morphologic and topographic analyses of debris aprons in the eastern hellas region mars this paper presents new detailed analyses of small scale morphologic and topographic characteristics of martian debris aprons that support viking based interpretations of debris aprons as ice rich flow features derived from local uplands fifty four debris apron complexes in the eastern hellas region of mars were examined using mars global surveyor data sets including mars orbiter camera images and mars orbiter laser altimeter topographic profiles consistent patterns in a suite of small scale surface textures and geomorphic features observed throughout the population reflect a history of viscous flow and surface degradation through wind ablation and loss of contained ice a wide variety of shapes seen in topographic profile reveal variations in distribution of contained ice and different stages of apron development and degradation the results of this study provide new evidence consistent with multiple models of apron formation including rock glacier debris covered glacier and ice rich landslide models typical eastern hellas debris aprons formed from a series of large scale events emplacing debris that was enriched initially or later by ground ice complemented by small scale mass wasting of multiple styles and postemplacement flow of apron masses

ice and debris in the fretted terrain mars viking moderate and high resolution images along the northern highland margin were studied monoscopically and stereoscopically to contribute to an understanding of the development of fretted terrain results suport the hypothesis that the fretting process involved flow facilitated by interstitial ice the process apparently continued for a long period of time and debris apron formation shaped the fretted terrain in the past as well as the present interstitial ice in debris aprons is most likely derived from ground ice obtained by sapping or scarp collapse debris aprons could have been removed by sublimation if they consisted mostly of ice or by deflation if they consisted mostly of debris to remove the debris wind erosion was either very intense early in martian history or was intermittent perhaps owing to climatic cycles the location of debris aprons in two midlatitudinal belts can be attributed to atmospheric conditions that permit ice to remain in the ground at moderate depth in those latitudes and climatic factors that permit temperatures to be warm enough for ice to flow channels have minimum gradients of 5 8 m km which permits flowing ice to deform by dislocation creep at exceedingly low strain rates alternately ice charged debris may have been buoyed by brines by analogy with the fretted channels ice could have flowed through the outflow channels if the atmospheric pressure was somewhat higher in the past and permitted ice to exist in the equatorial area

modification of the dichotomy boundary on mars by amazonian mid latitude regional glaciation 1 restoration of the dichotomy boundary to its original position to assess its origin requires a thorough knowledge of processes responsible for its degradation and retreat the unique fretted terrain located along the deuteronilus protonilus mensae northern mid latitude portion of the boundary has been long held to provide clues to dichotomy degradation processes we use new spacecraft data to show that fretted valleys display a multitude of characteristics typical of integrated valley glacial systems on earth multiple theater headed alcove like accumulation areas sharp arete like ridges typical of glacial erosion converging patterns of downslope valley flow valley lineation patterns typical of folding and shear wrap around features indicative of flow around obstacles and broad piedmont like lobes as the valley fill extends out into the northern lowlands the single integrated system containing these features covers about 30 000 km2 and is one of dozens of fretted valleys along the dichotomy boundary in this region these relationships suggest that the boundary area was subjected to very large scale regional glaciation during the amazonian recognition and documentation of this important late stage process provides information critical to reconstructing the original dichotomy boundary

on the icy edge at louth and korolev craters abstract the modern climate of mars has been well characterized from over a decade of orbiting spacecraft in situ measurements via landers rovers and theoretical advances in climate modeling nonetheless important questions remain unanswered including the present day mass balance of the north polar residual cap and its icy outliers exposed water ice mounds are found in craters and extend as far equatorward as 70 2 n due to their southerly location these ice mounds are likely more sensitive to ongoing changes in climate we analyze high resolution images of the louth crater ice mound and employ a coupled 1 d thermal and atmospheric model to estimate annual mass balance of both louth and korolev water ice we incorporate the effects of shallowly sloping surfaces and seasonally dependent water ice albedo no clear trend in the advance or retreat of louth crater water ice is observed in over 4 mars years of repeat high resolution images secular changes are either sufficiently small as to not be detected or the ice is in equilibrium modeled mass balance ranges from 6 to 2 mm of water ice per mars year at both sites with nominal cases being in near equilibrium

origin of martian northern hemisphere mid latitude lobate debris aprons lobate debris aprons in the martian mid to high latitudes northern and southern hemispheres have been interpreted as ice related features that indicate periglacial climate conditions as recently as late amazonian using mola topographic profiles perpendicular to apron flow fronts we surveyed 36 debris aprons in the northern hemisphere found in the regions of mareotis protonilus and deuteronilus mensae and acheron fossae the profiles of these aprons were compared with idealized simple plastic and viscous power law models for ice rock mixtures all aprons studied exhibit convex profiles similar to a simple plastic model this confirms previous interpretations that debris aprons are ice rich mixtures with rheologies similar to stagnant ice sheets thus indicating high ice concentrations 40 by volume about 60 of the surveyed debris apron population significantly deviates from the idealized simple plastic model profile this may be due to locally reduced ice content which primarily controls apron topography although post emplacement modification due to near surface ice sublimation plays a secondary role in defining the overall shape of aprons it causes conspicuous surface textures degradation by ice sublimation probably results in pitted and ridge and furrow surface textures revealed by high resolution moc images such textures may indicate decreased near surface ice stability since the formation of the aprons possibly due to mars current low obliquity after their emplacement high ice content inferred from topography suggests some debris aprons have ice cores potentially exploitable water resources for future robotic human operations that could prove invaluable for missions remote from polar regions

extensive valley glacier deposits in the northern mid latitudes of mars evidence for late amazonian obliquity driven climate change understanding spin orbital parameter driven climate change on mars prior to 20 ma ago requires geological evidence because numerical solutions for that period are chaotic and non unique we show geological evidence that lineated valley fill at low midlatitudes in the northern hemisphere of mars 37 58 n originated through regional snow and ice accumulation and underwent glacial like flow breached upland craters and theater headed valleys reveal features typical of erosion in association with terrestrial glaciers parallel converging and chevron like lineations in potentially ice rich deposits on valley floors indicate that flow occurred through constrictions and converged from different directions at different velocities together these martian deposits and erosional landforms resemble those of intermontaine glacial systems on earth particularly in their major morphology topographic shape planform and detailed surface features an inferred late amazonian age combined with predictions of climate models suggest that the obliquity of mars exceeded a mean of 458 for a sustained period during this time significant transfer of ice occurred from icerich regions e g the poles to mid latitudes causing prolonged snow and ice accumulation there and forming an extensive system of valley glaciers d 2005 elsevier b v all rights reserved

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

oxygen and carbon isotope stratigraphy of the palaeogene and cretaceous limestones in the bottaccione gorge and the contessa highway sections umbria italy we have made oxygen and carbon isotope measurements on limestone samples of albian to eocene age recovered from the bottaccione gorge section in the umbrian apennines central italy additional measurements have been made on topmost maastrichtian and palaeocene sediments from the adjacent contessa highway section our data from the bottaccione gorge show 13c maxima at the cenomanian turonian boundary and during the palaeocene as well as a pronounced 13c minimum 7 metres above the clay layer at the k t boundary our data from the contessa highway show a 13c minimum 9 metres above the k t boundary clay these minima are probably diagenetic artifacts in the bottaccione gorge there is evidence for a hiatus in the early middle eocene the palaeocene of the bottaccione gorge appears to have been affected by slumping or faulting in addition to the diagenetic overprinting giving a spurious 13c recovery after the k t boundary the contessa highway section appears to be more complete the coniacian maastrictian is characterized by relatively stable 13c values our data indicate an increase in 18o and therefore possible cooling across the cretaceous tertiary boundary in both the bottaccione and contessa highway sections

mars north polar deposits stratigraphy age and geodynamical response the shallow radar sharad on the mars reconnaissance orbiter has imaged the internal stratigraphy of the north polar layered deposits of mars radar reflections within the deposits reveal a laterally continuous deposition of layers which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice the packet interpacket structure can be explained by approximately million year periodicities in mars obliquity or orbital eccentricity the observed 100 meter maximum deflection of the underlying substrate in response to the ice load implies that the present day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers alternatively the response to the load may be in a transient state controlled by mantle viscosity both scenarios probably require that mars has a subchondritic abundance of heat producing elements

landform assemblage in isidis planitia mars evidence for a 3 ga old polythermal ice sheet abstract the floor of isidis planitia a giant impact basin located close to the martian equator exhibits a landform assemblage nicknamed thumbprint terrain made of arcuate ridges aligned cones isolated cones cone fields associated with a peripheral network of sinuous ridges linear depressions and mounds from a new comprehensive mapping initiative of these landforms and from comparisons with terrestrial analogues ribbed moraines dirt cones kettle holes eskers tunnel valleys and moraine plateaux we demonstrate that this distinctive assemblage is a glacial landsystem inherited from the presence of a massive polythermal ice sheet over the basin during the hesperian the flow of the ice sheet was controlled by its basal thermal regime wet based conditions led to the formation of arcuate ridges and aligned cones in most parts of the basin while a negative geothermal anomaly due to impact related crustal thinning was responsible for cold based conditions in its central part where only isolated cones and cones fields are present sinuous ridges linear depressions and mounds at the basin margins are interpreted as relicts of a radial network of subglacial channels which drained the glacial meltwater produced within the interior of the ice sheet across its cold based periphery

tropical to mid latitude snow and ice accumulation flow and glaciation on mars images from the mars express hrsc high resolution stereo camera of debris aprons at the base of massifs in eastern hellas reveal numerous concentrically ridged lobate and pitted features and related evidence of extremely ice rich glacier like viscous flow and sublimation together with new evidence for recent ice rich rock glaciers at the base of the olympus mons scarp superposed on larger late amazonian debris covered piedmont glaciers we interpret these deposits as evidence for geologically recent and recurring glacial activity in tropical and mid latitude regions of mars during periods of increased spin axis obliquity when polar ice was mobilized and redeposited in microenvironments at lower latitudes the data indicate that abundant residual ice probably remains in these deposits and that these records of geologically recent climate changes are accessible to future automated and human surface exploration

accumulation and erosion of mars south polar layered deposits mars polar regions are covered with ice rich layered deposits that potentially contain a record of climate variations the sounding radar sharad on the mars reconnaissance orbiter mapped detailed subsurface stratigraphy in the promethei lingula region of the south polar plateau planum australe radar reflections interpreted as layers are correlated across adjacent orbits and are continuous for up to 150 kilometers along spacecraft orbital tracks the reflectors are often separated into discrete reflector sequences and strong echoes are seen as deep as 1 kilometer in some cases the sequences are dipping with respect to each other suggesting an interdepositional period of erosion in australe sulci layers are exhumed indicating recent erosion

ice flow and rock glaciers on mars several geologic features suggest the presence of rock glaciers on the surface of mars these features include lobate debris aprons concentric crater fill and lineated valley fill the lateral extent of these rock glaciers can range from 5 km to over 20 km a simple time marching model is developed and used here to demonstrate the ability of ice and ice rock mixtures to flow under martian conditions for temperatures lower than about 220 k even pure ice becomes too rigid to flow and a glacier 5 km long could not have formed results from this model indicate temperatures 20 to 40 k higher than present average midlatitude temperatures 210 k an ice content of no less than 80 and a net accumulation rate of at least 1 cm year 1 are required to produce rock glaciers of the size seen on mars

probing supraglacial debris on mars 2 crater morphology abstract lobate debris aprons lda lineated valley fill lvf and concentric crater fill ccf on mars interpreted to be debris covered glaciers possess craters with a suite of distinct interior landforms called ring mold craters that have been attributed to the presence of glacial ice at depth or surface modification processes we tested current hypotheses for the formation of ring mold craters by conducting a comprehensive analysis of the size and morphology of 16 457 impact craters 125 m in diameter formed within glacial deposits in deuteronilus mensae two major groups bowl shaped craters and ring mold craters are found with at least nine distinct crater types while there is statistical difference in median diameters between these crater types this difference is relatively small and is within the estimated uncertainty in diameter measurements and may be related to more enhanced erosion of the rims of ring mold craters clear degradation sequences are observed supporting a role for post impact modification in producing at least some of the diversity in crater landforms the spatial density of ring mold craters is also directly correlated with the development of lda lvf and ccf surface textures flow lineations cross cut two ring mold crater types but they maintain their circular planforms in some cases suggesting that the craters initially formed completely within mantling layers deposited after glacial flow had ceased we also find analogous craters in non glacial units glacial ice is therefore not required to form the observed morphologic diversity our observations are most consistent with formation of crater landforms by emplacement and modification of at least two depositional episodes of icy dust i e mantle this mantle was initially tens of meters in thickness to support crater formation and has experienced much downwasting and erosion since emplacement derived crater retention ages of 460 ma for lda lvf and ccf features in the region therefore reflect deposition of mantle units and only give a very minimum age for the formation of lda lvf and ccf

method for anisotropic crystal orientation fabrics detection using radio wave depolarization in radar sounding of mars polar layered deposits the polar layered deposits plds provide a wealth of information about the past climate evolution of mars surface mass fluxes and ice flow mainly governed topography and layering of the pld china s mars probe including an orbiter and a landing rover will be launched by 2020 a new type satellite borne mars penetrating radar instrument has been selected to be a part of the payloads on the orbiter its main scientific objectives are to map the distribution of water water ice and to detect the soil characteristics at global scale on the martian crust compared with mars advanced radar for subsurface and ionospheric sounding and shallow radar the biggest difference is that the antenna system of this mars penetrating radar consists of two dipole antennas mutually perpendicular this special configuration enables the investigation of the ice flow of pld by detecting and analyzing the features of anisotropic crystal orientation fabric cof thus relying on the fact that the radio waves are depolarized while passing through an anisotropic cof layer in this paper a method for anisotropic cof detection based on this radar system is proposed the radar echo formulation of anisotropic cof is derived and the ratio of the signals measured by the two perpendicular antennas is used to analyze the anisotropy of cof we demonstrate that the ratio is an ideal criterion for the detection and analysis of cof since it contains all parameters about the anisotropy feature of cof and it is independent of the attenuation in the propagation path and the reflection coefficient in order to verify the validity of the derived analytical expression of the ratio for the detection of cof finite different time domain simulations are carried out based on a simple model of the subsurface of pld which contains an anisotropic cof layer the advantages of this method the potential application scenarios and the effects of the martian environment are also discussed

sharad sounding radar on the mars reconnaissance orbiter 1 sharad shallow radar is a sounding radar provided by agenzia spaziale italiana asi as a facility instrument on the mars reconnaissance orbiter mission its 20 mhz center frequency and 10 mhz bandwidth complement the lower frequency relatively narrower bandwidth capability of the marsis sounding radar a joint italian u s team has guided the experiment development and is responsible for data analysis and interpretation the radar transmits signals at a 700 hz pulse repetition frequency prf and collects reflections from both the surface and near subsurface of mars vertical and horizontal resolutions are respectively 15 m free space and 3 6 km cross track by 0 3 1 km along track the scientific objective of sharad is to map in selected locales dielectric interfaces to at least several hundred meters depth in the martian subsurface and to interpret these results in terms of the occurrence and distribution of expected materials including competent rock soil water and ice a signal to noise ratio of 50 db for a specular surface return is achieved with 10 w of radiated power by using range and azimuth focusing in ground data processing preprocessed data as well as range and azimuth focused data will be formatted according to planetary data system pds standards and be made available from the asi science data center asdc and from the geosciences node of the planetary data system pds important targets for sharad include the polar layered deposits sedimentary stacks especially in terra meridiani buried channel systems buried impact craters volcanic complexes and shallow ice deposits in equilibrium with the atmosphere

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

topographic analysis of features related to ice on mars this study analyses the new topographic data from mars global surveyor mgs through the lobate debris aprons of mars these features are usually interpreted as due to the creep of ground ice the comparison between measured topographic profiles and profiles calculated from rheological laws demonstrates that these features are due to the solid state deformation of ice the high volume of such debris aprons can not be explained by rock fall but only by landslides the ice involved in the flow may then come from the subsurface confirming the presence of large amount of ground ice

geology of the reull vallis region mars abstract the geology and stratigraphy of the reull vallis region 27 5 47 5 s 245 270 w of the southern highlands of mars are documented through geomorphic analyses and geologic mapping at 1 2 000 000 scale crater size frequency distributions are used to constrain relative ages of geologic units and determine the timing and duration of the various geologic events the origin and evolution of the reull vallis outflow system and the extent to which reull vallis and other fluvial features modified the surrounding highlands are also evaluated rugged highland terrains were formed by repeated impact events and were extensively degraded and embayed by a series of plains highland terrains incised with well developed valley networks record some of the earliest fluvial activity in the region reull vallis originates in hesperia planum and dissects units of various types and ages truncated and bisected wrinkle ridges in hesperia planum indicate that the formation of reull vallis postdates ridge formation the morphology of reull vallis suggests it had a long and complex history including subsurface and surface movement of fluids followed by extensive modification by mass wasting volcanic and sedimentary plains units in the region record evidence of erosion by surface flow possibly related to development of reull vallis features produced by mass wasting such as debris aprons and crater fill material and aeolian processes appear to form the youngest deposits exposed in the region

roughness and near surface density of mars from sharad radar echoes 1 we present a technique for estimating mars topographic roughness on horizontal scales from about 10 m to 100 m using shallow radar sharad sounding data our results offer a view of surface properties complementary to mars orbiter laser altimeter mola pulse width or baseline roughness maps and can be compared to sharad peak echo properties to infer deviations from the average near surface density latitudinal averaging of sharad derived roughness over arabia and noachis terrae shows good agreement with mola derived roughness and provides clear evidence for latitude dependent mantling deposits previously inferred from image data in northwestern gordii dorsum we find that bulk density in at least the upper few meters is significantly lower than in other units of the medusae fossae formation we observe the same behavior indicative of low near surface density in wind eroded crater fill in the southern highlands combining surface properties analysis subsurface sounding and high resolution optical images we show that the pavonis mons fan shaped deposit differs significantly from lobate debris aprons which sharad has shown to be ice cored there are no internal radar reflections from the smooth facies portion of the pavonis mons fan shaped deposit and we suggest that these deposits are either quite thin or have little dielectric i e density contrast with the underlying terrain future application of these techniques can identify other low density units across mars assist in the mapping of regional volatile rich mantling units and provide new constraints on the physical properties of the polar layered terrain

formation of lobate debris aprons on mars assessment of regional ice sheet collapse and debris cover armoring abstract lobate debris aprons lda are lobate shaped aprons surrounding scarps and isolated massifs that are concentrated in the vicinity of the northern dichotomy boundary on mars ldas have been interpreted as 1 ice cemented talus aprons undergoing viscous flow 2 local debris covered alpine like glaciers or 3 remnants of the collapse of a regional retreating ice sheet we investigate the plausibility that ldas are remnants of a more extensive regional ice sheet by modeling this process we find that as a regional ice sheet collapses the surface drops below cliff and massif bedrock margins exposing bedrock and regolith and initiating debris deposition on the surface of a cold based glacier reduced sublimation due to debris cover armoring of the proto lda surface produces a surface slope and consequent ice flow that carries the armoring debris away from the rock outcrops as collapse and ice retreat continue the debris train eventually reaches the substrate surface at the front of the glacier leaving the entire lda armored by debris cover using a simplified ice flow model we are able to characterize the temperature and sublimation rate that would be necessary to produce ldas with a wide range of specified lateral extents and thicknesses we then apply this method to a database of documented lda parameters height lateral extent from the dichotomy boundary region and assess the implications for predicted climate conditions during their formation and the range of formation times implied by the model we find that for the population examined here typical temperatures are in the range of 85 to 40 c and typical sublimation rates lie in the range of 6 14 mm a lobate debris apron formation times from the point of bedrock exposure to complete debris cover cluster near 400 500 ka these results show that lda length and thickness characteristics are consistent with climate conditions and a formation scenario typical of the collapse of a regional retreating ice sheet and exposure of bedrock cliffs this scenario helps resolve many of the unusual characteristics of lobate debris aprons lda and lineated valley fill lvf for example the distribution of lvf is very consistent with extensive flow of glacial ice from plateau icefields and the acquisition of a debris cover in the waning stages of retreat of the regional cover as the bedrock scarps are exposed the typical concentric development of lda around massifs is much more consistent with ice sheet retreat than insolation related local accumulation and flow we thus conclude that the retreating ice sheet model is robust and should be investigated and tested in more detail in addition these results clearly show that the lobate debris aprons in the vicinity of the dichotomy boundary could not have attained temperatures near or above the ice melting point and retained their current shape a finding that supports subzero temperatures for the last several hundred million years the age of the lda surfaces a further implication is that the lda ice has been preserved for at least several hundred million years and could potentially contain the record of the climate of mars preserved since that time below a sublimation lag deposit

formation of glaciers on mars by atmospheric precipitation at high obliquity surface conditions on mars are currently cold and dry with water ice unstable on the surface except near the poles however geologically recent glacierlike landforms have been identified in the tropics and the midlatitudes of mars the ice has been proposed to originate from either a subsurface reservoir or the atmosphere we present high resolution climate simulations performed with a model designed to simulate the present day mars water cycle but assuming a 45 obliquity as experienced by mars a few million years ago the model predicts ice accumulation in regions where glacier landforms are observed on the western flanks of the great volcanoes and in the eastern hellas region this agreement points to an atmospheric origin for the ice and reveals how precipitation could have formed glaciers on mars

design and performance of microlith implemented projectiles during the middle and the late epipaleolithic of the levant experimental and archaeological evidence abstract the study comprises an experimentally based investigation of interaction between temporal change in the morphology of microlithic tools and transformations in projectile technology during the late pleistocene in the levant archery experiments with differently designed arrows fitted with various types of microliths representing subsequent epipaleolithic cultures of the levant allowed analyzing performance abilities of the arrows identifying projectile damage types characteristic of particular hafting modes detecting factors influencing the frequency of projectile damage and estimating the frequency of projectile damage expected to be found in archaeological samples the data obtained through the experiments applied in the analysis of the archaeological microliths from geometric kebaran and natufian sites in israel indicate different approaches to the design of projectiles fitted with microliths characteristic for these cultures the shift in design associated with such important economic and social transformations as transition to sedentary settlements and a broad spectrum economy may reflect a demand for light flexible and efficient projectile weapons requiring low time and labor investment for preparation and retooling the use of such efficient weapons in conditions of growing population density and restricted areas available for natufian hunter gatherers can be considered as one of the factors that could have affected the subsequent transition to food production that took place in the early holocene

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

echo source discrimination in single pass airborne radar sounding data from the dry valleys antarctica implications for orbital sounding of mars the interpretation of radar sounding data from mars where significant topographic relief occurs will require echo source discrimination to avoid the misinterpretation of surface echoes as arising from the subsurface this can be accomplished through the identification of all radar returns from the surface in order to positively identify subsurface echoes we have developed general techniques for this using airborne radar data from the dry valleys of antarctica these data were collected in a single pass including taylor glacier ice covered lake bonney and an ice free area of taylor valley the pulsed radar 52 5 67 5 mhz was coherently recorded our echo discrimination techniques included a radar simulator using a digital elevation model dem to predict the location and shape of surface echoes in the radar data real and simulated echo strengths were used to calculate a signal to clutter ratio this was complemented by the cross track migration of radar echoes onto the surface these migrated echoes were superimposed on the dem and imagery in order to correlate with surface features using these techniques enabled us to identify a number of echoes in the radar data as arising from the surface and to identify subsurface echoes including a continuous reflector under the main trunk of taylor glacier and multiple reflectors beneath the terminus of taylor glacier surface based radar confirms the thickness of the glacier at three crossing points the results illustrate the importance of using complementary techniques the usefulness of a dem and the limitations of single pass radar sounding data

new slope normalized global gully density and orientation maps for mars we reanalyse the global distribution of gullies in order to provide a set of observational constraints that models of gully formation must explain we validate our results derived from the global data with four detailed case studies we show that the availability of steep slopes is an essential factor to consider when assessing the spatial distribution and abundance of gullies when the availability of steep slopes is taken into account it reveals with a few exceptions that gullies are found almost uniformly across the whole 30 90 latitude band our analysis also reveals that massive ice deposits are anti correlated with gullies and that the undulations in the equatorwards limits of the gully distribution could be explained by longitudinal variations in maximum surface temperatures controlled by variations in surface properties including thermal inertia and albedo we find a sharp transition in both hemispheres between pole facing gullies which extend from 30 to 40 to a more mixed but dominantly equator facing orientation of gullies polewards of 40 we have no definitive explanation for this transition but based on previous studies we suggest it could be linked to the availability of near surface ice deposits

enhanced erosion rates on mars during amazonian glaciation abstract observations of mars from the surface and from orbit suggest that erosion rates over the last 3 gyr the amazonian have been as slow as 10 5 m myr and have been dominated by aeolian processes while ancient noachian erosion rates may have been orders of magnitude higher due to impact bombardment and fluvial activity amazonian aged glacial deposits are widespread on mars but rates of erosion responsible for contributing debris to these remnant glacial deposits have not been constrained here we calculate erosion rates during amazonian glaciations using a catalog of mid latitude glacial landforms coupled with observational and theoretical constraints on the duration of glaciation these calculations suggest that erosion rates for scarps that contributed debris to glacial landforms are 4 7 orders of magnitude higher than average amazonian rates in non glaciated low slope regions these erosion rates are similar to terrestrial cold based glacier erosion and entrainment rates consistent with cold based glacier modification of parts of mars

evidence for recent climate change on mars from the identification of youthful near surface ground ice ground ice in the crust and soil may be one of the largest reservoirs of water on mars1 2 3 near surface ground ice is predicted to be stable at latitudes higher than 40 ref 4 where a number of geomorphologic features indicative of viscous creep and hence ground ice have been observed5 mid latitude soils have also been implicated as a water ice reservoir6 the capacity of which is predicted to vary on a 100 000 year timescale owing to orbitally driven variations in climate7 it is uncertain however whether near surface ground ice currently exists at these latitudes and how it is changing with time here we report observational evidence for a mid latitude reservoir of near surface water ice occupying the pore space of soils the thickness of the ice occupied soil reservoir 1 10 m and its distribution in the 30 to 60 latitude bands indicate a reservoir of 1 5 6 0 104 km3 equivalent to a global layer of water 10 40 cm thick we infer that the reservoir was created during the last phase of high orbital obliquity less than 100 000 years ago and is now being diminished

an extended period of episodic northern mid latitude glaciation on mars during the middle to late amazonian implications for long term obliquity history mars is the only planet other than earth in the solar system that has a preserved nonpolar geological record of glaciation on its surface nonpolar ice deposits on mars have been linked to variations in spin axis obliquity that cause mobilization of polar ice and redeposition at lower latitudes forming ice rich and glacial deposits remnant nonpolar glacial deposits are found across the northern mid latitudes where surface ice is not currently stable implying that different climatic conditions existed on mars in the past individual glacial deposits are often too small to date reliably using impact crater size frequency data we describe a novel approach that allows us to derive new information about when glaciation occurred in broad areas of the northern mid latitudes in this region we have classified 1 craters that superpose preexisting glacial deposits and were modified by later accumulation and therefore formed during an epoch when glaciation was occurring and 2 craters that are superposed on glacial deposits but are themselves unmodified by ice accumulation and thus post date significant glaciation the sparse population of post glacial craters reveals that the last period of extensive ice deposition of this type in this latitude band was recent late amazonian the substantial number of craters formed during the recurring glacial periods implies that northern mid latitude glaciation was a long lived recurring process occurring over a period of at least 600 m y on the basis of mars atmospheric general circulation models these results are consistent with higher obliquity being common in the past with recurring periods of obliquity exceeding the 25 axial tilt of mars today these observations support the statistical prediction of j laskar and colleagues that the median obliquity during the amazonian was 35 40

radar sounding evidence for buried glaciers in the southern mid latitudes of mars lobate features abutting massifs and escarpments in the middle latitudes of mars have been recognized in images for decades but their true nature has been controversial with hypotheses of origin such as ice lubricated debris flows or glaciers covered by a layer of surface debris these models imply an ice content ranging from minor and interstitial to massive and relatively pure soundings of these deposits in the eastern hellas region by the shallow radar on the mars reconnaissance orbiter reveal radar properties entirely consistent with massive water ice supporting the debris covered glacier hypothesis the results imply that these glaciers formed in a previous climate conducive to glaciation at middle latitudes such features may collectively represent the most extensive nonpolar ice yet recognized on mars

radar soundings of the subsurface of mars the martian subsurface has been probed to kilometer depths by the mars advanced radar for subsurface and ionospheric sounding instrument aboard the mars express orbiter signals penetrate the polar layered deposits probably imaging the base of the deposits data from the northern lowlands of chryse planitia have revealed a shallowly buried quasi circular structure about 250 kilometers in diameter that is interpreted to be an impact basin in addition a planar reflector associated with the basin structure may indicate the presence of a low loss deposit that is more than 1 kilometer thick