Water soluble cations and the fluvial history of mars

The electrical conductivity and water soluble Na, K, Ca, and Mg of aqueous solutions of terrestrial soils and finely divided igneous and metamorphic rocks were determined. Soils from dry terrestrial basins with a history of water accumulation as well as soils from the topographic lows of valleys accumulated water soluble cations, particularly Na and Ca. These soils as a group can be distinguished from the rocks or a second group of soils (leached upland soils and soils from sites other than the topographic lows of valleys) by significant differences in their mean electrical conductivity and water soluble Na + Ca content. Similar measurements on multiple samples from the surface of Mars, collected by an automated long-range roving vehicle along a highlands to basin transect at sites with morphological features resembling dry riverlike channels, are suggested to determine the fluvial history of the planet.     

Global distribution and migration of subsurface ice on mars

A thermal/diffusive model of H₂O kinetics and equilibrium was developed to investigate the long-term evolution and depth distribution of subsurface ice on Mars. The model quantitatively takes into account (1) obliquity variations; (2) eccentricity variations; (3) long-term changes in the solar luminosity; (4) variations in the argument of subsolar meridian (in planetocentric equatorial coordinates); (5) albedo changes at higher latitudes due to seasonal phase changes of CO₂ and the varying extent of CO₂ ice cover; (6) planetary internal heat flow; (7) temperature variations in the regolith as a function of depth, time, and latitude due to the above factors; (8) atmospheric pressure variations over a 10⁴-year time scale; (9) the effects of factors (1) through (5) on seasonal polar cap temperatures; and (10) Knudsen and molecular diffusion of H₂O through the regolith. The migration of H₂O into or out of the regolith is determined by two boundary conditions, the H₂O vapor pressure at the subsurface ice boundary and the annual average H₂O concentration at the base of the atmosphere. These are controlled respectively by the annual average regolith temperature at the given depth and seasonal temperatures at the polar cap. Starting from an arbitrary initial uniform depth distribution of subsurface ice, H₂O fluxes into or out of the regolith are calculated for 100 selected obliquity cycles, each representing a different epoch in Mars' history. The H₂O fluxes are translated into ice thicknesses and extrapolated over time to give the subsurface ice depth as a function of latitude and time. The results show that obliquity variations influence annual average regolith temperatures in varying degrees, depending on latitude, with the greatest effect at the poles and almost no effect at 40° lat. Insolation changes at the pole, due to obliquity, argument of subsolar meridian, and eccentricity variations can produce enormous atmospheric H₂O concentration variations of ≈6 orders of magnitude over an obliquity cycle. Superimposed on these cyclic variations is a slow, monotonic change due to the increasing solar luminosity. Albedo changes at the polar cap due to seasonal phase changes of CO₂ and the varying thickness of the CO₂ ice cover are critically important in determining annual average atmospheric H₂O concentrations. Despite the strongly oscillating character of the boundary conditions, only small amounts of H₂O are exchanged between the regolith and the atmosphere per obliquity cycle (<10 g/cm²). The net result of H₂O migration is that the regolith below 30–40° lat is depleted of subsurface ice, while the regolith above 30–40° lat contains permanent ice due to the depth of penetration of the annual thermal wave. This result is supported by recent morphological studies. The rate of migration of H₂O is strongly dependent on average pore/capillary radius for which we have assumed values of 1 and 10 μm. We estimate that the H₂O ice removed from the regolith would produce a permanent ice cap with a volume between 2 × 10⁶ and 6 × 10⁶ km³. This generally agrees with estimates deduced from deflationary features at lower latitudes, depositional features at higher latitudes, and the mass of the polar caps.     

Geomorphic knobs of Candor Chasma, Mars: New Mars Reconnaissance Orbiter data and comparisons to terrestrial analogs

High Resolution Imaging Science Experiment (HiRISE) imagery and digital elevation models of the Candor Chasma region of Valles Marineris, Mars, reveal prominent and distinctive positive-relief knobs amidst light-toned layers. Three classifications of knobs, Types 1, 2, and 3, are distinguished from a combination of HiRISE and Thermal Emission Imaging System (THEMIS) images based on physical expressions (geometries, spatial relationships), and spectral data from Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Type 1 knobs are abundant, concentrated, topographically resistant features with their highest frequency in West Candor, which have consistent stratigraphic correlations of the peak altitude (height). These Type 1 knobs could be erosional remnants of a simple dissected terrain, possibly derived from a more continuous, resistant, capping layer of pre-existing material diagenetically altered through recrystallization or cementation. Types 2 and 3 knobs are not linked to a single stratigraphic layer and are generally solitary to isolated, with variable heights. Type 3 are the largest knobs at nearly an order of magnitude larger than Type 1 knobs. The variable sizes and occasional pits on the tops of Type 2 and 3 knobs suggest a different origin, possibly related to more developed erosion, preferential cementation, or textural differences from sediment/water injection or intrusion, or from a buried impact crater. Enhanced color HiRISE images show a brown coloration of the knob peak crests that is attributable to processing and photometric effects; CRISM data do not show any detectable spectral differences between the knobs and the host rock layers, other than albedo. These intriguing knobs hold important clues to deducing relative rock properties, timing of events, and weathering conditions of Mars history.     

Evidence of an eolian ice-rich and stratified permafrost in Utopia Planitia,Mars

Western Utopia Planitia (UP) is dotted with scalloped depressions, small-sized polygons and pingo-like mounds. Within the planetary science community, there seems to be a general agreement that these relatively recent landscape features are indicative of an ice-rich permafrost. However, questions about the concentration of ice-content and the origin of the permafrost remain unanswered. The scalloped depressions (～100 m to few km in diam.) are thought to be the product of degradation of ground-ice by thawing or sublimation. Indeed, most of the scalloped depressions display bright bands on their floors. These have been described as possible exposed sedimentary layers, markers of recessional ponded water or slumped material by previous works. As the depressions could represent probes of the permafrost, therefore the study of the inner bands could help to investigate the permafrost. Here, we evaluate the disparate hypotheses of band origin using several HiRISE images and a HiRISE DEM. We show that the depressions have an inner stepped-profile. This profile is reminiscent of exhumed and tilted sedimentary layers of different cohesion. Using ArcGIS, we estimate the dip of several layers (n=52). The stratification is complex comprising layers of ～2–4 m thick having different shallow dips with generally a north or south plunge sense. This geometry of tilted layers is typical on Earth of fluviatile or eolian sedimentation. In the last few years, several evidences on Mars, among them the subkilometer-scale smoothing of the topography and climatic simulations, suggested that the northern mid-latitudes have been influenced by eolian processes. The inferred complex stratification inside scalloped depressions may support an eolian origin of the permafrost in UP. In periglacial regions on Earth where thermokarst lakes are formed by extensive thawing of ground-ice, ice-rich permafrost are composed of fluvial or eolian sediments containing ～15–80% of ice by volume. By analogy, the wide occurrence of kilometric scalloped depressions in UP could assume an ice-rich permafrost of possibly same ice-content. The presence of this ice-rich and stratified permafrost raises interesting questions about its relatively recent formation and climatic significance.     

Evaporation of ice in planetary atmospheres: Ice-covered rivers on mars

The evaporation rate of water ice on the surface of a planet with an atmosphere involves an equilibrium between solar heating and radiative and evaporative cooling of the ice layer. The thickness of the ice is governed principally by the solar flux which penetrates the ice layer and then is conducted back to the surface. These calculations differ from those of Lingenfelter et al. [(1968) Science161, 266–269] for putative lunar channels in including the effect of the atmosphere. Evaporation from the surface is governed by two physical phenomena: wind and free convection. In the former case, water vapor diffuses from the surface of the ice through a lamonar boundary layer and then is carried away by eddy diffusion above, provided by the wind. The latter case, in the absence of wind, is similar, except that the eddy diffusion is caused by the lower density of water vapor than the Martian atmosphere. For mean Martian insolations the evaporation rate above the ice is ～ 10^?8 g cm^?2 sec^?1. Thus, even under present Martian conditions a flowing channel of liquid water will be covered with ice which evaporates sufficiently slowly that the water below can flow for hundreds of kilometers even with quite modest discharges. Evaporation rates are calculated for a wide range of frictional velocities, atmospheric pressures, and insolations and it seems clear that at least some subset of observed Martian channels may have formed as ice-choked rivers. Typical equilibrium thicknesses of such ice covers are ～ 10 to 30 m; typical surface temperatures are 210 to 235°K. Ice-covered channels or lakes on Mars today may be of substantial biological interest. Ice is a sufficiently poor conductor of heat that sunlight which penetrates it can cause melting to a depth of several meters or more. Because the obliquity of Mars can vary up to some 35°, the increased polar heating at such times seems able to cause subsurface melting of the ice caps to a depth which corresponds to the observed lamina thickness and may be responsible for the morphology of these polar features.     

The effect of radiative transfer on shear-flow instability in the atmospheres on mars and venus

The results of two theoretical investigations concerning the destabilizing effects of radiative transfer on stably stratified shear flows are applied to the CO₂ atmospheres Mars and Venus. It is found that radiatively modified critical Richardson numbers remain below plausible atmospheric values throughout the stratospheres of both planets. Above certain altitudes, however, in the upper stratospheres of these planets (≈50 km on Mars and ≈100 km on Venus), critical Richardson numbers begin to increase significantly above the nonradiating critical value. This trend continues until, in the lower thermosphere, critical Richardson numbers eventually surpass atmospheric values. This effect could lead to observably greater turbulent mixing in the upper atmospheres of Mars and Venus than might be expected from terrestrial observation and from nonradiating theoretical calculations.     

Instrument development to search for biomarkers on mars: Terrestrial acidophile, iron-powered chemolithoautotrophic communities as model systems

Recent findings by the MER rover opportunity confirming the presence of iron minerals that can only be formed in the presence of water emphasize the study of analogous environments to Mars on Earth. The study of chemolithoautotrophic communities living in acidic iron-rich habitats is highly relevant in order to identify Mars analog environment-specific biomarkers. Iron oxidizing bacteria like Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans have ways of life for which it is feasible to identify a past or present hypothetical niche on Mars. We have developed a strategy for biomarker identification based on: (i) search for biosignatures on acid and metal-rich environments; (ii) development of an immunosensor microarray; and (iii) integration into an instrument for autonomous and remote operation. The instrument that we have built, called Signs Of LIfe Detector (SOLID), is capable of processing a variety of samples for the detection of specific biomarkers. Antibodies against several bacterial strains have been developed and tested in a microarray biosensor on SOLID. Tests with field samples have been successfully performed, allowing the detection of L. ferrooxidans, A. ferrooxidans present in sediment samples.     

Climatic implications of correlated Upper Pleistocene glacial and fluvial deposits on the Cinca and Gállego Rivers (NE Spain) based on OSL dating and soil stratigraphy

We correlate Upper Pleistocene glacial and fluvial deposits of the Cinca and Gállego River valleys (south central Pyrenees and Ebro basin, Spain) using geomorphic position, luminescence dates, and time-related trends in soil development. The ages obtained from glacial deposits indicate glacial periods at 85 ± 5 ka, 64 ± 11 ka, and 36 ± 3 ka (from glacial till) and 20 ± 3 ka (from loess). The fluvial drainage system, fed by glaciers in the headwaters, developed extensive terrace systems in the Cinca River valley at 178 ± 21 ka, 97 ± 16 ka, 61 ± 4 ka, 47 ± 4 ka, and 11 ± 1 ka, and in the Gállego River valley at 151 ± 11 ka, 68 ± 7 ka, and 45 ± 3 ka. The times of maximum geomorphic activity related to cold phases coincide with Late Pleistocene marine isotope stages and Heinrich events. The maximum extent of glaciers during the last glacial occurred at 64 ± 11 ka, and the terraces correlated with this glacial phase are the most extensive in both the Cinca (61 ± 4 ka) and Gállego (68 ± 7 ka) valleys, indicating a strong increase in fluvial discharge and availability of sediments related to the transition to deglaciation. The global Last Glacial Maximum is scarcely represented in the south central Pyrenees owing to dominantly dry conditions at that time. Precipitation must be controlled by the position of the Iberian Peninsula with respect to the North Atlantic atmospheric circulation system. The glacial systems and the associated fluvial dynamic seem sensitive to 1) global climate changes controlled by insolation, 2) North Atlantic thermohaline circulation influenced by freshwater pulses into the North Atlantic, and 3) anomalies in atmospheric circulation in the North Atlantic controlling precipitation on the Iberian Peninsula. Our scenario of glacial and fluvial evolution during the Late Pleistocene in northern Spain could be extrapolated to other glaciated mountainous areas in southern Europe.     

Alteration mineralogy of Home Plate and Columbia Hills—Formation conditions in context to impact,volcanism, and fluvial activity

The Mars Exploration Rover Spirit investigated the igneous and alteration mineralogy and chemistry of Home Plate and its surrounding deposits. Here, we focus on using thermochemical modeling to understand the secondary alteration mineralogy at the Home Plate outcrop and surrounding Columbia Hills region in Gusev crater. At high temperatures (300 °C), magnetite occurs at very high W/R ratios, but the alteration assemblage is dominated by chlorite and serpentine over most of the W/R range. Quartz, epidote, and typical high‐T phases such as feldspar, pyroxene, and garnet occur at low W/R. At epithermal temperatures (150 °C), hematite occurs at very high W/R. A range of phyllosilicates, including kaolinite, nontronite, chlorite, and serpentine are precipitated at specific W/R. Amphibole, with garnet, feldspar, and pyroxene occur at low W/R. If the CO₂ content of the system is high, the assemblage is dominated by carbonate with increasing amounts of an SiO₂‐phase, kaolinite, carpholite, and chlorite with lower W/R. At temperatures of hydrous weathering (13 °C), the oxide phase is goethite, silicates are chlorite, nontronite, and talc, plus an SiO₂‐phase. In the presence of CO₂, the mineral assemblage at high W/R remains the same, and only at low W/R, i.e., with increasing salinity, carbonate precipitates. The geochemical gradients observed at Home Plate are attributed to short‐lived, initially high (300 °C) temperature, but fast cooling events, which are in agreement with our models and our interpretation of a multistage alteration scenario of Home Plate and Gusev in general. Alteration at various temperatures and during different geological processes within Gusev crater has two effects, both of which increase the habitability of the local environment: precipitation of hydrous sheet silicates, and formation of a brine, which might contain elements essential for life in diluted, easily accessible form.     

Secondary uranium mineralization in southern Finland and its relationship to recent glacial events

Uranium series dating has been carried out on secondary uranyl silicate minerals formed during sub-glacial and post-glacial weathering of Proterozoic uraninite ores in south west Finland. The samples were obtained from two sites adjacent to the Salpauselkä III ice marginal formation and cover a range of depths, from the surface to more than 60 m. Measured ages fall into three distinct groups, 70–100 ka, 28–36 ka and < 2500 yr. The youngest set is associated with surface exposures and the crystals display clear evidence of re-working. The most likely trigger for uranium release at depths below the surface weathering zone is intrusion of oxidising glacial melt water. The latter is often characterised by very high discharge rates along channels, which close once the overpressure generated at the ice margin is released. There is excellent correspondence between the two Finnish sites and published data for similar deposits over a large area of southern and central Sweden. None of the seventy samples analysed gave a U–Th age between 40 and 70 ka; a second hiatus is apparent at 20 ka, coinciding with the Last Glacial Maximum. Thus, the process responsible for uranyl silicate formation was halted for significant periods, owing to a change in geochemical conditions or the hydrogeological regime. These data support the presence of interstadial conditions during the Early and Middle Weichselian since in the absence of major climatic perturbations the uranium phases at depth are stable. When viewed in conjunction with proxy data from mammoth remains it would appear that the region was ice-free prior to the Last Glacial Maximum.     

Distribution and state of H2O in the high-latitude shallow subsurface of mars

A quantitative model of the state, distribution, and migration of water in the shallow Martian regolith is presented. Reported results are confined to the region of the planet greater than 40° lat. The calculations take into account (1) expected thermal variations at all depths, latitudes, and times resulting from seasonal and astronomically induced insolation variations; (2) variations in atmospheric P_H2O and P_CO2 resulting from polar insolation variations and regolith adsorptive equilibria; (3) feedback effects related to latent heat and albedo variations resulting from condensation of atmospheric constituents; (4) two possible regolith mineralogies; (5) variable total H₂O content of the regolith; (6) kinetics of H₂O transport through the Martian atmosphere and regolith; and (7) equilibrium phase partitioning of H₂O between the condensed, adsorbed, and vapor phases. Results suggest that the adsorptive capacity of the regolith is important in controlling the state and distribution of high-latitude H₂O; unweathered mafic silicates favor the development of shallow ground ice at all temperate and polar latitudes, while heavily weathered clay-like regolith materials leads to a deeper ground ice interface and far more extensive quantities of adsorbed H₂O. The capacity of the high-latitude regolith for storage of H₂O and the total mass of H₂O exchanged between the atmosphere, polar cap, and subsurface over an obliquity cycle is found to be relatively independent of mineralogy. The maximum exchanged volume is found to be 3.0 × 10⁴ km³ of ice per cycle. Implications for the history of the polar caps and the origin of the layered terrain are discussed. Results also suggest that seasonal thermal waves act to force adsorbed H₂O into the solid phase over a wide variety of latitude/obliquity conditions. Seasonal phase cycling of regolith H₂O is most common at high latitudes and obliquities. Such phase behavior is highly dependent on regolith mineralogy. In a highly weathered regolith, adsorbed H₂O is annually forced into the solid phase at all latitudes ≥40° at obliquities greater than approximately 25°. Seasonal adsorption-freezing cycles which are predicted here may produce geomorphologic signatures not unlike those produced by terrestrial freeze-thaw cycles.     

On the abundances of carbon dioxide isotopologues in the atmospheres of mars and earth

The isotopic composition of carbon dioxide in the Martian atmosphere from the measurements of Mars Science Laboratory have been used to estimate the relative abundances of CO₂ isotopologues in the Martian atmosphere. Concurrently, this study has revealed long-standing errors in the amounts of some of low-abundance CO₂ isotopologues in the Earth’s atmosphere in the databases of spectroscopic parameters of gases (HITRAN, etc.).     

A Quaternary uplift record for the Auckland region, North Island, New Zealand, based on marine and fluvial terraces

Marine and fluvial terrace sequences near the Waitakere Ranges on the North Island of New Zealand have been surveyed, yielding an inventory of 13 fluvial and 12 marine terrace levels. Based on sparse tephra age control and correlation with the global palaeoclimatic record, rates of regional Quaternary uplift have been reconstructed. Between 1000 ka and 345 ka the time-averaged uplift rate was 0.072 mm a^− 1, between 345 ka and 50 ka it increased to 0.278 mm a^− 1, accelerating to 0.42 mm a^− 1 since 50 ka. The fluvial terrace sequence did not yield clear sedimentary records or other datable material. However, although others have disputed the existence of marine terraces in this study region, a pattern of accelerating regional uplift, superimposed onto glacio-eustatic sea-level changes, is substantiated as the only possible mechanism for maintaining the considerable relief and the active denudation processes inland. The observed uplift is similar to that in other regions where the uplift has been attributed to coupling between surface processes and lower-crustal flow, making this a likely mechanism in the North Island of New Zealand. Regarding the fluvial terrace sequence, the proposed general model is of an actively incising river, carving out on average one strath terrace every ~ 16,000 years. The incision phases are reactivated by sea-level lowering and interrupted by net aggradation events due to landslides triggered by cyclones and/or fires within the catchment; volcanic ash falls also cause transient increases in sediment supply.     

Mars Reconnaissance Orbiter observations of light-toned layered deposits and associated fluvial landforms on the plateaus adjacent to Valles Marineris

We have used data from the Mars Reconnaissance Orbiter to study 30-80 m thick light-toned layered deposits on the plateaus adjacent to Valles Marineris at five locations: (1) south of Ius Chasma, (2) south of western Melas Chasma, (3) south of western Candor Chasma, (4) west of Juventae Chasma, and (5) west of Ganges Chasma. The beds within these deposits have unique variations in brightness, color, mineralogy, and erosional properties that are not typically observed in light-toned layered deposits within Valles Marineris or many other equatorial areas on Mars. Reflectance spectra indicate these deposits contain opaline silica and Fe-sulfates, consistent with low-temperature, acidic aqueous alteration of basaltic materials. We have found valley or channel systems associated with the layered deposits at all five locations, and the volcanic plains adjacent to Juventae, Ius, and Ganges exhibit inverted channels composed of light-toned beds. Valleys, channels, and light-toned layering along the walls of Juventae and Melas Chasmata are most likely coeval to the aqueous activity that affected the adjacent plateaus and indicate some hydrological activity occurred after formation of the chasmata. Although the source of water and sediment remains uncertain, the strong correlation between fluvial landforms and light-toned layered deposits argues for sustained precipitation, surface runoff, and fluvial deposition occurring during the Hesperian on the plateaus adjacent to Valles Marineris and along portions of chasmata walls.     

Soil investigations, offshore mid Norway: A case study of glacial influence on geotechnical properties

Fine-grained glaciomarine and glacial deposits on the outer Mid Norwegian continental shelf show complex variations in shear strength and degree of consolidation. At the Smørbukk Sør field (approx. 65°N, 7°E) about 80 m of variably overconsolidated clayey till is found on top of normally- or possibly underconsolidated glaciomarine and marine sediments. A high gas content is found below 60 m, and the porewater in the rather soft sediments in the lower part of the borehole may have been partly trapped by gas hydrates when the overlying hard till was deposited. The variations in geotechnical properties of the 80 m thick till section are suggested to result mainly from compaction below grounded ice during the last glaciation, and we interpret the strength variations in the till to reflect shifts between freeze of sediment porewater onto the base of the ice causing highly overconsolidated intervals, and thermal equilibrium or melting at the ice sole resulting in intervals of softer till.A large ridge northwest of Smørbukk (Skjoldryggen) is probably partly formed by ice push during ice flow oscillations at the same time as the described till at Smørbukk was deposited. This ridge retarded the ice flow and hence the frictional heating at the end of surges, creating pulses of net freezing base ice and consolidation of the substratum. The described process has possibly affected a wide area up-ice of Skjoldryggen, and may be common in areas with a complex glacial history and a fine-grained substratum.     

Disks, tori, and cocoons: emission and absorption diagnostics of AGN environments

One of the most important problems in the study of active galaxies is understanding the detailed geometry, physics, and evolution of the central engines and their environments. The leading models involve an accretion disk and torus structure around a central dense object, thought to be a supermassive black hole. Gas found in the environment of active galactic nuclei (AGN) is associated with different structures: molecular accretion disks, larger scale atomic tori, ionized and neutral “cocoons” in which the nuclear regions can be embedded. All of them can be studied at radio wavelengths by various means. Here, we summarize the work that has been done to date in the radio band to characterize these structures. Much has been learned about the central few parsecs of AGN in the last few decades with contemporary instruments but the picture remains incomplete. In order to be able to define a more accurate model of this region, significant advances in sensitivity, spectral and angular resolution, and bandpass stability are required. The necessary advances will only be provided by the Square Kilometer Array and we discuss the possibilities that these dramatic improvements will open for the study of the gas in the central region of AGN.     

Geological evolution of Ares Vallis on Mars: Formation by multiple events of catastrophic flooding, glacial and periglacial processes

Ares Vallis is one of the greatest outflow channels of Mars. Using high-resolution images of recent missions to Mars (MGS, 2001 Odyssey, and Mars Express), we investigated Ares Vallis and its valley arms, taking advantage of 3-dimensional analysis performed using the high-resolution stereo capability of the Mars Express High Resolution Stereo Camera (HRSC). In our view, Ares Vallis is characterized by catastrophic flood landscapes partially superimposed by ice-related morphologies. Catastrophic flood landforms include erosional terraces, grooved terrains, streamlined uplands, giant bars, pendant bars, and cataract-like features. Ice-related morphologies include probable kame features, thermokarstic depressions, and patterned grounds. Our investigations outline that throughout the Hesperian age, Ares Vallis and its valley arms had been sculpted by several, time-scattered, catastrophic floods, originating from Iani, Hydaspis and Aram Chaos. Geomorphological evidence suggests that catastrophic floods were ice-covered, and that climatic conditions of Mars at this time were similar to those of the present day. At the end of each catastrophic flood, ice masses grounded, forming a thick stagnant dead-ice body. Each catastrophic flood was followed by a relatively brief period of warmer-wetter climatic conditions, originated as a consequence of catastrophic flooding. During such periods thermokarstic depressions originated, liquid water formed meandering channels, and ice-contact deposits were emplaced by ice-walled streams. Finally, the climate turned into cold-dry conditions similar to the present-day ones, and ice masses sublimated.