the shape of mars before global surveyor results from reanalysis of the viking control point network three dimensional coordinates of 3739 globally distributed control points derived from photogrammetric analysis of viking orbiter image data are studied with respect to the shape and large scale morphology of mars spheres spheroids spherical functions and a digital terrain model dtm of 50 km grid spacing are fitted to the data prominent topographic features in the terrain model include the tharsis volcanoes olympus mons alba patera and prominent mare and highland regions as well as the major impact basins while the global dichotomy is clearly visible in our data our model does not reveal any distinct signature associated with the presumed dichotomy boundary at this global scale rather it suggests a smooth topographic transition from southern to northern hemisphere this model is unique among existing topographic data sets for mars as it combines global coverage a spatial resolution sufficient to resolve regional topography and absolute elevation data more accurate than in previous control point network analyses formal errors and a comparison with the first released topographic profiles obtained by mars global surveyor s laser altimeter mola suggest that 70 and 90 of the dtm grid elements represent the topography of the planet to better than 1000 m and 2000 m respectively

complex evolution of paleolacustrine systems on mars an example from the holden crater 1 the 150 km wide holden crater lies in an area characterized by high density of valley networks implying conditions conducive to forming of water related environments we undertook geological mapping and a stratigraphic survey in order to probe the evolution of water related landforms and their paleoenvironmental implications our investigations lead us to propose that the holden area was subjected to a wet lacustrine phase of hesperian age and an icy phase during the amazonian deltaic coastal and lacustrine environments occurred during the wet phase some displaying a cyclic depositional pattern presumably related to autogenic processes water was delivered to the basin by the uzboi vallis and by surface runoff channels from a series of drainage basins along the crater walls fan delta geometries and coastal onlap enabled estimation of major water levels two levels of major stand of the water have been recognized possibly reflecting allogenic controls geologic units related to this wet lacustrine phase were subsequently eroded by glacial abrasion and plucking and were disconformably overlain by glacial deposits of amazonian age defining an icy phase these features are consistent with a warm based glacier entering the holden crater through the wide uzboi vallis to form a proglacial lake in the central part of the crater changes in sedimentary units reflect changes of depositional environments probably connected with climatic variation

horizontal viscoelastic gravitational displacement due to a rectangular dipping thrust fault in a layered earth model calculations of horizontal displacements due to a rectangular finite thrust fault in a viscoelastic gravitational layered earth model are presented the earth model consists of a single elastic gravitational layer overlying a viscoelastic gravitational half space a review of the full three dimensional theoretical solutions is presented along with the explicit solutions for horizontal displacements several examples of computations for dipping faults with various angles and located at different depths are shown the results indicate that viscoelasticity introduces a long wavelength component into the interseismic deformation field which is not present in published elastic techniques and also that a proper consideration of gravity is necessary only for near field computations at longer periods of time a pattern is found in the cumulative displacement of cycled earthquakes which indicates that the viscoelastic displacements are visible for longer recurrence time events and that these may serve as a time index for the various stages between cycles

mars and earth comparison of cold climate features abstract on earth glacial and periglacial features are common in areas of cold climate on mars the temperature of the present day surface is appropriate for permafrost and the presence of water is suspected from data relating to the outgassing of the planet from remote sensing measurements over the polar caps and elsewhere on the martian surface and from recognition of fluvial morphological features such as channels these observations and the possibility that ice could be in equilibrium with the atmosphere in the high latitudes north and south of 40 latitude suggest that glacial and periglacial features should exist on the planet morphological studies based mainly on viking pictures indicate many features that can be attributed to the action of ice among these features are extensive talus aprons debris avalanches flows that resemble glaciers or rock glaciers ridges that look like moraines various types of patterned ground scalloped scarps and chaotically collapsed terrain that could be attributed to thermokarst processes and landforms that may reflect the interaction of volcanism and ice

transport mixing and stirring processes in a louisiana estuary a model study transport and mixing processes in a broad and shallow estuary in louisiana terrebonne timbalier basin are examined using a depth integrated two dimensional numerical model using current meter records previously obtained the model calibration yielded correlation coefficients between simulated and observed current components of 0 89 0 95 it appears that the bottom friction in the bay is relatively large with a manning s coefficient of 0 07 producing the best results the large bottom friction appears to be due to a combined effect of currents and the surface wave field which is not explicitly accounted for in the numerical model despite the small tidal range tidal forcing dominates circulation in the bay during equatorial tides tidal currents on the order of 20 cm s 1could develop in a broad area of the bay while in tidal passes currents could reach 50 60 cm s 1 during tropic tides strengths of the currents in the bay could easily be double those during equatorial tides local wind forcing is also important in controlling general flow direction inside the bay in particular during equatorial tides flushing time estimated by a particle tracking technique was 27 days that appears to be in agreement with observations horizontal diffusivities computed using tracer particles are comparable to the previous estimates of horizontal diffusion coefficients compiled by okubo 1974 the larger values appear to be due to coastal trapping mixing of water masses based on particle tracking is found to consist of continuous stretching folding and break up of material lines due to interaction of wind driven and tidal currents with bottom and coastal topography time evolution of the boundary between the two water masses depends on the initial tidal phase however this dependence lasts only until coastal trapping becomes dominant in controlling the time evolution of the boundary coastal trapping appears to be an important process by which stirring and mixing processes are enhanced thus making stirring and mixing more efficient and chaotic those observations point to the need to resolve small scale shear flow patterns in both space and time and detailed bottom and coastal topography in order to understand transport stirring and mixing processes in the broad shallow estuaries typical of the northern gulf of mexico

subkilometer martian volcanoes properties and possible terrestrial analogs kilometer to subkilometer cones with large central craters are the most numerous volcanic structures in the northern plains of mars based on examination of more than 12 000 high resolution viking orbiter images most of these very small cones are located in parts of eastern acidalia and utopia isidis elysium planitia measurements of base and pit diameter for some 2000 well resolved features show small variations in the histogram of base diameters between and within regions but remarkable similarity in the distribution of crater cone diameter ratios this suggests that the small cones had a similar origin with only minor variations in local conditions the acidalia cones are generally larger more widely distributed and occur on a greater variety of terrains than those in utopia isidis elysium based on morphology distribution and the crater cone ratio histograms the smallest martian cones may be similar to icelandic pseudocraters somewhat larger steeper cones with smaller crater cone ratios which also occur in eastern acidalia may be analogs of terrestrial cinder cones

transitional morphology in west deuteronilus mensae mars implications for modification of the lowland upland boundary abstract west deuteronilus mensae which lies along the lowland upland boundary of mars at 45 latitude 345 longitude exhibits both gradational l a rossbacher 1985 in models in geomorphology woldenberg ed pp 343 372 allen unwin boston and fretted terrain r p sharp 1973 j geophys res 78 4073 4083 boundary types to the west the boundary is gradational and to the east it is defined by fretted terrain the two types of boundaries do not merge with one another within the west deuteronilus mensae region however the gradational boundary materials appear to overlap the fretted terrain by about 500 km contacts between units associated with the gradational boundary and the fretted terrain boundary can both be recognized in the region of overlap the fretted terrain can be identified as much as 300 km north of the gradational boundary in this region lowland units associated with the gradational boundary embay canyons of the fretted terrain in a topographically conformal fashion changes in the fretted terrain across the gradational boundary from uplands to lowlands include a reduction of canyon wall slopes and depths such that the fretted terrain north of the gradational boundary appears mantled but not obscured there are at least two major classes of processes which might explain the lateral overlap 1 erosion of stratified upland terrain and 2 deposition of plains materials onto the sloping upland margin and fretted terrain erosion of stratified upland terrain does not adequately explain the plainward decrease in crater densities across the gradational boundary nor is it consistent with evidence that lowland plains material appears to onlap the sloping upland margin in several places of the possible plains emplacement mechanisms eolian deposition would not produce the sharp apparently topographically conformal gradational unit contacts volcanics plains emplacement would not preserve the complex geometry of the underlying fretted terrain sediment deposition in either a liquid or ice covered sea could produce the draped appearance of the fretted terrain outflow channels along the lowland upland boundary particularly those of the circum chryse and west elysium regions may have flooded the northern lowlands to depths of tens to hundreds of meters the gradational unit contacts may represent the shorelines of such a sea the scale of characteristic morphologies along these contacts may require an unfrozen condition of sufficient duration to allow lacustrine style wave erosion and redistribution of material along the contacts our limited understanding of the martian paleoclimate and h 2 o inventories allows the possibility of clement periods in the past and other geological evidence e g small valley networks and outflow channels strongly suggests an extensive role of liquid water

coastal geomorphology of the martian northern plains the paper considers the question of the formation of the outflow channels and valley networks discovered on the martian northern plains during the mariner 9 mission parker and saunders 1987 and parker et al 1987 1989 data are used to describe key features common both in the lower reaches of the outflow channels and within and along the margins of the entire northern plains it is suggested that of the geological processes capable of producing similar morphologies on earth lacustrine or marine deposition and subsequent periglacial modification offer the simplest and most consistent explanation for the suit of features found on mars

observations of the north polar region of mars from the mars orbiter laser altimeter elevations from the mars orbiter laser altimeter mola have been used to construct a precise topographic map of the martian north polar region the northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5 kilometer deep hemispheric depression that is contiguous with the area into which most outflow channels emptied polar cap topography displays evidence of modification by ablation flow and wind and is consistent with a primarily h2o composition correlation of topography with images suggests that the cap was more spatially extensive in the past the cap volume of 1 2 3 10 6 to 1 7 3 10 6 cubic kilometers is about half that of the greenland ice cap clouds observed over the polar cap are likely composed of co 2 that condensed out of the atmosphere during northern hemisphere winter many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography

geology of the mer 2003 elysium candidate landing site in southeastern utopia planitia mars 1 the nasa mars exploration rover mer project has been considering a landing site ellipse designated ep78b2 in southeastern utopia planitia southwest of elysium mons the site appears to be relatively safe for a mer landing site because of its predicted low wind velocities in mesoscale atmospheric circulation models and its low surface roughness at various scales as indicated by topographic and imaging data sets previously the site s surface rocks have been interpreted to be marine sediments or lava flows in addition we suggest that late noachian to early hesperian collapse and mass wasting of noachian highland rocks contributed to the deposition of detritus in the area of the ellipse furthermore we document partial late hesperian to early amazonian resurfacing of the ellipse by flows and vents that may be of mud or silicate volcanic origin a rover investigation of the utopia landing site using the mer athena instrument package might address some fundamental aspects of martian geologic evolution such as climate change hydrologic evolution and magmatic and tectonic history

case for periodic colossal jokulhlaups from pleistocene glacial lake missoula two classes of field evidence firmly establish that late wisconsin glacial lake missoula drained periodically as scores of colossal jokulhlaups glacier outburst floods 1 more than 40 successive flood laid sand to silt graded rhythmites accumulated in back flooded valleys in southern washington hiatuses are indicated between flood laid rhythmites by loess and volcanic ash beds disconformities and nonflood sediment between rhythmites are generally scant because precipitation was modest slopes gentle and time between floods short 2 in several newly analyzed deposits of pleistocene glacial lakes in northern idaho and washington lake beds comprising 20 to 55 varves average 30 40 overlie each successive bed of missoula flood sediment these and many other lines of evidence are hostile to the notion that any two successive major rhythmites were deposited by one flood they dispel the notion that the prodigious floods numbered only a few the only outlet of the 2 500 km 3 glacial lake missoula was through its great ice dam and so the dam became incipiently buoyant before the lake could rise enough to spill over or around it like grimsvotn iceland lake missoula remained sealed as long as any segment of the glacial dam remained grounded when the lake rose to a critical level 600 m in depth the glacier bed at the seal became buoyant initiating underflow from the lake subglacial tunnels then grew exponentially leading to catastrophic discharge calculations of the water budget for the lake basin including input from the cordilleran ice sheet suggest that the lakes filled every three to seven decades the hydrostatic prerequisites for a jokulhlaup were thus re established scores of times during the 2 000 to 2 500 yr episode of last glacial damming j harlen bretz9s spokane flood outraged geologists six decades ago partly because it seemed to flaunt catastrophism the concept that lake missoula discharged regularly as jokulhlaups now accords bretz9s catastrophe with uniformitarian principles

origin of giant martian polygons extensive areas of the martian northern plains in utopia and acidalia planitiae are characterized by polygonal terrane polygonal terrane consists of material cut by complex troughs defining a pattern resembling mudcracks columnar joints or frost wedge polygons on earth however the martian polygons are orders of magnitude larger than these potential earth analogues leading to severe mechanical difficulties for genetic models based on simple analogy arguments plate bending and finite element models indicate that shrinkage of desiccating sediment or cooling volcanics accompanied by differential compaction over buried topography can account for the stresses responsible for polygon troughs as well as the large size of the polygons although trough widths and depths relate primarily to shrinkage the large scale of the polygonal pattern relates to the spacing between topographic elevations on the surface buried beneath polygonal terrane material geological relationships favor a sedimentary origin for polygonal terrane material but our model is not dependent on the specific genesis our analysis also suggests that the polygons must have formed at a geologically rapid rate

identification of volcanic rootless cones ice mounds and impact craters on earth and mars using spatial distribution as a remote sensing tool 1 this study aims to quantify the spatial distribution of terrestrial volcanic rootless cones and ice mounds for the purpose of identifying analogous martian features using a nearest neighbor nn methodology we use the statistics r ratio of the mean nn distance to that expected from a random distribution and c a measure of departure from randomness we interpret r as a measure of clustering and as a diagnostic for discriminating feature types all terrestrial groups of rootless cones and ice mounds are clustered r 0 51 0 94 relative to a random distribution applying this same methodology to martian feature fields of unknown origin similarly yields r of 0 57 0 93 indicating that their spatial distributions are consistent with both ice mound or rootless cone origins but not impact craters each martian impact crater group has r 1 00 i e the craters are spaced at least as far apart as expected at random similar degrees of clustering preclude discrimination between rootless cones and ice mounds based solely on r values however the distribution of pairwise nn distances in each feature field shows marked differences between these two feature types in skewness and kurtosis terrestrial ice mounds skewness 1 17 1 99 kurtosis 0 80 4 91 tend to have more skewed and leptokurtic distributions than those of rootless cones skewness 0 54 1 35 kurtosis 0 53 1 13 thus nn analysis can be a powerful tool for distinguishing geological features such as rootless cones ice mounds and impact craters particularly when degradation or modification precludes identification based on morphology alone

thermophysical properties of the mer and beagle ii landing site regions on mars 1 we analyzed remote sensing observations of the isidis basin gusev crater and meridiani planum landing sites for beagle ii mer a spirit and mer b opportunity spacecraft respectively we emphasized the thermophysical properties using daytime and nighttime radiance measurements from the mars global surveyor mgs thermal emission spectrometer and mars odyssey thermal emission imaging system themis and thermal inertias derived from nighttime data sets themis visible images mgs mars orbiter camera moc narrow angle images and mgs mars orbiter laser altimeter mola data are incorporated as well additionally the remote sensing data were compared with ground truth at the mer sites the isidis basin surface layer has been shaped by aeolian processes and erosion by slope winds coming off of the southern highlands and funneling through notches between massifs in the gusev region surface materials of contrasting thermophysical properties have been interpreted as rocks or bedrock duricrust and dust deposits these are consistent with a complex geological history dominated by volcanic and aeolian processes at meridiani planum the many layers having different thermophysical and erosional properties suggest periodic deposition of differing sedimentological facies possibly related to clast size grain orientation and packing or mineralogy

surface characteristics and degradational history of debris aprons in the tempe terra mareotis fossae region of mars abstract we have documented the surface characteristics and degradational history of a population of 65 lobate debris aprons in the tempe terra mareotis fossae region of mars these aprons were compared to other martian debris aprons to evaluate similarities and differences among different populations which can provide insight into the dominant controls on apron development tempe mareotis debris aprons found at the bases of isolated or clustered massifs escarpments and crater interior walls were studied using viking orbiter mars global surveyor and mars odyssey datasets in a gis database six textures related to degradation of apron surfaces are identified in moc images and they are divided into two groups an upper surface group and a lower surface group degradation occurs within an inferred smooth upper surface mantle of ice and debris producing a sequence of pitted ridge and valley and knobby textures of the upper surface group where upper surface materials have been removed smooth and ridged textures of the lower surface group are exposed degradation to various depths may expose lower surface materials which may consist of the main apron mass remnants of mantling deposits or both a combination of geologic processes may have caused the degradation including ice sublimation ice melt and eolian activity apron surfaces have lower maximum thermal inertias and mean surface temperatures than adjacent plains surfaces which may be explained by the trapping of unconsolidated materials in low lying pits and valleys formed by surface degradation or from the disruption of crusts on degraded portions of apron surfaces one feature observed only on tempe mareotis debris aprons are broad ridges which mimic the shape of massif bases for tens of kilometers we propose these to be constructional features that could have formed during cycles of increased debris production apron morphometric parameters including area volume slope thickness relief and h l were compiled and the results show that tempe mareotis aprons have average surface areas volumes and frontal thicknesses that are 2 3 times smaller than eastern hellas aprons within the tempe mareotis population escarpment related aprons are larger than massif related aprons suggesting that aprons with larger source areas have potentially greater volatile accumulation translating into longer apron travel distances and lower h l values

planetary science refilling the oceans of early mars the northern plains of mars are thought to have harboured an ocean more than 3 6 billion years ago delta deposits and river valley termini ring the proposed seabed and define an equipotential palaeoshoreline

possible ancient oceans on mars evidence from mars orbiter laser altimeter data high resolution altimetric data define the detailed topography of the northern lowlands of mars and a range of data is consistent with the hypothesis that a lowland encircling geologic contact represents the ancient shoreline of a large standing body of water present in middle mars history the contact altitude is close to an equipotential line the topography is smoother at all scales below the contact than above it the volume enclosed by this contact is within the range of estimates of available water on mars and a series of extensive terraces parallel the contact in many places

origin and large scale erosional features of glacial lake spillways in the northern great plains deglaciation of the northern great plains produced two basic types of fluvial systems 1 depositional regimes produced by the action of glacial melt water that formed outwash plains and 2 highly erosive systems produced by the sudden rapid drainage of glacial lakes that formed spillways spillways are huge deeply incised trenches that display all of the characteristics of fluvial channels glacial lakes drained in weeks or months and discharges of 10 5 m 3 s were attained at bankfull stage seven spillway systems studied were formed as a consequence of the sudden rapid draining of glacial lakes many other large valleys in the mid continent area and other glaciated regions were probably formed by the same process spillways consist of deeply incised inner channels commonly flanked by broad scoured outer zones initial stages of flow produced shallow anastomosing channels continued erosion produced longitudinal grooves streamlined erosional residuals and surficial boulder lag deposits inner channels developed by the enlargement of one or more centrally located longitudinal grooves the development of erosional residuals was initiated by the incision of shallow anastomosing channels the interchannel areas were progressively modified from irregular quadrilateral or elliptical shapes to an equilibrium minimum drag lemniscate shape as glacial lake drainage proceeded correlations between length and width length and area width and area and length width ratio and k a shape parameter of the lemniscate loop are very high for all erosional residuals studied although only 20 of the residuals display an equilibrium lemniscate shape stable relationships between length width and area of erosional residuals are therefore established very early and are maintained throughout the erosional modification to the lemniscate shape the only shape factor tested which can be used to quantitatively differentiate lemniscate from nonlemniscate erosional residuals is the position of maximum width as measured by the ratio of the length from the lee to the point of maximum width to the total length xm l the mean xm l ratio for erosional residuals in a spillway segment is an indication of the relative duration of flood flows that produced the spillway

a comparison of the thermal and radar characteristics of mars abstract there is a correlation between martian thermal inertia and radar cross section data centered on 22 latitude the correlation is strongest with 70 cm radar except between longitudes 10 and 90 where there is a slight anticorrelation and gets progressively weaker at 12 5 and 3 8 cm wavelengths respectively a correlation is expected because of the dependence of both properties on density but an increase in the average particle size of the surface with increasing dielectric constant is also required in order to explain the data this may take the form of an increased number of small rocks the anticorrelation may result from either the effects of atmospheric dust on the surface temperature or from the effects on radar of local variations in large scale roughness or scattering by rocks the relative behavior between the wavelengths can be understood in terms of appropriately sized rocks which act as radar scatterers the trend of the correlation agrees with the dichotomy of the planet into two types of terrain as noted in other remote sensing data and is consistent with an erosional versus depositional surface nature variations in the surface dielectric constant inferred from the 3 8 cm radar data can explain discrepancies between 2 8 cm radio emission observations and a simple model based on the global distribution of thermal inertia and albedo

the giant polygons of utopia northern martian plains much of utopia planitia is underlain by polygonal terrane most of the troughs defining the polygons are 250 m to 1 km wide typical diameters of polygons are 4 5 km these dimensions are orders of magnitude greater than the corresponding dimensions for familiar polygonal structures on earth consequently the earth structures are not valid mechanical analogues crater and superposition relationships indicate that trough formation was coeval with deposition of the polygonal terrane material based on crater age correlations with elysium volcanism and outflow channel activity either a volcanic or a sedimentary source for this material is possible tensile stresses responsible for the troughs were produced by cooling or dessication shrinkage plus differential compaction over a rough buried surface that is the structurally disrupted remnant of the cratered highlands shrinkage alone will produce polygons orders of magnitude smaller than those present but differential compaction will reflect the scale and pattern of the buried topography and thus control the scale and pattern of the giant polygons of utopia

generation of martian chaos and channels by debris flows abstract a debris flow mechanism is proposed to account for the formation of chaos and the large channels debouching into chryse planitia from the adjacent southern uplands of mars the debris is thought to have originated through a mechanism of collapse in the chaotic terrains which exist at the head of these channels as well as locally along the channels this proposition is based on the detailed morphologic similarities between martian channel source areas and the heads of both subaerial and subaqueous terrestrial debris flows the downslope movement of the debris produced the channels through a modification of earlier collapse areas b active bed erosion and c loading induced collapse the large scale channel geometry and the assemblage of related morphologic features on mars correspond tto that observed in subaqueous debris flow chutes on the mississippi delta front through various mechanisms of strain dependent viscosity decrease the debris flow gained mobility downstream turned into a debris avalanche and moved onto chryse planitia at very high velocities this high velocity avalanche eroded a series of streamlined remnants near the channel mouths and deposited its load as a thin blanket over a large area of the basin creating virtually no depositional relief

variations in the onset diameter for martian layered ejecta morphologies and their implications for subsurface volatile reservoirs we investigated regional variations in the onset diameter of craters displaying a single layer ejecta morphology within 30 latitude using viking imagery our results generally agree with those of previous studies which show onset diameters of 5 to 6 km in the equatorial region but we have identified localized regions with unusually small onset diameters the largest region is located in solis and thaumasia planae the 3 5 km onset diameter range in this area indicates a near surface ice rich reservoir depth 110 m this unusual concentration of near surface ice may have resulted from magmatic driven uplifts associated with the tharsis rise which modified parts of a regional aquifer drainage basin system and resulted in the transfer and concentration of subsurface volatiles in this region

origin of martian outflow channels the eolian hypothesis the ancient outflow channels on mars exhibit fossil flow patterns similar to current flow patterns in terrestrial desert regions eroded by wind we have modeled outflow channel formation by a cascade process in which sand sized particles produced by rock weathering in the chaotic terrain source areas of the outflow channels were transported by the wind across the adjacent plateau surfaces and sand blasting and deflating the surface comparisons of model predictions with photogeologic data suggest that rates of rock breakdown by physical and chemical action along the channels during the channel forming era must have been much higher than they have been on similar terrains formed after the channel era ended a tenuous atmosphere comparable to the present one could have transported materials sufficiently rapidly to excavate outflow channels in about 106 years however there may be difficulties in explaining how abrading particles could survive high velocity impacts in a thin atmosphere over the many hundreds or even thousands of kilometers that they were transported in outflow channels it is difficult to avoid the conclusion that a climate change affecting rock breakdown rates atmospheric density or both occurred early in martian history to end the era of outflow channel formation particulate materials generated during this era may be important components of the north circumpolar dune field and the polar layered deposits

oceans on mars formed early the geometry of putative ancient shorelines on mars suggests that these features were deformed by the growth of a massive volcanic region a finding that has implications for the climate geology and hydrology of early mars the geometry of putative ancient shorelines on mars suggests that these features were deformed by the growth of a massive volcanic region a finding that has implications for the climate geology and hydrology of early mars

ice sculpture in the martian outflow channels many landforms in martian outflow channels have characteristics that suggest sculpture by glaciers ice streams or ice sheets viking orbiter and terrestrial satellite images were examined at similar resolution to compare features of the martian outflow channels to features produced by the movement of ice on earth many resemblances were found they include the anastomoses sinuosities and u shaped cross profiles of valleys hanging valleys and linear scour marks on valley walls grooves and ridges on valley floors and streamlining of bedrock highs the question of whether ice could have moved in the martian environment is investigated since gradients on martian channel floors are extremely low or even reversed a certain thickness of ice is required to initiate glacial motion if ice filled the martian channels to the level of interior plateaus flow could have occurred even under present climatic conditions although warmer climates in the past would have been more favorable additionally if the channel fluids were brines ice might have been wet based and would have moved readily by slipping over the ground it is envisioned that springs or small catastrophic outbursts discharged fluids from structural outlets or chaotic terrains the fluids built icings that may have grown into substantial masses and eventually flowed like glaciers down preexisting valleys alternatively the fluids may have formed rivers or floods that formed ice jams and consolidated into icy masses in places where obstacles blocked their flow these masses of ice or slush were probably episodic and temporary but where they occurred within the channels they may have produced landforms that are characteristic of glacial sculpture on earth

sedimentary deposits in the northern lowland plains mars the lowland plains on mars have surfaces marked by large polygonal fracture patterns it was recently proposed that the fracture patterns were developed on sedimentary deposits from outflow channels we support this hypothesis because of the following observations 1 polygonal fracture patterns tend to occur in low areas on mars that apparently received influx of sediments the area of northern plains in which the fractures occur also forms a regional low 2 the fracture patterns are concentrated near reentrants of the plains projecting into the southern highlands not only are these reentrants associated with outflow channels but channels and polygonally fractured deposits have similar ages 3 sinuous ridges at the mouths of martian outflow channels resemble ridges in antarctic ice streams and ice shelves the similarity suggests that the martian material was transported from the southern highlands toward the northern plains as the antarctic material is transported from the continent toward the adjacent ocean overall it appears that a massive transfer of material took place midway in martian history either through the outflow channels or elsewhere along the northern highland scarp and that this material probably formed the deposits now characterized by polygonal fracture patterns

utopia basin mars characterization of topography and morphology and assessment of the origin and evolution of basin internal structure recently obtained mars orbiter laser altimeter mola topography has permitted a new assessment of the morphology structure and history of utopia planitia the new topographic data convincingly demonstrate that the utopia region is an impact basin as originally proposed by mcgill 1989 whose major topographic expression is a circular 1 3 km deep depression 3200 km in diameter utopia basin is the largest easily recognizable impact structure in the northern hemisphere of mars and is the only portion of the northern lowlands that exhibits a distinct large scale impact signature its presence there and its ancient age verify that a significant part of the northern lowlands dates back to the noachian period using slope maps derived from gridded topography we have mapped a series of linear slope anomalies within the basin and have analyzed their origin these features can be classified into two groups one oriented dominantly radial to the basin and the other oriented dominantly circumferential the circumferential features are tens of kilometers wide and hundreds of kilometers long and appear to remain relatively constant with respect to elevation we explore end member hypotheses 1 that the features formed by the direct action of water ice or 2 that they are tectonic wrinkle ridges we interpret the majority of these features to be due to tectonic deformation primarily wrinkle ridge formation modified by later sedimentation associated with the emplacement of the outflow channels and the formation of the vastitas borealis formation on the basis of the characteristics of these features and their association with polygonal terrain thumbprint terrain smoothness of units and evidence of sedimentary deposits we find that our results support earlier hypotheses proposing that a significant volume of water occupied utopia basin during the late hesperian period of outflow channel formation utopia basin differs significantly in depth and degradation state from the deeper and fresher appearing hellas basin although the two are both noachian in age a significant part of this difference seems reasonably interpreted to be the result of the extensive sedimentary and volcanic infilling history of the northern lowlands

scenarios for the evolution of life on mars received 10 march 2005 revised 2 august 2005 accepted 7 september 2005 published 22 november 2005 1 as the environmental histories of earth and mars have diverged drastically after the first few hundred million years so would the history of any life on them while earth has had liquid water on its surface for billions of years mars most likely had long dry and cold environments interspersed with warmer and wetter periods life thrived on earth but may have been severely restricted on mars there it could be present today in liquid water in or beneath ice sheets or glaciers in subterranean aqueous reservoirs especially in regions of elevated heat flow or in protected habitats such as lava tubes caves or cracks and fissures the potential for life is enhanced in regions where elevated heat flow may occur such as in parts of the tharsis and elysium volcanic provinces possible organisms would be chemoautotrophic psychrophiles adapted to a nutrient poor environment or photoautotrophic life in selected near surface habitats alternatively life may have evolved alternating cycles between active and dormant forms in which case microbes could be present in dormant forms close to the surface and in active forms in protected environments periodic liquid water on mars could have provided opportunities for biologic activity as well as evolutionary progress at the surface during the short lived climatic perturbations ancient organisms from any of these environments may also have left a detectable fossil record

search for signs of ancient life on mars expectations from hydromagnesite microbialites salda lake turkey the 9white rock9 constituting a portion of what may be a lacustrine sedimentary sequence near the margin of a crater c 90 km across in sabaea terra mars measures 18 15 km 180 540 m high it is re interpreted as a lens of magnesium carbonate precipitated where ground waters seeped into an ancient evaporating crater lake were life to have emerged on mars as seems feasible then the 9white rock9 might be expected to comprise a complex of stromatolitic mounds salda golu lake in turkey is taken as an analogue this enclosed lake is nearly surrounded and underlain by partially serpentinized harzburgite hydromagnesite stromatolites microbialites up to 7 m high coalesce to form a group of small islands 200 m across the microbialites are seen to be growing near the mouth of the usually dry salda river in the southwestern sector smaller developments of hydromagnesite encircle the lake and image processing of satellite data reveals a second extensive zone beneath the lake surface over a delta in the southeast individual columns a few centimetres high constitute bulbous mounds which are about 2 m in diameter these columns terminate in domes a centimetre or so across the domes are often annulated and are covered with a green biofilm a few millimetres thick comprised of cyanobactrial filaments the columns consist of alternating fine and coarse hydromagnesite layers differentiated on a millimetric scale the coarser layers near the surface still contain traces of the biofilm fossil microbialites were also discovered in the friable hydromagnesite cliffs shoreward of the main developments though the structures of the individual microbes have not survived instead the vestiges of microbialites are easily recognized and delineated by their coarse grain size and high porosity annular structures on their upper surfaces can be seen in places the intervening and overlying material also comprised of hydromagnesite is a semi lithified mud bulbous megascopic structures separated by finer grained magnesium carbonate mudstone within strata in the 9white rock9 would be strong evidence of a photosynthetic microbial genesis another deposit of white rock on the western margin of juventae chasma could have a similar origin

geology and mer target site characteristics along the southern rim of isidis planitia mars 1 the southern rim of the isidis basin contains one of the highest densities of valley networks several restricted paleolake basins and the stratigraphically lowest oldest terrain on mars geologic mapping in viking mgs moc and mola data odyssey themis data and other multispectral data products supports the presence of extensive fans of debris and sediments deposited along the inner rim of the isidis basin where large valleys enter the lowlands additional processes subsequent to the period of intense fluvial activity including mass flow analogous to some glacial processes have contributed to the materials accumulated on the margins of the isidis basin these have occurred along preexisting channels and valleys at the termini of major channels where they enter the plains along the highland lowland boundary if the abundant valley networks in highland terrains are the result of runoff accompanied by saturated groundwater flow as has been suggested in previous studies of ancient fluvial highland terrains then the extreme age and abundance of early valley networks in the libya montes highland rocks should have resulted in deposition of materials that record evidence for the long term presence of water in the form of aqueous alteration of polycrystalline constituents the material deposited along the basin margin is likely to consist of ancient altered highland rocks in several physical states weathered rounded and angular exposing both weathered and altered surfaces and exposures of alteration profiles in fractured faces and unweathered material from rock interiors debris fans shed off the southern rim of isidis planitia should contain materials that have experienced possible saturated groundwater flow residence within paleolake basins and derivative materials deposited during the most fluvially intensive part of martian geologic history many of these materials have also been reworked by ice related processes in situ measurements of the ancient crustal materials in the form of rocks within the debris fans and the weathered condition of the rocky material are potential sources for mineralogical evidence of climatic conditions in earliest martian geologic history the absence of alteration within rocks would on the other hand support the hypothesis that fluvial runoff during the earliest history of mars was geologically brief rather than long term and that long term saturated groundwater flow was not present determination of the presence or absence of alteration would have corresponding implications for hypotheses requiring the long term presence of aqueous solutions i e complex organic compounds and life a proposed mer site along the margin addresses realistic field science objectives of the mars exploration rover mission and the current goals of the mars exploration program in situ measurements may be important in deriving estimates of the longevity and intensity of past wetter climates

late pleistocene basaltic ash and volcanic eruptions in the bonneville basin utah microprobe analyses of glass and radiocarbon dating of samples associated with three basaltic volcanic ashes in the deposits of lake bonneville make the ashes useful stratigraphic markers for correlation within the bonneville basin two of the ashes were derived from tuff cones pavant butte and tabernacle hill that erupted into lake bonneville in what is now the black rock desert of south central utah near kanosh utah the pavant butte ash is interbedded with barrier beach lagoon marl that is slightly less than 16 000 yr old five radiocarbon dates on carbonate materials stratigraphically associated with the ash elsewhere in the sevier desert average 15 300 yr b p lake bonneville was in its transgressive phase about 15 m below the bonneville shoreline when the pavant butte eruption began at the tabernacle hill tuff cone a basalt flow that has pillows wave rounded cobbles and tufa on its outer margins was erupted into lake bonneville shortly after the tuff cone at or near the provo shoreline the tabernacle hill tuff cone and basalt flow are older than a radio carbon date of about 14 300 yr b p on tufa collected from the outer margin of the basalt flow but younger than the bonneville flood at about 14 500 yr b p the third ash informally termed the thiokol ash has been found interbedded with lake bonneville deposits in two exposures in northern utah and in sediment cores from the great salt lake it is about 25 000 yr old and may have been erupted from a volcanic field on the northwest shore of great salt lake or from the snake river plain microprobe analyses of glass from samples of the black rock desert ashes show them to have similar chemical compositions but glass from tabernacle hill can be distinguished from pavant butte glass by its higher concentrations of cao and p 2 o 5 systematic differences in chemical composition between samples of pavant butte glass can be explained by comagmatic processes thiokol glass has less sio 2 ai 2 o 3 mgo and na 2 o but greater total iron and p 2 o 5 than do the black rock desert glasses

mars a water rich planet abstract mars had outgassed at least 0 5 to 1 km of water 10 to 20 bar of co2 and 0 1 to 0 3 bar of n2 the volatiles that have been retained are mostly in the cratered uplands terrain softening fretted channels debris flows and closed depressions indicate that at least the upper 2 km of the cratered uplands at high latitudes 30 contain ice in amounts that exceed the porosity estimated to be 10 20 theoretical studies and lack of these features in the cratered uplands at low latitudes suggest that the upper 1 km of the uplands at low latitudes is ice poor however valley networks indicate that water was present near the surface early in the planet s history although in amounts smaller than at high latitudes the entire upper 1 km planetwide is estimated to have contained 75 125 m of water at the end of heavy bombardment the largest sink for water is the megaregolith below 1 km episodic eruption of water from the deep megaregolith cut many of the large outflow channels from the volume of water needed to cut the circum chryse channels and assuming uniform planetwide distribution of water the deep megaregolith is estimated to have contained at least 350 m of water at the end of heavy bombardment thereby giving a total minimum inventory of 424 475 m planetwide most of the water lost from the low latitude uplands by diffusion and in cutting the valley networks is now believed to be in the polar layered terrains most of the water involved in cutting the outflow channels is in the low lying northern plains where a variety of features that have been attributed to ground ice is present a large fraction of the planet s surface has been overplated with water poor volcanics of which we have samples in the snc meteorites the younger volcanics have reacted extensively with the old volatile rich basement some of the co2 and n2 outgassed was lost during heavy bombardment by impact erosion of the atmosphere and other processes the remaining was fixed carbonates and folded deep into the megaregolith during heavy bombardment

the utopia isidis overlap possible conduit for mud volcanism on mars abstract the largest areal concentration of pitted cones on mars is located in the southwest section of utopia basin this particular area of pitted cones has been attributed to mud volcanism several factors may have facilitated extensive mud volcanism at this location the concentration of pitted cones is located where utopia basin intersects isidis basin both features are multi ring impact basins on earth seismic investigations have shown that the outer rings of the chicxulub multi ring impact basin extend to the mohorovicic discontinuity moho if this is true on mars as well the fractures could act as conduits for water from utopia planitia the site of a large putative water body it has been shown that methane can be generated at the mantle on earth on mars this possible source of methane could combine with the infiltrated water to generate clathrates while methane is not currently being released at the location of the pitted cones it could have been in the past three locations of methane release have been observed on mars two of which are located on the same outer ring of isidis basin that intersects the pitted cone population the area of utopia basin that contains the large population of pitted cones is adjacent to the highland lowland boundary where extensive deposition would have occurred extensive deposition combined with the potential for methane release may have contributed to the large population of pitted cones in this area of the utopia basin

extensive hesperian aged south polar ice sheet on mars evidence for massive melting and retreat and lateral flow and ponding of meltwater local and regional mars orbiter laser altimeter mola topographic data support the presence of an extensive hesperian aged volatile rich south polar deposit the dorsa argentea formation hd and related units underlying the present amazonian aged polar cap api residual ice and apl layered terrain and covering a surface area that could be as large as 2 94 106 km2 about 2 of the surface of mars over twice the area of the present amazonian aged south polar deposits the deposit characteristics indicate that it contained significant quantities of water ice in amounts comparable to present day polar deposits several lines of evidence for melting indicate that the ice sheet deposits underwent melt back and liquid water drainage into surrounding lows including a large valley near the crater schmidt and the argyre basin narrow sinuous ridges lie in a broad linear depression extending from a high near the present polar cap continuously downslope to near the distal portion of hd the new topographic data support the interpretation of these ridges as eskers representing meltwater distribution networks at the base of the receding deposit extensive development of large pits and depressions cavi have previously been interpreted as eolian etching or basal melting of ice rich deposits analysis of mola topography supports the interpretation that they represent basal melting of ice rich deposits and shows that they have links to the esker systems volumetric considerations and topographic lineations suggest that some of the basal melting occurred beneath regions presently occupied by apl and that some of the liquid water formed ponds and lakes in the distal parts of hd the presence of pedestal craters is further evidence of the removal of extensive volatile rich deposits and contributes to the quantitative measure of the former deposit thickness where did the melt products go inspection of the margins of the dorsa argentea formation reveals several large channels that begin there and drain downslope for distances between 900 and 1600 km onto the floor of the argyre basin some 3 5 4 0 km below their origin these channels do not exhibit tributaries their broad lateral distribution supports other evidence that deposit melting was areally very widespread and volumetrically significant and that a large part of the meltwater entered the surface distribution system and was deposited on the floor of the argyre basin over 1000 km away estimates of the present deposit thicknesses together with amounts of the deposit removed by meltback suggest that the original volume could have been as much as 5 9 106 km3 equivalent to a global layer of water 20 m deep if the deposit consisted of 50 volatiles a portion of these volatiles migrated across the surface to pond in adjacent valleys and basins and into the groundwater system a significant portion of the volatiles remain in the deposit representing a net removal from the atmosphere and from the active hydrologic system in early to middle mars history and forming an accessible record of aqueous conditions and possible biological environments dating from that time

the mars observer laser altimeter investigation the primary objective of the mars observer laser altimeter mola investigation is to determine globally the topography of mars at a level suitable for addressing problems in geology and geophysics secondary objectives are to characterize the 1064 nm wavelength surface reflectivity of mars to contribute to analyses of global surface mineralogy and seasonal albedo changes to assist in addressing problems in atmospheric circulation and to provide geodetic control and topographic context for the assessment of possible future mars landing sites the principal components of mola are a diode pumped neodymium doped yttrium aluminum garnet laser transmitter that emits 1064 nm wavelength laser pulses a 0 5 m diameter telescope a silicon avalanche photodiode detector and a time interval unit with 10 ns resolution mola will provide measurements of the topography of mars within approximately 160 m footprints and a center to center along track foot print spacing of 300 m along the mars observer subspacecraft ground track the elevation measurements will be quantized with 1 5 m vertical resolution before correction for orbit and pointing induced errors mola profiles will be assembled into a global 0 2 deg x 0 2 deg grid that will be referenced to mars center of mass with an absolute accuracy of approximately 30 m other data products will include a global grid of topographic gradients corrected individual profiles and a global 0 2 deg x 0 2 deg grid of 1064 nm surface reflectivity

an assessment of evidence for pingos on mars using hirise pingos are small hills with cores of ice formed by injection and freezing of pressurized water the possibility of pingos on mars is of particular interest because of the associated implications for liquid water we have systematically searched for candidate pingos using images from the high resolution imaging science experiment hirise camera since pingos are expected to develop surface fractures due to extension of the frozen ground over the ice core we have searched for fractured features and identified a variety of mounds these features are confined to the martian mid latitudes in the bands where gullies are also most common the observed fractured mounds have a variety of morphologies and are likely of multiple origins isolated fractured mounds found on the floors of gullied craters in the southern hemisphere match the general morphologic characteristics of terrestrial pingos and are the best candidates for martian pingos but there is currently no direct evidence for presence of ice cores and it is difficult to produce the necessary water volumes so these features should still be interpreted with caution other fractured mounds appear more likely to be erosional remnants of an unusual mantling layer or possibly thermokarst structures flat topped mounds in utopia have some characteristics fracture pattern and latitudinal distribution consistent with pingos but differ in other aspects such as shape and setting while we do not rule out a pingo origin we prefer an erosional model for these enigmatic features

putative shorelines in northern arabia terra mars 1 three putative shorelines first proposed by parker et al 1989 are topographically and morphologically evaluated within a 700 000 km2 study area in northern arabia terra mars results are consistent with a shoreline interpretation for the arabia and deuteronilus contacts but do not support the proposed acidalia shoreline the arabia contact follows an equipotential surface with a mean elevation of 3707 m and a mean deviation of 13 m for deuteronilus results suggest that the originally proposed shoreline represents two distinct regional shorelines because two separate portions of the original deuteronilus contact approximate equipotential surfaces of 4200 m 5 m and 4000 m 6 m for both the deuteronilus and arabia contacts there is geomorphic evidence for erosion and some landforms are similar to analogous terrestrial coastal landforms these results permit but do not prove the past existence of an ocean ponded within the northern lowlands possibly as recently as the amazonian

ground ice on mars inventory distribution and resulting landforms abstract most 90 of the estimated original volume of outgassed water on mars cannot be satisfactorily accounted for by exospheric escape or storage in the atmosphere as frost or in the permanent north polar ice cap the balance may be stored as ground ice in the martian cryosphere a zone of permanently frozen ground that is protected from the atmosphere by a debris cover ground ice can exist throughout the entire cryosphere but it need not fill it if the ground ice does fill the cryosphere then excess water can exist in a confined aquifer the theoretical distribution of ground ice can be tested by identification of forms on the martian surface that may be related to the presence of subsurface ice the observed features that are most likely to reflect ground ice are thermokarst like pits and debris flows landforms with ambivalent origins include polygonally patterned ground lobate ejecta blankets craters with central pits and curvilinear features the most persuasive morphologic evidence for ground ice is thermokarst pits and debris flows the thermokarst pits are primarily located in the volcanic regions of tharsis and elysium the association of ice related features with these volcanic areas suggests that these forms are not directly latitude dependent activation by orbital variations could produce periodic multiple episodes of melting that are dependent upon latitude the presence of ice related features in both hemispheres and the equatorial region of mars indicates that ground ice may be or have been present over the entire planet as predicted by the cryosphere model

amazonian geologic history of the echus chasma and kasei valles system on mars new data and interpretations abstract new high resolution datasets have prompted a mapping based study of the 2500 km long echus chasma and kasei valles system that utilizes geomorphic details stratigraphic relations and cratering statistics derived from the new datasets our results suggest that between the hesperian and amazonian epochs on mars 3 7 ga to recent the study area was affected by at least 4 episodes of widespread volcanic activity and 4 periods of episodic fluvio glacial activity this paper discusses the amazonian