exploring the oxygen isotope fingerprint of dansgaard oeschger variability and heinrich events abstract we present the first transient simulations of marine isotope stage 3 mis 3 performed with an oxygen isotope enabled climate model our simulations span several dansgaard oeschger cycles and three heinrich stadials and are directly compared with oxygen isotope records from 13 sediment and 2 ice cores our results are consistent with a 30 50 weakening of the atlantic meridional overturning circulation during dansgaard oeschger stadials and a complete shutdown during heinrich stadials we find that the simulated 18 o anomalies differ significantly between heinrich stadials and non heinrich stadials this difference is mainly due to different responses in ocean circulation and therefore climate impacting oceanic 18 o while the volume of 18 o depleted meltwater plays a secondary role

effects of soil heterogeneity on martian ground ice stability and orbital estimates of ice table depth abstract data from the mars odyssey gamma ray spectrometer grs instrument suite and results from numerical simulations of subsurface ground ice stability have been used to estimate the depth of martian ground ice geographic correlation between these estimates is remarkable the relative ice table depth distributions also agree well however grs based estimates of ice table depth are generally deeper than predictions based on ground ice stability simulations this discrepancy may be related to heterogeneities in the martian surface such as rocks dust and albedo variations we develop a multi dimensional numerical model of ground ice stability in a heterogeneous martian subsurface and use it to place the first quantitative constraints on the response of the ice table to meter scale heterogeneities we find that heterogeneities produce significant undulations topography in the ice table at horizontal length scales of a few meters decimeter scale rocks create localized areas of deep ice producing a vertical depression of 10 60 cm in the ice table over a horizontal range of 1 2 rock radii decimeter scale dust lenses produce locally shallow ice however the magnitude of the vertical deflection of the ice table is small 1 4 cm the effects of decimeter scale albedo variations on the ice table are nearly negligible although albedo very weakly enhances the effects of dark rocks and bright dust on the ice table additionally we investigate the role played by rocks in estimates of ice table depth based on orbital data surface rocks can account for more than half of the discrepancy between ice table depths inferred from grs data and those predicted by theoretical ice stability simulations that utilize thermophysical observations our results have considerable relevance to the up coming mars scout mission phoenix because they indicate that the uncertainty in the ice table depth of a given region is greater than differences between current depth estimates likewise small scale depth variability due to heterogeneities at the eventual landing site is potentially greater than differences between current depth estimates

concentric crater fill in utopia planitia history and interaction between glacial brain terrain and periglacial mantle processes abstract at martian mid to high latitudes the surfaces of potentially ice rich features including concentric crater fill lobate debris aprons and lineated valley fill typically display a complex texture known as brain terrain due to its resemblance to the complex patterns on brain surfaces in order to determine the structure and developmental history of concentric crater fill and overlying latitude dependent mantle ldm material brain terrain and polygonally patterned ldm surfaces are analyzed using hirise images from four craters in utopia planitia containing concentric crater fill brain terrain and mantle surface textures are classified based on morphological characteristics 1 closed cell brain terrain 2 open cell brain terrain 3 high center mantle polygons and 4 low center mantle polygons a combined glacial and thermal contraction cracking model is proposed for the formation and modification of the brain terrain texture of concentric crater fill a similar model related to thermal contraction cracking and differential sublimation of underlying ice is proposed for the formation and development of polygonally patterned mantle material both models require atmospheric deposition of ice likely during periods of high obliquity but do not require wet active layer processes crater dating of brain terrain and mantled surfaces suggests a transition at martian mid latitudes from peak glacial conditions occurring within the past 10 100 my to a quiescent period followed by a cold desert periglacial period during the past 1 2 my

age and evolution of the lower nw flank of the hecates tholus volcano mars based on crater size frequency distribution on ctx images abstract we present results of crater size frequency distribution sfd analysis of the lower nw flank of the hecates tholus volcano elysium volcanic province of mars by the use of images acquired by the context ctx instrument on board of mars reconnaissance orbiter 6 m pixel in resolution previous similar works were focused on the caldera complex of the volcano and some sectors of the lower nw flank in this study we analyzed the complete crater population of the main geomorphological units characterizing this sector of the volcano de pablo m a centeno j d 2012 journal of maps 8 3 208 2014 discarding areas with possible clustering to avoid erroneous results in total 16 areas corresponding to 10 geomorphological units were measured and absolute model ages were derived for them the ages correspond to ages of origin as well as of the end of resurfacing events depending on the analyzed sector resulting in some cases in more than one age per area our results are in general in agreement with previous works and establish that the age of the origin of the hecates tholus volcano could be at least 3 8 ga with possible volcanic eruptions occurring until at least 335 ma glacial events were also dated at 90 ma 30 ma 16 ma and 6 ma although it is possible to recognize ages which could also be related to the recent ice ages of mars between 2 and 0 4 ma our results allowed us to determine that glacial processes could have been active as far back as 1 4 ga with possible events at intermediate ages we deduced from the resulting ages and our observations on ctx images and the available geomorphological map of the area that glacial related processes played an important role in sculpting this flank of the volcano and the possible level of the glacial sheet at the edge of the main depression of this flank was also deduced with altitudes ranging between 2035 m and 2490 m in agreement with the presence of smooth outcrops and roche moutonnees in the area finally a possible evolution of this region of the hecates tholus volcano is proposed and discussed establishing the sequence of the most important geological events which occurred in the area and their possible timings

hydrated states of mgso4 at equatorial latitudes on mars 1 the stability of water ice epsomite and hexahydrite to loss of h2o molecules to the atmosphere at equatorial latitudes of mars was studied to determine their potential contributions to the measured abundance of water equivalent hydrogen weh calculation of the relative humidity based on estimates of yearly averages of water vapor pressures and temperatures at the martian surface was used for this purpose water ice was found to be sufficiently unstable everywhere within 45 of the equator that if the observed weh is due to water ice it requires a low permeability cover layer near the surface to isolate the water ice below from the atmosphere above in contrast epsomite or hexahydrite may be stable in many near equatorial locations where significant amounts of weh are observed

compact reconnaissance imaging spectrometer for mars observations of northern martian latitudes in summer 1 this paper brings together initial results obtained of the high northern latitudes in mars years 28 and 29 between october 2006 and october 2008 these measurements confirm many previous models and shed new light on the nature of polar surface materials particularly in intermediate albedo units of the polar layered deposits many of which are found to be ice rich we identify hydrated non ice materials present in many low albedo troughs as well as in the circumpolar erg that was previously associated with gypsum we identify icy outlier deposits that may be related to subsurface thermophysical properties and permafrost new observations of the gypsum rich dune material constrain models for its formation and distribution intrinsic properties of ice content and grain size are found to be independent of the albedo of fine layered units and may provide a novel method for stratigraphic identification and correlation

viking landing sites remote sensing observations and physical properties of martian surface materials abstract important problems that confront future scientific exploration of mars include the physical properties of martian surface materials and the geologic processes that formed the materials the design of landing spacecraft roving vehicles and sampling devices and the selection of landing sites vehicle traverses and sample sites will be in part guided by the physical properties of the materials four materials occur in the sample fields of the viking landers 1 drift 2 crusty to cloddy 3 blocky and 4 rock the first three are soillike drift materials is weak loose and porous we estimate that it has a dielectric constant near 2 4 and a thermal inertia near 1 10 3 to 3 10 3 cal cm 2 sec 1 2 k 1 because of its low bulk density fine grain size and small cohesion crusty to cloddy material is expected to have a dielectric constant near 2 8 and a thermal inertia near 4 10 3 to 7 10 3 because of its moderate bulk density and cementation of grains blocky material should have a dielectric constant near 3 3 and a thermal inertia near 7 10 3 to 9 10 3 because of its moderate bulk density and cementation common basaltic rocks have dielectric constans near 8 and thermal inertias near 30 10 3 to 60 10 3 comparisons of estimated dielectric constants and thermal inertias of the materials at the landing sites with those obtained remotely by earth based radars and viking orbiter thermal sensors suggest that the materials at the landing sites are good analogs for materials elsewhere on mars correlation of remotely estimated dielectric constant and thermal inertias indicates two modal values for paired values of dielectric constants and thermal inertias near a 2 and 2 10 3 and b 3 and 6 10 3 respectively these two modes are comparable to the dielectric constants and thermal inertias for drift and crusty to cloddy material respectively dielectric constants and thermal inertias for blocky material are larger but conistent with values in the northern plains our interprertations are compatible with an aeolian origin for drift and similar materials elsewhere on mars the postulate that moderate dielectric constants and thermal inertias larger than 3 or 4 10 3 are produced by cementation of soillike materials is partly consistent with the data the average dielectric constant and thermal inertia and their correlation with one another suggest that most of the surface of mars should present few difficulties to future surface exploration but some surfaces may present difficulties for spacecraft that are not suitably designed

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

size frequency distributions of rocks on the northern plains of mars with special reference to phoenix landing surfaces 1 the size frequency distributions of rocks 1 5 m diameter fully resolvable in high resolution imaging science experiment hirise images of the northern plains follow exponential models developed from lander measurements of smaller rocks and are continuous with rock distributions measured at the landing sites dark pixels at the resolution limit of mars orbiter camera thought to be boulders are shown to be mostly dark shadows of clustered smaller rocks in hirise images an automated rock detector algorithm that fits ellipses to shadows and cylinders to the rocks accurately measured within 1 2 pixels rock diameter and height by comparison to spacecraft of known size of 10 million rocks over 1500 km2 of the northern plains rock distributions in these counts parallel models for cumulative fractional area covered by 30 90 rocks in dense rock fields around craters 10 30 rock coverage in less dense rock fields and 0 10 rock coverage in background terrain away from craters above 1 5 m diameter hirise resolves the same population of rocks seen in lander images and thus size frequency distributions can be extrapolated along model curves to estimate the number of rocks at smaller diameters extrapolating sparse rock distributions in the phoenix landing ellipse indicate 1 chance of encountering a potentially hazardous rock during landing or that could impede the opening of the solar arrays extrapolations further suggest rocks large enough to depress the ground ice table and small enough to be picked up or pushed by the robotic arm should be present within reach for study after landing

driven by excess climatic implications of new global mapping of near surface water equivalent hydrogen on mars abstract we present improved mars odyssey neutron spectrometer mons maps of near surface water equivalent hydrogen weh on mars that have intriguing implications for the global distribution of excess ice which occurs when the mass fraction of water ice exceeds the threshold amount needed to saturate the pore volume in normal soils we have refined the crossover technique of feldman et al 2011 by using spatial deconvolution and gaussian weighting to create the first globally self consistent map of weh at low latitudes our new maps indicate that weh exceeds 15 in several near equatorial regions such as arabia terra which has important implications for the types of hydrated minerals present at low latitudes at high latitudes we demonstrate that the disparate mons and phoenix robotic arm ra observations of near surface weh can be reconciled by a three layer model incorporating dry soil over fully saturated pore ice over pure excess ice such a three layer model can also potentially explain the strong anticorrelation of subsurface ice content and ice table depth observed at high latitudes at moderate latitudes we show that the distribution of recently formed impact craters is also consistent with our latest mons results as both the shallowest ice exposing crater and deepest non ice exposing crater at each impact site are in good agreement with our predictions of near surface weh overall we find that our new mapping is consistent with the widespread presence at mid to high martian latitudes of recently deposited shallow excess ice reservoirs that are not yet in equilibrium with the atmosphere

maps of subsurface hydrogen from the high energy neutron detector mars odyssey after 55 days of mapping by the high energy neutron detector onboard mars odyssey we found deficits of high energy neutrons in the southern highlands and northern lowlands of mars these deficits indicate that hydrogen is concentrated in the subsurface modeling suggests that water ice rich layers that are tens of centimeters in thickness provide one possible fit to the data

mars exploration program 2007 phoenix landing site selection and characteristics 1 to ensure a successful touchdown and subsequent surface operations the mars exploration program 2007 phoenix lander must land within 65 to 72 north latitude at an elevation less than 3 5 km the landing site must have relatively low wind velocities and rock and slope distributions similar to or more benign than those found at the viking lander 2 site also the site must have a soil cover of at least several centimeters over ice or icy soil to meet science objectives of evaluating the environmental and habitability implications of past and current near polar environments the most challenging aspects of site selection were the extensive rock fields associated with crater rims and ejecta deposits and the centers of polygons associated with patterned ground an extensive acquisition campaign of odyssey thermal emission imaging spectrometer predawn thermal ir images together with 0 31 m pixel mars reconnaissance orbiter high resolution imaging science experiment images was implemented to find regions with acceptable rock populations and to support monte carlo landing simulations the chosen site is located at 68 16 north latitude 233 35 east longitude areocentric within a 50 km wide n s by 300 km long e w valley of relatively rock free plains surfaces within the eastern portion of the valley are differentially eroded ejecta deposits from the relatively recent 10 km wide heimdall crater and have fewer rocks than plains on the western portion of the valley all surfaces exhibit polygonal ground which is associated with fracture of icy soils and are predicted to have only several centimeters of poorly sorted basaltic sand and dust over icy soil deposits

global distribution of neutrons from mars results from mars odyssey global distributions of thermal epithermal and fast neutron fluxes have been mapped during late southern summer northern winter using the mars odyssey neutron spectrometer these fluxes are selectively sensitive to the vertical and lateral spatial distributions of h and co 2 in the uppermost meter of the martian surface poleward of 60 latitude is terrain rich in hydrogen probably h 2 o ice buried beneath tens of centimeter thick hydrogen poor soil the central portion of the north polar cap is covered by a thick co 2 layer as is the residual south polar cap portions of the low to middle latitudes indicate subsurface deposits of chemically and or physically bound h 2 o and or oh

seasonal defrosting of the phoenix landing site 1 the retreat of the seasonal polar cap at the phoenix landing site is analyzed through observations of high resolution images and thermal modeling of the co2 frost mass numerical simulations indicate that the onset of co2 frost formation occurs around ls 220 at 68 n however the polar hood prevented imaging of the surface during this time in the late winter early spring a continuous layer of frost coated the surface obscuring the underlying polygonal patterns however rocks are clearly evident indicating that the frost depth was relatively shallow rare dark fans originating from rocks are also observed in an image from early spring frost dissipated from the polygon centers first and lingered longer in polygon troughs polygon centers were first exposed on ls 13 9 and the polygon troughs were frost free by ls 57 frost distributions varied slightly between geologic units however in general global observations at similar latitudes are consistent with what is seen in the phoenix region a series of hypotheses is also explored to explain the preference for the co2 frost to linger in the troughs lower thermal inertia material in the troughs aeolian redistribution of frost burial of the ice table via aeolian redistribution of dust and shadowing each of these hypotheses has drawbacks to explaining this phenomenon as stand alone components shadows do play a role in keeping the co2 frost on the surface however this effect is small and cannot alone account for the observations

the stability of ground ice in the equatorial region of mars consideration of the partial pressure of h2o in the martian atmosphere and the range of mean annual temperatures at the martian surface suggests that the occurrence of ground ice in equilibrium with the atmosphere is restricted to latitudes poleward of 40 however there is a growing body of morphologic evidence that indicates that substantial quantities of ground ice may have been present in the equatorial regolith throughout martian geologic time the accepted explanation for this apparent contradiction has been that the h2o found near the equator is a relic emplaced very early in martian geologic history 3 5 b y ago and under substantially different climatic conditions it is generally believed that this fossil ground ice layer has been preserved to the present day by the diffusion limiting properties of a relatively shallow layer 10 m of fine grained regolith to evaluate this hypothesis the lifetime of a 200 m layer of ground ice buried below 100 m of ice free regolith has been examined for the latitudes between 30 on mars twelve model pore size distributions representative of silt and clay type soils found on earth were selected to simulate the pore structure of the martian regolith the parallel pore model of gaseous diffusion was then used to calculate the flux of escaping h2o molecules from the buried ground ice layer the potential effects of such factors as depth of burial the martian geothermal gradient regolith porosity adsorption surface diffusion and climatic change were also considered based on our analysis the most important factors affecting the stability of equatorial ground ice appear to be 1 soil structure 2 the magnitude of the geothermal gradient and 3 the climatic desorption of co2 from the regolith we conclude that while the conditions necessary for the long term survival of ground ice may exist in isolated regions within the equatorial regolith on the global scale it appears unlikely that a fossil ground ice layer has been preserved throughout martian geologic history if massive ground ice does presently exist in the equatorial regolith then its presence may imply the existence of some continuous or periodic process of replenishment

seasonal h2o and co2 ice cycles at the mars phoenix landing site 1 prelanding crism and hirise observations 1 the condensation evolution and sublimation of seasonal water and carbon dioxide ices were characterized at the mars phoenix landing site from martian northern midsummer to midspring ls 142 ls 60 for the year prior to the phoenix landing on 25 may 2008 ice relative abundances and grain sizes were estimated using data from the compact reconnaissance imaging spectrometer for mars and high resolution imaging science experiment aboard mars reconnaissance orbiter and a nonlinear mixing model water ice first appeared at the phoenix landing site during the afternoon in late summer ls 167 as an optically thin layer on top of soil co2 ice appeared after the fall equinox by late winter ls 344 the site was covered by relatively pure co2 ice 30 cm thick with a small amount of 100 m diameter water ice and soil as spring progressed co2 ice grain sizes gradually decreased a change interpreted to result from granulation during sublimation losses the combined effect of co2 sublimation and decreasing h2o ice grain sizes allowed h2o ice to dominate spectra during the spring and significantly brightened the surface co2 ice disappeared by early spring ls 34 and h2o ice by midspring ls 59 spring defrosting was not uniform and occurred more rapidly over the centers of polygons and geomorphic units with relatively higher thermal inertia values

periglacial landforms at the phoenix landing site and the northern plains of mars 1 we examine potentially periglacial landforms in mars orbiter camera moc and high resolution imaging science experiment hirise images at the phoenix landing site and compare them with numerical models of permafrost processes to better understand the origin nature and history of the permafrost and the surface of the northern plains of mars small scale 3 6 m polygonal patterned ground is ubiquitous throughout the phoenix landing site and northern plains larger scale 20 25 m polygonal patterns and regularly spaced 20 35 m rubble piles localized collections of rocks and boulders are also common rubble piles were previously identified as basketball terrain in moc images the small polygon networks exhibit well developed and relatively undegraded morphology and they overlay all other landforms comparison of the small polygons with a numerical model shows that their size is consistent with a thermal contraction origin on current day mars and are likely active in addition the observed polygon size is consistent with a subsurface rheology of ice cemented soil on depth scales of about 10 m the size and morphology of the larger polygonal patterns and rubble piles indicate a past episode of polygon formation and rock sorting in thermal contraction polygons while the ice table was about twice as deep as it is presently the pervasive nature of small and large polygons and the extensive sorting of surface rocks indicates that widespread overturning of the surface layer to depths of many meters has occurred in the recent geologic past this periglacial reworking has had a significant influence on the landscape at the phoenix landing site and over the martian northern plains

thermophysical properties of alaskan loess an analog material for the martian polar layered terrain the martian surface has several regions where thermal inertia measurements indicate a porous ice free insulating surface yet are mechanically competent enough to sustain substantial slopes in support of the interpretation of those regions within the martian polar layered terrain we report measurements of thermal conductivity for loess from the field and in the usa crrel permafrost tunnel permafrost tunnel loess is a desiccated material that can form vertical walls but is of low density 800 1000 kg m modest shear strength 4 kpa and has a low thermal conductivity 0 1 w m k at 1 bar these properties are similar to the inferred properties of the martian polar layered terrain the birch hill field sample has a density of 1160 kg m and a conductivity of 0 15 w m k the chena spur road sample has a density of 1360 kg m and a conductivity of 0 7 w m k the relatively high conductivity for the chena spur road is due to the cementation of soil grain contacts its higher density coarser grain size and higher quartz grain content

modeling vapor diffusion within cold and dry supraglacial tills of antarctica implications for the preservation of ancient ice abstract we modeled water vapor diffusion within mullins till a relatively dry supraglacial till in southern victoria land antarctica that rests directly on mullins glacier purportedly one of the oldest alpine glaciers in the world like most supraglacial tills in cold desert environments mullins till contains three characteristic facies a weathered facies representing the oxidation of iron bearing minerals and the physical disintegration of surface rocks a sand wedge facies representing the episodic infill of thermal cracks associated with contraction crack polygons and an underlying fresh facies representing the addition of englacial debris sourced from rockfall as overlying ice sublimes using a one dimensional model for fickian vapor diffusion through porous media we show that the rate of subsurface ice sublimation varies by 5 5 beneath till facies and that over timescales of 10 5 years diffusion through porous sand wedges contributes to the development of deep troughs surrounding high centered polygons applying site specific meteorological data collected over a four year period we show that ice loss at the stagnant terminus of mullins glacier is 6 6 10 5 m a 1 a value that although low and assuming an ice thickness of 150 m is consistent with complete ice loss under current environmental forcing in 2 5 ma our sensitivity tests indicate that the vast majority of sublimation occurs during the summer months calculated summertime losses drop to zero with either a reduction in soil and ice surface temperatures of 6 4 c or an increase in atmospheric relative humidity from 44 to 75 both of which could arise from an increase in cloud cover over mullins glacier sublimation responses to meteorological forcing are not uniform across mullins glacier a summer increase in soil temperature of 2 c results in negligible change in ice sublimation at mullins terminus but a 27 increase in ice loss in upper mullins valley the key factor is the thickness of mullins till which is greater near the glacier terminus for till thicknesses exceeding 25 cm non linear variations in soil temperature result in downward vapor fluxes capable of producing thin cm scale lenses of secondary pore that cap the surface of buried glacier ice this downward vapor flow sourced from modern snowfall and or elevated atmospheric relative humidity is one of the key factors that enable long term preservation of buried glacier ice overall our results highlight the subtle relations among changes in till texture till thickness and meteorological forcing on the rate of subsurface ice loss and provide insight into the plausible range of conditions under which multi million year old ice can exist beneath thin supraglacial tills

high resolution subsurface water ice distributions on mars theoretical models predict that the depth at which water ice is stable in the subsurface of mars will vary due to local surface features such as rocks and slopes and the thermal inertia of the ground above the water so far measurements have been limited to overviews of the several hundred kilometre footprint covered by the ray spectrometer on board the mars odyssey spacecraft but joshua bandfield has now used the seasonal temperature response of the martian surface from odyssey s themis package to map water ice distribution at the sub kilometre scale the observations reveal significant regional and local water ice depth variability at potential landing sites for the mars phoenix mission due for launch later this year the phoenix lander s robotic arm will be able to dig up to half a metre or so into the soil to search for water ice and these results suggest that it may encounter considerable variation in the depth to the ice layer the seasonal temperature response of the martian surface is used to map local surface heterogeneities such as rocks slopes and thermal inertia of ground cover at subkilometre scale these observations show significant regional and local water ice depth variability and indicate that the depth to the water ice table is highly variable in the potential phoenix spacecraft landing ellipses theoretical models indicate that water ice is stable in the shallow subsurface depths of 1 2 m of mars at high latitudes1 2 3 4 5 6 7 these models have been mainly supported by the observed presence of large concentrations of hydrogen detected by the gamma ray spectrometer suite of instruments on the mars odyssey spacecraft8 9 10 the models and measurements are consistent with a water ice table that steadily increases in depth with decreasing latitude more detailed modelling has predicted that the depth at which water ice is stable can be highly variable owing to local surface heterogeneities such as rocks and slopes and the thermal inertia of the ground cover11 12 13 measurements have however been limited to the footprint several hundred kilometres of the gamma ray spectrometer suite preventing the observations from documenting more detailed water ice distributions here i show that by observing the seasonal temperature response of the martian surface with the thermal emission imaging system on the mars odyssey spacecraft14 it is possible to observe such heterogeneities at subkilometre scale these observations show significant regional and local water ice depth variability and in some cases support distributions in the subsurface predicted by atmospheric exchange and vapour diffusion models the presence of water ice where it follows the depth of stability under current climatic conditions implies an active martian water cycle that responds to orbit driven climate cycles15 16 17 several regions also have apparent deviations from the theoretical stability level indicating that additional factors influence the ice table depth the high resolution measurements show that the depth to the water ice table is highly variable within the potential phoenix spacecraft landing ellipses and is likely to be variable at scales that may be sampled by the spacecraft

in situ analysis of ice table depth variations in the vicinity of small rocks at the phoenix landing site 1 prior to the phoenix mission ice stability simulations predicted that surface rocks at the landing site would produce depressions in the ice table the boundary between dry and ice cemented soil if ground ice at the site were in diffusive equilibrium with atmospheric water vapor we use stereo images and digital elevation models to investigate variations in the depth of the ice table near two decimeter scale rocks at the phoenix landing site and compare the observed depth variations to ice stability simulations we find that ice table depth variations observed near rocks at the landing site are consistent with our theoretical predictions based on our results we conclude that 1 water transport in the near surface regolith occurs primarily via vapor diffusion 2 environmental conditions in which water transport is dominated by diffusion have been persistent at the landing site for 100s to 1000s of years or longer that is ground ice is in diffusive equilibrium with atmospheric water vapor and 3 in diffusive equilibrium thermal stability dictates the depth of the ice table on horizontal length scales as small as centimeters

ice table depth variability near small rocks at the phoenix landing site mars a pre landing assessment abstract we combine thermal simulations of ground ice stability near small rocks with extrapolations of the abundance of rocks at the phoenix landing site based on hirise rock counts to estimate the degree of ice table depth variability within the 3 8 m 2 workspace that can be excavated during the mission detailed predictions of this kind are important both to test current ground ice theory and to optimize soil investigations after landing we find that phoenix will very likely have access to at least one rock in the diameter range 5 cm to 1 m our simulations which assume the ice to be in diffusive equilibrium with atmospheric water vapor indicate that all rocks in this size range are associated with an annulus of deep ice free soil ice table depth variability of 1 5 cm is very likely at the landing site due to the presence of small rocks further there are scenarios in which phoenix might exploit the presence of individual large rocks and or the arrangement of small rocks to sample soils at depths 10 cm below the average depth predicted from orbit 4 cm scale analysis to constrain uncertainties in simulation results indicates that estimates of maximum depths may be somewhat conservative and that ice table depressions associated with individual rocks could be deeper and laterally more extended than indicated by formal predictions by mm to cm

results from the mars phoenix lander robotic arm experiment 1 the mars phoenix lander was equipped with a 2 4 m robotic arm ra with an icy soil acquisition device capable of excavating trenches in soil deposits grooming hard icy soil surfaces with a scraper blade and acquiring icy soil samples using a rasp tool a camera capable of imaging the scoop interior and a thermal and electrical conductivity probe were also included on the ra a dozen trench complexes were excavated at the northern plains landing site and 31 samples including water ice bearing soils were acquired for delivery to instruments on the lander during the 152 sol mission deliveries included sprinkling material from several centimeters height to break up cloddy soils on impact with instrument portals excavations were done on the side of the humpty dumpty and the top of the wonderland polygons and in nearby troughs resistive forces encountered during backhoe operations show that soils above the 3 5 cm deep icy soil interfaces are stronger with increasing depth further soils are similar in appearance and properties to the weakly cohesive crusty and cloddy soils imaged and excavated by the viking lander 2 which also landed on the northern plains adsorbed h2o is inferred to be responsible for the variable nature and cohesive strength of the soils backhoe blade chatter marks on excavated icy soil surfaces combined with rasp motor currents are consistent with laboratory experiments using grain supported icy soil deposits as is the relatively rapid decrease in icy soil strength over time as the ice sublimated on mars

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

high resolution thermal inertia mapping from the mars global surveyor thermal emission spectrometer abstract high resolution thermal inertia mapping results are presented derived from mars global surveyor mgs thermal emission spectrometer tes observations of the surface temperature of mars obtained during the early portion of the mgs mapping mission thermal inertia is the key property controlling the diurnal surface temperature variations and is dependent on the physical character of the top few centimeters of the surface it represents a complex combination of particle size rock abundance exposures of bedrock and degree of induration in this work we describe the derivation of thermal inertia from tes data present global scale analysis and place these results into context with earlier work a global map of nighttime thermal bolometer based thermal inertia is presented at 1 4 per pixel resolution with approximately 63 coverage between 50 s and 70 n latitude global analysis shows a similar pattern of high and low thermal inertia as seen in previous viking low resolution mapping significantly more detail is present in the high resolution tes thermal inertia this detail represents horizontal small scale variability in the nature of the surface correlation with albedo indicates the presence of a previously undiscovered surface unit of moderate to high thermal inertia and intermediate albedo this new unit has a modal peak thermal inertia of 180 250 j m 2 k 1 s 1 2 and a narrow range of albedo near 0 24 the unit covering a significant fraction of the surface typically surrounds the low thermal inertia regions and may comprise a deposit of indurated fine material local 3 km resolution maps are also presented as examples of eolian fluvial and volcanic geology some impact crater rims and intracrater dunes show higher thermal inertias than the surrounding terrain thermal inertia of aeolian deposits such as intracrater dunes may be related to average particle size outflow channels and valleys consistently show higher thermal inertias than the surrounding terrain generally correlations between spatial variations in thermal inertia and geologic features suggest a relationship between the hundred meter scale morphology and the centimeter scale surface layer

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

cold and dry processes in the martian arctic geomorphic observations at the phoenix landing site and comparisons with terrestrial cold desert landforms 1 we analyze surface stereo imager observations of rocks sediments and permafrost related landforms in the vicinity of the phoenix lander comparing the imaged features to analogous examples of physical weathering and periglacial processes observed in the antarctic dry valleys observations at the phoenix landing site of pitted rocks puzzle rocks undergoing in situ breakdown perched clasts and thermal contraction crack polygon morphologies strikingly similar to terrestrial sublimation polygons all strongly suggest that stable non churning permafrost processes dominate the phoenix landing site morphological evidence suggests that cold desert processes in the absence of wet active layer cryoturbation and largely driven by sublimation of buried ice either pore ice excess ice or both are shaping the landscape

geomorphologic and mineralogic characterization of the northern plains of mars at the phoenix mission candidate landing sites 1 a suite of remote sensing data is used to evaluate both geomorphology and mineralogy of the candidate landing sites for the 2007 phoenix mission three candidate landing site boxes are situated in the northern plains of mars on the distal flank of alba patera in the region from 67 n to 72 n and from 230 e to 260 e geomorphology is mapped at subkilometer spatial scales using thermal emission imaging system themis visible and mars orbiter laser altimeter mola topographic data supplemented by images from the high resolution imaging science experiment hirise and context imager ctx mineralogy and spectral properties are examined using compact reconnaissance imaging spectrometer for mars crism visible and near infrared multispectral mapping and targeted hyperspectral data at 200 and 20 m pixel respectively geomorphic mapping supports the idea that terrains along the boundary between the amazonian scandia region and vastitas borealis marginal geologic units have undergone extensive modification intercrater plains are disrupted to form mesas and interlocking blocks while irregular depressions and knobby terrain are consistent with erosion subsidence and local deposition despite the varied morphology the present day surface is nearly homogeneous with spectral signatures dominated by nanophase iron oxides and basaltic sand and rocks similar to that of the gusev crater plains at the mars exploration rover mer landing site the compilation of geomorphic and spectral information for the candidate phoenix landing sites provides a framework for the mission s in situ observations to be extrapolated to the northern plains as a whole

regional dust deposits on mars physical properties age and history major dust storms on mars play an important role in the deposition and removal of fine dust material thermal radar and visual remote sensing observations provide important constraints on the martian regolith which have been used to determine the location and physical properties of regional dust deposits these deposits are located in three northern equatorial regions tharsis 20 s to 50 n 60 to 190 w arabia 5 s to 30 n 300 to 360 w and elysium 10 to 30 n 210 to 225 w they are covered by fine 2 40 m bright albedo 0 27 particles with fewer exposed rocks and coarse deposits than found elsewhere dust is currently deposited uniformly throughout the equatorial region at a rate of 40 m global storm over geologic time the rate of accumulation may vary from 0 to 250 m yr due to changes in atmospheric conditions produced by orbital variations dust deposited during global storms is subsequently removed only from dark regions resulting in a net accumulation in the low inertia bright regions the thickness of these current dust deposits is 0 1 2 m the thermal inertia places a lower limit of 0 1 m on the thickness of these deposits while the sparse but ubiquitous presence of exposed rocks and the degree of visible mantling indicate that the thickness is less than 5 m dual polarization radar observations of a very rough texture in tharsis are consistent with this model with a 2 m thick dust layer burying most of the surface rocks but permitting radar sampling of the rough subsurface based on their thickness and rate of accumulation the age of these deposits is 105 106 years suggesting a cyclic process of deposition and removal one possible cause may be cyclic variations in the magnitude and location of maximum wind velocities related to variations in mars orbit at present perihelion and maximum wind velocities occur in the south whereas regional dust deposits occur in the north suggesting net transport from south to north orbital parameters oscillate with periods ranging from 5 104 to 106 years the agreement between these periods and the dust deposit age suggests a possible link at different stages in orbit evolution maximum wind velocities will occur in the north with subsequent erosion and redistribution of the accumulated fines based on this model much of the uppermost martian surface is very young and is being continually reworked

on the orbital forcing of martian water and co2 cycles a general circulation model study with simplified volatile schemes 1 variations in the martian water and co2 cycles with changes in orbital and rotational parameters are examined using the geophysical fluid dynamics laboratory mars general circulation model the model allows for arbitrary specification of obliquity eccentricity and argument of perihelion as well as the position and thickness of surface ice exchange of co2 between the surface and atmosphere is modeled generating seasonal cycles of surface ice and surface pressure water is allowed to exchange between the surface and atmosphere cloud formation is treated and both cloud and vapor are transported by modeled winds and diffusion exchange of water and co2 with the subsurface is not allowed and radiative effects of water vapor and clouds are not treated the seasonal cycle of co2 is found to become more extreme at high obliquity as suggested by simple heat balance models maximum pressures remain largely the same but the minima decrease substantially as more co2 condenses in the more extensive polar night vapor and cloud abundances increase dramatically with obliquity the stable location for surface ice moves equatorward with increasing obliquity such that by 45 obliquity water ice is stable in the tropics only ice is not spatially uniform but rather found preferentially in regions of high thermal inertia or high topography eccentricity and argument of perihelion can provide a second order modification to the distribution of surface ice by altering the temporal distribution of insolation at the poles further model simulations reveal the robustness of these distributions for a variety of initial conditions our findings shed light on the nature of near surface ice rich deposits at midlatitudes and low latitudes on mars

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

a recent ice age on mars evidence for climate oscillations from regional layering in mid latitude mantling deposits 1 two end member hypotheses have been proposed to account for the emplacement and distribution of ice in the near subsurface of mars at mid to high latitudes during recent spin axis orbital variation induced climate change in the first diffusion of atmospheric water vapor into and out of a porous regolith forms ice cemented soils whose latitudinal stability migrates as a function of orbitally controlled climatic conditions in the alternative hypothesis atmospheric deposition of ice snow and dust produces dusty ice rich layers during periods of higher obliquity new image data reveal meters thick layered deposits exposed on mid latitude pole facing slopes supporting the latter hypothesis these observations suggest that the near surface ice detected by the grs instrument suite and the phoenix lander at high latitudes is linked to thick buried ice that was atmospherically deposited during recent ice ages and that significant amounts of subsurface ice may remain today in the 30 50 mid latitude regions where fresh craters imaged by hirise expose abundant ice

the thermal stability of near surface ground ice on mars the existence of subsurface water ice on mars has been predicted in several theoretical studies1 5 but there are no definitive observations of its present distribution geomorphic features on the surface of mars have been widely interpreted as evidence for the presence of ground ice6 12 but many of these features are found at near equatorial latitudes where thermal models have predicted that near surface water ice should not be stable under present climate conditions3 13 14 here i present the results of thermal calculations which show that observed geographic variations in the thermal and reflectance properties of martian soils significantly affect subsurface temperatures my results indicate that in certain regions ground ice deposits could exist much closer to the surface and much closer to the equator than previously thought in the future these deposits could be a valuable resource for human exploration15

global distribution and migration of subsurface ice on mars a thermal diffusive model of h2o kinetics and equilibrium was developed to investigate the long term evolution and depth distribution of subsurface ice on mars the model quantitatively takes into account 1 obliquity variations 2 eccentricity variations 3 long term changes in the solar luminosity 4 variations in the argument of subsolar meridian in planetocentric equatorial coordinates 5 albedo changes at higher latitudes due to seasonal phase changes of co2 and the varying extent of co2 ice cover 6 planetary internal heat flow 7 temperature variations in the regolith as a function of depth time and latitude due to the above factors 8 atmospheric pressure variations over a 104 year time scale 9 the effects of factors 1 through 5 on seasonal polar cap temperatures and 10 knudsen and molecular diffusion of h2o through the regolith the migration of h2o into or out of the regolith is determined by two boundary conditions the h2o vapor pressure at the subsurface ice boundary and the annual average h2o concentration at the base of the atmosphere these are controlled respectively by the annual average regolith temperature at the given depth and seasonal temperatures at the polar cap starting from an arbitrary initial uniform depth distribution of subsurface ice h2o fluxes into or out of the regolith are calculated for 100 selected obliquity cycles each representing a different epoch in mars history the h2o fluxes are translated into ice thicknesses and extrapolated over time to give the subsurface ice depth as a function of latitude and time the results show that obliquity variations influence annual average regolith temperatures in varying degrees depending on latitude with the greatest effect at the poles and almost no effect at 40 lat insolation changes at the pole due to obliquity argument of subsolar meridian and eccentricity variations can produce enormous atmospheric h2o concentration variations of 6 orders of magnitude over an obliquity cycle superimposed on these cyclic variations is a slow monotonic change due to the increasing solar luminosity albedo changes at the polar cap due to seasonal phase changes of co2 and the varying thickness of the co2 ice cover are critically important in determining annual average atmospheric h2o concentrations despite the strongly oscillating character of the boundary conditions only small amounts of h2o are exchanged between the regolith and the atmosphere per obliquity cycle 10 g cm2 the net result of h2o migration is that the regolith below 30 40 lat is depleted of subsurface ice while the regolith above 30 40 lat contains permanent ice due to the depth of penetration of the annual thermal wave this result is supported by recent morphological studies the rate of migration of h2o is strongly dependent on average pore capillary radius for which we have assumed values of 1 and 10 m we estimate that the h2o ice removed from the regolith would produce a permanent ice cap with a volume between 2 106 and 6 106 km3 this generally agrees with estimates deduced from deflationary features at lower latitudes depositional features at higher latitudes and the mass of the polar caps

concentrated perchlorate at the mars phoenix landing site evidence for thin film liquid water on mars 1 nasa s phoenix mission which landed on the northern plains of mars in 2008 returned evidence of the perchlorate anion distributed evenly throughout the soil column at the landing site here we use spectral data from phoenix s surface stereo imager to map the distribution of perchlorate salts at the phoenix landing site and find that perchlorate salt has been locally concentrated into subsurface patches similar to salt patches that result from aqueous dissolution and redistribution on earth we propose that thin films of liquid water are responsible for translocating perchlorate from the surface to the subsurface and for concentrating it in patches the thin films are interpreted to result from melting of minor ice covers related to seasonal and long term obliquity cycles

apparent thermal inertia and the surface heterogeneity of mars abstract thermal inertia derivation techniques generally assume that surface properties are uniform at horizontal scales below the footprint of the observing instrument and to depths of several decimeters consequently surfaces with horizontal or vertical heterogeneity may yield apparent thermal inertia which varies with time of day and season to investigate these temporal variations we processed three mars years of mars global surveyor thermal emission spectrometer observations and produced global nightside and dayside seasonal maps of apparent thermal inertia these maps show broad regions with diurnal and seasonal differences up to 200 j m 2 k 1 s 1 2 at mid latitudes 60 s to 60 n and 600 j m 2 k 1 s 1 2 or greater in the polar regions we compared the seasonal mapping results with modeled apparent thermal inertia and created new maps of surface heterogeneity at 5 resolution delineating regions that have thermal characteristics consistent with horizontal mixtures or layers of two materials the thermal behavior of most regions on mars appears to be dominated by layering with upper layers of higher thermal inertia e g duricrusts or desert pavements over fines prevailing in mid latitudes and upper layers of lower thermal inertia e g dust covered rock soils with an ice table at shallow depths prevailing in polar regions less common are regions dominated by horizontal mixtures such as those containing differing proportions of rocks sand dust and duricrust or surfaces with divergent local slopes other regions show thermal behavior that is more complex and not well represented by two component surface models these results have important implications for mars surface geology climate modeling landing site selection and other endeavors that employ thermal inertia as a tool for characterizing surface properties

creep of water ices at planetary conditions a compilation many constitutive laws for the flow of ice have been published since the advent of the voyager explorations of the outer solar system conflicting data have occasionally come from different laboratories and refinement of experimental techniques has led to the publication of laws that supersede earlier ones in addition there are unpublished data from ongoing research that also amend the constitutive laws here we compile the most current laboratory derived flow laws for water ice phases i ii iii v and vi and ice i mixtures with hard particulates the rheology of interest is mainly that of steady state and the conditions reviewed are the pressures and temperatures applicable to the surfaces and interiors of icy moons of the outer solar system advances in grain size dependent creep in ices i and ii as well as in phase transformations and metastability under differential stress are also included in this compilation at laboratory strain rates the several ice polymorphs are rheologically distinct in terms of their stress temperature and pressure dependencies but with the exception of ice iii have fairly similar strengths hard particulates strengthen ice i significantly only at high particulate volume fractions ice iii has the potential for significantly affecting mantle dynamics because it is much weaker than the other polymorphs and its region of stability which may extend metastably well into what is nominally the ice ii field is located near likely geotherms of large icy moons

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

subsurface ice on mars with rough topography high latitude ground ice on mars discovered by the gamma ray spectrometer suite is thought to be thermally stable owing to the presence of vapor in the martian atmosphere however local slopes can alter surface and subsurface temperatures substantially and hence allow ground ice to persist at locations where it would otherwise be unstable global statistics of the topography of mars are computed processed and extrapolated to derive a description of surface roughness on spatial scales to which ground ice should be sensitive this slope distribution is convolved with a new thermal model for the dependence of subsurface ice on slope to produce a prediction of the global ice distribution that includes the effect of topographic roughness in the highest latitudes slopes reduce the amount of buried ice while in lower latitudes the ice fraction increases widening the geographic boundary of the ice table at the high latitudes where ice is stable beneath horizontal ground the estimated reduction of ice is small compared to the existing ice volume areas in the midlatitudes with high surface roughness that have previously been predicted to be ice free are predicted to contain quantities of ice that may be detectable at present and accessible in the future slopes cause ground ice to be stable to latitudes of about 25 degrees in both hemispheres including for example areas within the northern olympus mons aureole deposits hecates tholus and hellas basin ice is unstable at equatorial latitudes even when accounting for surface slopes

quantitative analysis of submarine flow deposit shape in the marnoso arenacea formation what is the signature of hindered settling from dense near bed layers abstract submarine sediment density flows are one of the volumetrically most important processes for sediment transport across earth the sediment concentration of flows that reach the deep ocean has never been measured directly and understanding these long runout flows remains a major challenge the miocene marnoso arenacea formation in the italian apennines is the only ancient sequence where individual submarine sediment density flow deposits single beds have been mapped out for more than 100 km down flow here we document the external shape and internal architecture of thirty two individual beds that record flow evolution and can be compared to deposit shapes in mathematical or experimental models the large number of beds allows modes of flow behavior to be identified larger volume turbidites are typically dominated by massive ta or planar laminated tb sandstone intervals that have a broad thickness maximum this shape is important because it suggests that massive and planar laminated sandstones record hindered settling from dense near bed layers which have high 10 by volume sediment concentrations previously some authors have inferred that planar laminated sandstones tb are deposited mainly by dilute flows the position of the broad thickness maximum moves basinward as the volume of sand in the flow increases this is consistent with mathematical modeling that suggests the position of the thickness maximum depends on flow thickness flow speed and sediment settling velocity as well as sediment concentration variations in seawater entrainment rate and local changes in seafloor gradient smaller volume turbidite sandstone intervals are finer grained and dominated by ripple cross lamination tc and have a near exponential decay in thickness that is consistent with deposition from a dilute sediment suspension the rate of near exponential thinning is controlled by sandstone volume in contrast turbidite mudstone intervals show an approximately linear increase in thickness with distance flows that entered the basin in opposite directions produced turbidite mudstone intervals that thicken towards the same location indicating that muddy turbidity currents can drain back over long distances to basinal lows

localization and physical property experiments conducted by opportunity at meridiani planum the location of the opportunity landing site was determined to better than 10 m absolute accuracy from analyses of radio tracking data we determined rover locations during traverses with an error as small as several centimeters using engineering telemetry and overlapping images topographic profiles generated from rover data show that the plains are very smooth from meter to centimeter length scales consistent with analyses of orbital observations solar cell output decreased because of the deposition of airborne dust on the panels the lack of dust covered surfaces on meridiani planum indicates that high velocity winds must remove this material on a continuing basis the low mechanical strength of the evaporitic rocks as determined from grinding experiments and the abundance of coarse grained surface particles argue for differential erosion of meridiani planum

surface energy budget and thermal inertia at gale crater calculations from ground based measurements the analysis of the surface energy budget seb yields insights into soil atmosphere interactions and local climates while the analysis of the thermal inertia i of shallow subsurfaces provides context for evaluating geological features mars orbital data have been used to determine thermal inertias at horizontal scales of 104 m2 to 107 m2 here we use measurements of ground temperature and atmospheric variables by curiosity to calculate thermal inertias at gale crater at horizontal scales of 102 m2 we analyze three sols representing distinct environmental conditions and soil properties sol 82 at rocknest rck sol 112 at point lake pl and sol 139 at yellowknife bay ykb our results indicate that the largest thermal inertia i 452 j m 2 k 1 s 1 2 si units used throughout this article is found at ykb followed by pl with i 306 and rck with i 295 these values are consistent with the expected thermal inertias for the types of terrain imaged by mastcam and with previous satellite estimations at gale crater we also calculate the seb using data from measurements by curiosity s rover environmental monitoring station and dust opacity values derived from measurements by mastcam the knowledge of the seb and thermal inertia has the potential to enhance our understanding of the climate the geology and the habitability of mars

a prelanding assessment of the ice table depth and ground ice characteristics in martian permafrost at the phoenix landing site 1 we review multiple estimates of the ice table depth at potential phoenix landing sites and consider the possible state and distribution of subsurface ice a two layer model of ice rich material overlain by ice free material is consistent with both the observational and theoretical lines of evidence results indicate ground ice to be shallow and ubiquitous 2 6 cm below the surface undulations in the ice table depth are expected because of the thermodynamic effects of rocks slopes and soil variations on the scale of the phoenix lander and within the digging area which can be advantageous for analysis of both dry surficial soils and buried ice rich materials the ground ice at the ice table to be sampled by the phoenix lander is expected to be geologically young because of recent climate oscillations however estimates of the ratio of soil to ice in the ice rich subsurface layer suggest that that the ice content exceeds the available pore space which is difficult to reconcile with existing ground ice stability and dynamics models these high concentrations of ice may be the result of either the burial of surface snow during times of higher obliquity initially high porosity soils or the migration of water along thin films measurement of the d h ratio within the ice at the ice table and of the soil to ice ratio as well as imaging ice soil textures will help determine if the ice is indeed young and if the models of the effects of climate change on the ground ice are reasonable

recent ice rich deposits formed at high latitudes on mars by sublimation of unstable equatorial ice during low obliquity observations from the gamma ray spectrometer instrument suite on the mars odyssey spacecraft have been interpreted as indicating the presence of vast reservoirs of near surface ice in high latitudes of both martian hemispheres1 2 3 4 5 ice concentrations are estimated to range from 70 per cent at 60 latitude to 100 per cent near the poles possibly overlain by a few centimetres of ice free material in most places4 this result is supported by morphological evidence of metres thick layered deposits that are rich in water ice6 7 8 9 and periglacial like features10 11 found only at high latitudes diffusive exchange of water between the pore space of the regolith and the atmosphere has been proposed to explain this distribution12 but such a degree of concentration is difficult to accommodate with such processes9 13 14 alternatively there are suggestions that ice rich deposits form by transport of ice from polar reservoirs and direct redeposition in high latitudes during periods of higher obliquity9 13 but these results have been difficult to reproduce with other models here we propose instead that during periods of low obliquity less than 25 high latitude ice deposits form in both hemispheres by direct deposition of ice as a result of sublimation from an equatorial ice reservoir that formed earlier during a prolonged high obliquity excursion using the ice accumulation rates estimated from global climate model simulations we show that over the past ten million years large variations of mars obliquity have allowed the formation of such metres thick sedimentary layered deposits in high latitude and polar regions

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

measurement of h2o adsorption under mars like conditions effects of adsorbent heterogeneity new measurements of the adsorption of h2o onto terrestrial materials under mars like conditions disagree with predictions made on the basis of the most frequently used adsorption isotherms we report here on additional measurements which confirm that previous estimates of h2o adsorptive coverage of martian surface minerals were too high this discrepancy is a result of extrapolating an empirical expression for adsorption that can be shown to contain unrealistic assumptions new isotherms developed to describe adsorption on heterogeneous surfaces are well suited to describing adsorption at mars like conditions the new isotherms predict that the adsorptive capacity of the regolith is lower than previously thought if normalized for available surface area the adsorptive behavior of the regolith materials to first order can be predicted on the basis of their specific surface area without regard to composition for a given specific surface area of a few tens of square meters per gram we show that vapor diffusion is more rapid and that predawn near surface ground ice must occur more commonly than previously thought we find that the presence of a few percent of smectites in the upper few centimeters of the regolith can dominate the adsorption cycle

ice concentration and distribution near the south pole of mars synthesis of odyssey and global surveyor analyses 1 mars odyssey gamma ray spectrometer grs neutron spectrometer data are analyzed to determine the concentration and boundary of buried water ice near the south pole the measurements are consistent with a circumpolar layer of average ice concentration from 35 to 100 by weight and superposed dust with thickness density product 30 to 40 g cm2 the region of buried water ice extends from near the south pole to latitudes 48s to 58s the equatorward boundary of the ice rich region compares favorably with the boundary of an ice rich dust mantle inferred from mars orbiter laser altimeter data and the locations of dissected terrain inferred from mars orbiter camera images the ice rich mantle is identified as the source of enhanced hydrogen sensed by the neutron spectrometer

redistribution of water in terrestrial soils at subfreezing temperatures a review of processes and their potential relevance to mars 1 any study of water behavior in the martian regolith should begin with an examination of our current understanding of subsurface water in terrestrial cold regions the terrestrial analog provides a wealth of readily available information to help formulate and test new ideas about possibilities on mars this paper discusses the major mechanisms driving the phenomenal ability of capillary media to redistribute moisture when freezing it examines both thermally induced and freezing induced redistribution of moisture the magnitude of which can vastly exceed the transport expected from fickian diffusion alone if the martian crust is truly water rich then these processes in response to transient thermal disturbances caused by impacts volcanic and magmatic activity changes in climate and potential future human activities may induce substantial changes in the local distribution of subsurface ice

ultrahigh resolution topographic mapping of mars with mro hirise stereo images meter scale slopes of candidate phoenix landing sites 1 the objectives of this paper are twofold first to report our estimates of the meter to decameter scale topography and slopes of candidate landing sites for the phoenix mission based on analysis of mars global surveyor mgs mars orbiter camera moc images with a typical pixel scale of 3 m and mars reconnaissance orbiter mro high resolution imaging science experiment hirise images at 0 3 m pixel 1 and second to document in detail the geometric calibration software and procedures on which the photogrammetric analysis of hirise data is based a combination of optical design modeling laboratory observations star images and mars images form the basis for software in the u s geological survey integrated software for imagers and spectrometers isis 3 system that corrects the images for a variety of distortions with single pixel or subpixel accuracy corrected images are analyzed in the commercial photogrammetric software socet set bae systems yielding digital topographic models dtms with a grid spacing of 1 m 3 4 pixels that require minimal interactive editing photoclinometry yields dtms with single pixel grid spacing slopes from moc and hirise are comparable throughout the latitude zone of interest and compare favorably with those where past missions have landed successfully only the mars exploration rover mer b site in meridiani planum is smoother moc results at multiple locations have root mean square rms bidirectional slopes of 0 8 4 5 at baselines of 3 10 m hirise stereopairs one per final candidate site and one in the former site yield 1 8 2 8 slopes at 1 m baseline slopes at 1 m from photoclinometry are also in the range 2 3 after correction for image blur slopes exceeding the 16 phoenix safety limit are extremely rare

crater morphology and evolution at the phoenix landing site insights into timing of modern geological processes and subsurface ice abstract we report results of an in depth study of the morphology of small km scale and smaller craters over a 4000 km2 region on mars that includes the phoenix landing ellipse focused on the nature and timing of geological processes that have been active in the region the study seeks to constrain regolith depositional rates thickness of ground ice layer abundance of ice in the subsurface and the rate of crater degradation measurements of the size of ejecta blocks around craters show that the region has not been a net depositional site over the last billion years most craters smaller than 200 350 m lack ejecta blocks regardless of age indicating that there is a layer approximately 20 35 m deep that either does not form or does not retain ejecta blocks this layer is expressed both within and outside the extended ejecta blanket of heimdal crater implying that it is not associated with the ejecta blanket we propose that this unconsolidated layer consists dominantly of ice cemented soil which raises questions about the emplacement of ice at depth we also note clear progression in crater degradation morphology which allows us to place constraints on the rate and style of crater degradation small craters 20 to 200 m in diameter appear to lose their relief due to slow infilling of the bowl over time scales of 5 100 kyr the infilling of small craters perhaps by a combination of ice and dust presents a mechanism by which ice is buried down to a few tens of meters on the other hand larger craters 200 m to 1 km do not exhibit evidence for infilling but do exhibit concentric sets of fractures within and outside the rim we propose that loss of relief of the larger craters is due to viscous creep over time scales of a few to tens of myr this latter interpretation would require the presence of water ice in abundances greater than pore filling down to depths of at least tens of meters

patterns in mobility and modification of middle and high latitude southern hemisphere dunes on mars nasa mars data analysis program mdap nnx14ao96g mdap grant nnx12aj38g nnx16aj43g 123117

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

localization and physical properties experiments conducted by spirit at gusev crater the precise location and relative elevation of spirit during its traverses from the columbia memorial station to bonneville crater were determined with bundle adjusted retrievals from rover wheel turns suspension and tilt angles and overlapping images physical properties experiments show a decrease of 0 2 per mars solar day in solar cell output resulting from deposition of airborne dust cohesive soil like deposits in plains and hollows bright and dark rock coatings and relatively weak volcanic rocks of basaltic composition volcanic impact aeolian and water related processes produced the encountered landforms and materials

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

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

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