thermal properties of lobate ejecta in syrtis major mars implications for the mechanisms of formation 1 this paper reports an analysis of the thermal properties of ejecta layers of single and double lobe impact craters on mars first observations of thermal properties were made at low resolution from the phobos 88 mission and did not allow mapping of variations of thermal properties inside the ejecta layer the themis instrument on board the mars odyssey mission provides new high resolution thermal mapping of the surface of mars from these data we observe a systematic temperature increase at night at the edge of the ejecta we evaluate first the possible influences on the surface temperatures at night of postimpact modification processes given the topography of an impact crater and its ejecta we show that the observed thermal signature is more likely related to a particle size distribution inherited immediately after the impact event during the emplacement of ejecta we propose that the kinetic sieving process observed in experimental and natural granular flows like pyroclastic flows is responsible for the accumulation of larger particles at the ejecta flow front and thus is responsible for the temperature increase despite evidence of aeolian activity at syrtis major these craters offer an example of preserved surface physical properties resulting from geological processes which have occurred since the formation of the volcanic shield of syrtis major further studies are underway with the mars express ongoing observations produced by the hrsc and omega instruments in order to explore the interplay between the surface physical properties and the spectroscopic signatures seen at syrtis major

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

thermokarst landforms and processes in ares vallis mars abstract with a length of 1500 km ares vallis is one of the largest martian outflow channels and is inferred to have been formed by cataclysmic floods of water conveyed from source areas which are marked by chaotic terrain to chryse planitia near its downstream outlet 14 n 28 w the floor of ares widens to 100 km from its average 25 km width this area of widened channel floor is marked by a complex of irregular terraces elongated depressions linear ridges sinuous ridges and other indicators of highly irregular dissection of a formerly continuous surface thermokarst processes following either glacial or alluvial histories seem best to explain these relationships various indicators of fluctuating discharge for water and sediment ponding of debris and prolonged flow suggest the emplacement of ice rich debris in the anomalous reach of ares vallis post flood or post glacial thawing of the ice rich sediments would then generate the thermokarst landscape these processes which are consistent with other indicators of anomalously warm climatic conditions imply a profound change from the modern martian environment

possible pingo fields in the utopia basin mars geological and climatical implications abstract the presence of pingos on mars has been hypothesized since the period of the viking mission in fact a diverse range of pingo like features has been found at various martian sites including elysium chryse and utopia planitiae in the northern lowlands due to the morphology and the geological setting some of those features were interpreted in different ways creating some controversies as happened in athabasca valles this reflects the complexity of interpreting these features by remote sensing and multiple plausible interpretations of the same feature with the objective of identifying new possible pingos or rootless cones on mars we selected a study area in utopia planitia 10 55 n 210 260 w where the presence of both features is possible due to its geological history volcanic and hydrological we analyzed more than 2100 mars orbiter camera moc narrow angle images in addition to viking thermal emission imaging system themis and high resolution stereo camera hrsc images together with mars orbiter laser altimeter mola derived digital elevation models dems with a geographic information system gis we found in 94 moc narrow angle images dome cone and ring shaped features we analyzed them from morphological and morphometrical points of view in order to compare them with relevant features on mars and earth we tested different possible origins for those features following the approach of multiple working hypotheses we conclude that the dome cone and ring shaped features could be pingos which is in agreement with their geological settings regarding the driving heat source for the formation of the purported pingos we propose the existence of a heat source possibly a magma chamber underneath the surface of the utopia basin together with possible climatic shifts the past activities of the heat source may have caused melting of ground ice the pingo growth due to freezing of the water would have occurred during the following cold climatic conditions

comparing landslides to fluidized crater ejecta on mars 1 we use the mars global surveyor and viking data sets to compare and contrast the geomorphology of four large martian landslides located in valles marineris to fluidized ejecta of seven fresh martian craters located in lunae planum both mass movements have flowed over the martian surface and possess characteristics seen in terrestrial mass movements we combine these comparisons with simple flow models to determine how the planar geometry of landslides and the cylindrical geometry of ejecta can generate different topographic expressions for the same input constraints our purpose is to better understand the emplacement processes of both types of mass movements our geomorphic analyses are consistent with previous views that the large martian landslides resemble large terrestrial long run out flows the planar flow model supports this inference martian landslides probably flowed as a basal glide where motion is limited to a narrow interface at the base of the mass movement geomorphic investigations of fresh multilayered ejecta indicate that their inner portions with their subtle rampart probably flowed like their landslide counterparts as a basal glide distal pronounced contiguous ramparts however resemble features akin to terrestrial debris flows the cylindrical flow model shows that differences in geometry can mask the dynamics of flow emplacement this model suggests as expected a basal glide origin for the inner portions of the ejecta surprisingly basal glide also best explains the topography of the distal ejecta ramparts

gpr a ground penetrating radar for the netlander mission in the coming decade several missions are planned that will land on the surface of mars landers or instrumented geophysical stations among the scientific objectives of these projects one of the most important will be to unravel the many unknowns in the geological and hydrological history of the planet the netlander mission offers a unique opportunity to explore the interior of mars its subsurface its atmosphere and its distant environment from four landing sites that will be selected to offer a variety of different geophysical conditions we have thus proposed to fly on these four landers a ground penetrating radar gpr to explore the geological characteristics of the subsurface and search for water reservoirs down to a depth which may be sufficient to allow a possible detection of liquid water we provide in this paper a short description of this radar which is based on a new concept to allow a 3 d imaging of the subsurface by determining the range and direction of the underground reflectors in order to access to deep layers it will operate at a low frequency of 2 mhz some results obtained by a numerical modeling of the radar operation in an electromagnetic model of the martian subsurface are presented in order to illustrate the main capabilities of the radar in the last section preliminary results from an initial field test are reported in addition to its primary goal as a ground penetrating radar the gpr will also be operated on mars as an ionospheric sounder and in a passive mode as a hf receiver to measure the radio electric background

evolution of periglacial landforms in the ancient mountain range of the thaumasia highlands mars possible periglacial and relict glacial landforms in the ancient mountain range of the thaumasia highlands mars are described the landforms include large scale mantling lineated crater and valley fill materials debris aprons protalus lobes and ramparts the most pristine icerelated landforms appear to be small scale protalus lobes and ramparts with no visible distinct impact craters at both medium high resolution stereo camera hrsc and high mars orbiter camera moc narrow angle na context camera ctx spatial resolution these small landforms are possibly active at present and post date more extensive features such as crater fills possibly formed during high obliquity climatic periods in contrast to the rock glacier like landforms with distribution preferentially occurring on southfacing slopes possibly controlled by enhanced exposure to the sun older less pristine lineated fill materials show a less systematic distribution of flow directions suggesting a more generalized periglacial and possibly glacial environment in the thaumasia highlands

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

sub kilometre intra crater mounds in utopia planitia mars character occurrence and possible formation hypotheses abstract at the middle latitudes of utopia planitia 35 45 n 65 101 e hundreds of small sized mounds located in sub kilometre impact craters dot the landscape their shape varies from circular to crescentic and their height ranges from 10 to 50 m often metre to decametre pitting is observed as is metres thick banding or stratification mound albedo is relatively high i e 0 16 the plain s terrain in the region previously linked to the latitude dependent mantle ldm of ice dust displays pitting and albedo similar to the small intra crater mounds some workers have suggested that the mounds and the plain s terrain share a common ice dust origin if so then scrutinising the mounds could provide analogical insight on the key geological characteristics and spatial distribution of the ldm itself other workers have hypothesised that the mounds are eroded sedimentary landforms or periglacial mounds underlain by a perennial ice core closed system pingos in this article we develop and then discuss each of the three mound hypotheses in a much more substantial manner than has been done hitherto towards this end we use high resolution images present a detailed regional map of mound distribution and establish a regional platform of topographical analysis using mola data superposed on a large scale ctx mosaic although the ice dust hypothesis is consistent with some observations and measurements we find that a loess based sedimentary hypothesis shows greater plausibility of the three hypotheses evaluated the pingo or periglacial one is the weakest

radar sounding of temperate permafrost in alaska analogy to the martian midlatitude to high latitude ice rich terrains 1 radar detection of subsurface ice on mars has been widely debated in part because the dielectric signature of ice as deduced from the dielectric constant can be confused with dry silicate rich materials to identify the ice dielectric signature it is crucial to estimate the imaginary part of the dielectric permittivity inferred from the dielectric attenuation after removing the scattering loss unfortunately the latter remains poorly quantified at both mars advanced radar for subsurface and ionospheric sounding marsis and shallow subsurface radar sharad frequencies to address this ambiguity we conducted multiple frequency ground penetrating radar and resistivity investigations in well characterized temperate permafrost in fairbanks alaska the area shows several geomorphologic similarities to midlatitude and high latitude terrains on mars this approach allowed us to quantify the dielectric and scattering losses in temperate permafrost over the 10 to 1000 mhz frequency band at 20 mhz our results suggest an average dielectric loss rate of 0 25 0 03 db m whereas the corresponding average scattering loss rate is 0 94 0 37 db m the scattering loss was found to represent 69 of the total signal attenuation considering this result and the study by heggy et al 2006a in volcanic environments we revised the interpretation of the attenuation coefficient calculated from sharad data over the deuteronilus mensae region and amazonis planitia we then used the reevaluated dielectric loss to estimate the imaginary part of the dielectric permittivity our results suggest that even if deuteronilus mensae deposits and the vastitas borealis formation may have similar dielectric constants their imaginary parts are different this implies that the two regions have different bulk compositions with the former being ice rich sediments and the latter being nonconsolidated volcanic deposits

modeling and observational occurrences of near surface drainage in utopia planitia mars during the past 15 years evidence for an ice rich planet mars has rapidly mounted become increasingly varied in terms of types of deposits and types of observational data and has become more widespread across the surface the mid latitudes of mars especially utopia planitia show many types of interesting landforms similar to those in periglacial landscapes on earth that suggest the presence of ice rich permafrost these include thermal contraction polygonal networks scalloped terrains similar to thermokarst pits debris flows small mounds like pingos and rock glaciers here we address questions concerning the influence of meltwater in the utopia planitia up landscape using analogs of near surface melting and drainage along ice wedge troughs on bylot island northern canada in utopia planitia based on the identification of sinuous channel like pits within polygonal networks we suggest that episodic underground melting was possible under severe periglacial climate conditions in up the collapse pattern and morphology of unconnected sinuous elongated pits that follow the polygon crack are similar to underground melting in bylot island nunavut canada based on this terrestrial analogue we develop a thermal model that consists of a thick insulating dusty layer over ice saturated dust during a period of slight climatic warming relative to today s climate in the model the melting point is reached at depths down to 150 m we suggest that small scale melting could have occurred below ground within ground ice polygonal fractures and pooled in underground cavities then the water may have been released episodically causing mechanical erosion as well as undermining and collapse after melting the dry surface dusty layer might have been blown away thus exposing the degraded terrain of the substrate layer

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

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

grid mapping the northern plains of mars using morphotype and distribution of ice related landforms to understand multiple ice rich deposits in utopia planitia this work in utopia planitia is the first continuous regional mapping of ice related landforms integrated into an effort to study the three main basins arcadia acidalia utopia planitiae in the northern plains the distribution and morphotypes of these landforms sharad detections and crater size frequency distribution measurements 50 m in diameter were used to understand the permafrost cryolithology and its past evolution in relation to climate in utopia planitia three assemblages of landforms were identified based on their spatial correlation and correlation with mola surface roughness along a strip from 30 n to 80 n at 30 38 n the assemblage is formed by km scale polygons high albedo mounds and thumbprint terrains this assemblage is associated with a lobate deposit of 30 m in thickness with a crater retention age of 1 ga at 38 47 n the assemblage is comprised of large scallops 100 m diameter polygons pits and mantled deposits this assemblage is correlated with a deposit of 80 m in thickness containing excess ice 50 85 by volume with a crater retention age of about 10 ma at 47 78 n the assemblage is composed of mantled deposits textured terrains and 30 m diameter polygons this assemblage is related to the ice rich debris covered latitude dependent mantle that has a crater retention age of about 1 5 ma utopia planitia appears to be a region of combined depositions of sediment and continuous cold climatic conditions that leaded to a complex distribution of ground ice

observations of a reversal in vertical and horizontal strain rate regime during a motion event on unteraargletscher bernese alps switzerland during a motion event on unteraargletscher bernese alps switzerland in spring 1996 surface velocities were measured up to eight times a day at four different locations along the central flowline using global positioning system equipment in addition accumulated vertical strains over the uppermost 50 and 100 m were measured at a location where the total ice thickness is 260 m the motion event was accompanied by high horizontal and vertical strain rates as compared to annual mean values a reversal in strain regime was observed with horizontal strain rates changing to extension while vertical strain rates became compressive this strain rate reversal coincided within the temporal resolution of the data with a maximum in vertical ice displacement at the surface within a day variations in vertical strain from 0 04 a 1 to 0 06 a 1 were observed over the uppermost 100 m vertical stretching is estimated to have contributed to at least 20 of the anomalous vertical ice movement at the surface there were significant differences between measured longitudinal strain averaged over a distance corresponding to a few ice thicknesses and measured vertical strain in spring 1997 a similar but more detailed set of measurements was collected at the same measuring site and vertical strain rates were found to vary non uniformly with depth with the largest values closest to the surface

dating martian climate change abstract geological evidence indicates that low latitude polygonally patterned grounds on mars generally thought to be the product of flood volcanism are periglacial in nature and record a complex signal of changing climate by studying the martian surface stratigraphically in terms of the geometrical relations between surface landforms and the substrate rather than genetically by form analogy with earth we have identified dynamic surfaces across one fifth of martian longitude new stratigraphical observations in the elysium amazonis plains have revealed a progressive surface polygonisation that is destructive of impact craters across the region this activity is comparable to the climatically driven degradation of periglacial landscapes on earth but because it affects impact craters the martian chronometer it can be dated here we show that it is possible to directly date this activity based on the fraction of impact craters affected by polygon formation nearly 100 of craters of all diameters are superposed by polygonal sculpture considering the few 100 ma age of the substrate this suggests that the process of polygon formation was active within the last few million years surface polygonisation in this region often considered to be one of the signs of young plains forming volcanism on mars is instead shown to postdate the majority of impact craters seen we therefore conclude that it is post depositional in origin and an artefact of thermal cycling of near surface ground ice stratigraphically controlled crater counts present the first way of dating climate change on a planet other than earth a record that may tell us something about climate change on our own planet parallel climate change on these two worlds an ice age mars coincident with earth s glacial quaternary period might suggest a coupled system linking both we have previously been unable to generalise about the causes of long term climate change based on a single terrestrial example with the beginnings of a chronology for climate change on our nearest planetary neighbour we can

impact of iron on nuclear glass alteration in geological repository conditions a multiscale approach abstract interactions between nuclear glass and fe were investigated in a clayey environment to better understand the mechanisms and driving forces controlling the long term behavior of high level waste glass in a geological repository an integrated experiment involving a glass iron clay gic stack was run at a laboratory scale in anoxic conditions for 2 years and the interfaces were characterized by a multiscale approach using scanning electron microscopy coupled with energy dispersive spectroscopy transmission electron microscopy raman microspectroscopy and scanning transmission x ray microscopy at the sls synchrotron the characterization of glass alteration patterns on cross sections revealed an increase in glass alteration with the fe content and the proximity between the glass and fe the alteration layers are polyphase and stratified with an inner porous gel layer incorporating fe and an outer layer composed of nanocrystalline fe silicates several mechanisms which could affect the glass alteration kinetics and the transport properties of the alteration layer are proposed to explain this pattern i consumption of hydrolyzed silica by precipitation of fe silicates ii penetration of fe within the gel porosity probably as precipitates such as fe oxyhydroxide or fe silicates these new data may imply some consequences when considering the long term behavior of glass in geological disposal conditions

outwash plains and thermokarst on mars abstract the spatial distribution of different types of rampart craters on mars suggests a hemispheric asymmetry in the distribution of ground ice the northern plains especially major topographic depressions near the terminations of outflow channels have high percentages of rampart craters two of these basins acidalia and utopia planitiae received extraordinarily large amounts of water and sediment from the chryse and elysium outflow channels in both regions the analysis of high resolution viking pictures 12 m pixel indicates a concentration of kilometer scale depressions that are similar in size and form to thermokarstic features in yakutia siberia and parts of the arctic coastal plain of north america accordingly we infer that 1 utopia planitia and acidalia planitia may contain thick laterally continuous ice rich sedimentary deposits related to outflow channel forming floods and 2 these areas of mars may have experienced thermokarstic processes similar to modern thermokarstic processes in some periglacial regions of earth

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

sparse subsurface radar reflectors in hellas planitia mars abstract geomorphological features potentially related to subsurface ice such as scalloped depressions expanded craters pedestal craters and banded terrain are present in and around hellas planitia mars we present a radar survey of the region using the shallow radar sharad instrument on board the mars reconnaissance orbiter mro to identify candidate subsurface reflectors that may be due to the presence of potentially ice rich deposits we found that the majority of radar returns are likely from off nadir surface topography clutter arising from the rough topography of the region there is no widespread radar return from any subsurface interfaces however we identify a group of six reflectors adjacent to each other on a plateau in malea patera in which we have higher confidence landforms associated with a likely ice rich mantle are associated with the plateau but the thickness of this mantle does not correspond to the expected depth of the reflectors however layers beneath the mantle and marginal pitting at the edge of the plateau are similar to those associated with pedestal craters which may be ice rich and are a similar thickness to the expected depth of the reflectors malea patera has been interpreted to be a volcanic caldera so the reflectors may be associated with a volcanic deposit within the plateau although the evidence for this is inconclusive because this radar detection is localized and its origin ambiguous we cannot use it to make conclusions about the thickness of subsurface deposits in the hellas region as a whole the lack of widespread radar reflectors in this region as compared to the northern mid latitudes where extensive radar reflections have been mapped may be due in part to higher surface roughness which creates radar clutter that may obscure subsurface reflectors however on the southern rim of the basin and south of the basin the lack of reflectors may indicate that the possible ice rich deposits observed geomorphologically in this region are too thin to be resolved by sharad are dielectrically similar to the underlying unit or have a gradual vertical transition in ice content that is not reflective for the radar this would imply that recent climate processes may have favored widespread thick ice deposition or preservation in the northern hemisphere as compared to the southern hemisphere

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

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

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

ice rich periglacial vs icy glacial depressions in the argyre region mars a proposed cold climate dichotomy of landforms on mars so called scalloped depressions are widely observed in utopia planitia up and malea planum mp typically they are rimless metres to decametres deep incised sharply tiered inwardly polygonised and sometimes pitted the depressions seemingly incise terrain that is icy and possibly thermokarstic i e produced by the thermal destabilisation of the icy terrain agewise the depressions are thought to be relatively youthful originating in the late amazonian epoch here we report the presence of similar depressions in the argyre region ar 30 60 s 290 355 e more importantly we separate and differentiate these landforms into two groups ice rich periglacial depressions type 1 and icy glacial depressions type 2a c this differentiation is presented to the mars community for the first time based on a suite of morphological and geological characteristics synonymous with ice complexes in the lena peninsula eastern russia and the tuktoyaktuk coastlands northwest territories canada we propose that the type 1 depressions are ice rich periglacial basins that have undergone volatile depletion largely by sublimation and as the result of thermal destabilisation in keeping with the terms and associated definitions derived of terrestrial periglacial geomorphology ice rich refers to permanently frozen ground in which ice lenses or segregation ice collectively referenced as excess ice have formed we suggest that the depressions are the product of a multi step cold climate geochronology 1 atmospheric precipitation and surface accumulation of an icy mantle during recent high obliquities 2 regional or local triple point conditions and thaw evaporation of the mantle either by exogenic forcing i e obliquity driven rises of aerial and sub aerial temperatures or endogenic forcing i e along argyre impact related basement structures 3 meltwater migration into the regolith at least to the full depth of the depressions 4 freeze thaw cycling and the formation of excess ice 5 sublimation of the excess ice and depression formation as high obliquity dissipates and near surface ice becomes unstable the type 2 depressions exhibit characteristics suggestive of supra glacial dead ice basins and snow ice suncups observed in high alpine landscapes on earth e g the swiss alps and the himalayas like the type 1 depressions the type 2 depressions could be the work of sublimation however the latter differ from the former in that they seem to develop within a glacial like icy mantle that blankets the surface rather than within an ice rich and periglacially revised regolith at near the surface interestingly the type 2 depressions overlie the type 1 depressions at some locations if the periglacial glacial morphological and stratigraphical dichotomy of depressions is valid then this points to recent glaciation at some locations within the ar being precursed by at least one episode of periglaciation this also suggests that periglaciation has a deeper history in the region than has been thought hitherto moreover if the hypothesised differences amongst the argyre based depressions are mirrored in utopia planitia and malea planum then perhaps this periglacial glacial dichotomy and its associated geochronology are as relevant to understanding late period landscape evolution in these two regions as it is in the ar

effect of volatiles and target lithology on the generation and emplacement of impact crater fill and ejecta deposits on mars impact cratering is an important geological process on mars and the nature of martian impact craters may provide important information as to the volatile content of the martian crust terrestrial impact structures currently provide the only ground truth data as to the role of volatiles and an atmosphere on the impact cratering process recent advancements based on studies of several well preserved terrestrial craters have been made regarding the role and effect of volatiles on the impact cratering process combined field and laboratory studies reveal that impact melting is much more common in volatile rich targets than previously thought so impact melt rocks melt bearing breccias and glasses should be common on mars consideration of the terrestrial impact cratering record suggests that it is the presence or absence of subsurface volatiles and not the presence of an atmosphere that largely controls ejecta emplacement on mars furthermore recent studies at the haughton and ries impact structures reveal that there are two discrete episodes of ejecta deposition during the formation of complex impact craters that provide a mechanism for generating multiple layers of ejecta it is apparent that the relative abundance of volatiles in the near surface region outside a transient cavity and in the target rocks within the transient cavity play a key role in controlling the amount of fluidization of martian ejecta deposits this study shows the value of using terrestrial analogues in addition to observational data from robotic orbiters and landers laboratory experiments and numerical modeling to explore the martian impact cratering record