrate the importance of the ice emissivity of the seasonal CO2 polar caps in regulating the effects of airborne dust on the martian CO2 cycle. Simulated results show that atmospheric dust suppresses CO2 condensation when the CO2 ice emissivity is high but enhances it when the CO2 ice emissivity is low. This raises the possibility that the reason for the repeatable nature of the CO2 cycle in the presence of a highly variable dust cycle is that the CO2 ice emissivity is “neutral” - the value that leads to no change in CO2 condensation with changing atmospheric dust. For this GCM, the “neutral” emissivity is approximately 0.55, which is low compared to observed cap emissivities. This inconsistency poses a problem for this hypothesis. However, it is clear that the CO2 ice emissivity is a critical physical parameter in determining how atmospheric dust affects the CO2 cycle on Mars.  相似文献   

7.
Joseph Levy  James W. Head 《Icarus》2010,209(2):390-404
Hypotheses accounting for the formation of concentric crater fill (CCF) on Mars range from ice-free processes (e.g., aeolian fill), to ice-assisted talus creep, to debris-covered glaciers. Based on analysis of new CTX and HiRISE data, we find that concentric crater fill (CCF) is a significant component of Amazonian-aged glacial landsystems on Mars. We present mapping results documenting the nature and extent of CCF along the martian dichotomy boundary over −30 to 90°E latitude and 20-80°N longitude. On the basis of morphological analysis we classify CCF landforms into “classic” CCF and “low-definition” CCF. Classic CCF is most typical in the middle latitudes of the analysis area (∼30-50°N), while a range of degradation processes results in the presence of low-definition CCF landforms at higher and lower latitudes. We evaluate formation mechanisms for CCF on the basis of morphological and topographic analyses, and interpret the landforms to be relict debris-covered glaciers, rather than ice-mobilized talus or aeolian units. We examine filled crater depth-diameter ratios and conclude that in many locations, hundreds of meters of ice may still be present under desiccated surficial debris. This conclusion is consistent with the abundance of “ring-mold craters” on CCF surfaces that suggest the presence of near-surface ice. Analysis of breached craters and distal glacial deposits suggests that in some locations, CCF-related ice was once several hundred meters higher than its current level, and has sublimated significantly during the most recent Amazonian. Crater counts on ejecta blankets of filled and unfilled craters suggests that CCF formed most recently between ∼60 and 300 Ma, consistent with the formation ages of other martian debris-covered glacial landforms such as lineated valley fill (LVF) and lobate debris aprons (LDA). Morphological analysis of CCF in the vicinity of LVF and LDA suggests that CCF is a part of an integrated LVF/LDA/CCF glacial landsystem. Instances of morphological continuity between CCF, LVF, and LDA are abundant. The presence of formerly more abundant CCF ice, coupled with the integration of CCF into LVF and LDA, suggests the possibility that CCF represents one component of the significant Amazonian mid-latitude glaciation(s) on Mars.  相似文献   

8.
HiRISE images of Mars with ground sampling down to 25 cm/pixel show that the dust-rich mantle covering the surfaces of the Tharsis Montes is organized into ridges whose form and distribution are consistent with formation by aeolian saltation. Other dusty areas near the volcanoes and elsewhere on the planet exhibit a similar morphology. The material composing these “reticulate” bedforms is constrained by their remote sensing properties and the threshold curve combined with the saltation/suspension boundary, both of which vary as a function of elevation (atmospheric pressure), particle size, and particle composition. Considering all of these factors, dust aggregates are the most likely material composing these bedforms. We propose that airfall dust on and near the volcanoes aggregates in situ over time, maybe due to electrostatic charging followed by cementation by salts. The aggregates eventually reach a particle size at which saltation is possible. Aggregates on the flanks are transported downslope by katabatic winds and form linear and “accordion” morphologies. Materials within the calderas and other depressions remain trapped and are subjected to multidirectional winds, forming an interlinked “honeycomb” texture. In many places on and near the volcanoes, light-toned, low thermal inertia yardangs and indurated surfaces are present. These may represent “duststone” formed when aggregates reach a particle size below the threshold curve, such that they become stabilized and subsequently undergo cementation.  相似文献   

9.
The case for an ocean having once occupied the northern lowlands of Mars has largely been based indirectly on the debouching of the outflow channels into the lowlands, and directly on erosional features along the margins of the lowlands interpreted to be the result of wave action. Two global shorelines were previously mapped from albedo variation, embayment relationships, and scarps interpreted as coastal cliffs. However, not since the early, Viking-based studies, has there been a focused assessment of the presence or absence of coastal constructional landforms such as barrier ridges and spits, located on or near the mapped “shorelines.” Such constructional landforms are typically found in association with coastal erosional features on Earth, and therefore warrant a detailed search for their presence on Mars. All presently available THEMIS VIS and MOC NA images located on or near either of the two “shorelines,” within the Chryse Planitia/Arabia Terra region (10° to 44° N; 300° to 0° E) and the Isidis Planitia region (0° to 30° N; 70° to 105° E), were examined in search of any features that could reasonably be considered candidate coastal ridges. Additionally, raw MOLA profiles were used in conjunction with a technique developed from Differential Global Positioning System profiles across terrestrial paleo-shorelines, to search for coastal ridges throughout these same regions. Out of 447 THEMIS VIS and 735 MOC NA images examined, only four candidates are observed that are plausibly interpreted as coastal ridges; no candidate coastal ridges are observed in the MOLA profiles. This overwhelming paucity of candidate features suggests one of five possible scenarios in terms of the existence of standing bodies of water within the martian lowlands: (1) No ocean existed up to the level of either of the previously mapped “shorelines”; (2) An ocean existed, however wave action, the primary agent responsible for construction of coastal landforms, was minimal to non-existent; (3) An ocean existed, but sediment input was not significant enough to form coastal deposits; (4) An ocean existed, but readily froze, and over time sublimated; and lastly (5) An ocean existed and coastal landforms were constructed, but in the intervening time since their formation they have nearly all been eroded away.  相似文献   

10.
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11.
Slope streaks are gravity-driven albedo features observed on martian slopes since the Viking missions. The debated mechanism of formation could involve alternatively dry granular flow or wet mass wasting. A systematic mapping of slope streaks from the High Resolution Stereo Camera is presented in this paper. Two regions known for their slope streaks activity have been studied, the first one is located close to Cerberus lava flow, and the second one is inside the Olympus Mons Aureole. The statistics of slope streaks shapes measured from orthorectified images confirm previous results from Mars Orbiter Camera surveys. Preferential orientations of slope streaks are reported. Slope streaks occur preferentially on west facing slopes at latitudes lower than 30° N for Olympus and on south-west facing slopes for Cerberus. Wind directions derived from a General Circulation Model during the dusty season correlate with these orientations. Furthermore, west facing slopes at Olympus have a thicker dust cover. These observations indicate that slope streaks are dust avalanches controlled by the preferential accumulation of dust in the downstream side of the wind flow. The paucity of slope streaks at high latitudes and their preferential orientation on south-facing slopes have been presented as an evidence for a potential role of H2O phase transition in triggering or flow. The potential role of H2O cannot be ruled out from our observations but the dust avalanche model together with the atmospheric circulation could potentially explain all observations. The role of H2O might be limited to a stabilizing effect of dust deposits on northward facing slopes at intermediate latitudes (30° N-33° N) and on all slopes further north.  相似文献   

12.
At martian mid-to-high latitudes, the surfaces of potentially ice-rich features, including concentric crater fill, lobate debris aprons, and lineated valley fill, typically display a complex texture known as “brain terrain,” due to its resemblance to the complex patterns on brain surfaces. In order to determine the structure and developmental history of concentric crater fill and overlying latitude-dependent mantle (LDM) material, “brain terrain” and polygonally-patterned LDM surfaces are analyzed using HiRISE images from four craters in Utopia Planitia containing concentric crater fill. “Brain terrain” and mantle surface textures are classified based on morphological characteristics: (1) closed-cell “brain terrain,” (2) open-cell “brain terrain,” (3) high-center mantle polygons, and (4) low-center mantle polygons. A combined glacial and thermal-contraction cracking model is proposed for the formation and modification of the “brain terrain” texture of concentric crater fill. A similar model, related to thermal contraction cracking and differential sublimation of underlying ice, is proposed for the formation and development of polygonally patterned mantle material. Both models require atmospheric deposition of ice, likely during periods of high obliquity, but do not require wet active layer processes. Crater dating of “brain terrain” and mantled surfaces suggests a transition at martian mid-latitudes from peak “glacial” conditions occurring within the past ∼10-100 My to a quiescent period followed by a cold-desert “periglacial” period during the past ∼1-2 My.  相似文献   

13.
D. Möhlmann  K. Thomsen 《Icarus》2011,212(1):123-377
Brines, i.e. aqueous salty solutions, increasingly play a role in a better understanding of physics and chemistry (and eventually also putative biology) of the upper surface of Mars. Results of physico-chemical modeling and experimentally determined data to characterize properties of cryobrines of potential interest with respect to Mars are described. Eutectic diagrams, the related numerical eutectic values of composition and temperature, the water activity of Mars-relevant brines of sulfates, chlorides, perchlorides and carbonates, including related deliquescence relative humidity, are parameters and properties, which are described here in some detail. The results characterize conditions for liquid low-temperature brines (“cryobrines”) to evolve and to exist, at least temporarily, on present Mars.  相似文献   

14.
Series of numerical experiments are performed using a general circulation model to gain insights on the hydrologic cycle on ancient Mars. Since the state of the ancient Mars atmosphere is not well constrained, we did not try to simulate an ancient Mars climate under warm and wet condition. In stead, we used an idealized model and tried to extract general features of the hydrologic cycle by modeling an ideal land planet that has no ocean on its surface. Four different climate regimes, “warm-upright,” “warm-oblique,” “frozen-upright,” and “frozen-oblique” regimes, are recognized depending on the inclination of the spin axis (obliquity) and average surface temperature. The period of active hydrologic cycle suggested from the geomorphology on Mars seems to be consistent with that at the “warm-oblique” regime, which appears at warm (above-freezing) environment with high-obliquity (higher than about 30°) condition.  相似文献   

15.
Radar observations in the Deuteronilus Mensae region by Mars Reconnaissance Orbiter have constrained the thickness and dust concentration found within mid-latitude ice deposits, providing an opportunity to more accurately estimate the rheology of ice responsible for the formation of lobate debris aprons based on their apparent age of ∼100 Myr. We developed a numerical model simulating ice flow under martian conditions using results from ice deformation experiments, theory of ice grain growth based on terrestrial ice cores, and observational constraints from radar profiles and laser altimetry. By varying the ice grain size, the ice temperature, the subsurface slope, and the initial ice volume we determine the combination of parameters that best reproduce the observed LDA lengths and thicknesses over a period of time comparable to the apparent ages of LDA surfaces (90-300 Myr). We find that an ice temperature of 205 K, an ice grain size of 5 mm, and a flat subsurface slope give reasonable ages for many LDAs in the northern mid-latitudes of Mars. Assuming that the ice grain size is limited by the grain boundary pinning effect of incorporated dust, these results limit the dust volume concentration to less than 4%. However, assuming all LDAs were emplaced by a single event, we find that there is no single combination of grain size, temperature, and subsurface slope which can give realistic ages for all LDAs, suggesting that some or all of these variables are spatially heterogeneous. Based on our model we conclude that the majority of northern mid-latitude LDAs are composed of clean (?4 vol%), coarse (?1 mm) grained ice, but regional differences in either the amount of dust mixed in with the ice, or in the presence of a basal slope below the LDA ice must be invoked. Alternatively, the ice temperature and/or timing of ice deposition may vary significantly between different mid-latitude regions. Either eventuality can be tested with future observations.  相似文献   

16.
Our study investigates possible formation mechanisms of the very recent bright gully deposits (BGDs) observed on Mars in order to assess if liquid water was required. We use two models in our assessment: a one-dimensional (1D) kinematic model to model dry granular flows and a two-dimensional (2D) fluid-dynamic model, FLO-2D (O’Brien et al., 1993, FLO Engineering), to model water-rich and wet sediment-rich flows. Our modeling utilizes a high-resolution topographic model generated from a pair of images acquired by the High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter. For the 1D kinematic modeling of dry granular flows, we examine a range of particle sizes, flow thicknesses, initial velocities, flow densities, and upslope initiation points to examine how these parameters affect the flow run-out distances of the center of mass of a flow. Our 1D modeling results show that multiple combinations of realistic parameters could produce dry granular flows that travel to within the observed deposits’ boundaries. We run the 2D fluid-dynamic model, FLO-2D, to model both water-rich and wet sediment-rich flows. We vary the inflow volume, inflow location, discharge rate, water-loss rate (water-rich models only), and simulation time and examine the resulting maximum flow depths and velocities. Our 2D modeling results suggest that both wet sediment-rich and water-rich flows could produce the observed bright deposits. Our modeling shows that the BGDs are not definitive evidence of recent liquid water on the surface of Mars.  相似文献   

17.
We have used the Mars Global Surveyor Mars Orbiter Camera Wide Angle (MGS MOC WA) dataset to study albedo trends on the martian northern residual cap. Six study regions were selected, the Chasma Boreale source region, three regions near the center of the cap (“fish hook” region, latitude = 87°; “bottle opener” region, latitude = 87°, “steep-shallow” region, latitude = 85°), and two lower latitude regions (crater, latitude = 77°, and polar outlier, latitude = 82°), and the albedos of these six regions were examined. These regions were chosen due to their good temporal coverage in the MOC dataset, as well as having been studied by other researchers (Bass et al., 2000, Icarus 144, 382-396; Calvin and Titus, 2004, Lunar Planet. Sci. XXXV, Abstract 1455). The picture which emerges is complex. Most areas experience a combination of darkening and brightening through the northern summer; only one area consistently brightens (the polar outlier region). A good deal of interannual repeatability in each region's albedo behavior is seen, however. Possible causes for the observed complex behaviors include dust deposition from late summer storms, sintering of frost grains over the course of the summer, and cold trapping of volatiles on bright, cold surfaces.  相似文献   

18.
Springtime low albedo features, called Dark Dune Spots, on the seasonal frost covered dunes on Mars between 77°N and 84°N latitude have been analyzed. Two groups of these spots have been identified: “small” and “large” ones, where large spots have diameters above 4 m, and complex internal structure. From these “large” spots branching seepage-like features emanate and grow on the steep slopes. They show a characteristic sequence of changes: first only wind-blown features emanate from them, while later a bright circular and elevated ring forms, and dark seepage-features start from the spots. These streaks grow with a speed between 0.3 m/day and 7 m/day respectively, first only from the spots, later from all along the dune crest.During this “seepage period” the temperature is between 150 K and 180 K at a 3-9 km spatial resolution scale, indicating that CO2 ice-free parts must be present at the observed dark spots. Around the receding northern seasonal CO2 cap, an annulus of water ice lags behind, which is probably present in the spots too where the CO2 frost has sublimated. Our model estimates show in the present work and in Kereszturi et al. (Kereszturi, A., Möhlmann, D., Berczi, Sz., Ganti, T., Kuti, A., Sik, A., Horvath, A. [2009b]. Icarus 201, 492-503) that the warming driven by solar insolation may produce not only interfacial water, but also bulk brines around the dune grains. The brine can support the movement of liquids and dune grains, enhances the sublimation of CO2 frost, and produce the dark features, as well as liquid modifies the optical properties of the surface.Signs of movement of dune material after the total defrosting of the terrain is also visible but it is uncertain because of the limit of resolution. In our previous work (Kereszturi et al., 2009b) we showed that resembling seepage-like streaks at the southern hemisphere might have been formed by ephemeral interfacial water, as well as these northern features. Such wet environments may have astrobiological importance too.  相似文献   

19.
The surface of Mars is covered by weathered material. Mars' rusty red colour in particular is commonly ascribed to ferric iron-bearing minerals. The planet's surface is generally iron rich. Mössbauer spectroscopy is a powerful tool for quantitative mineralogical analysis of Fe-bearing minerals. Consequently, the miniaturized Mössbauer spectrometer MIMOS II is part of the payload of NASA's twin Mars Exploration Rovers “Spirit” and “Opportunity”, and ESA's ill-fated Mars Express lander “Beagle 2”. Both Mars Exploration Rovers are currently conducting successful surface operations on Mars. In this paper, we give a brief insight into mission operations with respect to the reconstruction of local weathering scenarios at the landing sites, which in turn will help to illuminate the climatic history of the planet. Mössbauer spectra obtained in preparation of the mission from the SNC meteorites Nakhla, Dar al Gani 476, and Sayh al Uhaymir, show weathering and other alteration features. Preliminary results of laboratory weathering experiments on Fe-bearing minerals (olivine and pyroxene) show the importance of analysing individual minerals to understand weathering of more complex mineral assemblages like, e.g., basalt.  相似文献   

20.
We have used the complete set of Mars Global Surveyor (MGS) Mars Daily Global Maps (MDGMs) to study martian weather in the southern hemisphere, focusing on curvilinear features, including frontal events and streaks. “Frontal events” refer to visible events that are morphologically analogous to terrestrial baroclinic storms. MDGMs show that visible frontal events were mainly concentrated in the 210-300°E (60-150°W) sector and the 0-60°E sector around the southern polar cap during Ls = 140-250° and Ls = 340-60°. The non-uniform spatial and temporal distributions of activity were also shown by MGS Thermal Emission Spectrometer transient temperature variations near the surface. “Streaks” refer to long curvilinear features in the polar hood or over the polar cap. They are an indicator of the shape of the polar vortex. Streaks in late winter usually show wavy segments between the 180° meridian and Argyre. Model results suggest that the zonal wave number m = 3 eastward traveling waves are important for their formation.  相似文献   

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