windblown sand on venus preliminary results of laboratory simulations abstract small particles and winds of sufficient strength to move them have been detected from venera and pioneer venus data and suggest the existence of aeolian processes on venus the venus wind tunnel vwt was fabricated in order to investigate the behavior of windblown particles in a simulated venusian environment preliminary results show that sand size material is readily entrained at the wind speeds detected on venus and that saltating grains achieve velocities closely matching those of the wind measurements of saltation threshold and particle flux for various particle sizes have been compared with theoretical models which were developed by extrapolation of findings from martian and terrestial simulations results are in general agreement with theory although certain discrepancies are apparent which may be attributed to experimental and or theoretical modeling procedures present findings enable a better understanding of venusian surface processes and suggest that aeolian processes are important in the geological evolution of venus

a comparative study of interior layered deposits on mars interior layered deposits ilds of the eastern valles marineris and adjacent chaos regions were analysed using high resolution imagery topography and spectral data in order to detect possible correlations we find that ilds are susceptible to erosion and weathering as proven by their shapes mesa buttes surface structures pitted fluted yardangs stair stepped morphologies at different scales and metre sized boulders and talus ilds bear hydrated sulphates consequently we conclude that aqueous conditions dominated during their formation subhorizontal layering and parallel bedding of the ilds could then indicate that deposition took place under low energy aquatic conditions their superposition on chaotic terrain suggests that they are younger than chaotic terrain and hence younger than late hesperian for the hydrated ilds which show polyhydrated on top of monohydrated sulphates we think that formation within an evaporative body is not conceivable and we assume instead that a conversion of sulphates by post formational humidity changes took place as hydrated ilds correlate well with rock fragmentation we suppose that volume changes due to water content are responsible for rock fragmentation despite the different ild settings the basic conditions during sedimentation and erosion of ilds could not have varied greatly because comparable mineralogies and morphologies are found among ilds

a geologic evaluation of thermal properties for the elysium and aeolis quadrangles of mars thermal inertias with spatial resolutions as small as 2 by 5 km were combined in a regional study of the elysium and aeolis quadrangles of mars 30 n to 30 s 180 w to 225 w the range of thermal inertias obtained was 1 14 10 3 cal cm 2 s k 1 41 84 j m 2 s k 1 with the lowest values corresponding to the elysium rise and the highest values correlating with dark patches of aeolian material in the southern highlands the thermal properties obtained from the high spatial resolution measurements are essentially identical to the results obtained from data with much poorer spatial resolution indicating a regional homogeneity of surface properties at scales greater than 5 km aeolian features both dark patches and bright materials associated with topographic obstacles such as craters have higher thermal inertias than do their surroundings other surface features do not display distinctive thermal properties even when clearly resolved from their surroundings comparison of the thermal inertias with global data sets shows a pronounced inverse correlation with albedo consistent with globally observed trends and brightnesses at red green and violet wavelengths but no prominent correlation with elevation thermal inertias for individual geologic units within the two quadrangles appear to be more strongly controlled by the location of the terrain in either the northern plains or the southern highlands than by properties intrinsic to the unit

polar margin dunes and winds on mars the approximately concentric arrangement of layered deposits and dune fields at the two martian poles may reflect a nearly steady state dispersal of material from the polar deposits data on effective surface winds from high resolution viking images combined with theory of local winds suggest that the northern dunes are in part confined to a latitude band by winds generated by their own low albedo dispersal of the dark sand from the southern polar region is not subject to this kind of feedback because the irregular topography prevents areal accumulations sufficiently extensive to produce winds

surficial properties in gale crater mars from mars odyssey themis data abstract we examine the nature of the surface layer in gale crater as determined from high resolution thermal and visible mars odyssey thermal emission imaging system themis data as well as how our conclusions compare to past analyses at themis resolution the thermal surface structure is dominated by local control thus providing us with detailed images that contain thermophysical information as well using these data sets we have created a map of the area defining units based primarily on their geomorphology as determined from the daytime thermal and visible images and then using the nighttime thermal data to interpret the nature of the surface layer within each unit seven units have been defined i partially blanketed knobby plateaus ii crater walls with terrain similar to that on the plateaus on the upper half and exposed rocky surfaces on the lower half iii v three floor units with varying combinations of bedrock and indurated and or particulate deposits vi sand sheets and vii a central mound consisting of indurated and or rocky material forming layers terraces and slides covered by particulate material that tapers in thickness downslope additionally dozens of channels have been observed on the crater walls and central mound the results indicate that aeolian processes have played a major role in shaping much of the present surface layer within gale and may still be active today because of the dramatic size and structure of gale the winds are most likely controlled by the local topography additionally the presence and frequency of channels within gale bolster hypotheses involving aqueous episodes in the history of the crater

compositional heterogeneity of the ancient martian crust analysis of ares vallis bedrock with themis and tes data 1 themis multispectral and thermophysical information combined with tes hyperspectral and albedo data is used as a powerful high spectral spatial resolution tool to investigate the mineralogic heterogeneity of ancient martian crust exposed in ares vallis bedrock three major spectral units are present in the upper ares vallis region 1 a regional unit that is composed primarily of a high silica si o 0 35 component with lesser amounts of plagioclase and pyroxene and is associated with channel wall rock and surrounding plains 2 a pyroxene and olivine rich rock unit exposed as a 250 m thick contiguous layer in the wall rock of ares vallis as well as in isolated exposures in the plains outside of the channel and 3 a unit composed of plagioclase pyroxene and lesser high silica component s si o 0 35 that primarily occurs as low albedo sand the spatial and stratigraphic distribution of these units suggests that the pyroxene and olivine enriched unit may be extrusive and or intrusive in origin indicating that this region experienced either a single stage or repeated episodes of olivine enriched magmatism during the first 1 5 gyr of crust formation this olivine enrichment may have been caused by a larger degree of mantle partial melting facilitated by higher mantle temperature melting from a more depleted mantle source and or less olivine fractionation relative to regional rock parent magmas the olivine rich unit is similar in thermophysical character to previously published olivine bearing terrains on mars but the derived modal mineralogy consists of 20 more pyroxene and less plagioclase than those terrains

hellas planitia mars site of net dust erosion and implications for the nature of basin floor deposits hellas planitia located within an enclosed basin which includes the lowest topography on mars appears to be undergoing net erosion dust is removed from the basin it probably contributes to global dust storms and should leave behind a coarse lag the particle size distributions and particularly the rock or boulder populations in this lag might be useful for distinguishing between processes which formed the lithologic units that comprise hellas planitia this report concludes that the abundance of rock particles larger than coarse sand is very low although this hypothesis awaits confirmation from forthcoming spacecraft data the origins for hellas floor deposits favored by this study are indurated volcanic airfall or ancient loess lacustrine deposits and some types of volcanic mud flows the conclusions of this study tend to disfavor such geologic processes as blocky lava flows glacial deposits e g moraines or boulder laden catastrophic flood outwash

on the origin of gypsum in the mars north polar region 1 we describe the distribution and concentration of the largest martian gypsum deposit discovered to date by the mars express omega observatoire pour le mineralogie l eau les glaces et l activite imaging spectrometer its relationship to the late amazonian aged north polar dunes in which it is found and its likely origin gypsum has not been discovered anywhere within the north polar region outside of the olympia undae dune sea in the areas of highest gypsum a concentration 35 pure gypsum grains of a few tens of micrometers in size mixed with 65 millimeter sized gypsum grains containing dark spectrally featureless inclusions best fit the omega observations the gypsum rich dunes contain no significant average albedo temperature or morphological anomalies we propose that water emanating from nearby channels carved during melting of the polar layered deposits infiltrated the eastern end of the polar dune sea percolating through the dunes deposits of gypsum resulted from a combination of direct in situ alteration of sulfide and high calcium pyroxene bearing dunes and from formation of evaporitic gypsum crystals in the pore spaces of these dunes this gypsum deposit formed in a unique local environment and is disconnected from sulfate forming events elsewhere on mars which are thought to have occurred much earlier during the late noachian and hesperian by various means sulfates have not been discovered in any other collection of dunes on mars

thermal behavior and ice table depth within the north polar erg of mars abstract we fully resolve a long standing thermal discrepancy concerning the north polar erg of mars several recent studies have shown that the erg s thermal properties are consistent with normal basaltic sand overlying shallow ground ice or ice cemented sand our findings bolster that conclusion by thoroughly characterizing the thermal behavior of the erg demonstrating that other likely forms of physical heterogeneity play only a minor role and obviating the need to invoke exotic materials thermal inertia as calculated from orbital temperature observations of the dunes has previously been found to be more consistent with dust sized materials than with sand since theory and laboratory data show that dunes will only form out of sand sized particles exotic sand sized agglomerations of dust have been invoked to explain the low values of thermal inertia however the polar dunes exhibit the same darker appearance and color as that of dunes found elsewhere on the planet that have thermal inertia consistent with normal sand sized basaltic grains whereas martian dust deposits are generally lighter and redder the alternative explanation for the discrepancy as a thermal effect of a shallow ice table is supported by our analysis of observations from the mars global surveyor thermal emission spectrometer and the mars odyssey thermal emission imaging system and by forward modeling of physical heterogeneity in addition our results exclude a uniform composition of dark dust sized materials and they show that the thermal effects of the dune slopes and bright interdune materials evident in high resolution images cannot account for the erg s thermal behavior

quantitative compositional analysis of martian mafic regions using the mex omega reflectance data 2 petrological implications abstract the primary objectives of this paper are to determine the modal mineralogy of selected low albedo terrains of different ages ranging from noachian to amazonian exposed on the surface of mars this analysis is conducted using the spectral modeling of the observatoire pour la mineralogie l eau les glaces et l activite omega reflectance data results from this work are consistent with the major results of previous spectroscopic studies plagioclase 40 60 in volume and high calcium pyroxene 20 40 hcp are the dominant minerals of the most regions low calcium pyroxene 10 15 lcp and minor amounts of olivine are also present the oldest terrains are characterized by the largest amount of lcp and the lowest concentration of plagioclase these overall compositions are consistent with two pyroxene basalts the particle sizes are in the range of a few hundreds of micrometers which is in good agreement with the thermal inertia of the martian low albedo regions in the region around the nili fossae localized concentrations of olivine up to 40 with millimeter particle size similar to picritic basalts observed in situ by the spirit rover in the gusev crater are inferred chemical compositions are calculated for the first time from omega spectra they are quite consistent with gusev rocks and shergottite compositions but they appear to be significantly sio2 poorer than thermal emission spectrometer data a decreasing low calcium pyroxene abundance with the decreasing age of the low albedo regions is reported this may be indicative of decreasing degree of partial melting as thermal flux decreases with time we propose that the ancient noachian aged lcp rich terrains could have been formed from h2o bearing melts then dry basaltic volcanism occurred leading to decreasing lcp abundance with time due to decreasing degree of partial melting the olivine bearing material modeled in nili fossae resembles the composition of alh77005 and chassigny meteorites consistent with prior studies implications on the formation of the basaltic shergottites are discussed

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

aeolian processes and dune morphology in gale crater abstract datasets at resolutions many times greater than previously available were used to study aeolian features within gale crater high resolution thermal inertia data allowed for detailed particle size estimation with the data sufficient to resolve dunefields a wide range of grain sizes have now been identified in the gale crater dunefields ranging from medium to very coarse sand high resolution imaging science experiment hirise and themis vis data allowed for detailed analysis of the dune morphology and slip faces which shows that the dunes have responded to topographic influences on prevailing wind directions under a present day wind regime this result was corroborated by a regional mesoscale model for the crater under dust storm conditions the central mound and smaller scale crater floor topography has altered the prevailing wind regime and dune patterns aeolian activity has thus played and continues to play an important role in shaping many of the present surface features of gale crater the arrival of a future lander mission such as the mars science laboratory would be able to sample these surface features directly and add a wealth of data to the understanding of gale crater

spectral and petrologic analyses of basaltic sands in ka u desert hawaii implications for the dark dunes on mars dark aeolian bedforms on mars are thought to consist of volcanic materials due to their mineral assemblages which are common to basalts however the sediment source is still debated and needs further affirmation basaltic dunes on earth are rare and can only be found in a few places including new zealand iceland the western usa peru and hawaii these dunes composed of volcaniclastic sediments are promising analogues for providing further insights into the assumed basaltic sand dunes on mars in our study we use basaltic dunes sands collected in hawaii s ka u desert which are especially interesting for addressing the source of martian dunes because of the co occurrence of active volcanic processes and dune development for these dunes we could prove that their material has been derived from airfall ashes from phreatomagmatic eruptions of kilaulea and reworked lava basaltic dunes sand from arizona builds a second set of terrestrial analogue samples in our study these sands have been collected from aeolian bedforms that are composed of reworked volcanic ash erupted from nearby sinter cones spectral analyses of the terrestrial samples show that the dune sands are enriched in pyroxene and olivine a basaltic composition similar to that of the martian dark dunes microprobe analyses show that the terrestrial sands are dominated by olivine pyroxene plagioclase and glasses resulting from the volcanic source of these aeolian sediments this result is consistent with modal mineralogy modeling of martian dunes sands these correlations prove the hypothesis of a similar origin of the martian and terrestrial dune sands consistent with reworked volcanic ash and lava

age relationship of basaltic and andesitic surface compositions on mars analysis of high resolution tes observations of the northern hemisphere 1 previous mars global surveyor thermal emission spectrometer tes results have identified two principal surface compositions on mars basaltic surfaces are found primarily in the southern highlands while andesitic surfaces are found in the northern lowlands and in smaller concentrations distributed throughout the southern highlands in 1 pixel per degree composition maps the exact boundary between the basaltic and andesitic compositions is obscured by large amounts of equatorial surface dust in this work high resolution tes surface spectral data are used to identify and characterize isolated regions of basalt within the equatorial dust regions and northern lowlands generally between 20 s 60 n 0 360 w in an effort to better understand the nature of the boundary between the two compositions the purpose of refining this boundary is to more accurately determine the relationship of the compositional dichotomy with global surface morphology and derived crustal thickness results show that the basaltic surface composition is closely associated with the ancient cratered terrain morphology but is not well correlated with crustal thickness the northern extent of the tes basalt composition is also established with four exceptions there are no significant concentrations 30 surface cover of basalt greater than 400 km2 in area within the northern plains three are located within or adjacent to knobby terrain which has been suggested to be erosional remnants of the cratered highlands the fourth exception is in milankovic crater and may represent a local basalt flow or basaltic material excavated during crater formation results from this work suggest that there is a stratigraphic relationship between the basaltic and andesitic surface compositions with younger andesitic materials overlying older basaltic materials throughout the equatorial and northern plains regions

the influence of local topography for wind direction on mars two examples of dune fields in crater basins in this work we perform an analysis of large dark dunes within moreux crater and herschel crater on mars using high resolution imaging science experiment hirise and context camera ctx data sets these data allow us to conduct a detailed analysis of dune morphology and slip faces concluding that the studied dune fields are influenced by topographically controlled complex wind directions our morphological analysis reveals that inside moreux crater in particular the topographic setting dominates the wind flow direction leading to the development of a sand transport pathway encircling the central peak of the crater the dune fields in herschel crater are also affected by winds controlled by variable topography as suggested by the presence of complex dunes and dune fields our analysis indicate that the studied dune systems is not the result of paleo wind regimes furthermore we perform thermal inertia measurements using thermal emission spectrometer tes data which indicate that the studied dune fields consist of medium sand 250 500 mm in diameter

thermal properties of sand from thermal emission spectrometer tes and thermal emission imaging system themis spatial variations within the proctor crater dune field on mars 1 thermal inertia a parameter calculated from surface temperatures obtained from spacecraft has long been used to quantify the amount of loose fine grained material on the martian surface with little ground truth available studies often refer to martian dune fields to calibrate thermal inertias the well understood physical properties of dune sand make it an ideal basis for comparison to more complex surfaces however higher resolution data sets available from the tes thermal emission spectrometer onboard mars global surveyor and themis thermal emission imaging system onboard mars odyssey show spatial variations in the thermal properties within dune fields calling into question their effectiveness as controls for thermal inertia studies in order to explain these variations we apply a thermal model developed for tes data to a commonly investigated dune field in noachis terra that on the floor of proctor crater we show that in this dune field the thermal variations on the scale of 30 j m 2 s 0 5 k 1 are present and correlate spatially with aeolian features in the dune field these variations correspond to three types of surfaces observed in the mars orbital camera narrow angle moc na images 1 dune sand 2 interdunes exposing the surface underlying the dune field and 3 sand covered interdunes or dune troughs both the interdunes and the dune troughs have cooler nighttime temperatures than the dune sand corresponding to lower thermal inertia values the dune troughs may be sand covered areas with either minor amounts of dust accumulation or a mean sand grain size lower than that of dune sand because fine sand grains tend to preferentially accumulate on dune crests rather than in dune troughs the second hypothesis is considered less likely than the first this has implications for the recent sedimentary history of the dune field dust accumulation in dune troughs may imply that sand saltation is not prevalent enough to scour away all of the dust settling out from suspension in the atmosphere however it is prevalent enough to keep the dunes crests themselves clear of dust

the western libya montes valley system on mars evidence for episodic and multi genetic erosion events during the martian history a valley network in the western libya montes region extending from 80 e to 83 4 e and 1 2 s to 3 9 n exhibits significant detail about water release processes and duration of erosional activities the valley system originates at the southeastern offshoot of syrtis major and drains down to isidis planitia over a distance of about 300 km midstream the valley network splits into a shorter eastern and a longer western part for most of its length the valley exhibits an interior channel which allows constraining discharges ranging from 15 000 m3 s to 430 000 m3 s and yielding sediment volumes up to 250 tons s based on stratigraphic relations the valley system evolved during a period of about 2 8 billion years with major wet episodes in the noachian 4 1 ga the hesperian 3 6 to 3 0 ga and the amazonian 2 8 to 1 4 ga while precipitation dominated the fluvial activity during the noachian era as indicated by dendritic drainage pattern the close correlation of lava deposits and valley source regions suggests that volcanic processes such as ground ice melting and or hydrothermal water release might have played a major role during the hesperian and amazonian fluvial activities in addition multiple volcanic events in the hesperian and amazonian ages show that syrtis major was active at least locally until 1 4 ga ago discharge estimates demonstrate a significant increase from precipitation induced to volcanic triggered water release fluvial erosion rates discharges sediment transport rates and the lack of any widespread chemical alteration products such as sulphates and phyllosilicates that are indicative for large long lasting standing bodies of water suggest relatively short valley formation times of only a few thousands of years compared with the total age of the valley system short episodic water release events separated by long dry and inactive periods of some hundreds of millions of years at least in the hesperian and amazonian seem to be more realistic rather than a continuous flow the youngest channel segment dates back to less than 1 4 ga this indicates the presence of surface runoff at that time which required atmospheric conditions that support water to be stable on the surface even late in martian history in summary the western libya montes valley system demonstrates episodic and multi genetic erosion events over most of the martian history with a clear change in the erosion style from precipitation to volcanic triggered water release during the early hesperian

a martian general circulation experiment with large topography abstract a three layer general circulation model used to simulate the martian atmosphere is described and results are presented the model assumes a dust free pure c02 atmosphere and allows for a diurnally varying convective boundary layer smoothed martian topography and albedo variations are incorporated the simulation described is for the period near southern winter solstice season of the viking landings the zonally averaged circulation mass heat and momentum balances and properties of stationary and transient waves are described in some detail and are compared with results of previous simulations of the martian general circulation with related features of the earth s general circulation and with observed characteristics of the martian atmosphere the principal conclusions are the following 1 the simulated zonally averaged circulation is not very sensitive to differences between this model and the earlier general circulation model of leovy and mintz 1969 and compares reasonably well wi

volcanic sands of iceland diverse origins of aeolian sand deposits revealed at dyngjusandur and lambahraun the origin formation and evolution of volcanic sands are less well known than the formation of the much more common quartz rich sand sheets combining active volcanism and a cold climate iceland is covered for about 21 of its surface by sandy areas the sands were analyzed in detail at two sites and results reveal their diverse origins the first site is dyngjusandur located north of vatnajokull and the second site is the lambahraun area located south of langjokull at both sites the sand origin is determined from field observations wind directions from ventifacts chemical and mineralogical analyses of rocks and sands at dyngjusandur the sand is dominated by glass grains a situation typical of sand plains in iceland hyaloclastite ridges presently buried beneath vatnajokull are the dominant source of the sand and only large size plagioclase crystals 0 5 cm in sands seem to be derived from the lava flows hyaloclastite ridges were crushed by glaciers and mechanically eroded sediments were washed out by melt water onto flood plains the sand chemical composition is spatially homogeneous and similar to the average composition of neighboring sub aerial lava flows reflecting efficient mixing of distinct sources below the glacier the presence of sand north of dyngjujokull can be taken as a way to explore the average chemical composition of non exposed volcanic material beneath the glacier in the case of lambahraun prevailing winds indicate several potential sources of sand at the north of the sand sheet comparison of chemical and mineralogical analyses of sands and rock samples helped to refine the exact origin in contrast with the first site the sand is dominated by crystals and is chemically consistent with a mixture of material derived from the lava flows of eldborgir and skersli shield volcanoes analysis of the contact between the lava flows and the glacier reveals that basaltic sand grains formed as the result of recent advances of the glacier abrading the rocks the direct interaction of glacial and fluvio glacial activity with basaltic plains appears to be necessary to produce a large amount of sands in a relatively short period of time 4000years this site appears to be an excellent natural laboratory for further studies concerning the sand evolution and physical sorting processes in basaltic material which have important implications for understanding aeolian processes on mars copyright c 2011 john wiley sons ltd

convection in a catastrophic flood deposit as the mechanism for the giant polygons on mars a formational mechanism for the large scale polygons that are defined by intersecting fractures in the northern plains of mars is proposed in this work the presented model is based on rayleigh convection of interstitial water driven by an unstable density temperature gradient within a saturated porous medium catastrophic emplacement of water rich sediments into the martian northern plain basins could have provided a thick sedimentary layer in which rayleigh convection could have occurred convection within this active layer is proposed to have differentially thawed an underlying ice rich permafrost layer that had been at the planet s surface before being rapidly buried the resulting morphology of the permafrost subsurface is thought to have resembled the scalloped solid liquid interface morphology produced in terrestrial convective flow visualization studies the exact size and shape of the scallops on the frozen subsurface would have been controlled by the dimensions of the convection cells which are estimated to have had width to depth ratios of between 3 4 and 4 5 subsequent stresses e g gravity and bending stresses would have produced maximum tensile stresses in the overlying sediments preferentially above the subsurface topographic highs as described previously by mcgill and hills 1992 additional desiccation of the sediments would have required contraction of the sediment cover and would have produced large scale polygonal fractures along the preexisting weaknesses located above the raised subsurface topography thus the underlying subsurface geometric morphology would have been translated to the surface and would be represented by the large scale polygonal fractures visible in the viking orbiter and mars global surveyor images of the martian northern plains

surface textures and dynamics of the 2005 lava dome at shiveluch volcano kamchatka shiveluch is one of the largest and most active andesitic volcanoes of the kuril kamchatka arc it commonly alternates between vulcanian explosive eruptions and periods of dome growth and subsequent dome collapse driven block and ash flows the volcano was in an extended period of heightened activity for most of the period 2004 2010 we examined this activity in detail using thermal infrared tir remote sensing as part of the urgent request protocol urp program of the advanced spaceborne thermal emission and reflection radiometer aster instrument and confirmed the results with ground based photography and airborne tir camera data high spatial resolution tir images were collected during both daytime and nighttime satellite overpasses prior to and following the large explosive event eruption of 27 february 2005 and the dome growth that followed during a field campaign in august 2005 a helicopter overflight designed to acquire visible and tir data of the active dome was performed this was a nadir looking low altitude overflight and the first ever of shiveluch volcano involving non russian scientists the image data revealed an active crease structure in the center of the dome with a distinctly different crescent shaped high temperature 380 c zone roughly perpendicular to the crease in order to provide a time context and estimate extrusion rates the airborne data were compared to the spaceborne aster data and long distance ground based photography of the dome acquired by our russian colleagues the presence of a crease structure and the complex thermal pattern on the surface were both unexpected discoveries that reveal the way in which exogenous dome growth was occurring at the time this highly active period at shiveluch provides a unique example to better understand silicic lava dome growth using tir data the results also demonstrate a straightforward approach for fusing ground air and spaceborne image data which could be applied to other active domes around the world

global mineral distributions on mars 1 determining the mineralogy of mars is an essential part of revealing the conditions of the surface and subsurface a deconvolution method was used to remove atmospheric components and determine surface mineralogy from thermal emission spectrometer data at 1 pixel per degree ppd minerals are grouped into categories on the basis of compositional and spectral similarity and global concentration maps are produced all binned pixels are fit well with rms errors of 0 005 in emissivity higher rms errors are attributed to short wavelength particle size effects on dust covered surfaces significant concentrations 0 10 of plagioclase high ca pyroxene sheet silicates high si glass and hematite are detected and display distributions consistent with previous studies elevated concentrations of plagioclase and high ca pyroxene are consistent with basaltic surfaces and are located in low albedo highlands regions north of 45 s significant concentrations of plagioclase and sheet silicates high si glass and low concentrations of high ca pyroxenes are consistent with andesitic surfaces and are concentrated in both southern and northern high latitude low albedo regions andesitic surfaces in the southern hemisphere have a lower spectral contrast than northern surfaces an isolated surface located in solis planum is spectrally distinct but compositionally similar to other surfaces interpreted to be andesitic in composition concentrations of olivine below the detection limit correctly identify its presence in two of three locations potassium feldspar low ca pyroxene basaltic glass olivine sulfate carbonate quartz and amphibole are not detected with confidence at 1 ppd the results presented here indicate a predominance of volcanic compositions within martian dust free surfaces

spectroscopic study of the moses lake dune field washington determination of compositional distributions and source lithologies 1 source lithologies and transport histories of materials within the ephrata fan are investigated data were collected using a variety of remote sensing laboratory spectroscopic and field observations and techniques laboratory thermal emission spectra were collected of bedrock within the grand coulee dune samples and clast deposits factor analysis target transformation and end member recovery techniques were applied to the set of dune samples as well as a set of grain size fractions the dune sample spectra are composed of three components that represent basalt granodiorite and clay compositions the basalt and granodiorite components are similar to spectra of clast and bedrock samples from the grand coulee and the ephrata fan the clay component is similar to weathering surfaces located within the dune field the same components were recovered from the set of grain size fractions from a single dune sample demonstrating a relatively higher basalt concentration with grain sizes greater than 250 m thermal infrared multispectral scanner tims data display significant intradune compositional variation and no discernable interdune compositional variation indicating that the basalt and granodiorite components were likely deposited simultaneously and subsequently separated by wind based on grain size basalt and granodiorite bedrock units within the channeled scablands are source materials for the deposits within the ephrata fan and moses lake dune field the columbia river located 20 km west of the dune field is not a likely source of material

variation in particle size distribution over a small dune the variation in particle size distribution for a sequence of sand samples collected from the surface of a small barchanoid dune along a sampling line parallel to the windflow is studied by means of the hyperbolic distribution the modal or typical value of the log size increases linearly with distance from the windward foot to the crest of the dune and falls off steeply on the lee side the spread of the log size distribution locally near the modal value is roughly constant on the windward side but decreases significantly down the slip face two other parameters of the four parameter hyperbolic distribution can be considered largely constant a comparison of the log size distributions for heavy and light mineral grains based on a selected set of the samples showed that heavy and light minerals follow different hyperbolic patterns however the difference in modal size of the distributions for the two types of minerals was virtually constant among the samples

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

dust transport and the question of desert loess formation although contemporary dust storms are frequent in arid and semi arid areas desert loess deposits are poorly developed much of the world s loess occurs in mid latitude areas which experienced glaciation during the pleistocene ocean core evidence indicates that dust transport from sub tropical deserts increased during cold stages of the pleistocene but loess formed only on certain desert margins for reasons which have not been fully explained this paper re examines the mechanisms of dust transport and deposition and the circumstances leading to the accumulation of thick loess typical loess is composed mainly of medium silt grains which are transported in short term suspension a few metres above the ground significant thicknesses of loess form only when dust is trapped within a limited area often relatively close to the source dust particles finer than 20 m are transported mainly in long term suspension over a greater height range and may be widely dispersed the availability of silt and the frequency magnitude and direction of dust transporting winds are important factors governing the potential for loess formation but the existence of a suitable dust trap is particularly important traps may be formed by topographic obstacles areas of moist ground or vegetated surfaces vegetation adjacent to glacial outwash plains and braided meltwater streams trapped dust in mid latitudes during the pleistocene dust blown during glacial periods from certain deserts notably in sinai soviet central asia and china accumulated as loess in neighbouring semi arid regions on the margins of other deserts loess formation was inhibited partly by the absence of vegetation traps during most of the holocene net dust deposition rates in all desert marginal areas have been too low for significant loess accumulation this is mainly due to a reduction in silt availability and a tendency towards landscape stability reported dust storm frequencies during the past 50 years over estimate the longer term holocene dust flux due to the effects of human activities much modern dust owes its origin to erosion of cultivated soils in semi arid areas and is finer than typical loess

eolianite grain size distributions as a proxy for large changes in planetary atmospheric density a digitized version of the ahlbrandt 1979 global dune dataset and data for distributions in figure are available at https github com erikgoosmann aeoliandata

high resolution investigations of transverse aeolian ridges on mars abstract transverse aeolian ridges tars are the most pervasive aeolian feature on mars their small size requires high resolution data for thorough analyses we have utilized mars reconnaissance orbiter mro context camera ctx and high resolution image stereo experiment hirise images along with mro compact reconnaissance imaging spectrometer for mars crism spectroscopic data to study tars in detail tar deposits along with related dark dune material and layered terrains have been mapped in six study areas in order to identify sediment pathways and determine whether tars are sourced locally or from global wind borne materials tar morphology and orientation were mapped in grids within each study area the results show that tars are probably locally sourced we constructed four hirise digital terrain models dtms to measure tar heights widths spacing areas symmetry and to calculate sediment volumes results show that tars have average heights of 1 5 m are very symmetrical and are similar in form to terrestrial megaripples orthorectified hirise images taken 3 years apart were analyzed for tar movement and none was found superposed craters on equatorial tars give ages of 2 ma suggesting that these are relatively ancient and generally inactive aeolian deposits crism data were analyzed over tar deposits dark dune material and light toned terrains although the surfaces were somewhat obscured by dust cover the results did not show any remarkable difference between tars and other deposits we conclude that tars may be sourced from local materials and form in a similar way to terrestrial megaripples

segregation of olivine grains in volcanic sands in iceland and implications for mars abstract basaltic sands cover several plains in volcanic regions on earth and dominate the aeolian sediments on mars but basaltic sands are not as well characterized as felsic sands the lambahraun sandy lava plain in iceland was chosen as a martian analog to study the physical sorting of basaltic sands the strong winds affecting the plain and its young age

spatial resolution and the geologic interpretation of martian morphology implications for subsurface volatiles abstract viking orbiter images of mars provide global coverage of the major geologic and tectonic provinces on the planet however only a fraction of the orbiter images are useful for assessing the processes responsible for the generation or modification of surface landforms an example from acheron fossae illustrates that aeolian dunes visible at 9 m pixel resolution are indistinguishable at 57 m pixel resolution dunes in acheron fossae valleys lend support to an aeolian interpretation for lineated valley fill at this location this result provides an alternative hypothesis for the proposed ice rich interpretation of this terrain consequently it seems unlikely that images with a spatial resolution 50 m pixel can provide strong constraints on the relative importance of various geologic processes that have acted upon the surface a survey of the best viking orbiter images with

evidence of ancient continental glaciation in the martian northern plains whorled ridges spaced about 2 6 km and forming lobate patterns with lobe widths of about 150 km occur at many locations in the northern plains of mars commonly in close association with sinuous troughs that contain medial ridges these landforms resemble moraines tunnel channels and eskers found in terrestrial glacial terrains such as the midcontinent of north america some martian landscapes may have formed by disintegration of continental glaciers that covered much of the northern plains into the early amazonian i e late in martian geologic history meltwater processes apparently were important in the collapse of these hypothesized ice sheets hence the glaciers apparently were wet based in part whereas striking similarities exist among areas of the northern plains and some glaciated pleistocene terrains on earth there are also important differences notably drumlin fields such as those in many glacial landscapes on earth are rare absent or not yet resolved in images of the martian northern plains another major difference is that postglacial fluvial and other water related modifications especially erosion of pleistocene terrains are substantial but similar modifications are not observed in the northern plains a virtually complete and sudden decline in the activity of liquid surface water following glaciation in the northern plains seems to be implied the climatic implications of the hypothesized martian glaciers and their decline are unclear we investigate two possibilities alternatively involving a relatively warm paleoclimate and the modern martian climate the hypothesized ice sheets in the basins within the northern plains generally at elevations lower than 1 km suggest a relationship of these frozen bodies of water with former regional lakes or seas which may have formed in response to huge discharges of water from martian outflow channels this possible relationship has been modeled glaciers may have evolved from seas by their progressive freezing and then grounding and sublimational redistribution of sea ice the transition to glaciation may have taken several million years if the climate was very cold comparable to today s or tens of thousands of years if the climate was as warm as modern antarctica a glacierized sea may have involved an extended period of glaciolacustrine and ice shelf processes

radar measurement of small scale surface texture syrtis major recent radar observations of syrtis major have shown it to be smooth and relatively homogeneous when sensed at centimeter wavelengths there is a gradual decrease in surface roughness east to west across the basin which correlates with an apparent decrease in small 1 km diameter crater density root mean square surface slopes range from more than 1 5 2 0 in the east to less than 0 5 along the western margin at 12 6 cm the surface appears somewhat rougher at 3 6 cm a 0 3 dependence is inferred radar reflectivity increases from about 5 to about 12 across syrtis major being greatest near the western margin high resolution 8 to 20 m pixel viking images suggest that an increasing amount of resurfacing has occurred in western syrtis major compared with the eastern parts the radar infrared and optical imaing evidence are consistent with resurfacing by geologically recent low viscosity lavas which were subsequently mantled by thin layers of aeolian material each data set may be taken as a unique source of scale dependent information on surface materials and properties from comparison of radar derived surface roughness with image derived crater density curves we conclude that processes other than cratering control the surface texture on 0 03 to 100 m surface scales

aeolian dunes as evidence for explosive volcanism in the tharsis region of mars two transverse dune fields occur among late amazonian volcanic and aeolian landforms in southwestern tharsis mars the first is located 70 km northwest of biblis patera around 5 n 125 w the second is located about 500 km northwest of arsia mons at 2 s 130 w the latter is the largest dune field thus far documented to occur in the equatorial latitudes of mars unlike other dunes on the planet both dune fields in tharsis have low thermal inertias 2 7 10 3cal cm 2sec 0 5k 1 and high albedos 0 26 that are indistinct from their surrounding terrain both dune fields have superposed features such as impact craters lava flows smooth surfaced units and bright wind streaks the dune fields therefore appear to be inactive and mantled by fine grained material i e particles 60 m to form aeolian dunes require a supply of sand on earth most dune sands are supplied by fluvial and littoral processes but this is not the case in tharsis on mars because they are superposed on a late amazonian surface the climate is assumed to have been hyper arid throughout the time that the dunes have existed under these conditions the only plausible source for quantities of sediment sufficient to form transverse dune fields is explosive volcanism therefore the two dune fields in tharsis are evidence that explosive volcanism has occurred in this region in the late amazonian epoch

downslope sediment transport by boiling liquid water under mars like conditions experiments and potential implications for martian gullies gullies are widespread morphological features on mars for which current changes have been observed liquid water has been one of the potential mechanisms to explain their formation and activity however under present day martian conditions liquid water is unstable and should only be transiently present in small amounts at the surface yet little attention has been paid to the mechanisms by which unstable water transports sediment under low atmospheric pressure here we present the results of laboratory experiments studying the interaction between liquid water owing over a sand bed under mars like atmospheric pressure c 9 mbar the experiments were performed in a mars simulation chamber at the open university uk in which we placed a test bed of ne sand at a 25 slope we chose to investigate the in uence of two parameters the temperature of the water and the temperature of the sand we performed 27 experiments with nine different combinations of water and sand temperatures ranging from 278 to 297 k under all experimental conditions the water was boiling we investigated and compared the types and timing of sediment transport events and the shapes characteristics and volumes of the resulting morphologies in agreement with previous laboratory studies we found that more intense boiling increased the volume of sediment transported for a given volume of water we found four main types of sediment transport entrainment by overland ow grain ejection grain avalanches and levitation of saturated sand pellets our results showed that increasing sand temperature was the main driving parameter in increasing the sand transport and in modifying the dominant sediment transport mechanism the temperature of the water played a negligible or minor role apart from the duration of sand ejection and avalanches which lasted longer at low water temperature at low sand temperature the majority of the sand was transported by overland ow of the liquid water at higher sand temperatures the transport was dominated by processes triggered by the boiling behaviour of the water at the highest temperatures sediment transport was dominated by the formation of levitating pellets dry avalanches and ejection of the sand grains this resulted in a transport volume about nine times greater at a sand temperature of 297 k compared with 278 k our heat transfer scaling shows that the boiling behaviour will be enhanced under martian low gravity resulting in more ef cient transport of sediment by levitating sand pellets even at temperatures close to the triple point our results showed that the boiling intensity played an important role in the physics of sediment transport by liquid water this implied that the amount of water required to produce morphological changes at the surface of mars could be lower than previously estimated by assuming stable liquid water boiling is a critical process to be considered when assessing gully formation and modi cation mechanisms mobilized by liquid water our work could have similar implications for any water formed landform on mars which could include recurring slope lineae dark dune ows and slope streaks

quantitative compositional analysis of martian mafic regions using the mex omega reflectance data 1 methodology uncertainties and examples of application abstract the mars express observatoire pour la mineralogie l eau les glaces et l activite omega collected an unprecedented visible and near infrared hyperspectral dataset covering the low albedo regions of mars we investigate the ability to infer modal abundance of surfaces of these regions from a radiative transfer model developed by shkuratov et al shkuratov y starukhina l hoffmann h arnold g 1999 icarus 137 235 246 and adapted to basaltic surfaces by poulet and erard poulet f erard s 2004 j geophys res 109 e2 doi 10 1029 2003je002179 from omega measurements of mafic surfaces we develop several sensitivity tests to assess the extent to which the model can be applied to predict pyroxene composition high calcium phase and low calcium phase abundance of almost neutral components plagioclase in the near infrared wavelength as well as grain sizes by using a library of selected end members results of the sensitivity tests indicate that the scattering model can estimate both abundances and grain sizes of major basaltic materials of low albedo regions within uncertainties 5 to 15 vol the model is then applied to data from dissected cratered terrains located in terra meridiani the derived grain size including uncertainties is in the 50 500 m range this is consistent with the thermal inertia and albedo of this region which indicates a fine sand sized surface with little dust the abundances of plagioclase 43 57 and pyroxenes 35 45 10 including 11 5 of low calcium phase are in good agreement with previous basalt like compositions of low albedo regions from thermal infrared spectral measurements the method presented in this paper will provide a valuable tool for evaluating the modal mineralogy of other mafic regions of mars observed in the near infrared wavelength range

martian north polar hazes and surface ice results from the viking survey completion mission viking infrared observations of the martian north polar regions taken during the 1979 1980 viking survey completion mission have been used to determine the location and nature of the retreating polar cap edge and of an accompanying atmospheric ice haze the haze is composed of water ice and its visible opacity is approximately unity equivalent to 1 2 precipitable microns of water ice during the polar cap retreat aerocentric longitude ls 340 60 the haze is nearly always present and extends from at most a few degrees south of the polar cap edge to an undetermined distance over the cap interior the transition from ice free ground to a predominantly ice covered surface at the cap edge spans 5 10 of latitude the ability of the viking infrared observations to distinguish haze from surface condensate yields a more accurate seasonal regression for the polar cap than can be determined from visual images generally the infrared observations presented here yield a regression similar to those determined from earth based and or spacecraft visual data for the same and for previous northern springs however there are differences concerning details of the cap retreat the thermal data indicate that the martian seasonal polar cap did extend south of 60 n during this particular late winter and that the midspring resumption of the cap retreat occurs at ls 50

surface properties of the pettit wind streak on mars implications for sediment transport abstract pettit crater 12 n 174 w is associated with a complex wind streak consisting of both type i bright streak and type ii dark streak materials broadband albedo measurements of the streak indicate a minimum of 20 and a maximum of 32 with 27 on the surrounding plains the darkest materials have the highest thermal inertias which can be related to an effective grain diameter typical of medium sand most of the dark streak materials have thermal inertias representative of fine sand the material most easily set in motion by the wind on mars the bright portions of the streak have thermal inertias higher than that of the surrounding plains the bright streak values are representative of very fine sand differences between temperatures measured at 11 and 20 m indicate there is no difference in the areal abundance of unresolved high thermal inertia materials e g blocks bedrock between the pettit streak and the surrounding plains the dark streak material is consistent with models involving sand saltation and transport but the bright streak thermal inertia is not consistent with a volumetrically significant enhancement of unconsolidated dust in the streak

grain size variations on a longitudinal dune and a barchan dune abstract the grain size characteristics of the sand upon two dunes a 40 m high longitudinal dune in the central namib desert and a 6 0 m high barchan in the jafurah sand sea of saudi arabia vary with position on the dunes on the longitudinal dune median grain size decreases sorting improves and the grain size distributions are less skewed and more normalized toward the crest though sand at the windward toe is distinct elsewhere on the dune the changes in grain size characteristics are gradual an abrupt change in grain size and sorting near the crest as described by bagnold 1941 pp 226 229 is not well represented on this dune coarse grains remain as a lag on concave slope units and small particles are winnowed from the sand on the steepest windward slopes near the crest avalanching down slipfaces at the crest acts only as a supplementary grading mechanism on the barchan dune median grain size also decreases near the crest but sorting becomes poorer though the grain size distributions are more symmetric and more normalized the dune profile is a gaussian curve with a broad convex zone at the apex upon which topset beds had accreted prior to sampling grain size increases and sorting improves down the dune s slipface however this grading mechanism does not influence sand on the whole dune because variations in wind regime bring about different modes of dune accretion on both dunes height and morphology appear to influence significantly the grain size characteristics

present wind activity on mars relation to large latitudinally zoned sediment deposits the relation of present martian winds to large latitudinally zoned sediment deposits has been investigated using global wind streak data and mapping of large sand and dust deposits dune sand deposits occur primarily in three latitude belts north polar 74 85 degrees north low latitude 5 degrees north 20 degrees south and south polar 40 80 degrees south comparison with wind streak data shows the high latitude dunes to be in areas of seasonally reversing winds the present winds can form latitudinal dune belts from a variety of initial dune distributions including uniform distribution and a polar source the presence of dune sand within the polar layered deposits the erosional state of the deposits and the present surface wind flow away from the poles indicate that both polar dune concentrations have been derived from erosion of the layered deposits the low latitude dunes are topographically confined in canyons and craters they are probably subject to long term reversal of orientations with climate cycles

triton s streaks as windblown dust the encounter of the voyager 2 spacecraft with neptune s satellite triton revealed many dark about 10 20 darker than the adjacent frost surface streaks in triton s southern hemisphere1 resembling the streaks that are due to windblown dust on mars2 it seems therefore that dust transport by winds in triton s tenuous atmosphere is required the main question being the mechanism for raising dust from the surface or sub surface the two obvious candidates are geyser like eruptions and direct lofting by surface winds1 here we show that despite triton s tenuous 16 3 bar atmosphere3 low cohesion grains with diameters of 5 m may be carried into suspension by aeolian surface shear stress given expected geostrophic wind speeds4 of l0ms 1 the wind velocities needed to lift grains as cohesive as those found on earth however are implausibly high for erupting plumes we show that dust settling timescales and expected wind velocities yield streak length scales in good agreement with those observed both candidate mechanisms therefore seem to be consistent with present observations of triton

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

evidence for locally derived ultramafic intracrater materials in amazonis planitia mars 1 we studied a dark intracrater feature in amazonis planitia using visible thermal and spectral data from the mars global surveyor mgs thermal emission spectrometer tes mgs mars orbiter camera moc and 2001 mars odyssey thermal emission imaging system ody themis instruments visible and thermal data indicate that there are heterogeneities within the dark feature at meter to kilometer scales and suggest that it represents eroded terrain containing inactive ripple like bed forms possibly armored or indurated as well as loose possibly actively saltating sediment in addition part of the dark intracrater material may be covered with dust either as an optically thin few microns thick layer or as thicker discontinuous patches the thermal properties of the dark material are consistent with a mixture of sand rock and bedrock whereas the rest of the crater floor has thermal characteristics of fine 35 m particulates spectral data indicate that the crater floor is covered by a layer of dust that is spectrally and compositionally similar to the globally homogenized surface dust in other high albedo regions on mars the mineralogy of the dark materials is mafic dominated modally by pyroxene and olivine however unlike other lithologies common in low albedo regions i e surface types i and ii its derived bulk chemistry indicates that it is an ultramafic lithology with the lowest silica content detected on mars to date sheet silicates and glasses are not identified above detection limits and as such the materials do not display evidence for significant chemical weathering the geomorphology and visible distribution of the dark intracrater materials combined with the lack of an obvious source in the region outside the crater suggest they are the product of erosion of a local source

martian intracrater splotches occurrence morphology and colors abstract martian intracrater splotches and related streaks are studied with global data on their occurrence and regional data on color and morphology the fraction of craters with splotches is greatest at high latitudes splotch occurrence is not strongly correlated with surface properties such as albedo and thermal inertia except where these correlate with substantial sediment cover large numbers of splotches are or include dunes especially at high southern latitudes color data show that the dune and nondune materials in splotches are part of one related group of materials that may be of similar composition but varying particle sizes the color data also show that some streaks are simply material deflated from splotches and mixed with local plains material while other streaks are more complex and may involve erosion of thin surface layers by material blown from the splotches splotches appear to be trapped eolian sand but probably have been formed by a great variety of mechanisms a large percentage of craters with splotches show evidence of complex histories of sediment deposition and erosion many splotches may be lag deposits from erosion of regional sediment cover present sediment budgets in splotches are not known but there is some evidence for loss of material and no evidence for resupply from outside the craters

saltation under martian gravity and its influence on the global dust distribution abstract dust and sand motion are a common sight on mars understanding the interaction of atmosphere and martian soil is fundamental to describe the planet s weather climate and surface morphology we set up a wind tunnel to study the lift of a mixture between very fine sand and dust in a mars simulant soil the experiments were carried out under martian gravity in a parabolic flight the reduced gravity was provided by a centrifuge under external microgravity the onset of saltation was measured for a fluid threshold shear velocity of 0 82 0 04 m s this is considerably lower than found under earth gravity in addition to a reduction in weight this low threshold can be attributed to gravity dependent cohesive forces within the sand bed which drop by 2 3 under martian gravity the new threshold for saltation leads to a simulation of the annual dust cycle with a mars gcm that is in agreement with observations

partial eclogitisation of gabbroic rocks in a late precambrian subduction zone zambia prograde metamorphism triggered by fluid infiltration gabbros and eclogites occur closely associated in a 200 km long and up to 40 km wide area of the zambezi belt in central zambia this area is interpreted to represent part of a late precambrian suture zone with the mafic rocks being relics of subducted oceanic crust gradual stages of prograde transformation from gabbro to eclogite are preserved by disequilibrium textures of incomplete reactions this resulted in kyanite omphacite bearing assemblages for eclogites that have al poor bulk compositions undeformed eclogites typically preserve features of a former gabbroic texture reflected by replacements of plagioclase and magmatic pyroxene by eclogite facies minerals textures of deformed eclogites range from sheared porphyroclastic to porphyroblastic relics of magmatic pyroxene are common and complete eclogitisation occurred only in millimetre to centimetre scale domains in most of the rocks no evidence for prograde blueschist or amphibolite facies mineral assemblages was found in eclogites in contrast the fine grained intergrowth of omphacite garnet kyanite and quartz which replace former plagioclase or was formed in the pressure shadow of magmatic pyroxene relics indicates that eclogitisation might have affected the gabbroic protoliths directly without any significant intervening metamorphic reactions eclogitisation took place under p t conditions of 630 690 degreesc and 26 28 kbar suggesting a large overstepping 10 kbar of reaction boundaries eclogitisation was initialised and accompanied by a channelised fluid flow resulting in veins with large subhedral grains of omphacite kyanite and garnet the gabbro to eclogite transformation was enhanced by a fluid which allowed the necessary material transport for the dissolution precipitation mechanism that characterises the metamorphic mineral replacements the process of eclogitisation was limited by reaction kinetics and dissolution precipitation rates rather than by the metamorphic p t conditions even though ductile deformation occurred and equilibrium phase boundaries were overstepped the infiltration of fluids was necessary for triggering the gabbro to eclogite transformation

eolian intracrater deposits on mars physical properties and global distribution abstract an investigation of martian intracrater materials has been made using their thermophysical properties as derived from viking irtm observations over one fourth of all craters larger than 25 km in diameter between 50 s and 50 n have localized deposits of coarse material on the floor which are associated with dark splotches seen visually assuming homogeneous unconsolidated materials the measured thermal inertias of these deposits i 0 003 10 3 to 0 026 10 3 cal cm 2 sec 1 2 k 1 imply effective grain sizes ranging from 0 1 mm to 1 cm with a modal value of 0 9 mm these deposits are coarser and darker than the surrounding terrains and the majority of the martian surface but are not compositionally distinct from materials with similar albedos they occur more frequently in the south in regions of relatively coarse material 0 2 to 2 mm and in relatively dark areas these features most likely formed by entrapment of marginally mobile material which can be transported into but not out of crater depressions by the wind very few have recognizable dune forms those that do have effective grain sizes less than 0 5 mm the majority of the splotch deposits are coarser than the dune forming materials found in the north polar region and inside extreme southern latitude craters and probably form low broad zibar dunes or lag deposits intracrater deposits are noticeably lacking from the interior of the large northern hemisphere low inertia region of arabia 10 s to 30 n 300 to 360 w interpreted to be a sink for suspended dust but do occur around the perimeter of this region this distribution suggests that the intracrater features have been buried in the interior of arabia and that the dust deposit is less extensive at the margins and may currently be expanding the occurrence of regional dust deposits in the north may be related to the maximum wind activity currently occurring in the southern hemisphere and suggests that the location of regional sinks may migrate with time as the solar insolation maximum migrates

north south asymmetry of eolian features in martian polar regions analysis based on crater related wind markers abstract a comparison of crater related wind markers in the north and south polar 40 90 latitude regions of mars has been made on the basis of comprehensive mapping from viking orbiter and mariner 9 images wind streaks show that present wind activity is most effective in both north and south in the southern spring and summer this asymmetry is consistent with the present asymmetry of climate the more massive intracrater dune fields are also oriented with the presently strongest winds this alignment may reflect a long term asymmetry in the effectiveness of northern and southern spring flow because reorientation times far exceed the period of cycles of hemispherical climate asymmetry 51 000 years streaks originating from dark crater splotches indicate that windflow away from the south pole is effective over a larger latitude range than it is in the north this difference may be partly responsible for the contrasting distribution of dune sand in the north and south polar regions

a heuristic examination of cohesive sediment bed exchange in turbulent flows abstract prediction of the concentration of suspended cohesive sediment in the marine environment is constrained by difficulties in interpreting experimental evidence on bed exchange i e erosion and deposition of particles which remains sparse in mechanistic details in this paper conditions under which bed exchange in turbulent flows collectively determines the concentration of suspended matter have been examined in the heuristic sense based on selective experimental data it is argued that interpretation of such data can be significantly facilitated when multi class representation of particle size collisional interaction between suspended particles and probabilistic representations of the bed shear stress along with variables describing particle behavior critical shear stress for deposition bed floc shear strength are taken into account aggregation floc growth and breakup kinetics brings about shifts in the suspended particle size distribution bed exchange is accordingly modulated and this in turn determines concentration dynamics probabilistic representation of the governing variables broadens the suspended sediment size spectrum by increasing the possibilities of inter particle interactions relative to the mean value representation simple models of bed exchange which essentially rely on single size assumption and mean value representation of variables overlook the mechanistic basis underpinning particle dynamics

saltation threshold on earth mars and venus new formulations valid for wide ranges of particle diameter and density and gas density are presented for prediction of saltation threshold speed for small particles a low air density wind tunnel was used to extend the range of previous investigations and to separate the effects of reynolds number and interparticle forces of cohesion the new formulations are used to predict saltation threshold for atmospheric conditions on the surface of the earth mars and venus

evidence for indurated sand dunes in the martian north polar region 1 we investigate the relevance of induration as an explanation for the occurrence of dunes of unusual morphology in the martian north polar region the evidence for induration of aeolian deposits on mars is reviewed an explanation for rounded elongated barchans in chasma boreale is presented the role played by induration in the formation of linear dunes is discussed our arguments are supported by the results of a computer simulation model

wind streaks in tharsis and elysium implications for sediment transport by slope winds detailed maps of wind streaks in tharsis and elysium have been compiled from viking orbiter observations spanning one complete martian year the streak pattern is controlled by slope winds on the central volcanoes and on the flanks of the tharsis bulge while the global circulation dominates in elysium dust erosion by downslope winds occurs over much of tharsis and in the vicinity of elysium mons this process is effective even at the low atmospheric pressures found near the summits of the large volcanoes erosional streaks are largely absent in elysium planitia net deposition of dust might have occurred during the period of our observations surface properties such as slope thermal inertia and roughness may influence the efficiency of slope wind production sufficiently to account for the pronounced differences in streak types and patterns present in these two regions

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

topography and geologic characteristics of aeolian grooves in the south polar layered deposits of mars abstract the topographic and geologic characteristics of grooves and groove like features in the south polar layered deposits near the mars polar lander deep space 2 landing sites are evaluated using mariner 9 images and their derived photoclinometry normalized using mars orbiter laser altimeter data although both mariner 9 and viking images of the south polar layered deposits were available at the time of this study mariner 9 images of the grooves were selected because they were generally of higher resolution than viking images the dimensions and slopes of the grooves together with orientations that nearly match the strongest winds predicted in the martian global circulation model and directions inferred from other wind indicators suggest that they formed by aeolian scour of an easily erodible surface most grooves are symmetric and v shaped in transverse profile inconsistent with an origin involving extensional brittle deformation although the grooves strike along slopes and terraces of the south polar layered deposits the variable depths and lack of terracing within the grooves themselves indicate that any stratigraphy in the uppermost 100 m of the polar layered deposits is composed of layers of similar and relatively low resistance the grooves do not represent landing hazards at the scale of the mariner 9 images 72 86 m pixel and therefore probably would not have affected mars polar lander and deep space 2 had they successfully reached the surface

the surface of syrtis major composition of the volcanic substrate and mixing with altered dust and soil syrtis major is an old low relief volcanic plateau near the equatorial regions of mars it is a persistent low albedo feature on the planet and is thought to contain a high abundance of exposed bedrock and or locally derived surface material and debris spatially resolved variations in surface spectral properties and therefore composition are investigated with data from the imaging spectrometer for mars ism instrument ism obtained 128 wavelength channel spectra from 0 76 to 3 16 m for contiguous pixels approximately 22 22 km in size across much of the plateau the value and spatial distribution of four primary spectral variables albedo continuum slope wavelength of the ferric ferrous band minimum area of the ferric ferrous absorption are mapped and coregistered to viking digital photomosaics analysis of these maps shows that although there is a high degree of overall spectral variability on the plateau the key indicators of mafic mineralogy are relatively homogeneous detailed examination of reflectance spectra from representative areas across the plateau indicate the volcanic surface is dominated by augite bearing basalts and the pyroxene composition in the basalts is estimated to be 0 275 0 075 ca ca fe mg and 0 3 0 1 fe fe ca mg additional mineral components may include olivine feldspar and glass most of the spectral variability on the plateau is interpreted to result from mixing of volcanic bedrock and or locally derived surface material and debris with highly altered dust and soil in western syrtis major the altered material is a transient component on the surface or occurs in large spatially coherent patches e g crater rims in eastern syrtis major it is apparent that the dust components are firmly fixed to the basaltic substrate as a stable oxide rind or coating

unsteady saltation on mars abstract saltation is an important process on mars as it contributes to dust raising bedform dynamics and aeolian abrasion lander measurements and mesoscale meteorological models suggest that winds in the martian atmosphere rarely exceed the fluid threshold value that is necessary to aerodynamically initiate saltation a fact in stark contrast to the existence of dunes and ripples on the planet many of which are in an active state of migration in an attempt to reconcile these observations we perform an unsteady simulation with a simple turbulence model to calculate the saltation transport rate sinusoidal wind variations are imposed on the saltation layer the numerical simulations verify that gusty transport is one of the main manifestations of martian sediment transport events a formula for the saltation transport rate is reported q m u u it p where u and u it are the friction velocity and impact threshold friction velocity the power p varies in the range of 0 7 1 8 on mars and 1 5 on earth depending on the period and amplitude of the gusty inflow wind our results show that the law of martian and terrestrial transport rate are not universal and hence one should be cautious when trying to extrapolate existing terrestrial results to mars

the m3 project 2 global distributions of mafic mineral abundances on mars abstract a radiative transfer model was used to reproduce several millions of omega observatoire pour la mineralogie l eau les glaces et l activite spectra representative of igneous terrains of mars this task provided the modal composition and grain sizes at a planetary scale the lithology can be summarized in five mineral maps at km scale we found that the low albedo equatorial regions of the martian surface from 60 s to 30 n are globally dominated by plagioclase with average abundance 50 vol and pyroxenes with total averaged abundance close to 40 vol an evolution of the lcp lcp hcp ratio is observed with time at the global scale suggesting an evolution of the degree of partial melting throughout the martian eras olivine and martian dust are minor components of the modelled terrains the olivine distribution is quite different from the other minerals because it is found on localized areas with abundance reaching 20 vol a statistical approach to classify the pixels of the abundances maps using k means clustering highlighted seven distinct mineral assemblages on the surface this classification illustrates that diverse mineralogical units are found in the noachian and hesperian terrains which suggests the presence of various and complex magmatic processes at a global scale during the two oldest eras the chemical composition was derived from the modal composition maps the omega derived chemical composition is quite consistent with several distinctive geochemical characteristics previously considered as fingerprints of the martian surface a major discrepancy is in regards to the fe content that is significantly smaller than soil and rock analyses from grs and in situ measurements the discrepancy could be partly explained by the assumptions used for the spectral modelling or could also indicate surface alteration rinds

extraterrestrial dunes an introduction to the special issue on planetary dune systems abstract aeolian dune fields have been described on earth mars venus and titan the plethora of data returned from recent planetary missions has enabled a new era in planetary geomorphic studies much of our understanding of planetary dune systems comes from the application of earth analogs wind tunnel experiments and modeling studies despite the range of atmospheric pressures composition and gravity many of the dune forms on extraterrestrial surfaces are similar to those on earth although some have notable differences in bedform scale and composition as an introduction to the special issue on planetary dune systems this paper summarizes the current state of knowledge of planetary dune studies and highlights outstanding questions that require further investigation

the particle size of martian aeolian dunes the effective particle size of unconsolidated materials on the martian surface can be determined from thermal inertia due to a pore size dependence of thermal conductivity at martian atmospheric pressures because dunes consist of a narrow range of well sorted unconsolidated particles they provide for a test of the relationship between particle size and thermal inertia calculated from midinfrared emission data for the martian surface we use two independent approaches first thermal inertia data indicate that martian dunes have an average particle size of about 500 100 m or medium to coarse sand second we determine expected dune particle sizes from grain trajectory calculations and the particle size transition from suspension to saltation on earth the transition occurs for a grain when the ratio of the terminal fall velocity to the wind friction speed u t is near unity for grains at u t this occurs at about 52 m terrestrial dune sands have a mean of 250 m and are composed entirely of grains 52 m the corresponding martian transition grain size is about 210 m suggesting that martian dunes should be significantly coarser than terrestrial dunes grain saltation path length as a function of particle size also shows that under martian conditions larger grains than on earth will become suspended both approaches indicate that martian dune sand should be coarser than terrestrial dune sand thus while terrestrial dune grains are in the fine to medium sand range the average martian dune sediments are probably medium to coarse sands these results closely match the grain sizes determined from thermal inertia models providing the first direct test of the validity of these models for actual martian surface materials

visual and infrared observations of wind streaks on mars abstract estimation of surface properties and physical setting of three common martian wind streak types bright dark and splotch related provides constraints on models of the formation and variability of streaks bright streaks form independently of surface properties other than local topography this is consistent with their formation being due to deposition of atmospheric dust in the lee of topographic features although they are widespread on mars dark streaks are noted as variable only in regions near 30 s latitude and elevations between 3 and 7 km and are associated with dark surfaces that have relatively high thermal inertias splotch related streaks occur at elevations between 0 and 6 km and in regions of relatively high thermal inertia splotch related streaks occur near the boundaries of thermally defined regions such as the south polar cap and other areas of either low or high thermal inertia these thermal conditions are responsible for the production of surface winds which form and modify these streaks the source of sidements which form splotch related streaks varies from dunes to well indurated stratified deposits regional studies of the various types in syrtis major syria planum claritas fossae oxia palus mesogea and pettit craters and noachis confirm that the correlations found at the global level occur at regional scales

a scaling law for aeolian dunes on mars venus earth and for subaqueous ripples abstract the linear stability analysis of the equations governing the evolution of a flat sand bed submitted to a turbulent shear flow predicts that the wavelength at which the bed destabilises to form dunes should scale with the drag length l drag s f d this scaling law is tested using existing and new measurements performed in water subaqueous ripples in air aeolian dunes and fresh snow dunes in a high pressure co2 wind tunnel reproducing conditions close to venus atmosphere and in the low pressure co2 martian atmosphere martian dunes the difficulty is to determine the diameter of saltating grains on mars a first estimate comes from photographs of aeolian ripples taken by the rovers opportunity and spirit showing grains whose diameters are smaller than on earth dunes in addition we calculate the effect of cohesion and viscosity on the dynamic and static transport thresholds it confirms that the small grains visualised by the rovers should be grains experiencing saltation finally we show that within error bars the scaling of with ldrag holds over almost five decades we conclude with a discussion on the time scales and velocities at which these bed instabilities develop and propagate on mars

aeolian processes in proctor crater on mars sedimentary history as analyzed from multiple data sets 1 proctor crater is a 150 km diameter crater in noachis terra within the southern highlands of mars the analysis leading to the sedimentary history incorporates several data sets including imagery elevation composition and thermal inertia mostly from the mars global surveyor mission the resulting stratigraphy reveals that the sedimentary history of proctor crater has involved a complex interaction of accumulating and eroding sedimentation aeolian features spanning much of the history of the crater interior dominate its surface including large erosional pits stratified beds of aeolian sediment sand dunes erosional and depositional streaks dust devil tracks and small bright bed forms that are probably granule ripples long ago up to 450 m of layered sediment filled the crater basin now exposed in eroded pits on the crater floor these sediments are probably part of an ancient deposit of aeolian volcaniclastic material since then some quantity of this material has been eroded from the top layers of the strata small bright dune forms lie stratigraphically beneath the large dark dune field relative to the large dark dunes the bright bed forms are immobile although in places their orientations are clearly influenced by the presence of the larger dunes their prevalence in the crater and their lack of compositional and thermal distinctiveness relative to the crater floor suggests that these features were produced locally from the eroding basin fill dust devil tracks form during the spring and summer following a west southwesterly wind early in the spring the dust devils are largely restricted to dark patches of sand as the summer approaches dust devil tracks become more plentiful and spread to the rest of the crater floor indicating that the entire region acquires an annual deposit of dust that is revealed by seasonal dust devils the dark dunes contain few dust devil tracks suggesting that accumulated dust is swept away directly by saltation rather than by the passage of dust devils spectral deconvolution indicates that the dark dunes have infrared spectra consistent with basalt like materials the average thermal inertia calculated from thermal emission spectrometer bolometric temperatures is 277 17 j m 2 s 0 5 k 1 leading to an effective grain size of 740 170 mm which is consistent with coarse sand and within the range expected for martian sand the coarse sand that composes the large dune field may have originated from outside the crater saltating in from the southwest most of the transport pathway that delivered this sand to the dune field has since been eroded away or buried the sand was transported to the east center of the crater floor where beneath the present day dunes a 50 m high mound of sand has accumulated dune slip faces indicate a wind regime consisting of three opposing winds some of these wind directions are correlated with the orientations of dust devil tracks and bright bed forms the combination of a tall mound of sand and three opposing winds is consistent with a convergent wind regime which produces the large reversing transverse and star dunes that dominate the dune field the dark dunes have both active slip faces and seemingly inactive slip faces suggesting that the dunes vary spatially in their relative activity nevertheless the aeolian activity that has dominated the history of proctor crater still continues today index terms 5415 planetology solid surface planets erosion and weathering 5470 planetology solid surface planets surface materials and properties 5410 planetology solid surface planets

a study of low albedo deposits within amazonis planitia craters evidence for locally derived ultramafic to mafic materials 1 we studied low albedo deposits in the floors of craters within the amazonis planitia region using infrared data from mars global surveyor thermal emission spectrometer tes and mars odyssey thermal emission imaging system themis high resolution visible images from the mars orbiter camera and themis and topographic data from the mars orbiter laser altimeter these deposits are found within subdued to sharp rimmed craters that impacted into thick basaltic lava flows from olympus mons these lava flows flooded the region and were subsequently eroded by aeolian processes tes spectral modeling of the low albedo deposits reveals a mineralogy that is dominated by mafic minerals olivine pyroxene with a derived bulk chemistry that ranges from ultramafic to mafic 40 52 wt sio2 in composition these bulk compositions are comparable to some martian lithologies but represent some of the lowest silica contents identified on mars the compositional range could be produced by either primary igneous processes or subsequent alteration by aeolian processes the spatial distribution of the compositions reveals weak to absent groupings and does not distinguish between the igneous or aeolian scenarios in some craters possible local sources have been identified within the crater walls floors and interiors local sources may be present in additional craters but obscured by dust no regional sources were identified within a reasonable distance in terms of sand transport but may also be obscured by dust therefore the low albedo deposits probably resulted from aeolian erosion of local intracrater basaltic materials that were subsequently redistributed within the floors of these craters

sand dune materials and polar layered deposits on mars abstract the relationship of dark sand dunes to the polar layered deposits of mars is investigated by mapping the colors and morphologic settings of the dunes in and near the polar deposits in the north polar region the dunes have restricted sources in the layered deposits that are associated with are arcuate scarps 10 50 km in length and

nature and origin of materials exposed in the oxia palus western arabia sinus meridiani region mars abstract mars observer will map physical elemental and mineralogical properties of surface materials a key to understanding the regional variations in crustal composition will be the extent to which in situ debris produced from bedrock can be separated from laterally mixed eolian sediments viking orbiter image and thermal data covering equatorial cratered terrain in western arabia eastern oxia and sinuses sabaeus and meridiani were evaluated to test whether local materials related to bedrock could be identified characterized and mapped crater obliteration models imply that kilometers of debris have been produced locally although obliteration rates for the past few billion years have been less than 8 10 3 m year fluvial and eolian landforms clearly indicate lateral transport and mixing of tens of meters of debris six sets of calibrated violet green and red viking images covering the study area were mosaicked and examined in combination with block abundance and fine component inertias from irtm data three major color thermal units can be discerned bright red dust storm deposits brown materials that are probably indurated and dark less red materials that are probably composed of lithic fragments in the medium sand size range the unit boundaries are independent of bedrock geology and erosional landforms the brightest red material apparently mixes with each of the darker units the presence of dark splotches streaks and dunes associated with large craters in oxia indicates that the dark less red material is also mobile the surficial units exposed over the 6 10 6 km 2 study area are therefore likely to represent mixed eolian deposits predominantly decoupled from the underlying bedrock unraveling the mixtures and assignment of components to local bedrock origins will be a major challenge for mars observer