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

surface wave effects on high frequency currents over a shelf edge bank abstractseveral acoustic doppler current profilers and vertical strings of temperature conductivity and pressure sensors deployed on and around the east flower garden bank efgb were used to examine surface wave effects on high frequency flows over the bank and to quantify spatial and temporal characteristic of these high frequency flows the efgb about 5 km wide and 10 km long is located about 180 km southeast of galveston texas and consists of steep slopes on southern and eastern sides that rise from water depths over 100 m to within 20 m of the surface three dimensional flows with frequencies ranging from 0 2 to 2 cycles per hour cph were observed in the mixed layer when wind speed and stokes drift at the surface were large these motions were stronger over the bank than outside the perimeter the squared vertical velocity w2 was strongest near the surface and decayed exponentially with depth and the e folding length of w2 was 2 times larger than that of stokes drift the 2 h averaged w2 i

volcanic terrain and the possible periglacial formation of excess ice at the mid latitudes of utopia planitia mars at the mid latitudes of utopia planitia up mars a suite of spatially associated landforms exhibit geomorphological traits that on earth would be consistent with periglacial processes and the possible freeze thaw cycling of water the suite comprises small sized polygonally patterned ground polygon junction and margin pits and scalloped rimless depressions typically the landforms incise a dark toned terrain that is thought to be ice rich here we investigate the dark toned terrain by using high resolution images from the hirise as well as near infrared spectral data from the omega and crism the terrain displays erosional characteristics consistent with a sedimentary nature and near infrared spectra characterised by a blue slope similar to that of weathered basaltic tephra we also describe volcanic terrain that is dark toned and periglacially modified in the kamchatka mountain range of eastern russia the terrain is characterised by weathered tephra inter bedded with snow ice wedge polygons and near surface excess ice the excess ice forms in the pore space of the tephra as the result of snow melt infiltration and subsequently in situ freezing based on this possible analogue we construct a three stage mechanism that explains the possible ice enrichment of a broad expanse of dark toned terrain at the mid latitudes of up 1 the dark toned terrain accumulates and forms via the regional deposition of sediments sourced from explosive volcanism 2 the volcanic sediments are blanketed by atmospherically precipitated h2o snow ice or an admixture of the two either concurrent with the volcanic events or between discrete events and 3 under the influence of high obliquity or explosive volcanism boundary conditions tolerant of thaw evolve and this in turn permits the migration cycling and eventual formation of excess ice in the volcanic sediments over time and through episodic iterations of this scenario excess ice forms to decametres of depth

an improved solution of the gravity field of mars gmm 2b from mars global surveyor a spherical harmonic solution of the mars gravity field to degree and order 80 goddard mars model 2b gmm 2b has been developed using x band tracking data of mars global surveyor mgs from october 1997 to february 2000 and altimeter crossovers formed from the mars orbiter laser altimeter mola data between march and december 1999 during the mapping mission mgs was located in a near polar 92 9 inclination and near circular orbit at a mean altitude of 400 km the tracking data from this orbit provide a detailed global and high resolution view of the gravity field of mars mars gravity solutions are stable to 60 60 even without application of a kaula power law constraint the valles marineris is resolved distinctly with lows reaching 450 mgals olympus mons and its aureole are both separately resolved and the volcano has a peak anomaly of 2950 mgals the global correlation of the gmm 2b gravity coefficients with mola derived topography is 0 78 through degree 60 and the correlation remains above 0 6 through degree 62 the global gravity anomaly error predicted from the gmm 2b error covariance through 60 60 is 11 mgal the global geoid error from gmm 2b through 60 60 is 1 8 m mgs orbit quality using gmm 2b as measured by overlapping orbital arcs is 1 m in the radial direction and 10 m in total position

thermokarst in siberian ice rich permafrost comparison to asymmetric scalloped depressions on mars 1 on earth the thawing of permafrost deposits with high ground ice content results in massive surface subsidence and the formation of characteristic large thermokarst depressions slope asymmetries within thermokarst depressions suggest lateral growth which occurs due to thermoerosion and gravimetric mass wasting along these slopes it has been proposed that rimless asymmetrically shaped depressions called scalloped depressions on mars were formed by insolation driven ground ice sublimation we investigated a large thermokarst depression in ice complex deposits in the siberian arctic as a terrestrial analogue for scalloped depressions in martian volatile rich mantle deposits our results from field studies insolation modeling and geomorphometric analyses suggest lateral thermokarst development in a northern direction this conclusion is obvious due to steeper slope angles of the south facing slopes insolation and surface temperatures are crucial factors directly influencing thermokarst slope stability and steepness comparative analyses of martian scalloped depressions in utopia planitia were conducted using high resolution high resolution imaging science experiment context camera and thermal infrared thermal emission imaging system satellite data by direct analogy we propose that the lateral scalloped depression development on mars was primarily forced on the steep pole facing slopes in the equator ward direction insolation modeling confirms that this must have happened in the last 10 ma during an orbital configuration of higher obliquity than today development would have been maximized if the orbit was both highly oblique and highly eccentric and or the martian summer coincided with perihelion relatively short events of increasing sublimation or even thawing of ground ice led to fast slumping processes on the steep pole facing slopes

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

modeling the development of martian sublimation thermokarst landforms abstract sublimation thermokarst landforms result from collapse of the surface when ice is lost from the subsurface on mars scalloped landforms with scales of decameters to kilometers are observed in the mid latitudes and considered likely thermokarst features we describe a landscape evolution model that couples diffusive mass movement and subsurface ice loss due to sublimation over periods of tens of thousands of mars years under conditions similar to the present the model produces scallop like features similar to those on the martian surface starting from much smaller initial disturbances the model also indicates crater expansion when impacts occur in surfaces underlain by excess ice to some depth with morphologies similar to observed landforms on the martian northern plains in order to produce these landforms by sublimation substantial quantities of excess ice are required at least comparable to the vertical extent of the landform and such ice must remain in adjacent terrain to support the non deflated surface we suggest that martian thermokarst features are consistent with formation by sublimation without melting and that significant thicknesses of very clean excess ice up to many tens of meters the depth of some scalloped depressions are locally present in the martian mid latitudes climate conditions leading to melting at significant depth are not required

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

standardizing the nomenclature of martian impact crater ejecta morphologies the mars crater morphology consortium recommends the use of a standardized nomenclature system when discussing martian impact crater ejecta morphologies the system utilizes nongenetic descriptors to identify the various ejecta morphologies seen on mars this system is designed to facilitate communication and collaboration between researchers crater morphology databases will be archived through the u s geological survey in flagstaff where a comprehensive catalog of martian crater morphologic information will be maintained

expanded secondary craters in the arcadia planitia region mars evidence for tens of myr old shallow subsurface ice abstract a range of observations indicates widespread subsurface ice throughout the mid and high latitudes of mars in the form of both pore filling and excess ice it is generally thought that this ice was recently emplaced and is not older than a hundred thousand to a few millions of years old based on ice stability and orbital induced climate change we analyze the distribution of subsurface ice in arcadia planitia located in the northern mid latitudes by mapping thermokarstically expanded secondary craters providing additional evidence for extensive excess ice down to fairly low latitudes less than 40 n we further infer the minimum age of this subsurface ice based on the ages of the four primary craters that are thought to be the source of a large portion of these secondaries which yields estimates on the order of tens of millions of years old much more ancient than anticipated this estimated ancient age suggests that ice can be preserved in the shallow subsurface for long periods of time at least in some parts of arcadia planitia where expanded secondary craters are especially abundant we estimate the amount of ice lost to sublimation during crater expansion based on measurements of expanded secondary craters in hirise digital terrain models the loss is equivalent to a volume of ice between 140 and 360 km 3 which would correspond to a global layer of 1 2 5 mm thick we further argue that much more ice at least 6000 km 3 is likely preserved beneath the un cratered regions of arcadia planitia since significant loss of this excess ice would have caused extensive terrain dissection and the removal of the expanded secondary craters both the loss of ice due to secondary crater expansion and the presence of this ice today have implications for the martian climate

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

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

the 3 5 mhz global reflectivity map of mars by marsis mars express implications for the current inventory of subsurface h2o abstract we extracted the surface echo power from 2 years of marsis measurements the retrieved values are calibrated to compensate for changes in the distance of the spacecraft to the surface and for the attenuation of the signal by the ionosphere the results are used to build the first global map of surface echo power at 3 5 mhz the surface echo power variations are primarily caused by kilometer scale surface roughness then we derive the values of dielectric constant of the shallow subsurface materials by normalizing the surface echo power map using a simulation of marsis signal from the mola topography as a result we obtain a map that characterizes the dielectric properties of the materials down to a few decameters below the surface dielectric properties vary with latitude with high values in mid latitudes belts 20 40 and lower values at both equatorial and high latitudes from the comparison of marsis reflectivity map to grs observations we conclude that the reflectivity decrease observed poleward of 50 60 corresponds to the onset of water ice occurrence within the regolith assuming homogenous ground composition and texture at the scale of the marsis resolution cell our inferred volume of ground water ice is of 106 km3 equivalent to a polar cap low reflectivity areas are also observed in equatorial regions from radar studies alone equatorial low dielectric constant values could have different interpretations but the correlation with grs hydrogen distribution rather points toward a water related explanation

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

coastal river plumes collisions and coalescence abstract plumes of buoyant river water spread in the ocean from river mouths and these plumes influence water quality sediment dispersal primary productivity and circulation along the world s coasts most investigations of river plumes have focused on large rivers in a coastal region for which the physical spreading of the plume is assumed to be independent from the influence of other buoyant plumes here we provide new understanding of the spreading patterns of multiple plumes interacting along simplified coastal settings by investigating i the relative likelihood of plume to plume interactions at different settings using geophysical scaling ii the diversity of plume frontal collision types and the effects of these collisions on spreading patterns of plume waters using a two dimensional hydrodynamic model and iii the fundamental differences in plume spreading patterns between coasts with single and multiple rivers using a three dimensional hydrodynamic model geophysical scaling suggests that coastal margins with numerous small rivers watershed areas 2 such as found along most active geologic coastal margins were much more likely to have river plumes that collide and interact than coastal settings with large rivers watershed areas 100 000 km 2 when two plume fronts meet several types of collision attributes were found including refection subduction and occlusion we found that the relative differences in pre collision plume densities and thicknesses strongly influenced the resulting collision types the three dimensional spreading of buoyant plumes was found to be influenced by the presence of additional rivers for all modeled scenarios including those with and without coriolis and wind combined these results suggest that plume to plume interactions are common phenomena for coastal regions offshore of the world s smaller rivers and for coastal settings with multiple river mouths in close proximity and that the spreading and fate of river waters in these settings will be strongly influenced by these interactions we conclude that new investigations are needed to characterize how plumes interact offshore of river mouths to better understand the transport and fate of terrestrial sources of pollution nutrients and other materials in the ocean

martian pedestal craters marginal sublimation pits implicate a climate related formation mechanism 1 pedestal craters on mars are defined by an outward facing scarp forming a plateau perched tens of meters above the surrounding terrain their origin has been attributed to impact armoring of the surface and subsequent removal of inter crater terrain by either eolian deflation or sublimation of an ice rich substrate we identified 2696 pedestal craters between 60 n and 60 s latitude 98 are poleward of 33 n and 40 s the majority of pedestal crater margins are smoothly sloped but 3 concentrated in utopia planitia and malea planum display distinctive marginal pits these pedestal crater scarps are anomalously tall usually 80 100 m and the pits resemble sublimation depressions seen on earth and elsewhere on mars providing evidence for sublimation of volatiles in the scarp where the armored surface has tapered the pitted scarps provide insight into the origin of the general pedestal crater population favoring formation via deposition of a volatile rich substrate impact armoring and sublimation of intervening volatiles crater densities and overlapping pedestal craters suggest multiple periods of emplacement and loss of these climate related latitude dependent deposits throughout the amazonian

topography of mars from global mapping by hrsc high resolution digital terrain models and orthoimages characteristics and performance abstract we report on the results of the mars express high resolution stereo camera hrsc experiment pertaining to one of its major aims mapping the surface of mars by high resolution digital terrain models dtm up to 50 m grid spacing and orthoimages up to 12 5 m resolution we introduce the specifications and characteristics of these data products and give an overview of the procedures that have been developed and are applied for their derivation we also address the performance characteristics of the mapping project related to different aspects of internal accuracy accuracy with respect to the global reference system and regional aspects using adaptive processing techniques for terrain reconstruction and a revised approach to the improvement of orientation data a mean precision of the resulting 3d points of about 12 m is obtained exceeding the mean ground resolution of the stereo images using mars orbiter laser altimeter mola data the hrsc models are firmly tied to the global reference system at the scale of the hrsc dtm grid spacing in the lateral dimension and to within few meters vertically hrsc high resolution dtms are typically generated using a grid size of about 2 times the mean ground resolution but usually not larger than 3 times the mean ground resolution and not smaller than 3 times the precision of the integrated 3d points derived from stereo image analysis statistically every grid cell is based on at least one measured 3d point thus horizontal dtm resolution is well established with regard to the precision and density of the derived 3d points while the concurrent aim of a detailed terrain representation at maximum possible resolution is pursued comparison with the dtm derived from mola data allows us to identify specific advancements related to this updated view of martian topography we also address the mapping performance of hrsc in comparison to mola with respect to latitude and to different surface types and morphologies finally comparison with mola highlights typical complementarities of the two different approaches for mapping planetary surfaces

morphometric properties of martian volcanoes 1 mars orbiter laser altimeter mola data have been used to construct digital elevation models dem of the martian volcanoes in order to determine height flank slope caldera depth and volumes summit elevations range from 21 1 km to 0 5 km and relief varies from 1 0 km to almost 22 km average flank slopes are in the range of 1 to 10 consistent with basaltic shield volcanism the very low slopes of highland patera are also consistent with pyroclastic volcanism minimum volumes range from 1012 to 1015 m3 estimates of the time required to build these volcanoes on the basis of long term terrestrial eruption rates range from hundreds of thousands to tens of millions of years

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

shallow radar sharad pedestal craters and the lost martian layers initial assessments 1 since their discovery martian pedestal craters have been interpreted as remnants of layers that were once regionally extensive but have since been mostly removed pedestals span from subkilometer to hundreds of kilometers but their thickness is less than 500 m except for a small equatorial concentration in the medusae fossae formation the nearly exclusive occurrence of pedestal craters in the middle and high latitudes of mars has led to the suspicion that the lost units bore a significant fraction of volatiles such as water ice recent morphological characterizations of pedestal deposits have further supported this view here we employ radar soundings obtained by the shallow radar sharad to investigate the volumes of a subset of the pedestal population in concert with high resolution imagery to assist our interpretations from the analysis of 97 pedestal craters we find that large pedestals diameter 30 km are relatively transparent to radar in their majority with sharad being able to detect the base of the pedestal deposits and possess an average dielectric permittivity of 4 0 5 in one of the cases of large pedestals in malea planum layering is detected both in sharad data and in high resolution imagery of the pedestal margins we find that clutter is a major issue in the analysis of radar soundings for smaller pedestals and tentative detection of the basal reflection occurs in only a few of the cases examined these detections yield a higher average permittivity of 6 the permittivity value derived for the larger pedestals for which a basal reflection is unambiguous is higher than that of pure water ice but lower than that of most silicate materials a mixture of ice and silicates or an ice free porous silicate matrix can explain a permittivity of 4 and radar alone cannot resolve this nonuniqueness data from the compact reconnaissance imaging spectrometer crism tentatively confirms a mafic component in at least one pedestal in malea planum interpretation of sharad results can support either a mixture of ice and silicates or a porous silicate the former is compatible with a model where nonpolar ice is periodically deposited in the midlatitudes as a result of obliquity variations the latter is compatible with ash deposits at least in where pedestals appear in volcanic centers such as malea planum

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

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

an atmospheric blast thermal model for the formation of high latitude pedestal craters although tenuous the atmosphere of mars affects the evolution of impact generated vapor early time vapor from a vertical impact expands symmetrically directly transferring a small percentage of the initial kinetic energy of impact to the atmosphere this energy in turn induces a hemispherical shock wave that propagates outward as an intense airblast due to high speed expansion of vapor followed by a thermal pulse of extreme atmospheric temperatures from thermal energy of expansion this study models the atmospheric response to such early time energy coupling using the cth hydrocode written at sandia national laboratories results show that the surface surrounding a 10 km diameter crater 6 km apparent diameter on mars will be subjected to intense winds 200 m s and extreme atmospheric temperatures these elevated temperatures are sufficient to melt subsurface volatiles at a depth of several centimeters for an ice rich substrate ensuing surface signatures extend to distal locations 4 apparent crater diameters for a case of 0 1 energy coupling and include striations thermally armored surfaces and or ejecta pedestals all of which are exhibited surrounding the freshest high latitude craters on mars the combined effects of the atmospheric blast and thermal pulse resulting in the generation of a crater centered erosion resistant armored surface thus provide a new very plausible formation model for high latitude martian pedestal craters

distribution and evolution of scalloped terrain in the southern hemisphere mars abstract scalloped depressions are a unique martian surface morphology found in the northern and southern hemisphere latitude dependent dust and ice rich surface mantles these features exhibit a distinct asymmetric north south slope profile characterized by steep pole facing scarps flat floors and gentle equator facing slopes we examined high resolution stereo camera hrsc images of the southern hemisphere to determine their longitudinal distribution which revealed that a majority of scalloped terrain is located in the region of the southern wall of the hellas basin and northern malea planum a detailed map of this area was produced where scallops were found to contour the southern wall of the basin and where the ice rich mantle was seen to be thickest scalloped terrain is concentrated along the topographic highs near the amphitrites and peneus paterae and areal extent and depth decreases with increasing depth into the basin we also examined existing hypothesis for the formation and evolution of scalloped depressions using high resolution imaging science experiment hirise images and data from the thermal emission imaging system infrared themis ir and the thermal emission spectrometer tes our approach provides regional context for the development of scalloped terrains within the southern hemisphere and offers detailed evidence of scallop depressions forming around small cracks presumably caused by thermal contraction morphometric measurements show that scalloped depressions can be as much as 40 m deep with typical depths of between 10 and 20 m our observations of scallop formation and development in the southern hemisphere support a solar insolation model proposed by previous researchers e g morgenstern a hauber e reiss d van gasselt s grosse g schirrmeister l 2007 j geophys res 112 citeid e06010 lefort a russell p s thomas n mcewen a s dundas c m kirk r l 2009a j geophys res 114 e04005 lefort a russell p s thomas n 2009b icarus in press observations made using hirise images suggest that scalloped depressions most likely form from small cracks in the mantle which become larger and deeper through sublimation of interstitial ice from within the mantle sublimation is likely enhanced on equator facing slopes because of increased solar insolation which accounts for the asymmetric slope profile and hemispherical orientation and is demonstrated by themis ir images we suggest that sublimation lag deposits can possibly be removed by dust devils or strong slope winds related to the hellas basin offering an explanation as to why scalloped terrain is so abundant only in this area of the southern hemisphere daytime maximum summer temperatures suggest that sublimation in the study area of malea planum is possible under current conditions if the sublimation lag is removed while it cannot be ruled out that scalloped terrain in malea planum is presently evolving we attribute the extensive distribution to geologically recent obliquity excursions when conditions were more conducive to mesoscale modification of the ice rich mantle

latitude dependence of martian pedestal craters evidence for a sublimation driven formation mechanism we report on the results of a survey to document and characterize pedestal craters on mars equatorward of similar to 60 degrees n and 65 degrees s latitude the identification of 2696 pedestal craters reveals a strong latitude dependence with the vast majority found poleward of 33 degrees n and 40 degrees s this latitudinal extent is correlated with many climate indicators consistent with the presence of an ice rich substrate and with climate model predictions of where ice is deposited during periods of higher obliquity in the amazonian we have measured key physical attributes of pedestal craters including the farthest radial extents of the pedestals pedestal heights and the circularity of the pedestal margins in conjunction with the geographic distribution our measurements strongly support a sublimation related formation mechanism this is in contrast to previous hypotheses which have relied on eolian deflation to produce the elevated plateaus the identification of marginal pits on the scarps of some pedestal craters interpreted to be sublimation pits provide direct evidence for the presence of ice rich material underlying the armored surface of pedestal craters on the basis of our findings we propose a formation mechanism whereby projectiles impact into a volatile rich dust snow ice substrate tens to hundreds of meters thick overlying a dominantly fragmental silicate regolith the area surrounding the resulting crater becomes armored pedestals extend to a distance of multiple crater radii farther than typical ejecta deposits necessitating an armoring mechanism that is capable of indurating the surface to a distance greater than the reach of the ejecta return to low obliquity causes sublimation of the volatile rich layer from the intercrater plains lowering the elevation of the regional terrain this yields generally circular pedestal craters elevated above the surrounding plains as a result the armored surfaces of pedestal craters have preserved a significant record of amazonian climate history in the form of ice rich deposits

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

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

ground ice at the phoenix landing site stability state and origin 1 a primary objective of the phoenix mission was to examine the characteristics of high latitude ground ice on mars we report observations of ground ice its depth distribution and stability characteristics and examine its origins and history high latitude ground ice was explored through a dozen trench complexes and landing thruster pits over a range of polygon morphological provinces shallow ground ice was found to be abundant under a layer of relatively loose ice free soil with a mean depth of 4 6 cm which varied by more than 10x from trench to trench these variations can be attributed mainly to slope effects and thermal inertia variations in the overburden soil affecting ground temperatures the presence of ice at this depth is consistent with vapor diffusive equilibrium with respect to a mean atmospheric water content of 3 4 1019 m 3 consistent with the present day climate significant ice heterogeneity was observed with two major forms ice cemented soil and relatively pure light toned ice ice cemented soils which comprised about 90 of the icy material exposed by trenching are best explained as vapor deposited pore ice in a matrix supported porous soil light toned ice deposits represent a minority of the subsurface and are thought to consist of relatively thin near surface deposits the origin of these relatively pure ice deposits appears most consistent with the formation of excess ice by soil ice segregation such as would occur by thin film migration and the formation of ice lenses needle ice or similar ice structures

distribution of mid latitude ground ice on mars from new impact craters new impact craters at five sites in the martian mid latitudes excavated material from depths of decimeters that has a brightness and color indicative of water ice near infrared spectra of the largest example confirm this composition and repeated imaging showed fading over several months as expected for sublimating ice thermal models of one site show that millimeters of sublimation occurred during this fading period indicating clean ice rather than ice in soil pores our derived ice table depths are consistent with models using higher long term average atmospheric water vapor content than present values craters at most of these sites may have excavated completely through this clean ice probing the ice table to previously unsampled depths of meters and revealing substantial heterogeneity in the vertical distribution of the ice itself

sharad soundings and surface roughness at past present and proposed landing sites on mars reflections at phoenix may be attributable to deep ground ice we use the shallow radar sharad on the mars reconnaissance orbiter to search for subsurface interfaces and characterize surface roughness at the landing sites of viking landers 1 and 2 mars pathfinder the mars exploration rovers spirit and opportunity the phoenix mars lander the mars science laboratory curiosity rover and three other sites proposed for curiosity only at the phoenix site do we find clear evidence of subsurface radar returns mapping out an interface that may be the base of ground ice at depths of 15 66 m across 2900 km2 in the depression where the lander resides at the opportunity spirit and candidate curiosity sites images and altimetry show layered materials tens to hundreds of meters thick extending tens to hundreds of kilometers laterally these scales are well within sharad s resolution limits so the lack of detections is attributable either to low density contrasts in layers of similar composition and internal structure or to signal attenuation within the shallowest layers at each site we use the radar return power to estimate surface roughness at scales of 10 100 m a measure that is important for assessing physical properties landing safety and site trafficability the strongest returns are found at the opportunity site indicating that meridiani planum is exceptionally smooth returns of moderate strength at the spirit site reflect roughness more typical of mars gale crater curiosity s ultimate destination is the smoothest of the four proposed sites we examined with holden crater eberswalde crater and mawrth vallis exhibiting progressively greater roughness

deposition and degradation of a volatile rich layer in utopia planitia and implications for climate history on mars 1 we investigate the surface morphology of a study area in western utopia planitia mars which is characterized by a variety of landforms that resemble those of terrestrial periglacial landscapes polygonally fractured ground and thermokarst like depressions are found to be located in a young mantling deposit with a thickness of several tens of meters we observe a latitudinal dependence of the degradation of this mantling deposit larger depressions whose floors reveal the underlying basement rocks cover a higher fraction of the total terrain in the southern part of the study area than in the northern part indicating a more intense degradation of the mantle in the south all depressions have an asymmetric cross section in north south direction interpreted to be the result of the different solar radiation on differently oriented slopes on the basis of our morphological observations we develop a conceptual model for landscape evolution in western utopia planitia it involves subaerial deposition of a layered ice rich mantle and its subsequent degradation by polygon formation and sublimation a terrestrial analog to the polygonally fractured mantling deposit and its thermokarst like depressions is the siberian ice complex or yedoma which consists of subaerial ice rich deposits and is connected to nonglaciated landscapes with highly continental cold climatic environmental conditions our comparison suggests that no unusual or exotic processes need to be invoked to explain the current morphology of western utopia however the young age of the deposition and degradation implies climatic excursions in the very recent past on mars

the presence and stability of ground ice in the southern hemisphere of mars abstract we calculate new estimates of ground ice stability and the depth distribution of the ice table the depth boundary between ice free soil above and ice cemented soil below and compare these theoretical estimates of the distribution of ground ice with the observed distribution of leakage neutrons measured by the neutron spectrometer instrument of the mars odyssey spacecraft s gamma ray spectrometer instrument suite our calculated ground ice distribution contains improvements over previous work in that we include the effects of the high thermal conductivity of ice cemented soil at and below the ice table we include the surface elevation dependence of the near surface atmospheric humidity and we utilize new high resolution maps of thermal inertia albedo and elevation from mars global surveyor observations results indicate that ground ice should be about 5 times shallower than in previous predictions while results are dependent on the atmospheric humidity depths are generally between a few millimeters and a few meters with typical values of a few centimeters results are also geographically similar to previous predictions with differences due to the higher resolution of thermal inertia and the inclusion of elevation effects on humidity comparison with the measured epithermal neutron count rates in the southern hemisphere indicate that the geographic distribution of the count rate is best correlated with ground ice in equilibrium with 10 to 20 pr m precipitable micrometers column abundance of atmospheric water assuming a uniform distribution with co2 however given the uncertainties 5 to 30 pr m also may be viable this water abundance represents a longer term average over 100 to 1000 yr there is a high degree of correlation between the depth of the ice table and the epithermal count rate that agrees remarkably well with predicted count rates as a function of ice table depth these results indicate that ground ice in the upper meter of the martian soil is in diffusive equilibrium with the atmosphere since ground ice in this depth zone is expected to undergo saturation desiccation cycles with orbital variations this ice should be younger than about 500 kyr and was emplaced under similar cold and dry climate conditions of today remaining differences between the predicted depths of the ice table and those inferred from the neutron data are likely to be due to subpixel heterogeneity in the martian surface including the presence of rocks slopes and patches of soil with varying thermophysical properties