the effect of salt crust on the thermal conductivity of one sample of fluvial particulate materials under martian atmospheric pressures 1 a line heat source apparatus was used to measure thermal conductivities of a lightly cemented fluvial sediment salinity 1 1 g kg 1 and the same sample with the cement bonds almost completely disrupted under low pressure carbon dioxide atmospheres the thermal conductivities of the cemented sample were approximately 3 higher over the range of atmospheric pressures tested than the thermal conductivities of the same sample after the cement bonds were broken a thermal conductivity derived particle size was determined for each sample by comparing these thermal conductivity measurements to previous data that demonstrated the dependence of thermal conductivity on particle size actual particle size distributions were determined via physical separation through brass sieves when uncemented 87 of the particles were less than 125 m in diameter with 60 of the sample being less than 63 m in diameter as much as 35 of the cemented sample was composed of conglomerate particles with diameters greater than 500 m the thermal conductivities of the cemented sample were most similar to those of 500 m glass beads whereas the thermal conductivities of the uncemented sample were most similar to those of 75 m glass beads this study demonstrates that even a small amount of salt cement can significantly increase the thermal conductivity of particulate materials as predicted by thermal modeling estimates by previous investigators

microbially induced cementation of carbonate sands are micritic meniscus cements good indicators of vadose diagenesis characteristic fabrics such as micrite envelopes calcified filaments and micritic grain to grain bridges are observed in a modern subtidal firmground wood cay bahamas and in a variety of firm and hardgrounds of lower cretaceous and upper jurassic platform carbonates swiss and french jura mountains their similarity to microbial fabrics described in grapestones and in intertidal to continental vadose environments suggests that microbial activity played an important role in the initial stabilization and cementation of carbonate sands meniscus type cements to distinguish them from vadose meniscus cements which clearly formed in subtidal environments are related to filament calcification trapping of percolating micrite and microbially induced carbonate formation such meniscus type cements are commonly micritic but meniscus shaped precipitation of fibrous aragonite or sparitic calcite around organic filaments is also observed therefore an interpretation of vadose early diagenesis should not be based on meniscus cements alone similarly subtidally formed filamentous structures can strongly resemble alveolar septal structures and be interpreted incorrectly as related to subaerial exposure

chloride bearing materials in the southern highlands of mars chlorides commonly precipitate during the evaporation of surface water or groundwater and during volcanic outgassing spectrally distinct surface deposits consistent with chloride bearing materials have been identified and mapped using data from the 2001 mars odyssey thermal emission imaging system these deposits are found throughout regions of low albedo in the southern highlands of mars geomorphologic evidence from orbiting imagery reveals these deposits to be light toned relative to their surroundings and to be polygonally fractured the deposits are small

mosaicking of global planetary image datasets 2 modeling of wind streak thicknesses observed in thermal emission imaging system themis daytime and nighttime infrared data 1 large scale seamless global mosaics such as the thermal emission imaging system themis mosaics can be used to assess regional and local scale relative thermophysical properties morphology geology and other compositional investigations in this paper we use the themis global mosaics as reconnaissance tools to assess the relative thermophysical properties of materials and target a specific location to examine with a quantitative thermal model this example highlights the utility of these new data sets through an investigation of the thermophysical properties of wind streaks near the syrtis major and uranius mons regions in this study we quantitatively model depositional wind streak thicknesses near syrtis major for a thermophysically homogeneous substrate and a top layer consistent with air fall dust using this two layer thermal model we calculate that wind streaks near syrtis major are likely 30 200 m thick depending on the top layer thermal inertia given predicted dust deposition and removal rates we calculate that these wind streaks likely formed in 200 mars years and represent some of the youngest aeolian features on mars the regional wind patterns identified using the themis daytime and nighttime temperature mosaics were related to general circulation model data to constrain the season and time of day that best match the observed wind directions the themis global mosaics provide excellent context for integrating data from other instruments and provide the basis for interpreting many physical mineralogical and morphologic aspects of mars

thermophysical properties along curiosity s traverse in gale crater mars derived from the rems ground temperature sensor abstract the rems instrument onboard the mars science laboratory rover curiosity has measured ground temperature nearly continuously at hourly intervals for two mars years coverage of the entire diurnal cycle at 1 hz is available every few martian days we compare these measurements with predictions of surface atmosphere thermal models to derive the apparent thermal inertia and thermally derived albedo along the rover s traverse after accounting for the radiative effects of atmospheric water ice during fall and winter as is necessary to match the measured seasonal trend the rems measurements can distinguish between active sand other loose materials mudstone and sandstone based on their thermophysical properties however the apparent thermal inertias of bedrock dominated surfaces 350 550 j m 2 k 1 s are lower than expected we use rover imagery and the detailed shape of the diurnal ground temperature curve to explore whether lateral or vertical heterogeneity in the surface materials within the sensor footprint might explain the low inertias we find that the bedrock component of the surface can have a thermal inertia as high as 650 1700 j m 2 k 1 s for mudstone sites and 700 j m 2 k 1 s for sandstone sites in models runs that include lateral and vertical mixing although the results of our forward modeling approach may be non unique they demonstrate the potential to extract information about lateral and vertical variations in thermophysical properties from temporally resolved measurements of ground temperature

effect of periodic melting on geochemical and isotopic signals in an ice core from lomonosovfonna svalbard 1 we examine the quality of atmospherically deposited ion and isotope signals in an ice core taken from a periodically melting ice field lomonosovfonna in central spitsbergen svalbard the aim is to determine the degree to which the signals are altered by periodic melting of the ice we use three diagnostics 1 the relation between peak values in the ice chemical and isotopic record and ice facies type 2 the number of apparent annual cycles in these records compared with independently determined number of years represented in the ice core and 3 a statistical comparison of the isotopic record in the ice core and the isotope records from coastal stations from the same region we find that during warm summers as much as 50 of the annual accumulation may melt and percolate into the firn in a median year this decreases to similar to25 as a consequence of percolation the most mobile acids show up to 50 higher concentrations in bubble poor ice facies compared with facies that are less affected by melt most of the other chemical species are less affected than the strong acids and the stable water isotopes show little evidence of mobility annual or biannual cycles are detected in most parameters and the water isotope record has a comparable statistical distribution to isotopic records from coastal stations we conclude that ice cores from sites like lomonosovfonna contain a useful environmental record despite melt events and percolation and that most parameters preserve an annual or in the worst cases a biannual atmospheric signal

initial results from the mini tes experiment in gusev crater from the spirit rover the miniature thermal emission spectrometer mini tes on spirit has studied the mineralogy and thermophysical properties at gusev crater undisturbed soil spectra show evidence for minor carbonates and bound water rocks are olivinerich basalts with varying degrees of dust and other coatings dark toned soils observed on disturbed surfaces may be derived from rocks and have derived mineralogy 5 to 10 of 45 pyroxene 20 ca rich pyroxene and 25 pigeonite 40 sodic to intermediate plagioclase and 15 olivine forsterite 45 5 to 10 two spectrally distinct coatings are observed on rocks a possible indicator of the interaction of water rock and airfall dust diurnal temperature data indicate particle sizes from 40 to 80 microm in hollows to approximately 0 5 to 3 mm in soils

martian high latitude permafrost depth and surface cover thermal inertia distributions 1 martian high latitudes have thermal properties consistent with an extensive high thermal inertia permafrost layer near the surface surface cover thermal inertias and permafrost depths at martian high latitudes 50 80 n s are derived from thermal emission spectrometer tes data and compared with previously published water ice depths determined from the mars odyssey neutron spectrometer mons the depth to the permafrost layer is correlated with surface cover thermal inertia albedo and latitude in general agreement with predicted trends of water ice stability comparison of permafrost depths with water ice rich layer depths derived from mons data displays good qualitative agreement although a divergence is present at greater burial depths this disparity may be due to the presence of hydrated minerals at shallow depths or a lower than expected permafrost thermal inertia corresponding with low water ice concentrations at greater depths surface cover thermal inertias are greater in the northern high latitudes than in the south and differences between these and previous results will have significant effects on the predicted depth of martian water ice stability several regions in the northern hemisphere display high surface cover thermal inertia associated with possible receding water ice deposits that are shallow enough to influence diurnal surface temperatures significant lateral and vertical heterogeneity in water ice distributions are present and the martian regolith is likely more complicated than can be described by simple two layered models and a single mode of water ice emplacement

a model for formation of dust soil and rock coatings on mars physical and chemical processes on the martian surface 1 a model is presented here to explain the generation of surface material on mars using chemical magnetic and spectroscopic data from mars and geologic analogs from terrestrial sites one basic premise is that the dust soil units are not derived exclusively from local rocks but are rather a product of global and possibly remote weathering processes another assumption in this model is that there are both physical and chemical interactions of the atmosphere with dust particles and that these two processes create distinctly different products physical processes distribute dust particles on rocks and drift units forming physically aggregated layers these are reversible processes chemical reactions of the dust soil particles create alteration rinds on rock surfaces and cohesive crusted surface units between rocks both of which are relatively permanent materials according to this model the dominant components of the dust soil particles are derived from alteration of volcanic ash and tephra and contain primarily nanophase and poorly crystalline ferric oxide oxyhydroxide phases as well as silicates these phases are the alteration products that formed in a low moisture environment these dust soil particles also contain a smaller amount of material that was exposed to more water and contains crystalline ferric oxides oxyhydroxides sulfates and clay silicates these components could have formed through hydrothermal alteration at steam vents or fumeroles thermal fluids or through evaporite deposits wet dry cycling experiments are presented here on mars soil analogue mixtures containing poorly crystalline and crystalline components dominated by nanophase to 2 m diameter particles cemented products of these soil mixtures are formed in these experiments and variation in the surface texture was observed for samples containing smectites nonhydrated silicates or sulfates reflectance spectra were measured of the initial particulate mixtures the cemented products and ground versions of the cemented material the spectral contrast in the visible near infrared and midinfrared regions is significantly reduced for the cemented material compared to the initial soil and somewhat reduced for the ground cemented soil compared to the initial soil the results of this study suggest that transient fluvial activity on mars will have a profound effect on the texture and spectral properties of the dust soil particles on the surface the model developed in this study provides an explanation for the generation of cemented or crusted soil units and rock coatings on mars and may explain albedo variations on the surface observed near large rocks or crater rims

oceans on mars an assessment of the observational evidence and possible fate the edges of the northern plains and interpreted to be shorelines remaining from these former standing bodies of water we examine the elevations and geologic relations along these contacts in detail and find little support for their interpretation as shorelines some contacts are clearly of volcanic origin and all have significant variations in elevation better support for the former presence of water over large parts of the northern plains is provided by the vastitas borealis formation vbf most of the post noachian fill within the northern basin is ridged plains of lower hesperian age interpreted to be volcanic in origin overlying the ridged plains is the vbf a thin veneer of material of upper hesperian age the vbf may have been deposited from large floods support for this interpretation is the similarity in age between the outflow channels and the vbf the presence of the vbf at the lower ends of the outflow channels and identification of numerous features in the outcrop areas of the vbf that are suggestive of basal melting of an ice sheet to cover all the area over which the vbf is exposed would require 2 3 10 7 km 3 of water spread over the entire surface of mars this volume is equal to a global layer global equivalent layer or gel 156 m deep we find no support for the larger estimates of ocean volumes that range up to 3 10 8 km 3 and which imply comparable amounts of water per unit area as are currently present on the surface of the earth under present climatic conditions on mars an ocean would freeze in a geologically short time period 10 4 years then would sublimate away at rates strongly dependent on the presence or absence of debris on the ice surface the present vbf is interpreted as a sublimation residue from the ponded outflow channel effluents the fate of a volume of water thought to have been emplaced by the outflow channels 2 3 10 7 km 3 is largely accounted for by the presence of other existing reservoirs on the planet an approximately 20 30 m gel of water is estimated to be in the present polar caps and a 50 m gel may have escaped to space since the hesperian leaving 80 m gel unaccounted for this amount may be partly trapped in other volatile rich deposits on the surface and a significant amount could have reentered the groundwater system by south polar basal melting and been progressively cold trapped at the base of a growing cryosphere on the basis of our assessment of the hesperian aged deposits we predict that testing of the clifford and parker 2001 hypothesis that a noachian aged ocean covered up to one third of the surface of mars will be made very difficult by the enhanced degradation rates in the noachian and subsequent geological events in the northern lowlands index terms 6225 planetology solar system objects mars 4267 oceanography general paleoceanography 5407 planetary sciences atmospheres evolution 5470 planetary sciences surface materials and properties 1635 global change oceans 4203 keywords mars oceans channels shorelines hesperian

a model of thermal conductivity for planetary soils 2 theory for cemented soils 1 a numerical model of heat conduction through particulate media made of spherical grains cemented by various bonding agents is presented the pore filling gas conductivity volume fraction and thermal conductivity of the cementing phase are tunable parameters cement fractions 0 001 0 01 in volume have small effects on the soil bulk thermal conductivity a significant conductivity increase factor 3 8 is observed for bond fractions of 0 01 to 1 in volume in the 1 to 15 bond fraction domain the conductivity increases continuously but less intensely 25 100 conductivity increase compared to a 1 bond system beyond 15 of cements the conductivity increases vigorously and the bulk conductivity rapidly approaches that of bedrock the composition of the cements i e conductivity has little influence on the bulk thermal inertia of the soil especially if the volume of bond 10 these results indicate that temperature measurements are sufficient to detect cemented soils and quantify the amount of cementing phase but the mineralogical nature of the bonds and the typical grain size are unlikely to be determined from orbit on mars a widespread surface unit characterized by a medium albedo 0 19 0 26 and medium high thermal inertia 200 600 j s 0 5 m 2 k 1 has long been hypothesized to be associated with a duricrust the fraction of cement required to fit the thermal data is less than 1 5 by volume this small amount of material is consistent with orbital observations confirming that soil cementation is an important factor controlling the thermal inertia of the martian surface

high resolution thermal inertia derived from the thermal emission imaging system themis thermal model and applications 1 thermal inertia values at 100 m per pixel are determined using nighttime temperature data from the thermal emission imaging system themis on the mars odyssey spacecraft producing the highest resolution thermal inertia data set to date themis thermal inertia values have an overall accuracy of 20 a precision of 10 15 and are consistent with both thermal emission spectrometer orbital and miniature thermal emission spectrometer surface thermal inertia values this data set enables the improved quantification of fine scale surface details observed in high resolution visible images in the tharsis region surface textures and crater rims observed in visible images have no corresponding variation in the themis thermal inertia images indicating that the dust mantle is pervasive at themis scales and is a minimum of a few centimeters and up to 1 2 m thick the thermal inertia of bed form material indicates particle diameters expected for aeolian sediments and these materials are likely currently saltating variations in the thermal inertia within interior layered deposits in hebes chasma can be distinguished and the thermal inertia is too low to be consistent with bedrock or a lava flow thus a secondary emplacement of volcanic material or a volcanic ash deposit is a more likely method of formation higher resolution themis thermal inertia enables the identification of exposed bedrock on the martian surface in nili patera and ares vallis bedrock material corresponds to distinct compositional and morphologic surfaces indicating that a specific unit is exposed and is likely currently being kept free of unconsolidated material by aeolian processes

rock abundance on mars from the thermal emission spectrometer 1 nighttime infrared spectral observations returned from the mars global surveyor thermal emission spectrometer tes are well suited for determining the subpixel abundance of rocks on the surface of mars the algorithm used here determines both the areal fraction of rocky material and the thermal inertia of the fine grained nonrock component present on the surface rock is defined as any surface material that has a thermal inertia 1250 j m 2 k 1 s 1 2 this can be bedrock boulders indurated sediments or a combination of these on a surface mixed with finer grained materials over 4 9 million observations were compiled to produce the 8 pixels per degree global rock abundance and fine component inertia maps total coverage is 45 of the planet between latitudes 60 and 60 less than 1 of the planet has rock abundances greater than 50 and 7 of the mapped surface has greater than 30 rocks rocky regions on mars correspond primarily to the high inertia surfaces observed in thermal inertia data sets the fine component inertia data set is used to identify high inertia exposures that contain few rocks and more homogeneous materials

global duricrust on mars analysis of remote sensing data global remote sensing data for mars are analyzed to obtain a simple self consistent model for the surface layer the data sets discussed include radar cross section measurements at several wavelengths radio whole disk thermal emission observations at two wavelengths the global distribution of thermal inertia deviations of diurnal temperatures from those of a homogeneous model and thermal spectral estimates of surface rock abundance and of the thermal inertia of the nonrocky component of the surface the data sets which most constrain the interpretation are the rock abundance map and the correlation of thermal inertia with radar cross section these require the rock abundance to not vary significantly from place to place and simultaneously require the density and thermal inertia of the fines to vary in a consistent manner the simplest model which can explain all of the data involves a global case hardened crust duricrust which varies spatially in its degree of formation in general low thermal inertia regions have a poorly developed crust and highinertia regions have a well developed crust there are however regions that consist of coarse particles and which do not fit this model e g chryse this model is consistent with the ages of low inertia regions and with aeolian mechanisms for their development the duricrust is thought to form via the mobilization of salt ions within a layer of water adsorbed within the regolith and its formation may be associated with the exchange of water between the regolith and atmosphere which occurs on the 105 and 106 year time scale

physical properties of the mars exploration rover landing sites as inferred from mini tes derived thermal inertia 1 the miniature thermal emission spectrometer mini tes on board the two mars exploration rovers provides the first opportunity to observe thermal properties from the martian surface relate these properties to orbital data and perform soil conductivity experiments under martian conditions the thermal inertias of soils bedforms and rock at each landing site were derived to quantify the physical properties of these features and understand geologic processes occurring at these localities the thermal inertia for the gusev plains rock target bonneville beacon 1200 j m 2 k 1 s 1 2 is consistent with a dense basaltic rock but the rocks at the columbia hills have a lower thermal inertia 620 j m 2 k 1 s 1 2 suggesting that they have a volcaniclasic origin bedforms on the floors of craters at both landing sites have thermal inertias of 200 j m 2 k 1 s 1 2 consistent with a particle diameter of 160 m this diameter is comparable to the most easily moved grain size in the current atmosphere on mars suggesting that these bedforms may have formed under current atmospheric conditions along the meridiani plains the thermal inertia is lower than that derived from tes and thermal emission imaging system themis orbital data this discrepancy is not well understood mini tes derived thermal inertias at gusev along a 2 5 km traverse follow trends in thermal inertia measured from orbit with tes and themis however along the traverse there are variability and mixing of particle sizes that are not resolved in the orbital thermal inertia data due to meter scale processes that are not identifiable at larger scales

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

large alluvial fans on mars 1 several dozen distinct alluvial fans 10 to 40 km long downslope have been observed in highlands craters within a search region between 0 and 30 s alluvial fan containing craters were found only between 18 and 29 s and they all occur at around 1 km of the mola defined martian datum within the study area they are not randomly distributed but instead form three distinct clusters fans typically descend 1 km from where they disgorge from their alcoves longitudinal profiles show that their surfaces are very slightly concave with a mean slope of 2 many fans exhibit very long narrow low relief ridges radially oriented downslope often branching at their distal ends suggestive of distributaries morphometric data for 31 fans were derived from mola data and compared with terrestrial fans with high relief source areas terrestrial low gradient alluvial ramps in inactive tectonic settings and older martian alluvial ramps along crater floors the martian alluvial fans generally fall on the same trends as the terrestrial alluvial fans whereas the gentler martian crater floor ramps are similar in gradient to the low relief terrestrial alluvial surfaces for a given fan gradient martian alluvial fans generally have greater source basin relief than terrestrial fans in active tectonic settings this suggests that the terrestrial source basins either yield coarser debris or have higher sediment concentrations than their martian counterpoints martian fans and terrestrial basin and range fans have steeper gradients than the older martian alluvial ramps and terrestrial low relief alluvial surfaces which is consistent with the construction of martian fans from dominantly gravel sized sediment rather than sand and silt martian fans are relatively large and of low gradient similar to terrestrial fluvial fans rather than debris flow fans although gravity scaling uncertainties make the flow regime forming martian fans uncertain however evidence of bedforms accentuated by differential erosion such as scroll bars supports the contention that these are fluvially formed fans martian fans at least those in holden crater apparently formed around the time of the noachian hesperian boundary we infer that these fans formed during an episode of enhanced precipitation probably snow and runoff which exhibited both sudden onset and termination

spectroscopic evidence for hydrous iron sulfate in the martian soil 1 despite in situ analyses by several landers the composition of the martian soil remains unclear recently constituent minerals in the soil have been proposed from thermal emissivity and mossbauer spectroscopic data from mars these data were interpreted to show spectral evidence for carbonate and an unspecified mineral containing bound water as well as olivine here we present an alternative interpretation suggesting that these spectral features can be satisfied by a single type of mineral namely hydrous iron sulfates acidic waters necessary for production of hydrous iron sulfates would preclude carbonate formation and indicate a dramatically different chemical environment on mars in which olivine would be highly unstable and unlikely to survive soil formation regardless of its presence in the rocks hydrous iron sulfates are efflorescent salts and may be crusting agents in the martian soils

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

perennial water ice identified in the south polar cap of mars the inventory of water and carbon dioxide reservoirs on mars are important clues for understanding the geological climatic and potentially exobiological evolution of the planet1 from the early mapping observation of the permanent ice caps on the martian poles2 3 the northern cap was believed to be mainly composed of water ice whereas the southern cap was thought to be constituted of carbon dioxide ice however recent missions nasa missions mars global surveyor and odyssey have revealed surface structures4 altimetry profiles5 underlying buried hydrogen6 and temperatures of the south polar regions that are thermodynamically consistent with a mixture of surface water ice and carbon dioxide7 here we present the first direct identification and mapping of both carbon dioxide and water ice in the martian high southern latitudes at a resolution of 2 km during the local summer when the extent of the polar ice is at its minimum we observe that this south polar cap contains perennial water ice in extended areas as a small admixture to carbon dioxide in the bright regions associated with dust without carbon dioxide at the edges of this bright cap and unexpectedly in large areas tens of kilometres away from the bright cap

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

soil like deposits observed by sojourner the pathfinder rover most of the soil like materials at the pathfinder landing site behave like moderately dense soils on earth with friction angles near 34 39 and are called cloddy deposits cloddy deposits appear to be poorly sorted with dust sized to granule sized mineral or rock grains they may contain pebbles small rock fragments and clods thin deposits of porous compressible drifts with friction angles near 26 28 are also present drifts are fine grained cohesions of both types of deposits are small there may be indurated soil like deposits and or coated or crusted rocks cloddy deposits may be fluvial sediments of the ares tiu floods but other origins such as ejecta from nearby impact craters should be considered drifts are probably dusts that settled from the martian atmosphere remote sensing signatures of the deposits inferred from rover observations are consistent with those observed from orbit and earth

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

kaolinitic meniscus bridges as an indicator of early diagenesis in nubian sandstones sinai egypt abstract characteristic meniscus geometries formed by kaolinitic in ltration areobserved in nubian sandstones collected on the western coast of the sinaipeninsula egypt based on petrographic and scanning electron microscope sem observations the kaolinite forming the menisci consists of mixed sizediscrete platelets that gather into the corners around the framework grain to grain contacts speci cally the internal fabric of menisci indicates a generalorganizing trend from 1 the centre where the platelets coat the frameworkgrains 2 to the peripheral zone where they are oriented tangentially to grainsurfaces 3 to the pore linings with curvatures that are consistent withtheoretical considerations of air water interfaces this typical arrangementsuggests a detrital origin of kaolinite platelets by mechanical in ltration intosediments lying above the tablewater in vadose conditions this type of claycementation occurring during early diagenesis can prevent delay deep burialdiagenetic processes and therefore preserve excellent reservoir properties keywords clay minerals kaolinite nubian sandstone sandstone diagenesis introductionearly diagenesis of sediment can occur shortlyafter deposition depending on depositional envi ronment the early lithi cation i e the rstdeveloped bonding agent occurs as carbonateprecipitation or particle in ltration that linksframework grains by forming meniscus bridges such grain to grain bridges grow preferentially inthe corners of pore space close to grain contacts dunham 1971 speci cally by developing inconformity to the water air interface the menis cus as a result of differential capillarity pres sures these cements or in ltrating material areassumed to be related to vadose environments dunham 1971 the meniscus geometry forming pore roundinghabit has been described frequently in modernsedimentary environments where carbonate pre cipitation produces beachrocks from carbonatesands meyers 1987 hillga rtner et al 2001 these types of precipitated meniscus cementsconsist mainly of crypto to microcrystallinecalcite or aragonite that display laments whichgenerally grow perpendicular to grain rim miller 1988 rao et al 1994 hillga rtner et al 2001 incontrast precipitated menisci of goethitic ferru ginous material have been reported for a lateriticpro le in basalt horva th et al 1999 several studies have also dealt with the men iscus shape displayed by mechanically in ltratedclay particles in clastic sediments walker 1976 kessler 1978 meyers 1987 matlack et al 1989 moraes de ros 1990 owing to the micro metre scale size of particles the detrital clays aretransported along connected pores by uidscirculating between skeleton grains walker 1976 during a drying period the detrital claysgather where the capillarity pressure preserves uids therefore the accumulated clays exhibitgrain coatings and meniscus shaped bridgeslinking neighbouring grains thus the meniscuscements typically indicate vadose conditionswhere pore spaces are not permanently saturated i e water table level uctuates walker 1976 matlack et al 1989 moraes de ros 1990 sedimentology 2003 50 1221 1229

acid sulfate weathering of synthetic martian basalt the acid fog model revisited the acid fog model has received considerable attention as a model of soil formation on mars previous evaluations of this model have focused on experimental weathering of terrestrial basalt samples however these samples differ significantly from what now is thought to be typical of martian basalt the acid fog model is tested here using synthetic basaltic analogs derived from mars pathfinder soil and rock compositions reaction of synthetic basalt with various acidic solutions and subsequent evaporation has led to the formation of several putative secondary mineral phases many of these phases were not produced in prior experimental studies aimed at aqueous interactions on mars of these alteration phases mg fe ca and al sulfates were identified in addition secondary ferric oxide phases formed via rapid fe oxidation under relatively high ph levels buffered by basalt dissolution amorphous silica is a ubiquitous product in these experiments and has formed by precipitation from solution and by the dissolution of minerals and glasses leaving behind leached surface layers composed of residual silica the secondary products formed in these experiments demonstrate the importance of primary mineralogy when testing models of aqueous interactions on mars new constraints are placed on both the reactivity of primary basalt and the secondary mineralogy present at the martian surface copyright 2004 by the american geophysical union

discovery of a widespread low latitude diurnal co2 frost cycle on mars while the detection of co2 ice has only been reported outside the martian polar regions at very high elevation i e elysium olympus mons and the tharsis montes nighttime surface observations by the mars climate sounder on board the mars reconnaissance orbiter document the widespread occurrence of atmospherically corrected ground temperatures consistent with the presence of extensive carbon dioxide frost deposits in the dusty low thermal inertia units at middle low latitudes thermal infrared emissivities interpreted in conjunction with mass balance modeling suggest micrometer size co2 ice crystals forming optically thin layers never exceeding a few hundreds of microns in thickness i e 10 2 kg m 2 locally which is insufficient to generate a measurable diurnal pressure cycle 0 1 of the martian atmosphere atmospheric temperatures at middle low latitudes are not consistent with precipitation of co2 ice suggesting that condensation occurs on the surface the recurring growth and sublimation of co2 ice on martian dusty terrains may be an important process preventing soil induration and promoting dynamic phenomena soil avalanching and fluidization and regolith gardening maintaining a reservoir of micrometer size dust particles that are mobile and available for lifting the discovery of this diurnal co2 cycle represents an important step forward in our understanding of the way the martian atmosphere interacts with the surface

ancient oceans in the northern lowlands of mars evidence from impact crater depth diameter relationships 1 we present depth d and diameter d data for 2269 martian impact craters in the diameter range 6 216 km distributed over 11 52 106 km2 of terrain that samples several geologic settings and the full range of latitudes and elevations throughout the northern lowlands of mars our data indicate that there are three major crater types that fall into two major populations those craters that contain vastitis borealis formation vbf and those that do not the deepest type 1 craters comprise a late hesperian early amazonian age population that does not contain vbf type 2 type 3 and subdued type 1 craters comprise a population of hesperian age craters partially buried by the vbf the unique d d distribution of type 3 craters and photogeologic evidence suggest an erosional style for the vbf that requires sublimation processes indicating that the vbf contained a substantial amount of ice type 3 craters occur throughout the northern lowland plains at elevations below 2400 m if the vbf is a sedimentary deposit left by a large body of standing water in the northern lowlands of mars then the northern lowland plains contained a body of water with a volume of 6 107 km3 or the equivalent of a 430 m global ocean during the late hesperian early amazonian this also implies that the vbf contains 4 106 km3 of material in agreement with the estimated amount of material eroded from the outflow channels surrounding chryse basin and washed into the northern lowlands

the spatial distribution of rocks on mars abstract the spatial distribution of rocks exposed at the surface of mars has been mapped using viking infrared thermal mapper irtm observations overall there are no regions on the surface of mars at a scale of 1 1 in latitude and longitude that are rock free the modal value of rock abundance is 6 areal coverage with no areas having more than 30 35 rock cover the model developed to determine rock abundance relates the thermal emission in each of the four surface sensing irtm bands to temperature contrasts within the field of view non unit thermal emissivity due to absorption bands in the surface materials and the absorption and scattering of the outgoing energy by atmospheric dust and water ice each of these effects produce characteristic spectral and diurnal signatures allowing them to be separated the temperature contrasts provide a means to determine both the abundance of exposed rocks and the fine component thermal intertia rock abundance alone does not produce the observed variation in bulk thermal inertia of the surface low inertia fine bright surfaces have fewer rocks exposed than do high inertia coarse dark surfaces rock abundance does not correlate well with the rms slope nor reflectivity determined from delay doppler radar measurements there is however a possible correlation between rms slope determined from continuous wave radar observations dual polarization radar measurements which provide the best radar measure of small scale roughness indicate that the tharsis volcanic region is very rough whereas thermal measurements indicate very few rocks and a covering of dust together these observations suggest an approximately 1 m thick mantle of fines covering a very rough subsurface this fine material may be an aeolian deposit of dust storm fallout valles marineris together with several major channels and chaotic terrains have high rock abundances as does the acidalia planitia basin this observed distribution may reflect the initial deposition of coarse material associated with channel formation syrtis major is unique in having a high inertia but a very low rock abundance together with low radar roughness these observations are consistent with mantling of rocks by sand the observed distribution of rocks and fines indicates that aeolian processes both erosional and depositional play a dominant role in shaping the present martian surface

chemical divides and evaporite assemblages on mars assemblages of evaporite minerals record detailed physical and chemical characteristics of ancient surficial environments accordingly newly discovered regions of saline minerals on mars are high priority targets for exploration the chemical divide concept of evaporite mineral formation is used successfully to predict evaporite mineralogy and brine evolution on earth however basaltic weathering largely controls fluid compositions on mars and the robust predictive capabilities of terrestrial chemical divides cannot be used to interpret martian evaporites here we present a new chemical divide system that predicts evaporite assemblages identified in snc type meteorites ancient evaporites discovered on meridiani planum by the opportunity rover and mars express omega data we suggest that a common fluid type that has been buffered to different ph levels by basaltic weathering controls the variability among martian evaporite assemblages and that evaporite mineralogy and brine evolution is essentially established by the initial composition of the dilute evaporating fluid b 2005 elsevier b v all rights reserved

pancam multispectral imaging results from the spirit rover at gusev crater panoramic camera images at gusev crater reveal a rock strewn surface interspersed with high to moderate albedo fine grained deposits occurring in part as drifts or in small circular swales or hollows optically thick coatings of fine grained ferric iron rich dust dominate most bright soil and rock surfaces spectra of some darker rock surfaces and rock regions exposed by brushing or grinding show near infrared spectral signatures consistent with the presence of mafic silicates such as pyroxene or olivine atmospheric observations show a steady decline in dust opacity during the mission and astronomical observations captured solar transits by the martian moons phobos and deimos as well as a view of earth from the martian surface

thermal behavior of horizontally mixed surfaces on mars abstract current methods for deriving thermal inertia from spacecraft observations of planetary brightness temperature generally assume that surface properties are uniform for any given observation or co located set of observations as a result of this assumption and the nonlinear relationship between temperature and thermal inertia sub pixel horizontal heterogeneity may yield different apparent thermal inertia at different times of day or seasons we examine the effects of horizontal heterogeneity on mars by modeling the thermal behavior of various idealized mixed surfaces containing differing proportions of either dust sand duricrust and rock or slope facets at different angles and azimuths latitudinal effects on mixed surface thermal behavior are also investigated we find large several 100 j m 2 k 1 s 1 2 diurnal and seasonal variations in apparent thermal inertia even for small 10 admixtures of materials with moderately contrasting thermal properties or slope angles together with similar results for layered surfaces mellon m t putzig n e 2007 lunar planet sci xxxviii abstract 2184 this work shows that the effects of heterogeneity on the thermal behavior of the martian surface are substantial and may be expected to result in large variations in apparent thermal inertia as derived from spacecraft instruments while our results caution against the over interpretation of thermal inertia taken from median or average maps or derived from single temperature measurements they also suggest the possibility of using a suite of apparent thermal inertia values derived from single observations over a range of times of day and seasons to constrain the heterogeneity of the martian surface

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

new observations of martian southern mid latitude recurring slope lineae rsl imply formation by freshwater subsurface flows abstract southern mid latitude sml recurring slope lineae rsl are narrow 0 5 5 m dark albedo features that emanate from bedrock and incrementally lengthen down steep slopes that preferentially face the equator we observe that sml rsl begin lengthening prior to southern summer at a solar longitude ls of 245 11 when mars global surveyor thermal emission spectrometer tes derived near maximum surface temperatures are 296 5 k and mars reconnaissance orbiter mars climate sounder mcs and mars odyssey thermal emission imaging system themis derived mid afternoon surface temperatures are 273 k sml rsl continue to lengthen for 104 38 sols with an average near maximum surface temperature of 298 5 k the sml rsl then stop lengthening at ls 314 12 when mid afternoon surface temperatures drop below 273 k they remain dark for another 116 41 sols until ls 16 14 as surface temperatures continue to fall although the rsl recharge mechanism remains unknown our observation that the vast majority of rsl lengthen only when mid afternoon surface temperatures are 273 k supports the hypothesis that they are formed by shallow subsurface liquid water flows without significant freezing point depression the number and length of rsl at multiple sites increased dramatically following the mars year 28 globe encircling dust storm we interpret this increase to be due to warmer subsurface temperatures created by a dust laden greenhouse effect that may be unique to the southern mid latitudes near ls 270 therefore sml rsl flow is quite sensitive to ground temperature and may only occur under favorable orbital parameters when mean insolation during the rsl lengthening season is above that of the current southern mid latitude mean insolation value this value is currently at a peak that has not been attained for the last 100 ka meanwhile the rsl poor northern mid latitude mean insolation is near a minimum and has a value 27 lower than the southern value if sml rsl are indeed formed by shallow subsurface freshwater flows then they may be some of the best locations on mars to explore for extant life

exposed water ice discovered near the south pole of mars the mars odyssey thermal emission imaging system themis has discovered water ice exposed near the edge of mars southern perennial polar cap the surface h2o ice was first observed by themis as a region that was cooler than expected for dry soil at that latitude during the summer season diurnal and seasonal temperature trends derived from mars global surveyor thermal emission spectrometer observations indicate that there is h2o ice at the surface viking observations and the few other relevant themis observations indicate that surface h2o ice may be widespread around and under the perennial co2 cap

the opportunity rover s athena science investigation at meridiani planum mars the mars exploration rover opportunity has investigated the landing site in eagle crater and the nearby plains within meridiani planum the soils consist of fine grained basaltic sand and a surface lag of hematite rich spherules spherule fragments and other granules wind ripples are common underlying the thin soil layer and exposed within small impact craters and troughs are flat lying sedimentary rocks these rocks are finely laminated are rich in sulfur and contain abundant sulfate salts small scale cross lamination in some locations provides evidence for deposition in flowing liquid water we interpret the rocks to be a mixture of chemical and siliciclastic sediments formed by episodic inundation by shallow surface water followed by evaporation exposure and desiccation hematite rich spherules are embedded in the rock and eroding from them we interpret these spherules to be concretions formed by postdepositional diagenesis again involving liquid water

the spirit rover s athena science investigation at gusev crater mars the mars exploration rover spirit and its athena science payload have been used to investigate a landing site in gusev crater gusev is hypothesized to be the site of a former lake but no clear evidence for lacustrine sedimentation has been found to date instead the dominant lithology is basalt and the dominant geologic processes are impact events and eolian transport many rocks exhibit coatings and other characteristics that may be evidence for minor aqueous alteration any lacustrine sediments that may exist at this location within gusev apparently have been buried by lavas that have undergone subsequent impact disruption

evidence for persistent flow and aqueous sedimentation on early mars landforms representative of sedimentary processes and environments that occurred early in martian history have been recognized in mars global surveyor mars orbiter camera and mars odyssey thermal emission imaging system images evidence of distributary channelized flow in particular flow that lasted long enough to foster meandering and the resulting deposition of a fan shaped apron of debris indicate persistent flow conditions and formation of at least some large intracrater layered sedimentary sequences within fluvial and potentially lacustrine environments

martian surface mineralogy from observatoire pour la mineralogie l eau les glaces et l activite on board the mars express spacecraft omega mex global mineral maps 1 after 2 years of operation the observatoire pour la mineralogie l eau les glaces et l activite omega imaging spectrometer on board mars express has acquired data coverage of the martian surface with spatial resolution varying between 300 m and 4 8 km depending on the pericenter altitude of the spacecraft s elliptical orbit we report the global surface distributions of some minerals using the omega observations in the visible and near infrared vnir wavelength domains 0 35 2 5 m global maps of ferric phases mafic minerals pyroxenes and olivines and hydrated minerals have been derived from spectral parameters the limits of detection in terms of abundance for some minerals of different grain size distributions are given the distribution of pyroxenes is in general agreement with the mineral maps of previous telescopic and space observations the fe3 absorption feature in the visible wavelength region is present everywhere on the surface the spectra of the bright regions compare with anhydrous nanophase ferric oxides terrains with water bearing minerals cover a very small fraction of the martian surface olivine mg rich compositions is detected in more extensive regions of the pyroxene rich zones than previously reported olivine with higher iron content and or larger grain size 100 m is only detected in isolated areas the mineralogy of the northern low albedo regions is discussed in the light of these mineral maps chemical alteration or oxidation during extrusion producing a coating or varnish of anhydrous ferric phases over a dark basaltic surface best accounts for the vnir spectral properties of these regions although a glassy composition resulting from impact is also considered

some observations of wave current interaction abstract using data collected during the scawvex project the effect of depth and current changes particularly tidal on waves and the effect of waves on tidal currents were examined the possible interaction mechanisms between waves tides and surges are reviewed these include the effective surface wind stress bottom friction depth and current refraction and modulation of the absolute and relative wave period the usefulness of tidal periodicity in identifying both interactions in wave parameters and the effects of the waves on the tide is noted for correct analysis to obtain wave free tidal conditions or tidally averaged wave statistics it is particularly important to understand the interaction mechanisms for example the amplitude of the tidal current was found to be reduced in periods of high waves ideally waves and currents should always be measured simultaneously since the correct determination of either in shallow water requires knowledge of the other various remote sensing systems which can potentially do this are discussed since the algorithms are quite complex and may depend on a good first guess the future probably lies in combining remote sensing plus modelling together with ground truth in situ data

distribution of the ices exposed near the south pole of mars using thermal emission imaging system themis temperature measurements 1 understanding the present and past water cycle on mars requires an accurate knowledge of the distribution and amount of h2o available near the surface in this article we present a map of the distribution of the surface material exposed between 87 s and 70 s in the summer e g co2 and h2o ices dust based on temperature measurements made by thermal emission imaging system themis our compositional map 100 m per pixel is in good agreement with spectral mapping returned by observatoire pour la mineralogie l eau la glace et l activite omega and compact reconnaissance imaging spectrometer for mars crism exposed water ice covers a total surface area of approximately 40 000 km2 a large fraction of the water ice is exposed at the periphery of the co2 cap an approximately 25 000 km2 large patch centered at 83 5 s and 345 e is discovered and represents the largest exposure of water ice in the southern hemisphere it is not located on the south polar layered deposits but on the surrounding mantled terrains themis vis moc and hirise images indicate that the surface roughness of exposed water ice terrains is typically lower than that of the surrounding dust polygonal patterns are observed on the water ice but not exclusively there is a strong correlation between the surface albedo the composition of the exposed material and the timing of the initial seasonal co2 frost deposition and final removal these exposed water ice outcrops are not stable in the present environment and lose a vertical layer of tens to hundreds of micrometer a year to the atmosphere the spike of water vapor above the south pole during the southern summer occurs while the water ice is still covered by a layer of seasonal co2 frost indicating that the sublimation of the exposed water ice is not the main contributor of vapor for the southern atmosphere as water ice is not stable it may indicate the past location of part of the co2 perennial cap that has been eroded

insights into complex layered ejecta emplacement and subsurface stratigraphy in chryse planitia mars through an analysis of themis brightness temperature data layered ejecta craters on mars have been interpreted to indicate the presence of volatiles in the substrate making them important targets for the investigation of sites of astrobiological significance if the ejecta are associated with the presence of water in the substratum specific surface grain size trends are expected in this study we explore the distribution of grain sizes in the layered ejecta of impact craters located in chryse planitia using thermal emission imaging system themis thermal infrared data ejecta grain size trends in conjunction with ejecta mobility and lobateness values are applied to assess the degree of surface flow of the ejecta and in turn to constrain the plausible volatile abundance cohesion and fine particle content of the target materials craters with a larger fraction of small grain sizes in their ejecta showed greater ejecta mobility and lobateness consistent with a water rich and or a low cohesion target craters displaying decreasing grain size with increasing radius had smaller diameters and lower ejecta mobility and lobateness indicating only a minimal component of surface ejecta flow ejecta grain size trends varied with crater diameter from which the presence of vertical compositional stratigraphy in chryse planitia is inferred and interpreted our observations are synthesized into a number of plausible geologic scenarios for chryse planitia

mineralogy at meridiani planum from the mini tes experiment on the opportunity rover the miniature thermal emission spectrometer mini tes on opportunity investigated the mineral abundances and compositions of outcrops rocks and soils at meridiani planum coarse crystalline hematite and olivine rich basaltic sands were observed as predicted from orbital tes spectroscopy outcrops of aqueous origin are composed of 15 to 35 by volume magnesium and calcium sulfates a high silica component modeled as a combination of glass feldspar and sheet silicates 20 to 30 and hematite only minor jarosite is identified in mini tes spectra mini tes spectra show only a hematite signature in the millimeter sized spherules basaltic materials have more plagioclase than pyroxene contain olivine and are similar in inferred mineral composition to basalt mapped from orbit bounce rock is dominated by clinopyroxene and is close in inferred mineral composition to the basaltic martian meteorites bright wind streak material matches global dust waterlain rocks covered by unaltered basaltic sands suggest a change from an aqueous environment to one dominated by physical weathering

weathering of iron rich phases in simulated martian atmospheres in order to simulate the weathering of primary phases likely to occur on the martian surface metallic iron fe magnetite and pyrrhotite were aged in co 2 h 2 o or co 2 h 2 o 2 atmospheres at room temperature for 1 yr only the magnetite remained stable during experiments thus any magnetite on mars is likely to be inherited from primary bedrock whereas any metallic and most sulfide iron minerals are provided by meteoritic accretion metastable siderite neoformed from fe as well as sulfates and sulfur from pyrrhotite account for various martian in situ observations stepwise color changes are related either to changes in the relative proportions of neoformed phases or to atmosphere related changes in crystallinity rather than to fundamental mineralogical variations of iron phases goethite is the main crystalline iron bearing end product eventually associated with ferrihydrite if hematite is the actual dominant iron oxide that colors the red planet our results imply strong changes in water activities of the primary co 2 and h 2 o rich atmosphere i e evolution toward anhydrous conditions or long term evolution for goethite to further convert into hematite our experiments suggest that iron weathering may have been active until recent times and would not have required bodies of liquid water

evidence for episodic alluvial fan formation in far western terra tyrrhena mars a late noachian aged alluvial fan complex within harris crater in far western terra tyrrhena mars is comprised of two well defined source regions and associated discrete depositional lobes three fan units were recognized based on common morphological characteristics thermal properties and spectral signatures although the entire fan complex has been subjected to extensive erosional degradation the preserved morphologies record episodic fan formation and indicate the type of flow processes that occurred the bulk of the fan surface has morphology consistent with fluvial emplacement while one fan unit exhibits a rugged surface texture with boulders consistent with a debris flow this transition from fluvial to late stage debris flow s suggests a decline in available water and or change in sediment supply the thermal inertia values obtained for all three fan surface units mean values ranged from 318 to 344 j m 2 k

geologic characteristics of relatively high thermal inertia intracrater deposits in southwestern margaritifer terra mars 1 twenty one craters in southwestern margaritifer terra exhibit unusually warm interior deposits in nighttime thermal emission imaging system themis infrared images these deposits exhibit nighttime temperatures as high as 223 k and are 5 18 warmer than the surrounding plain thermal inertia values derived from thermal emission spectrometer tes data are greater for the deposits than the plains with maximum values between 455 and 675 j m 2 k 1 s 1 2 analysis of themis thermal inertia data having nearly an order of magnitude better spatial resolution shows that the deposits can have a thermal inertia as high as 1060 j m 2 k 1 s 1 2 albedo and dust cover index values suggest that both the deposits and the surrounding region are generally dust free compositional analysis with tes and themis data show that though a small number of the deposits may have isolated compositional differences the majority of the deposits have a composition similar to that of the surrounding plains the geomorphology of the craters as viewed from mars orbiter camera moc images shows that the deposits are coherent units rather than sand deposits an observation that is consistent with the relatively high thermal inertia values if these deposits are coherent rock units as the results of our study suggest possible methods of formation include emplacement of primary igneous material or lithification of sediments from surrounding terrain

evidence from opportunity s microscopic imager for water on meridiani planum the microscopic imager on the opportunity rover analyzed textures of soils and rocks at meridiani planum at a scale of 31 micrometers per pixel the uppermost millimeter of some soils is weakly cemented whereas other soils show little evidence of cohesion rock outcrops are laminated on a millimeter scale image mosaics of cross stratification suggest that some sediments were deposited by flowing water vugs in some outcrop faces are probably molds formed by dissolution of relatively soluble minerals during diagenesis microscopic images support the hypothesis that hematite rich spherules observed in outcrops and soils also formed diagenetically as concretions

in situ evidence for an ancient aqueous environment at meridiani planum mars sedimentary rocks at eagle crater in meridiani planum are composed of fine grained siliciclastic materials derived from weathering of basaltic rocks sulfate minerals including magnesium sulfate and jarosite that constitute several tens of percent of the rock by weight and hematite cross stratification observed in rock outcrops indicates eolian and aqueous transport diagenetic features include hematite rich concretions and crystal mold vugs we interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history the environmental conditions that they record include episodic inundation by shallow surface water evaporation and desiccation the geologic record at meridiani planum suggests that conditions were suitable for biological activity for a period of time in martian history