observations of periglacial landforms in utopia planitia with the high resolution imaging science experiment hirise 1 the region of western utopia planitia 80 105 e 40 55 n displays several types of landforms similar to earth periglacial features including scallop shaped depressions and networks of polygonal terrains the scalloped depressions have been proposed to originate from thermokarstic processes such as sublimation and or melting of near surface ground ice using hirise imagery we characterize these depressions and several associated distinct polygon networks in unprecedented morphologic and topographic detail and investigate support for an ice based degradation process the scalloped depressions and interior polygons and ridges are found to evolve together mainly influenced by sublimation local proximity of ground ice to the surface and obliquity variations

concentric crater fill in utopia planitia history and interaction between glacial brain terrain and periglacial mantle processes abstract 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

desiccation mechanism for formation of giant polygons on earth and intermediate sized polygons on mars results from a pre fracture model we present a pre fracture incrementally non linear elastic hydric model to constrain the models of formation of giant spacing of 20 300 m desiccation cracks on earth and possibly intermediate sized 80 to 350 m polygonal networks of cracks located in many impact craters on mars which have been interpreted to form by desiccation as opposed to thermal contraction el maarry et al 2010 the results of the model show that tensile stresses rise monotonically with desiccation however in soils with diffusivities below 10 4 m2 s it is not possible to generate high enough stresses to cause fracturing on the other hand intermediate values between 10 2 and 10 4 m2 s create optimum conditions for the formation of cracks at the time scales suggested for the formation of giant desiccation polygons on earth our model clearly shows that for typical diffusivity values of clayey soils with a considerable amount of smectites enough stress can build up to stimulate cracking of various spatial scales these results corroborate earlier assumptions that giant desiccation polygons on earth occur through lowering of the water table rather than surface evaporation extending the model to mars shows that soils would crack within similar diffusivity limits but in slightly longer periods of time owing to the lower gravity finally a model for formation of desiccation cracks on mars is presented that shows that two main conditions need to be fulfilled for desiccation cracks to occur under current martian climatic conditions namely that the thermal and soil diffusivity conditions 1 allow for the formation of an unsaturated zone with a considerable thickness while at the same time 2 limiting the growth of the permafrost downward which would disrupt the cracking process

boulder movement at high northern latitudes of mars 1 we examine a narrow latitudinal band 60 n 70 n on mars to place constraints on the seasonally averaged velocity q of boulder movements over patterned ground these latitudes comprise a region of the northern lowlands where patterned ground covers nearly every surface here boulders meters in diameter are consistently found to be concentrated at or near the cracks that define the polygonal networks indicating a mobilization process because impact craters are the source for many boulders we can use craters and their degradation to estimate the time scales for boulder movement we study and catalog 1018 degraded impact craters 100 m d 1 km in 55 high resolution imaging science experiment hirise images we find that crater degradation occurs on a time scale 1 ma which is too recent for melting related mechanisms in a past warmer epoch clustering of boulders occurs at a time scale of a few ma or shorter which means that boulders on 5 20 m diameter polygons move at seasonal velocities q 1 10 m yr or faster

north to south asymmetries in the water equivalent hydrogen distribution at high latitudes on mars 1 water content and burial depths derived from thermal and epithermal neutron currents measured by the mars odyssey neutron spectrometer are used to determine north to south asymmetries and intercorrelations at high latitudes on mars our goal is to contrast observed asymmetries with predictions based on current climate conditions and potential regolith thermophysical and chemophysical properties the average mass fraction of water equivalent hydrogen within the buried layer is higher on average in the south between 60 and 75 latitude and is strongly anticorrelated with burial depth in both hemispheres these results argue that the observed water content at high latitudes may require differing north to south thermophysical and or chemophysical properties of the regolith

the sound and speed of ice wedge cracking arctic canada rifle like sounds produced by ice wedge cracking although seldom heard have been reported in the permafrost literature for a century the sounds similar to those produced by the rapid cracking of lake ice indicate a high speed of crack propagation the speed of ice wedge crack propagation has been measured at two field sites for the 1966 1989 period no evidence of rapid crack propagation has been detected at these sites the fracture patterns of ribs as seen on vertical crack faces and the numerous short interacting cracks as seen in plan view suggest slow rates of cracking enquiries made of many northern residents indicate that rifle like sounds are uncommon along the mainland coast from the alaska yukon boundary eastward to coppermine n w t but are heard more frequently in the arctic islands high speeds of crack propagation appear associated with sharp drops in temperature windblown sites and long straight ice wedges as a preliminary estimate crack propagation rates exceeding about 200

effects of dispersed particulates on the rheology of water ice at planetary conditions we have investigated the effects of initial grain size and hard particulate impurities on the transient and steady state flow of water ice i at laboratory conditions selected to provide more quantitative constraints on the thermomechanical evolution of the giant icy moons of the outer solar system our samples were molded with particulate volume fractions of 0 001 to 0 56 and particle sizes of 1 to 150 m deformation experiments were conducted at constant shortening rates of 4 4 10 7 to 4 9 10 4 s 1 at pressures of 50 and 100 mpa and temperatures 77 to 223 k for the pure ice samples initial grain sizes were 0 2 0 6 mm 0 75 1 75 mm and 1 25 2 5 mm stress strain curves of pure ice i under these conditions display a strength maximum u at plastic strains e 0 01 after initial yield followed by strain softening and achievement of steady state levels of stress ss at e 0 1 to 0 2 finer starting grain size in pure ice generally raises the level of u petrography indicates that the initial transient flow behavior is associated with the nucleation and growth of recrystallized ice grains and the approach to ss evidently corresponds to the development of a steady state grain texture effects of particulate concentrations 0 1 are slight at these concentrations a small but significant reduction in u with respect to that for pure water ice occurs mixed phase ice with 0 1 is significantly stronger than pure ice the strength of samples with 0 56 approaches that of dry confined sand the magnitude of the strengthening effect is far greater than expected from homogeneous strain rate enhancement in the ice fraction or from pinning of dislocations orowan hardening this result suggests viscous drag occurs in the ice as it flows around the hard particulates mixed phase ice is also tougher than pure ice extending the range of bulk plastic deformation versus faulting to lower temperatures and higher strain rates the high pressure phase ice ii formed in 0 56 mixed phase ice during deformation at high stresses bulk planetary compositions of ice rock 0 4 0 5 are roughly 2 orders of magnitude more viscous than pure ice promoting the likelihood of thermal instability inside giant icy moons and possibly explaining the retention of crater topography on icy planetary surfaces

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

thermal contraction crack polygons on mars a synthesis from hirise phoenix and terrestrial analog studies thermal contraction crack polygons are complex landforms that have begun to be deciphered on earth and mars by the combined investigative efforts of geomorphology environmental monitoring physical models paleoclimate reconstruction and geochemistry thermal contraction crack polygons are excellent indicators of the current or past presence of ground ice ranging in ice content from weakly cemented soils to debris covered massive ice relative to larger topographic features polygons may form rapidly and reflect climate conditions at the time of formation preserving climate information as relict landforms in the geological record polygon morphology and internal textural characteristics can be used to distinguish surfaces modified by the seasonal presence of a wet active layer or dry active layer and to delimit subsurface ice conditions analysis of martian polygon morphology and distribution indicates that geologically recent thermal contraction crack polygons on mars form predominantly in an ice rich latitude dependent mantle more likely composed of massive ice deposited by precipitation than by cyclical vapor diffusion into regolith regional and local heterogeneities in polygon morphology can be used to distinguish variations in ice content deposition and modification history and to assess microclimate variation on timescales of ka to ma analyses of martian polygon morphology guided by investigations of terrestrial analog thermal contraction crack polygons strongly suggest the importance of excess ice in the formation and development of many martian thermal contraction crack polygons implying the presence of an ice rich substrate that was fractured during and subsequent to obliquity driven depositional periods and continually modified by ongoing vapor equilibration processes

distribution of polygon characteristic scale in martian patterned ground terrain in the northern hemisphere using the fourier transform 1 permafrost patterned ground forms on the surface of nearly all landscapes between 50 n and 70 n on mars this landform appears in satellite imagery as an interconnected network of polygonal shapes previous studies used geomorphologic observations to characterize patterned ground terrains on mars these classification systems prove useful but suffer from somewhat subjective methods we find objective analysis of the polygons comprising patterned ground terrains on the surface of mars feasible using high resolution imaging science experiment imagery acquired from orbit we perform a two dimensional fourier transform on 124 images of patterned surfaces to characterize the spatial scale pertinent to scenes and analyze the distribution of these properties on the surface of mars between 50 n and 70 n we find two distinct sets of polygons large polygons which form below 60 n and small polygons primarily above 60 n with exception for sites within acidalia planitia our findings show similar trends to those found in previous studies but also fundamental differences in the populations of polygons above and below 60 n the polygons within 60 n 70 n share roughly the same polygonal scale implying that seasonal temperature change is not the only factor forcing polygon development as previous models found in some cases our method indicates the presence of multiple scales of polygons although it cannot quantify the larger scale this method in conjunction with observational analysis improves our ability to characterize surfaces and examine patterned ground terrains on mars

martian seasonal co2 ice in polygonal troughs in southern polar region role of the distribution of subsurface h2o ice the mars orbiter camera onboard the mars global surveyor has obtained several images of polygonal features in the southern polar region in images taken during the end of the southern spring when the surrounding surface is free of the seasonal frost co2 ice still appears to be present within the polygonal troughs in earth s polar regions polygons such as these are indicative of water ice in the ground below we analyzed the seasonal evolution of the thermal state and the co2 content of these features our 2 d model includes condensation and sublimation of the co2 ice a self consistent treatment of the variations of the thermal properties of the regolith and the seasonal variations of the local atmospheric pressure which we take from the results of a general circulation model we find that the residence time of seasonal co2 ice in troughs depends not only on atmospheric opacity and albedo of the co2 ice but also and most significantly on the distribution of water ice in the regolith optical properties of the atmosphere and surface co2 ice can be independently obtained from observations to date this is not true about the distribution of water ice below the surface our analysis quantifies the dependence of the seasonal cycle of the co2 ice within the troughs on the assumed distribution of the water ice below the surface we show that presence of water ice in the ground at a depth smaller than the depth of the troughs reduces winter condensation rate of co2 ice this is due to higher heat flux conducted from the water ice rich regolith toward the facets of the troughs

antarctic dry valleys microclimate zonation variable geomorphic processes and implications for assessing climate change on mars the antarctic dry valleys adv are generally classified as a hyper arid cold polar desert the region has long been considered an important terrestrial analog for mars because of its generally cold and dry climate and because it contains a suite of landforms at macro meso and microscales that closely resemble those occurring on the martian surface the extreme hyperaridity of both mars and the adv has focused attention on the importance of salts and brines on soil development phase transitions from liquid water to water ice and ultimately on process geomorphology and landscape evolution at a range of scales on both planets the adv can be subdivided into three microclimate zones a coastal thaw zone an inland mixed zone and a stable upland zone zones are defined on the basis of summertime measurements of atmospheric temperature soil moisture and relative humidity subtle variations in these climate parameters result in considerable differences in the distribution and morphology of 1 macroscale features e g slopes and gullies 2 mesoscale features e g polygons including ice wedge sand wedge and sublimation type polygons as well as viscous flow features including solifluction lobes gelifluction lobes and debris covered glaciers and 3 microscale features e g rock weathering processes features including salt weathering wind erosion and surface pitting equilibrium landforms are those features that formed in balance with environmental conditions within fixed microclimate zones some equilibrium landforms such as sublimation polygons indicate the presence of extensive near surface ice identification of similar landforms on mars may also provide a basis for detecting the location of shallow ice landforms that today appear in disequilibrium with local microclimate conditions in the adv signify past and or ongoing shifts in climate zonation understanding these shifts is assisting in the documentation of the climate record for the adv a similar type of landform analysis can be applied to the surface of mars where analogous microclimates and equilibrium landforms occur 1 in a variety of local environments 2 in different latitudinal bands and 3 in units of different ages documenting the nature and evolution of the adv microclimate zones and their associated geomorphic processes is helping to provide a quantitative framework for assessing the evolution of climate on mars

fracture networks in frozen ground fractures in frozen ground self organize into networks through interactions between sequentially emplaced fractures tensile stress and the developing fracture pattern from this viewpoint we model the development of networks on a lattice representing the ground surface on which fractures initiate propagate and arrest under a combination of uniform thermally induced tensile stress stress reduction near existing fractures and stochastic parameterization of heterogeneity in frozen ground and in insulating snow tensile stress from cooling tensile strength propagation threshold fracture depth and elastic properties are chosen to approximate properties of frozen ground using these parameters model networks assemble with properties similar to natural ice wedge networks including 1 individual fracture paths have lengths ranging from tens to hundreds of meters 2 fractures intersect to enclose regions with characteristic spacing between fractures of approximately 22 m 3 intersections between fractures are predominantly orthogonal with less common three way approximately equiangular intersections joint distributions of relative orientation and spacing between fractures from modeled networks and ice wedge networks at espenberg alaska are comparable at the level of variability in natural examples this similarity is consistent with the hypotheses that networks self organize by stress interactions between sequentially placed fractures in frozen ground and that networks are insensitive to the many details of fracture dynamics omitted from the model spacing between fractures in modeled networks is influenced by sub optimal placement of fractures during network development and increases nonlinearly with the length scale of stress reduction around a fracture three way approximately equiangular intersections form where modeled fractures arrest on the outside of bends in earlier fractures

identification of sublimation type thermal contraction crack polygons at the proposed nasa phoenix landing site implications for substrate properties and climate driven morphological evolution 1 we identify a surface within the nasa phoenix landing site area d characterized by boulder topped polygonally patterned mounds comparable in radius and cross sectional morphology to terrestrial sublimation polygons found in antarctica both martian and antarctic polygons display topographic asymmetry with shallow equator facing slopes and steep pole facing slopes interpreted to indicate insolation dependent differential sublimation of buried ice on the basis of morphological similarities we classify the phoenix box 1 polygons as sublimation polygons terrestrial sublimation polygons form where ice volumes exceeding available pore space occur in the shallow subsurface and where near surface conditions are too cold and dry to permit the development of saturated active layers conditions comparable to those recently modeled for mars in the phoenix landing site area d box 1 the identification of sublimation polygons on mars would provide direct evidence for shallow ground ice exceeding pore ice volumes and shed light on the emplacement mechanism of this ice

sedimentology and climatic environment of alluvial fans in the martian saheki crater and a comparison with terrestrial fans in the atacama desert abstract the deflated surfaces of the alluvial fans in saheki crater reveal the most detailed record of fan stratigraphy and evolution found to date on mars during deposition of at least the uppermost 100 m of fan deposits discharges from the source basin consisted of channelized flows transporting sediment which we infer to be primarily sand and gravel sized as bedload coupled with extensive overbank mud rich flows depositing planar beds of sand sized or finer sediment flow events are inferred to have been of modest magnitude probably less than 60 m3 s of short duration and probably occupied only a few distributaries during any individual flow event occasional channel avulsions resulted in the distribution of sediment across the entire fan a comparison with fine grained alluvial fans in chile s atacama desert provides insights into the processes responsible for constructing the saheki crater fans sediment is deposited by channelized flows transporting sand through boulder sized material and overbank mudflows sand size and finer and wind erosion leaves channels expressed in inverted topographic relief the most likely source of water was snowmelt released after annual or epochal accumulation of snow in the headwater source basin on the interior crater rim during the hesperian to amazonian periods we infer the saheki fans to have been constructed by many hundreds of separate flow events and accumulation of the necessary snow and release of meltwater may have required favorable orbital configurations or transient global warming

clastic patterned ground in lomonosov crater mars examining fracture controlled formation mechanisms the area surrounding lomonosov crater on mars has a high density of seemingly organised boulder patterns these form seemingly sorted polygons and stripes within kilometre scale blockfields patches of boulder strewn ground which are common across the martian high latitudes several hypotheses have been suggested to explain the formation of clastic patterned ground on mars it has been proposed that these structures could have formed through freeze thaw sorting or conversely by the interaction of boulders with underlying fracture polygons in this investigation a series of sites were examined to evaluate whether boulder patterns appear to be controlled by the distribution of underlying fractures and test the fracture control hypotheses for their formation it was decided to focus on this suite of mechanisms as they are characterised by a clear morphological relationship namely the presence of an underlying fracture network which can easily be evaluated over a large area it was found that in the majority of examples at these sites did not exhibit fracture control although fractures were present at many sites there were very few sites where the fracture network appeared to be controlling the boulder distribution in general these were not the sites with the best examples of organization suggesting that the fracture control mechanisms are not the dominant geomorphic process organising the boulders in this area

the fracture of water ice ih a short overview this paper presents a short overview of the fracture of water ice ih topics include the ductile to brittle transition tensile and compressive strength compressive failure under multiaxial loading compressive failure modes and brittle failure on the geophysical scale arctic sea ice cover europa s icy crust emphasis is placed on the underlying physical mechanisms where appropriate comment is made on the formation of high latitude impact craters on mars

convection in a catastrophic flood deposit as the mechanism for the giant polygons on mars a formational mechanism for the large scale polygons that are defined by intersecting fractures in the northern plains of mars is proposed in this work the presented model is based on rayleigh convection of interstitial water driven by an unstable density temperature gradient within a saturated porous medium catastrophic emplacement of water rich sediments into the martian northern plain basins could have provided a thick sedimentary layer in which rayleigh convection could have occurred convection within this active layer is proposed to have differentially thawed an underlying ice rich permafrost layer that had been at the planet s surface before being rapidly buried the resulting morphology of the permafrost subsurface is thought to have resembled the scalloped solid liquid interface morphology produced in terrestrial convective flow visualization studies the exact size and shape of the scallops on the frozen subsurface would have been controlled by the dimensions of the convection cells which are estimated to have had width to depth ratios of between 3 4 and 4 5 subsequent stresses e g gravity and bending stresses would have produced maximum tensile stresses in the overlying sediments preferentially above the subsurface topographic highs as described previously by mcgill and hills 1992 additional desiccation of the sediments would have required contraction of the sediment cover and would have produced large scale polygonal fractures along the preexisting weaknesses located above the raised subsurface topography thus the underlying subsurface geometric morphology would have been translated to the surface and would be represented by the large scale polygonal fractures visible in the viking orbiter and mars global surveyor images of the martian northern plains

polygon pattern geomorphometry on svalbard norway and western utopia planitia mars using high resolution stereo remote sensing data abstract polygonal systems formed by thermal contraction cracking are complex landscape features widespread in terrestrial periglacial regions the manner in which cracking occurs is controlled by various environmental factors and determines dimension shape and orientation of polygons analogous small scale features are ubiquitous in martian mid and high latitudes and they are also inferred to originate from thermal contraction cracking we studied the geomorphometry of polygonally patterned ground on svalbard to draw a terrestrial analogy to small scale polygonal structures in scalloped terrain in martian mid latitudes we performed a comparative quantitative terrain analysis based on high resolution stereo remote sensing data hrsc ax and hirise in combination with terrestrial field data and multivariate statistics to determine the relationship of polygon geomorphometry to local environmental conditions results show that polygonal structures on svalbard and in utopia planitia on mars are similar with respect to their size and shape a comparable thermal contraction cracking genesis is likely polygon evolution however is strongly related to regional and local landscape dynamics individual polygon dimensions and orthogonality vary according to age thermal contraction cracking activity and local subsurface conditions based on these findings the effects of specific past and current environmental conditions on polygon formation on mars must be considered on both earth and mars the smallest polygons represent young recently active low centered polygons that formed in fine grained ice rich material small low centered martian polygons show the closest analogy to terrestrial low centered ice wedge polygons the formation of composite wedges could have occurred as a result of local geomorphological conditions during past martian orbital configurations larger polygons reflect past climate conditions on both earth and mars the present degradation of these polygons depends on relief and topographical situation on svalbard the thawing of ice wedges degrades high centered polygons in contrast the present appearance of polygons in utopia planitia is primarily the result of contemporary dry degradation processes

thermokarst lakes and ponds on mars in the very recent late amazonian past the history of water is fundamental to understanding the geological evolution of mars and to questions concerning the possible development of life on the red planet today mars is cold and dry it

louth crater evolution of a layered water ice mound we report on observations made of the 36 km diameter crater louth in the north polar region of mars at 70 n 103 2 e high resolution imagery from the instruments on the mars reconnaissance orbiter mro spacecraft has been used to map a 15 km diameter water ice deposit in the center of the crater the water ice mound has surface features that include roughened ice textures and layering similar to that found in the north polar layered deposits features we interpret as sastrugi and sand dunes show consistent wind patterns within louth over recent time crism spectra of the ice mound were modeled to derive quantitative estimates of water ice and contaminant abundance and associated ice grain size information these morphologic and spectral results are used to propose a stratigraphy for this deposit and adjoining sand dunes our results suggest the edge of the water ice mound is currently in retreat

thermal inertia mapping of mars from 60 s to 60 n twenty micrometer brightness temperatures are used to derive the thermal inertia for 81 of the martian surface between latitudes 60 these data were acquired by the two viking infrared thermal mappers in 1977 and 1978 following the two global dust storms of 1977 the spatial resolution used is 2 in latitude by 2 in longitude and the total range in derived inertia is 1 to 15 10 3 cal cm 2 sec 12 k 1 the distribution of thermal inertia is strongly bimodal with all values of thermal inertia less than 4 10 3 cal cm 2 sec 12 k 1 being associated with three disjoint bright regions mostly in the northern hemisphere sufficient dust is raised in global storms to provide fine material adequate to produce these low inertia areas but the specific deposition mechanism has not been defined at the low resolution used no complete exposures of clean rock were found there is some tendency for darker material to be associated with higher thermal inertia although the trend is far from one to one the distribution of high and low inertia areas is sufficiently nonrandom to produce a variation in whole disk brightness temperature with central meridian longitude this variation and the change in surface kinetic temperature associated with dust storms are factors in establishing the whole disk brightness temperature at radio and infrared wavelengths and will be important for those who use mars as a calibration source

amazonian modification of moreux crater record of recent and episodic glaciation in the protonilus mensae region of mars abstract morphologic characteristics of ice rich landforms in the martian mid latitudes record evidence for significant modification of the landscape in response to spin axis orbital parameter driven shifts in the late amazonian climate these landforms are spatially distributed across the mid latitudes and their co existing presence has so far not been observed from a single crater to infer how exactly a terrain has been modified while mars was undergoing major moderate minor shifts in its late amazonian climate we have therefore carried out an in depth investigation of moreux crater 135 km centered at 41 66 n 44 44 e in the protonilus mensae region for identification of features associated with recent and episodic glacial events and for emphasizing the role played by these glacial events in the modification of the crater evidence for extensive modification of the surfaces over crater rim wall and around central peak by emplacement of multiple scales of ice rich landforms that represents large history of glacial activities was found from our results we document phases of major moderate minor glacial activities within the crater as 1 piedmont lobes lobate debris aprons linear valley fills 1 ga 100 ma 2 viscous flow features 30 0 1 ma and 3 gullies thermal contraction crack polygons 2 1 0 4 ma the form and distribution of the random valleys observed within moreux suggests their formation by pressure induced melting and flow occurring beneath an extensive layer of ice we also suggest that central peak of moreux probably acted as the locus for accumulation of ice snow and the diversity of glacial periglacial features within the crater was possibly controlled by differences in the amount of accumulated ice snow and the rate at which the terrain responded to the shifts in climate during subsequent periods of obliquity changes taken together these ice rich deposits within moreux suggest that sequential modification of the crater surfaces over the rim wall and around central peak has occurred over the last tens of millions of years of martian history this new evidence thus adds another well documented case to rapidly accumulating evidences for widespread glacial activity in the middle latitudes of mars in recent martian history

geologically recent gully polygon relationships on mars insights from the antarctic dry valleys on the roles of permafrost microclimates and water sources for surface flow we describe the morphology and spatial relationships between composite wedge polygons and mars like gullies consisting of alcoves channels and fans in the hyper arid antarctic dry valleys adv as a basis for understanding possible origins for martian gullies that also occur in association with polygonally patterned ground gullies in the adv arise in part from the melting of atmospherically derived wind blown snow trapped in polygon troughs snowmelt that yields surface flow can occur during peak southern hemisphere summer daytime insolation conditions ice cemented permafrost provides an impermeable substrate over which meltwater flows but does not significantly contribute to meltwater generation relationships between contraction crack polygons and sedimentary fans at the distal ends of gullies show deposition of fan material in polygon troughs and dissection of fans by expanding polygon troughs these observations suggest the continuous presence of meters thick ice cemented permafrost beneath adv gullies we document strong morphological similarities between gullies and polygons on mars and those observed in the adv inland mixed microclimate zone on the basis of this morphological comparison we propose an analogous top down melting model for the initiation and evolution of martian gullies that occur on polygonally patterned mantled surfaces

geographic variations in the thermal and diffusive stability of ground ice on mars to investigate the stability of ground ice within the top several meters of the martian regolith time dependent models of the thermal and diffusive behavior of the regolith have been developed the geographic distribution of thermal inertia and albedo as well as the latitudinal variation in insolation have been included in calculations of surface and subsurface temperatures between 60 latitude ground ice was found to be stable where the annual mean surface and subsurface temperatures were below the atmospheric frost point this generally occurs poleward of the mid latitudes the latitude poleward of which ground ice is stable varies by about 20 to 30 from one longitude to another geographic variations in thermal inertia and albedo are the primary factors controlling regional variations in ice stability calculations of temperatures at high and low obliquity suggest that ground ice would be stable globally at high obliquity and would not be stable between 60 latitude at low obliquity thermally driven diffusion of atmospheric water vapor within the regolith was modeled accounting for both ordinary molecular and knudsen transport and equilibrium between ice vapor and adsorbed phases atmospheric water vapor was found to be able to supply the top few meters of the regolith with ice in regions where the annual mean surface temperature was below the atmospheric frost point ice was found to begin condensing in as short as 1000 martian years rapid accumulation of ice in the pore space of the upper layers of the regolith acted to choke transport to lower layers and slow the diffusion process even so after 105 martian years in some cases as much as 30 to 40 of the available pore space accumulated ice the total amount of subsurface ice ranged from a few to more than 25 g cm2 within the top few meters in regions of stability ground ice was found to form below a depth where the annual average vapor pressure over ice was equal to the annual average atmospheric vapor pressure near the surface atmospheric vapor was not found to accumulate as ice below a depth where the seasonal temperature oscillations gave way to the geothermal gradient the time scales for condensation of ground ice were found to be comparable to that of orbital oscillations suggesting that the present geographic distribution of ground ice may depend on the orbital history of mars

a model for co isotopic signatures of evolving ground ice in the cold dry environments of earth and mars abstract the basics of the model rego are summarized including diffusive water vapor transport ice content adsorption and the isotopic ratios of the various water species inclusion of a temperature and stress strain solution is also described as are the effects of cracking when the tensile breaking strengths are exceeded cracking is viewed as a multi scale phenomena whereby the larger cracks are produced by chaining together smaller ones after some validation the model is applied to the upper university valley antarctic dry valleys data and to the phoenix landing site at lat 69n on mars for the university valley the model when forced by measured diurnal temperature cycles and known relative humidity reproduces some of the complex the ice content and isotope structure found in the upper university valley ground ice cores the model takes a few hundred years to fill the pores just under the ice table the excess ice observed in the university valley cores can be produced by thermal cracking combined with the diurnal temperature cycle time taken to achieve the observed excess ice content is of order 10 4 years there is limited subsurface data for the phoenix site but there are measured ice table depths surface thermal properties and met variables there is enough to do diurnal and seasonal runs of the rego model as with the university valley the upper few tens of centimeters icing are controlled by the diurnal temperatures largely in the warmer part of the year the observed ubiquitous pore full ice right at the ice table could be produced from a dry soil in about 10 3 a and the nearly pure ice patches could be produced by the cracking diffusion mechanism in about million years if shear stresses are included emplacement of ice down to 10 m is possible using the seasonal temperature cycle and cracking excess ice in the upper meter could produced by the model in about 6 10 6 a if the temperature at the phoenix site was 10 20 deg warmer

small scale polygonal features on mars seasonal thermal contraction cracks in permafrost a time dependent viscoelastic model of thermal stress in martian ice rich permafrost is developed to test the hypothesis that small scale polygonal features observed from orbit and by the viking lander 2 are the result of thermal contraction cracking as commonly occurs in terrestrial permafrost results indicate that significant tensile stress occurs in martian ice rich permafrost as a result of seasonal cycles in the ground temperature using conservative rheological parameters appropriate for ice at low temperatures tensile stresses poleward of about 20 to 30 latitude easily exceed the tensile strength assumed to be 2 to 3 mpa and fractures should readily form in the equatorial regions special conditions may allow tensile stresses to approach the tensile strength these results support a thermal contraction origin of observed small scale polygonal features and emphasize the utility of these features as valuable morphological indicators of ground ice

initiation and growth of martian ice lenses abstract water ice in the upper meters of the martian regolith is a major volatile reservoir although the geographic extent burial depth and thermal stability of this shallow ice are well understood its origin history and stratigraphy are not over the past decade a growing body of observational evidence has indicated that shallow ground ice exceeds the pore volume of its host soil over large regions of both martian hemispheres this is confounding given that 1 the physical theory that accurately predicts the location of ground ice also assumes that ice should be pore filling in the upper meter of regolith and 2 the phoenix spacecraft uncovered far more pore filling ice than excess ice at its landing site in the northern hemisphere the development of ice lenses by low temperature in situ segregation analogous to the processes that generate frost heave on earth has been hypothesized to explain shallow excess ice on mars we have developed a numerical model of ice lens initiation and growth in the martian environment and used it to test this hypothesis for the first time we carried out a large suite of numerical simulations in order to place quantitative constraints on the timing and location of ice lens initiation and on the magnitude of ice lens growth in a variety of host soils we find that ice lens initiation is a ubiquitous process in the martian high latitudes but the ultimate magnitude of lens growth or frost heave is sensitive to the properties of the host soil depending on the specific properties of martian soils in situ segregation may be a very slow process sufficient to explain the excess ice observed in the dodo goldilocks trench at the phoenix landing site but without regionally significant effects alternatively if clay sized particles or perchlorate salts are present in situ segregation may be a vigorous process that has significantly affected the stratigraphy of ground ice in the upper meter of regolith throughout the high latitudes

co evolution of polygonal and scalloped terrains southwestern utopia planitia mars abstract thermal contraction crack polygons and scalloped depressions two of the most common landforms found in utopia planitia mars have previously been linked to the presence of ice rich deposits in the subsurface although the formation and evolution of these features individually are relatively well understood little to no effort has been directed towards elucidating possible interactions that occur between them during their development thus the overarching goal of this research was to investigate if there is an evolutionary link between polygonal and scalloped terrains by correlating metrics representing polygon and scallop maturity a variety of statistical analyses were performed using hirise and mola datasets to quantify interactions between four sets of polygonal and scalloped terrains our results demonstrate the existence of a negative relationship between polygonal subdivision and surface elevation indicating that polygon networks become more evolved as the surface subsides these results suggest that the permafrost landscape in utopia planitia may once have been extremely ice rich and that multiple geomorphic processes may be responsible for its evolution ultimately this work demonstrates that landscape reconstruction is more complete when a system approach is followed quantifying interactions between landforms as opposed to examining an individual landform in isolation

high latitude patterned grounds on mars classification distribution and climatic control patterned grounds such as polygonal features and slope stripes are the signature of the presence of ground ice and of temperature variations in cold regions on earth identifying similar features on mars is important to understand its past climate as well as the ground ice distribution in this study young patterned grounds are classed and mapped from the systematical analysis of mars observer camera high resolution images these features are located poleward of 55 latitude which fits the distribution of ground ice found by the neutron spectrometer onboard mars odyssey thermal contraction due to seasonal temperature variations is the predominant process of formation of polygons formed by cracks which sizes vary from 15 to 300 m the small 40 m widespread polygons are very recent and degraded by the desiccation of ground ice from the cracks which enhances the effect of ice sublimation the large polygons 50 to 300 m located only around the south co2 polar cap indicate the presence of ground ice and thus outline the limit of the co2 ice cap they could be due to the blanketing of water ice deposits by the advances and retreats of the residual co2 ice cap during the last thousand years large 50 250 m and homogeneous polygons similar to ice wedge polygons hillslope stripes and solifluction lobes may indicate that specific environments such as crater floors and hillslopes could have been submitted to freeze thaw cycles possibly related to higher summer temperatures in periods of obliquity higher than 35 these interpretations must be strengthened by higher resolution images such as those of the hirise mission of the mars reconnaissance orbiter because locations with past seasonal thaw could be of major interest as potential landing sites for the phoenix mission

stratigraphical evidence of late amazonian periglaciation and glaciation in the astapus colles region of mars abstract recent modeling of the meteorological conditions during and following times of high obliquity suggests that an icy mantle could have been emplaced in western utopia planitia by atmospheric deposition during the late amazonian period costard f m forget f madeleine j b soare r j kargel j s 2008 lunar planet sci 39 abstract 1274 madeleine b forget f head j w levrard b montmessin f 2007 lunar planet sci 38 abstract 1778 astapus colles aba is a late amazonian geological unit located in this hypothesized area of accumulation that comprises an icy mantle tens of meters thick tanaka k l skinner j a hare t m 2005 us geol surv sci invest map 2888 for the most part this unit drapes the early amazonian vastitas borealis interior unit abvi to a lesser degree it overlies the early amazonian vastitas borealis marginal unit abvm and the early to late hesperian up plains unit hbu2 tanaka k l skinner j a hare t m 2005 us geol surv sci invest map 2888 landscapes possibly modified by late amazonian periglacial processes costard f m kargel j s 1995 icarus 114 93 112 mcbride s a allen c c bell m s 2005 lunar planet sci 36 abstract 1090 morgenstern a hauber e reiss d van gasselt s grosse g schirrmeister l 2007 j geophys res 112 doi 10 1029 2006je002869 e06010 seibert n m kargel j s 2001 geophys res lett 28 899 902 soare r j kargel j s osinski g r costard f 2007 icarus 191 95 112 soare r j osinski g r roehm c l 2008 earth planet sci lett 272 382 393 and glacial processes milliken r e mustard j f goldsby d l 2003 j geophys res 108 e6 doi 10 1029 2002je002005 5057 mustard j f cooper c d rifkin m k 2001 nature 412 411 414 tanaka k l skinner j a hare t m 2005 us geol surv sci invest map 2888 have been reported within the region researchers have assumed that the periglacial and glacial landscapes occur within the same geological unit the aba i e morgenstern a hauber e reiss d van gasselt s grosse g schirrmeister l 2007 j geophys res 112 doi 10 1029 2006je002869 e06010 tanaka k l skinner j a hare t m 2005 us geol surv sci invest map 2888 in this study we use hirise high resolution image science experiment mars reconnaissance orbiter imagery to identify the stratigraphical separation of the two landscapes and show that periglacial landscape modification has occurred in the geological units that underlie the aba not in the aba itself moreover we suggest that the periglacial landscape extends well beyond the perimeter of the aba and could be the product of wet cold climate processes these processes involve freeze thaw cycles and intermittently stable liquid water at or near the surface by contrast we propose that the aba is a very recent late amazonian geological unit formed principally by dry cold climate processes these processes comprise accumulation by atmospheric deposition and ablation by sublimation

variability of rock texture and morphology correlated with the clay bearing units at mawrth vallis mars 1 the clay units at mawrth vallis have been well characterized in hyperspectral data however a similar study of high spatial resolution high resolution imaging science experiment hirise data has not been previously conducted here the textures of the clay units are described and related to mineralogy across the central mawrth vallis region the nontronite bearing rocks appear tan in hirise color data and are polygonally fractured with polygons 2 5 m across in some cases the fractures appear wider and or have darker fill or the rocks are a darker brown the montmorillonite bearing rocks appear blue with regular polygons 0 5 1 5 m across sometimes there are larger polygons surrounded by regular polygons a square fracture pattern or the color appears yellow or mottled blue yellow kaolinite rich rocks are the brightest outcrops and are nonpolygonally fractured regions with spectra consistent with hydrated silica or the ferrous mineral component do not have unique textures hydrated silica bearing rocks appear yellow or mottled with a regular polygonal texture or yellow with hummocky appearance with no polygons it is also possible that dust sand on the surface alters the montmorillonite spectrum to appear like that of hydrated silica the ferrous component may be expressed as mottled coloring or as a bright fracture fill the nontronite and montmorillonite bearing units have remarkably consistent textures in this region allowing them to be uniquely identified in the mawrth vallis region in nonhyperspectral data sets such as ctx and hirise the morphology of the polygons in these two units suggests that their formation is likely dominated by desiccation and controlled by composition

micro relief development in polygonal patterned ground in the dry valleys of antarctica polygonal patterned ground in polar regions of both earth and mars has received considerable attention in comparison with the size shape and arrangement of the polygons the diverse micro relief and topography termed here simply relief of polygonal patterned ground have been understudied and yet the relief reflects important conditions and processes occurring directly below the ground surface and it can be observed readily in the field and through remote sensing herein we describe the relief characteristic of the simplest and relatively young form of patterned ground in the dry valleys of antarctic we also develop a numerical model to examine the generation of relief due to subsurface material being shouldered aside contraction cracks by incremental sand wedges growth and to down slope creep of loose granular material on the surface we model the longterm subsurface deformation of ice cemented permafrost as a non linear viscous material our modeling is guided and validated using decades of field measurements of surface displacements of the permafrost and relief this work has implications for assessing the activity of surfaces on earth and mars and much larger scale potential manifestations of incremental wedging in icy material namely the distinct paired ridges on europa

spatial relationships between patterned ground and ground ice detected by the neutron spectrometer on mars 1 patterned grounds like polygonal features are the signature of climatic effects in periglacial regions on earth identifying similar features on mars is important for an understanding of the past martian climate in this study we mapped fresh patterned landforms from the systematic analysis of mars orbiter camera high resolution images we show that most of them are distributed at latitudes poleward of 55 making a climatic control likely this distribution correlates to the distribution of ground ice detected by the neutron spectrometer aboard mars odyssey this correlation is likely the consequence of the neutron spectrometer detecting ice no deeper than about 1 m patterned ground formation requires ice in this range of depth because these features are triggered by the propagation of a thermal wave that is driven by seasonal or diurnal changes in insolation which affect the temperature in the uppermost ground layers sublimation seems to play a role in the shaping of many of the small patterns observed at latitudes between 55 and 70 no widespread polygonal features are correlated to the equatorial regions where hydrogen is detected by the neutron spectrometer

analysis of polygonal cracking patterns in chloride bearing terrains on mars indicators of ancient playa settings the ancient southern highlands on mars 3 5 gyr old contain 600 regions that display spectral evidence in the infrared for the presence of chloride bearing materials many of these locations were previously reported to display polygonal cracking patterns we studied more than 80 of the chloride bearing terrains using high resolution 0 25 0 5 m pixel images as well as near infrared spectral data to characterize the surface textures and the associated cracking patterns and mineralogies our study indicates that 75 of the studied locations display polygonal cracks that resemble desiccation cracks while some resemble salt expansion thrust polygons furthermore we detect spectrally the presence of smectites in association with 30 of the studied fractured terrains we note that smectites are a special class of swelling clay minerals that can induce formation of large desiccation cracks as such we suggest that the cracking patterns are indicative of the presence of smectite phyllosilicates even in the absence of spectral confirmation our results suggest that many chloride bearing terrains have a lacustrine origin and a geologic setting similar to playas on earth such locations would have contained ephemeral lakes that may have undergone repeated cycles of desiccation and recharging by a near surface fluctuating water table in order to account for the salt phyllosilicates associations these results have notable implications for the ancient hydrology of mars we propose that the morphologies and sizes of the polygonal cracks can be used as paleoenvironmental as well as lithological indicators that could be helpful in planning future missions

hirise observations of gas sublimation driven activity in mars southern polar regions i erosion of the surface the high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro has imaged the sublimation of mars seasonal co2 polar cap with unprecedented detail for one complete martian southern spring in some areas of the surface beneath the conformal coating of seasonal ice radiallyorganized channels are connected in spidery patterns the process of formation of this terrain erosion by gas from subliming seasonal ice has no earthly analog the new capabilities high resolution color and stereo images of hirise enable detailed study of this enigmatic terrain two sites are analyzed in detail one within an area expected to have translucent seasonal co2 ice and the other site outside that region stereo anaglyphs show that some channels grow larger as they go uphill implicating gas rather than liquid as the erosive agent dark fans of material from the substrate are observed draped over the seasonal ice and this material collects in thin to thick layers in the channels possibly choking off gas flow in subsequent years resulting in inactive crisscrossing shallow channels in some areas there are very dense networks of channels with similar width and depth and fewer fans emerging later in the season are observed subtle variations in topography affect the channel morphology a new terminology is proposed for the wide variety of erosional features observed

geomorphological characterisation and interpretation of a mid latitude glacier like form hellas planitia mars we describe and interpret the surface terrain types associated with a widely reported 4 km long midlatitude martian viscous flow feature vff the feature is located in the southern hemisphere on the poleward facing rim of a 60 km diameter crater in eastern hellas planitia high resolution imaging science experiment hirise images analysed in both 2d and 3d reveal that the upper margin of the feature is bounded by steep 30 headwalls typically some tens of metres high that are formed from unconsolidated material and characterised by a series of slope parallel linear incisions below these incised headwalls the feature flows at a general angle of 10 from a broad upper basin to a confined lower tongue that is bounded by a nested sequence of elongate raised ridges these characteristics are typical of several vffs in the region and are strikingly similar to moraine bounded valley glaciers on earth and we sub classify this feature as a glacier like form glf 1 the glf comprises five distinctive surface terrain types that contrast sharply with surface characteristics outside its bounding moraines four of these terrains scaly terrain polygonized terrain linear terrain and mound and tail terrain are located within the glf s innermost bounding moraine while the fifth rectilinear ridge terrain is located between its frontal moraines these terrains are mapped characterised and associated with possible mechanisms of formation to draw inferences about the glf s glaciology and glacial history this analysis suggests that the glf reached its maximal extent in the geologically recent past and that it may have been partially wetbased at that time subsequent to this phase the glf experienced an extended period of general recession that has been punctuated by several episodes of still stand or advance currently the glf s basin appears to be composed of a lower zone that is dominated by an exposed former glacier bed and an upper zone that may still contain a now degraded and dust mantled viscous mass similar to many partially glacierized basins on earth

temperature distribution inside and around a lava tube abstract we propose a model describing the thermal effects of a lava tube the tube is a circular cylinder embedded in a solid medium and filled with a newtonian liquid flowing under the gravity force steady state conditions are considered the velocity field in the tube evaluated by the navier stokes equation is introduced into the heat equation taking into account the viscous dissipation the temperature distribution is evaluated both inside the tube and in the surrounding solid medium under the assumption that the lava tube is embedded in a solid half space the surface heat flow due to the presence of the tube is calculated it is shown that heat flow measurements at the earth s surface can give information on the depth size and temperature of the buried lava tube

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 m 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

small scale trench in the north polar region of mars evolution of surface frost and ground ice concentration in this paper we attempt to answer the question how formation of a small scale trench in the martian regolith affects local distribution of the subsurface ice we are especially interested in the consequences of digging a trench to search for buried ice as has been done during the phoenix mars lander mission however the results may be also applicable for natural troughs or cracks we present results of simulations of diurnal exchange of water between the regolith and the atmosphere our model includes the heat and vapor migration in the regolith surrounding the trench as well as formation of diurnal frost we take into account scattering of light in the atmosphere and on the trench facets as well as changes of atmospheric humidity on diurnal and seasonal time scales our calculations show that the measurements of ice content in a sample obtained within one or two days from the beginning of digging should not be affected however on somewhat longer time scale at the south facing site of the trench the regolith can be significantly depleted from ice this effect should be taken into account if the excavation and taking samples from different depths will be performed in stages separated in time by a month or more

origin and significance of decameter scale polygons in the lower peace vallis fan of gale crater mars abstract decameter scale polygons are extensively developed in the bedded fractured bf unit of the lower peace vallis fan the polygons occur in a likely extension of the gillespie lake member north of yellowknife bay the section first drilled by the mars science laboratory msl mission we examine hypotheses for the origin of these polygons to provide insight into the history of gale crater the polygons are 4 30 m across square to rectangular and defined by 0 5 4 m wide generally straight troughs with orthogonal intersections polygon networks are typically oriented orthogonal systems with occasional nearly circular patterns hundreds of meters across potential origins include cooling of lava and for sedimentary units syneresis unloading weathering desiccation impact processes and cold climate thermal contraction cold climate thermal contraction is the hypothesis most consistent with the sedimentary nature of the bf unit and the polygon morphology geometry networks and apparent restriction to the coarse grained gillespie lake member a periglacial setting further provides the best analogs for the circular networks and is consistent with geologic context and msl data most of the decametric polygons appear to be ancient they are confined to the hesperian bf unit and only a few of their bounding fractures extend into younger or recently exposed units in this regard they differ from the majority of proposed thermal contraction polygons on mars as those are generally thought to be young features and accordingly the history of formation preservation and reactivation of the decametric polygons is likely to be more complex than that of any proposed young polygons on mars the decametric polygons in the bf unit may represent landforms developed in a cold but still comparatively wet interlude between a clement early mars and the much drier and colder planet of today

hirise observations of new impact craters exposing martian ground ice twenty small new impact craters or clusters have been observed to excavate bright material inferred to be ice at mid latitudes and high latitudes on mars in the northern hemisphere the craters are widely distributed geographically and occur at latitudes as low as 39 n stability modeling suggests that this ice distribution requires a long term average atmospheric water vapor content around 25 precipitable micrometers more than double the present value which is consistent with the expected effect of recent orbital variations alternatively near surface humidity could be higher than expected for current column abundances if water vapor is not well mixed with atmospheric co2 or the vapor pressure at the ice table could be lower due to salts ice in and around the craters remains visibly bright for months to years indicating that it is clean ice rather than ice cemented regolith although some clean ice may be produced by the impact process it is likely that the original ground ice was excess ice exceeding dry soil pore space in many cases observations of the craters suggest small scale heterogeneities in this excess ice the origin of such ice is uncertain ice lens formation by migration of thin films of liquid is most consistent with local heterogeneity in ice content and common surface boulders but in some cases nearby thermokarst landforms suggest large amounts of excess ice that may be best explained by a degraded ice sheet

potential desiccation cracks on mars a synthesis from modeling analogue field studies and global observations potential desiccation polygons pdps are polygonal surface patterns that are a common feature in noachian to hesperian aged phyllosilicate and chloride bearing terrains and have been observed with size scales that range from cm wide by current rovers to 10s of meters wide the global distribution of pdps shows that they share certain traits in terms of morphology and geologic setting that can aid identification and distinction from fracturing patterns caused by other processes they are mostly associated with sedimentary deposits that display spectral evidence for the presence of fe mg smectites al rich smectites or less commonly kaolinites carbonates and sulfates in addition pdps may indicate paleolacustrine environments which are of high interest for planetary exploration and their presence implies that the fractured units are rich in smectite minerals that may have been deposited in a standing body of water a collective synthesis with new data particularly from the hirise camera suggests that desiccation cracks may be more common on the surface of mars than previously thought a review of terrestrial research on desiccation processes with emphasis on the theoretical background field studies and modeling constraints is presented here as well and shown to be consistent with and relevant to certain polygonal patterns on mars

scalloped terrains in the peneus and amphitrites paterae region of mars as observed by hirise abstract the peneus and amphitrites paterae region of mars displays large areas of smooth geologically young terrains overlying a rougher and older topography these terrains may be remnants of the mid latitude mantle deposit which is thought to be composed of ice rich material originating from airfall deposition during a high obliquity period less than 5 ma ago within these terrains there are several types of potentially periglacial features in particular there are networks of polygonal cracks and scalloped shaped depressions which are similar to features found in utopia planitia in the northern hemisphere this area also displays knobby terrain similar to the so called basketball terrains of the mid and high martian latitudes we use recent high resolution images from the high resolution imaging science experiment hirise along with data from previous mars missions to study the small scale morphology of the scalloped terrains and associated polygon network and knobby terrains we compare these with the features observed in utopia planitia and attempt to determine their formation process while the two sites share many general features scallops in peneus amphitrites paterae lack the diverse polygon network i e there is little variation in the polygon sizes and shapes and large curvilinear ridges observed in utopia planitia this points to a more homogeneous ice content within the substrate in the peneus amphitrites paterae region and implies that scallop formation is independent of polygon formation this work shows that as in utopia planitia sublimation of interstitial ice is a likely process explaining the formation of the scalloped depressions in the region of peneus amphitrites paterae therefore we provide a simplified scallop formation model based on sublimation of interstitial ice as proposed for utopia planitia we also show that the differences in scallop morphologies between the two regions may be explained by differences in near surface ice content sublimation rates and age of formation of the scalloped terrains

glacial and gully erosion on mars a terrestrial perspective the mid to high latitudes of mars host assemblages of landforms consistent with a receding glacial landscape on earth these landforms are postulated to have formed 5 ma under a different climate regime when mars orbital obliquity was on average 10 higher than today here we investigate the spatiotemporal relationship between gullies and glacial landforms both common in the mid latitudes gullies are kilometre scale landforms with a source alcove transportation channel and depositional apron the glacial landforms comprise 1 extant viscous flow features vff that extend from the base of crater walls into the interior of crater floors and are widely interpreted as debris covered glaciers containing extant ice and 2 landforms such as arcuate ridges at the base of crater walls that have been interpreted as relicts of more recent less extensive glacial advances focussed on crater walls we measure headwall retreat associated with glacial landforms and date their host craters to constrain minimum headwall retreat rates we record headwall retreat rates up to 102 m my 1 for the youngest suite of glacial landforms equivalent to erosion rates of wet based glaciers on earth and to headwall retreat rates associated with martian bedrock gully systems we find extensive evidence for a single erosional episode dating 5 10 ma which postdates emplacement of the majority of vff but seems to predate formation of the gullies we propose that the wet based glacial episode was associated with glaciation focussed on the crater walls rather than melting of the glacial ice deposits on the crater floors vff this is consistent with our observations of crater wall morphologies including the presence of arcuate ridges consistent with terrestrial glaciotectonic features that require liquid water to form textural alteration of the eroded bedrock surface consistent with ice segregation and frost shattering and the presence of downslope pasted on terrain tentatively interpreted here as glacial till deposits sourced from glacial erosion of the crater wall the pasted on terrain is usually interpreted as a thicker latitude dependant mantle located on sloping terrain formed from airfall of ice nucleated on dust but we suggest that it has been reworked by glaciation and is predominantly glacial in origin although our results cannot substantiate that gullies are produced by meltwater the discovery of this wet glacial event does provide evidence for widespread meltwater generation in mars recent history

deposition of 3 7 ga clay rich strata of the mawrth vallis group mars in lacustrine alluvial and aeolian environments

active tectonics seismicity and geomorphology with special reference to normandy france integrated studies based on tectonic seismotectonic and geomorphological analyses indicate that normandy northwest france has been an active area during the quaternary topography and landform discontinuities reflect the dislocation and differential uplift of a late cenozoic platform the tectonic activity is represented by i active faults indicated by linear scarps and seismic activity ii offsetting of pre existing surfaces iii plio pleistocene sedimen tation restricted within narrow subsiding zones and iv morphometric properties of drainage basins that indicate zones of differential uplift the inferred strain pattern involves i a shortening direction that strikes nw se as expected in the european context of alpine compression and ii a ne sw trending extension accommodated by nw se normal faults the geomorphological systems encountered in normandy preferentially record differential vertical displacements copy right 2000 john wiley sons ltd

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

a new sand wedge forming mechanism in an extra arid area abstract a survey found that sand wedges are widely distributed in the extremely extra arid gobi region of dunhuang china the sand wedges are still developing well developed sand wedges are surrounded by polygonal areas showing fractal structures the depth of a well developed sand wedge is 50 60 cm and its maximum width is 50 60 cm so the depth width ratio is 1 0 the interface between the wedge and matrix is arc shaped the mechanical composition of the sand wedges compared to the matrix is such that 76 72 of the particles have diameters 0 25 mm and show vertical sand laminations in the sand wedge while 55 19 of the particles in the matrix are 2 00 mm in diameter the particle diameters are consistent with the width of the sand wedge fractures the salt content in the sand wedges is 3 13 g kg while that of the matrix is 40 86 g kg the large salinity difference shows that the sand in the wedges comes from drift sand or cladding layers where salinity is lower and that the sand wedge was formed in an arid climate displacement and pressure are closely associated with the daily temperature variation they fluctuate significantly following the temperature measurements reveal the movement of thermal contraction fissures pressure monitoring identified that wet expansions occurred after rainfall which made the sand wedges become tightly joined to the matrix following this as the soil became desiccated and shrank a crack opened in the middle of the sand wedge this was then filled with drift sand with the next rainfall the system moved into another development cycle the current article reveals a new mechanism for forming sand wedges in extra arid conditions arid sand wedges are a unique drought induced surface landmark resulting from long term natural dry climate processes

modeling the formation of bright slope deposits associated with gullies in hale crater mars implications for recent liquid water abstract 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

crater floor polygons desiccation patterns of ancient lakes on mars 1 global mapping of intermediate size 100 200 m polygonal troughs occurring mainly in impact crater floors was carried out using high resolution images from spacecraft currently orbiting mars earlier works have classified these polygonal networks as periglacial features on account of their apparent occurrence at higher latitudes and morphological similarities to thermal contraction polygons tcps crater floor polygons cfps have diameters ranging from 15 to 350 m they morphologically resemble terrestrial tcps and desiccation cracks their size distribution however is significantly different from that of tcps that are ubiquitous in the high latitudes an analytical model based on fracture mechanics reveals that under current climatic conditions the maximum fracture spacing attainable by thermal stresses alone is 75 m at the most more reasonable values fall within 18 and 22 m which is the range for tcps on mars as a result we propose desiccation to be a dominant mechanism for the formation of cfps without ruling out thermal contraction as a possible contributor in some cases this implies that lakes or water rich sediments occupied the craters in the past many such aqueous environments have no apparent external source of water and thus hydrothermal processes occurring shortly after the impact event may be viable explanations for the observed evidence the association of features which correspond to terrestrial lakes such as sedimentary deposits mounds and shorelines corroborates lake formation and their eventual desiccation to form cfps the variation of cfp sizes with location can be indicative of different hydrologic environments

the distribution and behavior of martian ground ice during past and present epochs mars undergoes significant oscillations in its orbit which will have a pronounced effect on its climate and in particular on the behavior of subsurface water ice we explore and map the behavior of ice in the martian near surface regolith over the past 1 m y using a diffusion and condensation model presented in an earlier paper with two primary modifications to include orbitally induced variations in insolation and atmospheric water abundance we find that the past behavior of ground ice differs significantly from that at the present epoch primarily the result of high amplitude oscillations in obliquity presently 25 in midlatitude and equatorial regions ground ice will condense from atmospheric water during times of higher obliquity filling the top few meters of the regolith with significant amounts of ice at an obliquity of 32 ground ice becomes stable globally during times of lower obliquity ground ice will sublime and diffuse back into the atmosphere dessicating the regolith to a depth of about 1 to 2 m equatorward of 60 to 70 latitude in the high latitude regions these oscillations are considerably subdued below this depth of cyclic saturation and dessication a long term stability of ice exists in some geographic regions we present a map of the distribution of ice expected at the present epoch cyclic exchange of water between the global regolith and polar regions will have significant implications for surface geology and the polar layered deposits

high resolution imaging science experiment hirise observations of glacial and periglacial morphologies in the circum argyre planitia highlands mars 1 the landscape of the argyre planitia and adjoining charitum and nereidum montes in the southern hemisphere of mars has been heavily modified since formation of the argyre impact basin this study examines morphologies in the argyre region revealed in images acquired by the high resolution imaging science experiment hirise camera and discusses the implications for glacial and periglacial processes distinctive features such as large grooves semicircular embayments in high topography and streamlined hills are interpreted as glacially eroded grooves cirques and whalebacks or roche moutonnee respectively large boulders scattered across the floor of a valley may be ground moraine deposited by ice ablation glacial interpretations are supported by the association of these features with other landforms typical of glaciated landscapes such as broad valleys with parabolic cross sections and stepped longitudinal profiles lobate debris aprons interpreted as remnant debris covered glaciers or rock glaciers and possible hanging valleys aligned boulders observed on slopes may also indicate glacial processes such as fluting alternatively boulders aligned on slopes and organized in clumps and polygonal patterns on flatter surfaces may indicate periglacial processes perhaps postglaciation that form patterned ground at least portions of the argyre region appear to have been modified by processes of ice accumulation glacial flow erosion sediment deposition ice stagnation and ablation and perhaps subsequent periglacial processes the type of bedrock erosion apparent in images suggests that glaciers were at times wet based the number of superposed craters is consistent with geologically recent glacial activity but may be due to subsequent modification

habitable periglacial landscapes in martian mid latitudes subsurface permafrost environments on mars are considered to be zones where extant life could have survived for the identification of possible habitats it is important to understand periglacial landscape evolution and related subsurface and environmental conditions many landforms that are interpreted to be related to ground ice are located in the martian mid latitudinal belts this paper summarizes the insights gained from studies of terrestrial analogs to permafrost landforms on mars the potential habitability of martian mid latitude periglacial landscapes is exemplarily deduced for one such landscape that of utopia planitia by a review and discussion of environmental conditions influencing periglacial landscape evolution based on recent calculations of the astronomical forcing of climate changes specific climate periods are identified within the last 10 ma when thaw processes and liquid water were probably important for the development of permafrost geomorphology no periods could be identified within the last 4 ma which met the suggested threshold criteria for liquid water and habitable conditions implications of past and present environmental conditions such as temperature variations ground ice conditions and liquid water activity are discussed with respect to the potential survival of highly specialized microorganisms known from terrestrial permafrost we conclude that possible habitable subsurface niches might have been developed in close relation to specific permafrost landform morphology on mars these would have probably been dominated by lithoautotrophic microorganisms i e methanogenic archaea

periglacial mass wasting landforms on mars suggestive of transient liquid water in the recent past insights from solifluction lobes on svalbard abstract on earth periglacial solifluction is a slow mass wasting process related to freeze thaw activity we compare the morphology of small scale lobate features on mars to solifluction lobes in svalbard to constrain their processes of formation the analysis is based on high resolution satellite imagery of mars hirise 25 cm pxl aerial images of svalbard with a similar spatial resolution hrsc ax 20 cm pxl acquired through an air campaign in summer 2008 and ground truth obtained during two summer expeditions in 2009 and 2011 on svalbard we present a detailed study of two crater environments on mars displaying two types of lobate forms characterized as sorted clast banked and non sorted lobes on both svalbard and mars such lobes typically occur as clusters of overlapping risers lobe fronts pointing to differential velocities in the soil the martian small scale lobes have well defined arcuate risers and lobe treads surface lobe widths range between 14 and 127 m and tread lengths between 13 and 105 m riser height is estimated to be approximately 1 5 m the lobes on mars share the plan view morphology of solifluction lobes on svalbard and their morphometry is within the range of values of terrestrial solifluction lobes the lobes are distinct from permafrost creep landforms such as rock glaciers we show the results of a survey of 53 hirise images covering latitudes between 59 n and 81 n similar to svalbard the studied lobate features on mars occur in close spatial proximity to gullies and thermal contraction polygons the widespread distribution of the lobate forms in the northern hemisphere and their close association to ground ice and gullies are best explained by mass wasting processes related to frost creep gelifluction and or plug like flow this suggests a protracted process thousand to several thousands of years of freeze thaw activity at the northern high latitudes on mars age constraints on lobe deposits and superposition relationships with gullies and polygons imply a process involving liquid water within the last few million years

possible pingos and a periglacial landscape in northwest utopia planitia hydrostatic closed system pingos are small elongate to circular ice cored mounds that are perennial features of some periglacial landscapes the growth and development of hydrostatic pingos is contingent upon the presence of surface water freezing processes and of deep continuous ice cemented permafrost other cold climate landforms such as small sized polygonal patterned ground also may occur in the areas where pingos are found on mars landscapes comprising small elongate to circular mounds and other possible periglacial features have been identified in various areas including utopia planitia where water is thought to have played an important role in landscape evolution despite the importance of the martian mounds as possible markers of water most accounts of them in the planetary science literature have been brief and or based upon viking imagery we use a high resolution mars orbiter camera image eo300299 and superposed mars orbiter laser altimeter data tracks to describe and characterise a crater floor landscape in northwest utopia planitia 64 8 n 292 7 w the landscape comprises an assemblage of landforms that is consistent with the past presence of water and of periglacial processes this geomorphological assemblage may have formed as recently as the last episode of high obliquity a similar assemblage of landforms is found in the tuktoyaktuk peninsula of northern canada and other terrestrial cold climate landscapes we point to the similarity of the two assemblages and suggest that the small roughly circular mounds on the floor of the impact crater in northwest utopia planitia are hydrostatic pingos like the hydrostatic pingos of the tuktoyaktuk peninsula the origin of the crater floor mounds could be tied to the loss of ponded local water permafrost aggradation and the evolution of a sub surface ice core

climate and material controls on periglacial soil processes toward improving periglacial climate indicators one of the distinguished efforts of a l washburn was to reconstruct mean annual air temperature using periglacial features as climate indicators this paper reviews existing periglacial indicators and proposes a strategy to improve their thermal resolution based on recent periglacial process studies with a focus on solifluction and thermal contraction cracking and associated landforms structures landforms resulting from solifluction reflect both the depth subjected to freeze thaw and the thickness of frost susceptible soils the thickness of a solifluction structure can be used to infer the dominant freeze thaw regime and minimum seasonal frost depth ice wedge pseudomorphs have limited potential as a climate indicator because 1 they mainly reflect extreme winter temperatures 2 their thermal thresholds depend on the host material and 3 they need to be distinguished from frost wedges of other origin produced under different thermal and or material conditions monitoring studies of currently active ice wedges suggest that ice wedge cracking requires a combination of low temperature and large temperature gradients in the frozen active layer further field monitoring of periglacial processes and their controlling factors under various climate conditions and in various materials are needed however to improve the resolution of periglacial paleoclimate indicators

new constraints on equatorial temperatures during a late neoproterozoic snowball earth glaciation intense glaciation during the end of cryogenian time 635 million years ago marks the coldest climate state in earth history a time when glacial deposits accumulated at low tropical paleolatitudes the leading idea to explain these deposits the snowball earth hypothesis predicts globally frozen surface conditions and subfreezing temperatures with global climate models placing surface temperatures in the tropics between 20 c and 60 c however precise paleosurface temperatures based upon geologic constraints have remained elusive and the global severity of the glaciation undetermined here we make new geologic observations of tropical periglacial aeolian and fluvial sedimentary structures formed during the end cryogenian marinoan glaciation in south australia these observations allow us to constrain ancient surface temperatures we find periglacial sand wedges and associated deformation suggest that ground temperatures were sufficiently warm to allow for ductile deformation of a sandy regolith the wide range of deformation structures likely indicate the presence of a paleoactive layer that penetrated 2 4 m below the ground surface these observations paired with a model of ground temperature forced by solar insolation constrain the local mean annual surface temperature to within a few degrees of freezing this temperature constraint matches well with our observations of fluvial deposits which require temperatures sufficiently warm for surface runoff although this estimate coincides with one of the coldest near sea level tropical temperatures in earth history if these structures represent peak marinaon glacial conditions they do not support the persistent deep freeze of the snowball earth hypothesis rather surface temperatures near 0 c allow for regions of seasonal surface melting atmosphere ocean coupling and possible tropical refugia for early metazoans if instead these structures formed during glacial onset or deglaciation then they have implications for the timescale and character for the transition into or out of a snowball state

the periglacial landscape at the phoenix landing site 1 the mars scout mission phoenix landed in the northern high latitudes of mars in an area thought to be dominated by subsurface ground ice and has provided a unique detailed examination of periglacial morphology and topography that is not visible from orbit the landing site and surrounding terrain is dominated by polygonal patterned ground typical of the martian northern plains the polygons exhibit a gentle u shaped trough and rounded mound topography with an average trough depth of 17 cm and an average surface slopes of only 6 7 polygons an average 4 3 m across form a pattern superimposed on all other geologic landforms including larger 20 25 m polygons and kilometer long linear ridges the polygon morphology and the predominance of subsurface ice cemented soil are consistent with the formation of subsurface sand wedges in a permanently frozen arid climate small scale soil furrows and cracks into the ice cemented soil indicate that the thermal contraction process responsible for the formation of the polygons is active today rocks appear to be sorted within the polygon troughs indicating a process of cryoturbation within the permanently frozen polygons the complexity of the patterns crosscutting relations and rock distributions indicate advanced maturity of the polygon networks and shifting crack patterns possibly facilitated by crack and wedge annealing during times of low obliquity

possible open system hydraulic pingos in and around the argyre impact region of mars abstract we report the observation of possible hydraulic open system pingos osps at the mid latitudes 37 s in and around the argyre impact basin osps are perennial water ice cored mounds they originate and evolve in periglacial and pro glacial landscapes on earth where intra or sub permafrost water under hydraulic artesian pressure uplifts localised sections of surface or near surface permafrost that then freezes in situ we invoke three lines of evidence in support of our analogue based interpretation 1 similarities of shape size and summit traits between terrestrial osps and the martian mounds 2 clustered distribution and the slope side location of the mounds consistent with terrestrial permafrost environments where osps are found and 3 spatially associated landforms putatively indicative of periglacial and glacial processes on mars that characterise osp landscapes on earth this article presents five osp candidate locations and nests these mound locations within a new geological map of the argyre impact basin and margins it also presents three periglacial hypotheses about the possible origin of the water required to develop the mounds alternative non periglacial formation hypotheses also are considered however we show that their robustness is not equal to that of the periglacial ones