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

visible near infrared spectral diversity from in situ observations of the bagnold dune field sands in gale crater mars as part of the bagnold dune campaign conducted by mars science laboratory rover curiosity visible near infrared reflectance spectra of dune sands were acquired using mast camera mastcam multispectral imaging 445 1013 nm and chemistry and camera chemcam passive point spectroscopy 400 840 nm by comparing spectra from pristine and rover disturbed ripple crests and troughs within the dune field and through analysis of sieved grain size fractions constraints on mineral segregation from grain sorting could be determined in general the dune areas exhibited low relative reflectance a weak 530 nm absorption band an absorption band near 620 nm and a spectral downturn after 685 nm consistent with olivine bearing sands the finest grain size fractions occurred within ripple troughs and in the subsurface and typically exhibited the strongest 530 nm bands highest relative reflectances and weakest red near infrared ratios consistent with a combination of crystalline and amorphous ferric materials coarser grained samples were the darkest and bluest and exhibited weaker 530 nm bands lower relative reflectances and stronger downturns in the near infrared consistent with greater proportions of mafic minerals such as olivine and pyroxene these grains were typically segregated along ripple crests and among the upper surfaces of grain flows in disturbed sands sieved dune sands exhibited progressive decreases in reflectance with increasing grain size as observed in laboratory spectra of olivine size separates the continuum of spectral features observed between the coarse and fine grained dune sands suggests that mafic grains ferric materials and air fall dust mix in variable proportions depending on aeolian activity and grain sorting

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

transformations of mg and ca sulfate hydrates in mars regolith salt hydrates have an active role in regolith development on mars the mg sulfate system with highly variable values of n in the formula mgso 4 n h 2 o is particularly subject to transformations among several crystalline and amorphous forms the ca sulfate system caso 4 n h 2 o is likely to be associated with the mg sulfates in most occurrences but is less susceptible to transformations in n desiccation of mgso 4 n h 2 o occurs in exposed soils at the martian equator in summer where higher daytime temperatures at low relative humidity prevail against sluggish nighttime rehydration at high relative humidity desiccation and rehydration are both accelerated in the finest size fractions particularly in silt size aeolian particles subject to global redistribution by dust storms this redistribution and periodic excursions into long term episodes of high obliquity work to rehydrate desiccated mgso 4 n h 2 o to form epsomite mgso 4 7h 2 o at higher latitudes in the first case and more globally in the latter kieserite a monohydrate form of mgso 4 n h 2 o resistant to desiccation can survive equatorial summer conditions but not protracted high relative humidity preservation of kieserite at the surface may place limits on the equatorial distribution of ice during past episodes of high obliquity deeper horizons in equatorial regolith may preserve hydrated phases through repeated obliquity episodes raising the possibility of an ancient regolith archive of past hydration at shallower depths in the regolith in situ determination of the hydration states of the mg sulfates and possibly the ca sulfates may be used to constrain regolith dynamics if rates and modes of transitions in n can be fully characterized

factors determining desert dune type while most observers recognize four elemental types of desert dunes longitudinal transverse barchan and star1 3 there is little agreement about which factors determine these types the angular relationships between the resultant of sand shifting winds and both the crest and principal slipfaces of the elemental types have been discussed qualitatively for many decades these relationships have been quantified but the wide range of dune types that combine the elemental forms and the juxtaposition of different dune types show that wind regime is not the only determinant for example sand availability has been considered important we have now quantified the importance of both wind regime and sand availability as determinants of dune type we show here that the four elemental types occur in areas uniquely defined by both the equivalent sand thickness of sediments held in the dunes and a measure of directional variability of sand moving winds wind strength does not appear to be important vegetation has an ambiguous role and the particle size of dune sediments is unimportant

transverse aeolian ridges tars on mars aeolian processes are probably the dominant ongoing surface modification process on mars as demonstrated by observations of dunes ripples yardangs ventifacts wind streaks dust devils and dust storms large dark dunes ldds are particularly common and were first recognized in the 1960 s from mariner data however another population of smaller often brighter ripple like aeolian bed forms that are morphologically distinct from ldds has been observed in recent higher resolution images calculations of saltation path length under martian conditions suggest these small bed forms could have formed as small barchanoid dunes or as mega ripples also known as granule ripples these features have therefore been called transverse aeolian ridges tars as this label has no genetic inference we have begun a study of tars that examines all high resolution mars orbiter camera data 1 5 to 8 m pixel resolution in a 45o longitude wide pole to pole swath we aim to determine the geographic distribution of tars assess whether they are active and to identify possible sediment sources we have already made some key observations first we present a new classification of tar deposits based on crest ridge morphology of individual forms and the size and degree of topographic control of the entire sediment mass second we present associations of tars with ldds slope streaks dust devils tracks and small impact craters that provide clues as to whether tars are currently active finally we present preliminary pole to pole survey results for the northern hemisphere that show clusters of tar deposits in the low latitudes suggesting possible unique sediment sources in these regions

the martian surface as imaged sampled and analyzed by the viking landers the two viking landers touched down on the surface of mars in july and september of 1976 viking lander 1 renamed the mutch memorial station mms continued to operate for 3 martian years in chryse planitia the landing site is a rolling sparsely cratered plain impact crater size frequency distributions demonstrate that only meters of vertical erosion have occurred over the lifetime of the surface the site exhibits bedrock exposures numerous rocks excavated during cratering events indurated fine grained sediment blocky material mixed with dust and lithic fragments and aeolian drifts that overlie the blocky material and which probably accumulated during global dust storms lander 2 operated for approximately 2 martian years in utopia planitia a region subjected to volcanic impact aeolian and periglacial phenomena lander 2 is located west of the 100 km diameter crater mie on or near the distal end of the continuous ejecta deposits polygonal ground suggests that desiccation or freeze thaw processes have occurred the lander 2 site exhibits numerous rocks excavated from craters and exposed by erosion set in a matrix of crusty to cloddy sediment rare aeolian drifts overlie the crusty to cloddy material lander multispectral imaging of sediment exposures at both sites is best matched with iron rich claylike weathering products called palagonites the spectral characteristics are probably governed by thin deposits of dust from global and local dust storms darkest rocks have reflectance values that match iron rich igneous rocks although most rocks are covered with indurated coatings of the palagonitelike products chemical compositions of sediments at the two landing sites are strikingly similar suggesting an aeolian origin the compositions suggest an iron rich igneous source rock and are matched by an assemblage of clays and salts samples of blocky materials were found to have about 50 more cl and so3 than other samples implying cementation by salts the magnetic component in the sediment is silt sized or finer and may be maghemite or ultrafine grained hematite no indigenous organic compounds were found the materials were found to be highly reactive releasing o2 when h2o was added oxidizing organic nutrients on board the landers and fixing atmospheric co2 clay to silt sized particles were inferred for drift and crusty to cloddy materials no terrestrial samples have been found that replicate all the attributes of the viking samples approximately 10 m of h2o ice accumulated during both winters at lander 2 and each time evaporated over approximately 200 martian days thin layers of bright red dust from global and local dust storms accumulated at both sites during the first 2 martian years during the third winter strong winds generally scoured the mms site leaving behind a darker aeolian lag deposit bedrock at both sites formed billions of years ago and rocks have been generated and weathered slowly over geologic time but aeolian sediments accumulate become cemented and are subsequently eroded over time spans of millions of years or less the lifetime of the sedimentary deposits at the landing sites may be governed by the 105 to 106 year variations in climate due to quasi periodic changes in obliquity eccentricity and spin axis orientation

dark aeolian sediments in martian craters composition and sources our research focuses on the mineralogical characteristics of dark sediment deposits in martian craters dunes dune fields and sand sheets and their local sediment sources carried out on the basis of 70 selected localities morphological analyses reveal dark layers exposed in a number of crater walls showing indications of material transport from the layers downwall to the intracrater deposits additional sites show dark sediment emerging from several craters floors suggesting a dark material source beneath the crater floor spectral analyses of omega and crism data showed for the first time that a direct mineralogical connection exists between the dark layers in the crater walls and the intracrater dune and sand sheet material based on these findings it is shown that these layers are the local sources for the dark aeolian sediment inside the craters spectral analyses further indicate that all deposits are nearly of the same mafic mineralogical composition hinting at a similar origin we conclude that the mineralogical composition points to a volcanic origin of the material the dark layers which we infer to be the material sources might represent layers of volcanic ash almost globally deposited in early noachian times and subsequently covered by regolith groundwater impact erosion and crustal movement led to the highly fragmented situation of the dark layers today however burial protected the layers of dark sediment from chemical alteration caused by surficial fluvial processes impact erosion after the wet periods on mars led to the exposure and mobilization of the material today

geology of central chryse planitia and the viking 1 landing site implications for the mars pathfinder mission 1 500 000 scale geologic mapping in the central chryse planitia region of mars was correlated with ground truth data gathered by the viking 1 lander materials within the chryse basin can be subdivided into plains and channel units that are typically separated from one another by gradational contacts hesperian ridged plains materials unit 1 hr1 are the oldest materials mapped typically these materials contain numerous fresh impact craters and have sharply defined mare like wrinkle ridges similar to those appearing on the lunar maria these materials grade into hesperian ridged plains materials unit 2 hr2 which are characterized by buried and eroded impact craters and subdued wrinkle ridges from analyses of crater age dates and their associated geologic contacts channel materials appear to have formed at the same time as hr2 materials and it is likely both units represent fluvial sediments measurements of buried craters contained in hr2 materials suggest that in places this unit may be 50 m thick but crater size frequency distribution curves suggest that the areal average may be closer to 170 m based on these observations our interpretation is that hr2 materials were deposited into a standing body of water during channel formation this interpretation implies that many of the rocks visible in the viking 1 lander images were emplaced by fluvial processes possibly finer grained sediments remained in suspension and were subsequently transported out of chryse planitia and into the northern plains during draining of the ponded water east west trending surface undulations visible in lander views toward the south may represent aeolian dunes lava flow fronts or sediment waves formed at the bottom of the standing body of water broad physiographic units seen at the surface are not clearly visible in viking orbiter images however they can be projected at the resolution of the orbiter images these units show that concentrations of drift materials are oriented in a northwesterly direction contrary to the strongest prevailing wind direction which is toward the northeast these materials were probably deposited on ridged plains materials unit 2 during a period of time when aeolian processes were more active in the region both earth based radar and viking thermal data suggest that the mars pathfinder landing site will be similar geologically to the viking 1 site if this is true then the mars pathfinder mission provides the opportunity for building directly on results of the viking program some of the outstanding questions that mars pathfinder may be able to address include determining the aeolian modification history of the chryse planitia region the degree and possibly the relative rate of sediment induration the fraction of rocks and boulders emplaced by impact processes the possibility that some materials are the result of in situ weathering and whether materials were emplaced by fluvial processes and the associated depositional environment

chasma australe mars structural framework for a catastrophic outflow origin abstract chasma australe 500 km long and up to 80 km wide is the most remarkable of the martian south pole erosional reentrants carved in the polar layered deposits we have interpreted chasma australe erosional and depositional features as evidence for a flood origin which we have reconstructed using a modified manning equation the main characteristics of the flow are a water velocity between 30 and 50 m s 1 and discharge values between 7 10 8 and 3 10 9 m 3 s 1 very near to mgs data based estimations for martian outflow channels d e smith et al 1998 science 279 1686 1692 we thus postulate that chasma australe originated in a catastrophic flood the tectonic study of an area roughly 20 million km 2 in size around mars south pole included the measurement and projection in rose diagrams of more than 300 lineaments of which 85 were wrinkle ridges and the rest straight scarps the whole set of lineaments canbe explained by a stress field with a 1 n10 e in strike the wrinkle ridges being reverse faults and the other lineaments direct and strike slip faults the straight layout of parts of chasma australe almost 200 km long suggests that the chasma was carved following a fracture network the effectiveness of the erosional process the canyon is up to 1000 m deep leads us to suspect that this carving was preceded by a sapping period endogenetic and exogenetic processes would thus have contributed to the origin of this landform

geology of xanthe terra outflow channels and the mars pathfinder landing site the mars pathfinder landing site mpls was selected for its location at the mouths of ares and tiu valles outflow channels on mars where sediments from a variety of geologic units could have accumulated in a lacustrine environment recent geologic mapping at 1 2 m scale of the xanthe terra channels and chryse planitia near mpls reveals a progression of fluvial erosion and deposition throughout the hesperian period from the geology the watersheds of the channels were inferred and a sequence of paleogeologic maps was produced three outflow episodes are recognized 1 broad sheetwash during the early hesperian emanating from eastern valles marineris and equatorial chaos regions with initial erosion into highland plateau basement 2 early channel formation and 3 subsequent flooding which deepened the channels to their current morphologies the most recent flooding issued from simud and tiu valles during the late hesperian indicated by stratigraphic superposition striations along the floor of the channel and the orientation of streamlined islands in the flood direction this suggests that surface sediments deposited at mpls are most likely to have come from these channels and to a lesser extent from ares vallis a ranking scheme was developed to assess the potential origins for the sediments found at mpls the most abundant materials are inferred to have come from the noachian and hesperian highland plains and reworked sediments from previous floods underlying materials from earlier floods could also be found at mpls as ejecta from nearby impact craters

regional scale stratigraphy of surface units in tyrrhena and iapygia terrae mars insights into highland crustal evolution and alteration history 1 the compositional thermophysical and geologic characteristics of surface units in iapygia and tyrrhena terra 60 e 100 e 0 30 s provide new insights into the compositional stratigraphy of the region intercrater plains are dominated by two surface units the older unit unit 1 is deficient in olivine and more degraded and likely consists of a mixture of impact volcanic and sedimentary materials the younger unit unit 2 is enriched in olivine exhibits a resistant morphology and higher thermal inertia and likely represents volcanic infilling of plains units 1 and 2 bear a strong resemblance to those previously mapped in mare serpentis a section of highlands crust located northwest of hellas basin thus the two major intercrater plains units are even more widespread than previously thought and therefore likely constitute important components of mars highland stratigraphy many craters in the region contain high thermal inertia deposits unit 3 that are compositionally identical to unit 2 these may have formed via volcanic infilling or may represent sedimentary materials that have been eroded from crater walls and lithified less common units include olivine and or pyroxene rich massifs and crater central peaks these are primarily found within hellas basin rim units and may represent mantle materials brought toward the surface during the hellas impact putative chloride deposits are primarily associated with olivine deficient surfaces unit 1 that may be heavily degraded occurrences of unit 2 the observations raise a variety of questions related to martian crustal evolution and alteration that may have more widespread implications outside the study region

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

settling velocities of natural sand grains in air settling velocities in air were measured for natural quartz sand grains selected to provide a range of grain diameters and shapes roundness and sphericity the measured settling velocities w m obtained in an 11 2 m long settling tube are significantly lower than the settling velocity w s of a sphere having the same weight the two are empirically related by the equation w m 1 10w s super 0 90 with r 2 0 84 although this departure of the settling velocities of natural grains from the settling rates of spheres is most likely due to grain shape effects no dependence could be found on shape measures such as the corey shape factor simple gibbs type empirical equations are also obtained for sand grains settling in air one equation for the settling of spheres and a second for the irregular natural sand grains modified journal abstract

mars aeolian sand regional variations among dark hued crater floor features different regions on mars appear to have low albedo intracrater deposits that have distinct regional thermophysical and or aeolian dune characteristics thermal inertia derived from a carefully selected set of viking infrared thermal mapper observations of the dark features obtained in 1977 1978 supports this conclusion the observed similarities and differences among dark intracrater features on mars is probably a function of the combined influences of sand availability and regional wind conditions

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

occurrence and scale of compositional heterogeneity in martian dune fields toward understanding the effects of aeolian sorting on martian sediment compositions abstract aeolian transport and hydrodynamic sorting have been proposed to be a significant influence on martian sediment bulk compositions through laboratory experiments modeling and terrestrial analogies but to date few studies have directly examined compositional grain size relationships within sediment fields on mars thus the prevalence of hydrodynamic sorting as well as the scales at which sorting is important remain poorly understood to that end we assessed the degree and occurrence of thermophysical and compositional heterogeneity for 25 dune fields within a 42 000 000 km2 area on mars among these only four exhibit spatial heterogeneity in spectral properties and composition two of these four sites show a strong positive relationship between particle size and olivine abundance the rarity of compositional heterogeneity within dune fields in our study region 5 185 e 45 n 20 s may indicate phenocryst poor source rocks alternatively sorting within individual bedforms may be present but not at the scale of the full dune field 10 20 km compositional segregation correlated with grain size due to hydrodynamic sorting has been observed by rovers at scales much smaller than themis ground resolution 100 m pixel thus these small scales might be the operable relevant ones of hydrodynamic compositional sorting prevailing most commonly in martian dune fields

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

catastrophic flood sediments in chryse basin mars and quincy basin washington application of sandar facies model viking visible and thermal infrared observations and terrestrial catastrophic flood deposits provide clues to identify the outflow channel sediments that went into chryse basin on mars on earth sandar outwash plains formed by coalescence of many jokulhlaup floods are described in terms of three laterally adjacent facies proximal midfan and distal the missoula flood sediments deposited in quincy basin washington comprise a miniature analog of chryse basin the terminology and general characteristics of the sandar facies model are applied to quincy basin although the depositional environment and clast sizes are somewhat different higher energy flood larger clasts subaqueous rather than subaerial deposition for example the ephrata fan a deposit of boulders cobbles and pebbles forms the midfan facies analog a downfan sandy deposit reworked into a dune field comprises the distal facies analog in chryse basin the midfan is defined by a heterogeneous rocky 0 25 intermediate albedo 0 21 0 26 intermediate thermal inertia 260 460 j m 2 s 0 5 k 1 surface while the distal facies has a low albedo 0 14 0 16 and higher thermal inertia 340 700 j m 2 s 0 5 k 1 the chryse midfan unit has rocks and windblown dust exposed at the surface the sand of the distal facies in chryse acidalia is reworked by the wind as in quincy basin the viking 1 and mars pathfinder landing sites are located on the midfan unit observations that can be made at the mars pathfinder site might help in reevaluating whether or not viking 1 landed on outflow channel sediments

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

athena microscopic imager investigation 1 the athena science payload on the mars exploration rovers mer includes the microscopic imager mi the mi is a fixed focus camera mounted on the end of an extendable instrument arm the instrument deployment device idd the mi was designed to acquire images at a spatial resolution of 30 microns pixel over a broad spectral range 400 700 nm the mi uses the same electronics design as the other mer cameras but has optics that yield a field of view of 31 31 mm across a 1024 1024 pixel ccd image the mi acquires images using only solar or skylight illumination of the target surface a contact sensor is used to place the mi slightly closer to the target surface than its best focus distance about 66 mm allowing concave surfaces to be imaged in good focus coarse focusing 2 mm precision is achieved by moving the idd away from a rock target after the contact sensor has been activated the mi optics are protected from the martian environment by a retractable dust cover the dust cover includes a kapton window that is tinted orange to restrict the spectral bandpass to 500 700 nm allowing color information to be obtained by taking images with the dust cover open and closed mi data will be used to place other mer instrument data in context and to aid in petrologic and geologic interpretations of rocks and soils on mars

martian aeolian features and deposits comparisons with general circulation model results the development of a general circulation model gcm of mars atmosphere allows questions to be addressed concerning the relationships between near surface winds and the distribution of wind related features and deposits predictions of wind surface stress as a function of season and dust optical depth are used to investigate the distribution and orientation of wind streaks yardangs and rock abundance on the surface the occurrence and orientation of bright streaks are well accounted for by the gcm results suggest that bright streaks form during southern hemisphere summer by hadley cell circulation in which dust is raised in the southern hemisphere carried northward at high altitudes then deposited in the wake of craters and other topographic obstacles by the descending hadley cell the reduction in the number of bright streaks southward from 30 n is interpreted to reflect the depletion of dust by near surface winds blowing to the south although the winds responsible for the formation of the dark streaks are not well reproduced in all areas by gcm simulations a band of high wind surface stresses in the southern subtropics corresponding to the latitude band where most of the dark streaks are found are predicted at the height of the dust storm season southern hemisphere summer yardang orientations do not match the gcm simulations for any season their orientation is attributed to either structural control in the rocks such as joint patterns or to a change in wind patterns from the time when the yardangs formed the global distribution of rocks on the surface is correlated well with predicted wind stress particularly during dust storm season the rocky areas are sites of strong winds suggesting that fine material is swept away by the wind leaving rocks and coarser material behind

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

classification of wind streaks on mars abstract a classification of martian wind streaks has been developed to assist in investigations of eolian transport and related meteorological phenomena on mars streaks can be grouped by their albedo contrast with their surroundings and by the presence of either topographic obstacles or sediment deposits at their points of origin the vast majority of wind streaks can be included in three categories 1 bright streaks with no source deposit interpreted to be formed by preferential deposition of dust from suspension 2 dark streaks with no source deposit interpreted to be formed by preferential erosion of bright dust and its removal in suspension 3 dark streaks associated with deposits of sediment interpreted to be formed by deposition of dark material moved by saltation the orientations of the different streak types are distinctive and reflect both global flow patterns and slope controlled winds the wind directions derived from streaks and the geographical distribution of the features show a strong north south asymmetry consistent with the fact that perihelion and hence maximum wind activity occurs near southern summer solstice

new views of mars eolian activity materials and surface properties three vignettes from the mars global surveyor mars orbiter camera prior to the mars global surveyor mgs mission a very general view had emerged in which martian surface materials were seen as consisting of a mixture of bright dust dark sand and rocks the configuration of these materials and the winds that transport and deposit sand and dust have been thought to be directly linked to the albedo patterns that have been observed on mars for centuries high spatial resolution images 1 4 20 m pixel obtained by the mgs mars orbiter camera moc between september 15 1997 and july 4 1999 provide new information about the physical nature of the windblown material on the martian surface and show that the pre mgs view was much too simple in addition to bright dust and dark sand moc images show evidence of bright sediment that can be transported by saltation e g sand and dark material that can be transported in suspension e g silt new views of eolian wind streaks in daedalia planum show that part of this region thought to be mantled by bright dust based upon viking and mariner observations is instead covered by a thin veneer of bright windblown sand moc images of sinus sabaeus and parts of syrtis major two regions thought to be sandy based upon viking era observations exhibit thick mantles that are inferred to consist of fine grained sediment deposited from eolian suspension low albedo wind streaks in western arabia terra are also dark mantles and their association with eroded crater floors and megaripples dunes on these floors suggest that these particular wind streaks are deposits of silt sized material that was only briefly suspended before settling to the surface moc images also show evidence that some eolian dunes are active on mars today i e in 1998 and 1999 the evidence for activity is largely based upon wind and avalanche induced streaks superposed on or eroded into seasonal frost on high latitude dune fields moc images show that some other dunes are inactive but the albedo of dunes relative to surrounding terrain is not a good indicator of dune activity because some inactive dunes are not mantled by dust inactive dunes are best identified by superposed features such as impact craters landslide deposits and yardangs

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

geologic context of the mars radar stealth region in southwestern tharsis stealth is a region on mars that has no distinguishable radar return stealth was discovered in 1988 by muhleman et al 1991 in 3 5 cm earth based radar images and it was found to extend 2000 km along the martian equator west of arsia and pavonis montes stealth was proposed to be a deposit of unconsolidated granular material with a minimum thickness of several meters with the most likely explanation being that stealth is a volcanic tephra deposit muhleman et al 1991 1995 stealth overlies some of the youngest geologic units on mars including lava flows and a giant curvilinear ridged lobate unit on the west flank of arsia mons stealth also overlies part of a region of smooth and wind scoured materials called the medusae fossae formation examination of high resolution viking orbiter images suggests that stealth is the youngest of several discontinuous wind worked mantles of fine grained 1 cm sediment older deposits of fine sediment appear to be interbedded with lava flows and show evidence of aeolian deposition dunes and deposits in the lee of topographic obstacles and erosion yardangs and pedestal craters the geologic context supports a volcanic ash origin for stealth if stealth is composed of tephra then its extent and the nature of landforms in the region indicate that it resulted from multiple eruptions that occurred relatively late in martian history possible source vents include linear depressions flanked by constructive volcanic landforms that are located on the lower western slopes of arsia and pavonis montes

the southern westerlies in central chile during the two last glacial cycles as documented by coastal aeolian sand deposits and intercalating palaeosols abstract changes in the position and intensity of the southern westerly winds sww and related causal processes during the quaternary are controversial and not well understood here we present a record from continental central chile based on coastal aeolian sand and dunes with intercalated palaeosols reaching back 190 ka in time sixteen samples for luminescence dating and additional samples for geochemical procedures were analysed from three locations in the norte chico la serena los vilos las ventanas besides the recent bw horizons four palaeosols btb1 btb2 btb3 btb4 are identified they formed in periods with stable surface conditions and a relatively dense vegetation cover whereas sand accumulation reflects increased aeolian activity under dry conditions and in parts glacial sea level lowering three of these soils are well bracketed by luminescence data to

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

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

basaltic sand ripples at eagle crater as indirect evidence for the hysteresis effect in martian saltation abstract the rover opportunity documented small basaltic sand ripples at the bottom of eagle crater meridiani planum on mars these ripples are composed of fine basaltic sand 100 m diameter and their average wavelength and height are 10 cm and 1 cm respectively present theories on the transition between saltation and suspension predict that such light particles are suspended by turbulence at the fluid threshold which is the minimum wind speed required to initiate saltation consequently the existence of these 100 m ripples on mars indicates that either current suspension theories are incorrect or that saltation can take place at wind speeds substantially below the fluid threshold indeed recent studies point to the occurrence of hysteresis in martian saltation that is once initiated hysteresis can be maintained at much lower wind speeds than the fluid threshold we investigated the possible role of hysteresis in the formation of fine grained ripples on mars by coupling for the first time a detailed numerical saltation model comsalt with a dynamic model for sand ripple formation the results from the coupled model indicate that ripples with properties similar to those observed at eagle crater can be developed by the impact mechanism at shear velocities far below the fluid threshold these findings are consistent with the occurrence of hysteresis in martian saltation and support the hypothesis that hysteresis plays a role in the surprisingly large sand mobility observed at several locations on mars

a comparison of semiarid and subhumid terrestrial gullies with gullies on mars implications for martian gully erosion abstract comparison of martian hillside gullies with terrestrial analogues is a productive method for gaining an understanding of how surface processes operate on mars and on earth as well as their similarities and differences here we compare gullies within a semiarid region of island lagoon near woomera australia and periglacial gullies located at pasture hill new zealand with the martian gullies in noachis terra we discovered that fluvial processes dominate erosion at the terrestrial sites though in different forms concentration of overland flow and the presence of a resistant cap rock have played a key role in the location and shape of the island lagoon gullies the presence of steeper slopes and a greater abundance of volatiles such as water frost and snowmelt at pasture hill have helped carve channels equivalent in size to the martian gullies and the interaction of frost dry flows snowmelt and debris flows has led to a complex regime of gully erosion and deposition the observation of similar features on mars suggests that martian gully formation is not necessarily restricted to a single process in addition gully slopes are closely related to those of their host escarpment as well as the thickness of erodible material and presence of bedrock traditional indicators of water related activity such as slope and sinuosity need to be placed into the context of the environment of the study site

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

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

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

dark material in the polar layered deposits and dunes on mars viking infrared thermal mapping and bistatic radar data suggest that the bulk density of the north polar erg material is much lower than that of the average martian surface or of dark dunes at lower latitudes we have derived a thermal inertia of 245 280 j m 2 s 1 2 k 1 5 9 6 7 10 3 cal cm 2 s 1 2 k 1 for the proctor dune field and 25 150 j m 2 s 1 2 k 1 0 6 3 6 10 3 cal cm 2 s 1 2 k 1 for the north polar erg the uniqueness of the thermophysical properties of the north polar erg material may be due to a unique polar process that has created them the visible and near infrared spectral reflectance of the erg suggests that the dark material may be composed of basalt or ferrous clays these data are consistent with the dark material being composed of basaltic ash or filamentary sublimate residue fsr particles derived from erosion of the layered deposits dark dust may be preferentially concentrated at the surface of the layered deposits by the formation of fsr particles upon sublimation of water ice further weathering and erosion of these areas of exposed layered deposits may form the dark saltating material that is found in both polar regions dark fsr particles may saltate for great distances before eventually breaking down into dust grains re mixing with the global dust reservoir and being recycled into the polar layered deposits via atmospheric suspension

multiple episodes of aridity in southern africa since the last interglacial period there is generally a dearth of evidence of the nature of quaternary climate change within desert systems which has limited previous interpretations of past environmental change at low latitudes the last glacial maximum has previously been identified as the peak of late quaternary aridity when desert systems expanded to five times their present extent1 2 3 and low latitude aridity has been described for previous glaciations4 but little evidence has been derived directly for large desert basins particularly southern africa here we report new chronological optical dating evidence of arid episodes recorded in aeolian sediments from the mega kalahari sand sea episodic aeolian activity is recorded at the northeastern desert margin whereas more sustained activity is evident from the southwestern desert core several significant arid events are apparent since the last interglacial period with dune building arid phases at 95 115 41 46 20 26 and 9 16 kyr before present existing atmospheric general circulation model simulations and independent palaeoclimate data indicate that the changes in aridity are related to changes in the northeast southwest summer rainfall gradient which are in turn related to sea surface temperatures in the southeastern atlantic ocean

low albedo surfaces and eolian sediment mars orbiter camera views of western arabia terra craters and wind streaks 1 high spatial resolution 1 5 to 6 m pixel mars global surveyor mars orbiter camera images obtained september 1997 to june 2001 show that each of the large dark wind streaks of western arabia terra originate at a barchan dune field on a crater floor the streaks consist of a relatively thin 1 m coating of sediment deflated from the dune fields and their vicinity in most cases this sediment drapes over a previous mantle that more thickly covers nearly all of western arabia terra no concurrent eolian bedforms are found within the dark streaks nor do any dunes climb up crater walls to deliver sand via saltation to the streaks the relations between dunes wind streak and subjacent terrain imply that dark toned grains finer than those that comprise the dunes are lifted into suspension and carried out of the craters to be deposited on the adjacent terrain previous eolian physics and thermal inertia studies suggest that under modern martian conditions such grains likely include silt 3 9 62 5 m very fine sand 62 5 125 m and possibly fine sand to 210 m the streaks change in terms of extent relative albedo and surface pattern over periods measured in years however through june 2001 very little evidence for recent eolian activity dust plumes storms dune movement was observed

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

sea surface temperature variability in the pacific sector of the southern ocean over the past 700 kyr 1 in spite of the important role played by the southern ocean in global climate the few existing paleoceanographic records in the east pacific sector do not extend beyond one glacial interglacial cycle hindering circumpolar comparison of past sea surface temperature sst evolution in the southern ocean here we present three alkenone based pleistocene sst records from the subantarctic and subtropical pacific we use a regional core top calibration data set to constrain the choice of calibrations for paleo sst estimation our core top data confirm that the alkenone based uk37 and uk 37values correlate linearly with the sst in a similar fashion as the most commonly used laboratory culture based calibrations even at low temperatures down to 1 c rendering these calibrations appropriate for application in the subantarctic pacific however these alkenone indices yield diverging temporal trends in the pleistocene sst records on the basis of the better agreement with 18o records and other sst records in the subantarctic southern ocean we propose that the uk37 is a better index for sst reconstruction in this region than the more commonly used uk 37 index the uk37 derived sst records suggest glacial cooling of 8 c and 4 c in the subantarctic and subtropical pacific respectively such extent of subantarctic glacial cooling is comparable to that in other sectors of the southern ocean indicating a uniform circumpolar cooling during the pleistocene furthermore our sst records also imply massive equatorward migrations of the antarctic circumpolar current acc frontal systems and an enhanced transport of acc water to lower latitudes during glacials by the peru chile current

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

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

high and low latitude climate control on the position of the southern peru chile current during the holocene 1 we reconstructed changes of temperature salinity and productivity within the southern peru chile current during the last 8000 years from a high resolution sediment core recovered at 41 s using alkenones isotope ratios of planktic foraminifera biogenic opal and organic carbon paleotemperatures and paleosalinities reached maximum values at 5500 years ago and thereafter declined to modern values whereas paleoproductivity continuously increased throughout the last 8000 years we ascribe these long term holocene trends primarily to latitudinal shifts of the antarctic circumpolar current acc the concurrence with shifts in the position of the southern westerlies points to a common response of atmospheric and oceanographic circulation patterns off southern chile millennial to centennial scale fluctuations of paleotemperatures and paleosalinities on the other hand lag displacements in the position of the southern westerlies but reveal a significant correlation to short term temperature changes in antarctica indicating a high latitude control of the acc at these timescales

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

iodine 129 constraints on residence times of deep marine brines in the canadian shield comment and reply bottomley et al 2002 1 present 129i analyses of hypersaline brines from the con gold mine in yellowknife northwest territories the authors assume that the 129i formed by 238u fission within the metabasalt host rocks and diffused from the rock matrix into the fracture fluid explaining its

thermal and albedo mapping of the polar regions of mars using viking thermal mapper observations 1 north polar region we present the first maps of the apparent thermal inertia and albedo of the south polar region of mars the observations used to create these maps were acquired by the infrared thermal mapper irtm instruments on the two viking orbiters over a 30 day period in 1977 during the martian late southern summer season the maps cover the region from 60 s to the south pole at a spatial resolution of 1 of latitude thus completing the initial thermal mapping of the entire planet the analysis and interpretation of these maps is aided by the results of a one dimensional radiative convective model which is used to calculate diurnal variations in surface and atmospheric temperatures and brightness temperatures at the top of the atmosphere for a range of assumptions concerning dust optical properties and dust optical depths the maps show that apparent thermal inertias of bare ground regions decrease systematically from 60 s to the south pole in unfrosted regions close to the south pole apparent thermal inertias are among the lowest observed anywhere on the planet on the south residual cap apparent thermal inertias are very high due to the presence of co2 frost in most other regions of mars best fit apparent albedos based on thermal emission measurements are generally in good agreement with actual surface albedos based on broadband solar reflectance measurements however in the frost free region poleward of 75 s best fit apparent albedos are significantly higher than measured lambert albedos implying that measured brightness temperatures in this area are up to 15 k colder than would be expected for surfaces with the same measured albedos during this season the one dimensional atmospheric model calculations also predict anomalously cold brightness temperatures close to the pole during late summer and after considering a number of alternatives it is concluded that the net surface cooling due to atmospheric dust is the best explanation for this phenomenon the observed systematic decrease in apparent thermal inertia from 60 s to the south pole during this season is also consistent with the predictions of atmospheric model calculations the region of lowest apparent thermal inertia close to the pole which includes the south polar layered deposits is interpreted to be mantled by a continuous layer of aeolian material that must be at least a few millimeters thick the low thermal inertias mapped in the south polar region imply an absence of surface water ice deposits which is consistent with viking mars atmospheric water detector mawd measurements which show low atmospheric water vapor abundances throughout the summer season however these observations do not necessarily imply a complete absence of water thermal model calculations that can reproduce observed diurnal temperature variations in the south polar region show that annual maximum subsurface temperatures at depths ranging from 4 to 20 cm are cold enough to permit the stability of ground ice deposits even if they are in excellent diffusive contact with the atmosphere therefore the presence of near surface ground ice in the south polar region is not inconsistent with the viking irtm and mawd observations

formation and erosion of layered materials geologic and dust cycle history of eastern arabia terra mars 1 eastern arabia terra is mantled in a layer of dust a few centimeters to a meter thick yet contains morphologic features that suggest a history of multiple events of deposition and consolidation of fine grained material and a significant amount of erosion early in martian history this region was affected by volcanic and fluvial activity but has since been dominated by aeolian processes five craters in this region contain interior mound material that ranges in height from 1600 to 2100 m above the crater floor the fluted erosional pattern and the thermal inertia are suggestive of a weakly indurated material and the extensive layering implies that these mounds were formed by a repeated process or processes although these materials primarily occur within craters there are materials outside craters that have similar erosional features and fine laminations suggesting a more extensive deposit the most likely process to form this material is the deposition and cementation of air fall dust and is potentially related to martian obliquity changes the significant amount of erosion of the intracrater mounds unit indicates a dramatic change from a depositional environment to an erosional regime over the past 106 108 years currently dust is accumulating in this region in years with planet encircling dust events but global circulation model results indicate that dust devils may be removing slight amounts of dust from arabia terra these observations suggest that the thickness of the dust mantle may not be currently increasing and may instead be in equilibrium

absolute dune ages and implications for the time of formation of gullies in nirgal vallis mars 1 transverse dunes cover the valley floor of nirgal vallis a 670 km long valley network at 318 e and 29 s the dunes are superposed by small undeformed impact craters which implies that the dunes are inactive under present atmospheric conditions the last active phase of dune movement absolute age can be determined by crater size frequency distributions the derived absolute ages from high resolution mars global surveyor mars orbiter camera imagery range from approximately 300 000 years to 1 4 myr b p error of factor of 2 the dunes are also superposed by gully deposits aprons which implies a younger age of the gullies these superposition relationships show that the gullies in this midlatitude region are at the most 3 myr old but might be even younger than 300 000 years

presence and detection of carbonates on the martian surface the messages we receive from mars about the presence of carbonates are quite contradictory on the one hand images of the planet clearly show the signatures of past bodies of standing water where the accumulation of sedimentary deposits should have occurred on the other hand the apparent absence of carbonates in the homogeneous fines covering the martian surface raises the question where could carbonates hide now in this paper we discuss the subject and demonstrate that a proposed destruction mechanism the photodecomposition caused by uv radiation cannot account alone for the missing carbonates by means of simulations we show that the difficulties in detecting the carbonates can be ascribed to the low temperatures of the emitting zones observed up to now finally we derive the minimum amount of such minerals that could possibly be detected in future observations of mars and we compare the results of simulations with observed spectra

wind driven particle mobility on mars insights from mars exploration rover observations at el dorado and surroundings at gusev crater 1 the ripple field known as el dorado was a unique stop on spirit s traverse where dust raising active mafic sand ripples and larger inactive coarse grained ripples interact illuminating several long standing issues of martian dust mobility sand mobility and the origin of transverse aeolian ridges strong regional wind events endured by spirit caused perceptible migration of ripple crests in deposits sse of el dorado erasure of tracks in sandy areas and changes to dust mantling the site localized thermal vortices swept across el dorado leaving paths of reduced dust but without perceptibly damaging nearly cohesionless sandy ripple crests from orbit winds responsible for frequently raising clay sized dust into the atmosphere do not seem to significantly affect dunes composed of more easily entrained sand sized particles a long standing paradox this disparity between dust mobilization and sand mobilization on mars is due largely to two factors 1 dust occurs on the surface as fragile low density sand sized aggregates that are easily entrained and disrupted compared with clay sized air fall particles and 2 induration of regolith is pervasive light toned bed forms investigated at gusev are coarse grained ripples an interpretation we propose for many of the smallest linear light toned bed forms of uncertain origin seen in high resolution orbital images across mars on earth wind can organize bimodal or poorly sorted loose sediment into coarse grained ripples coarse grained ripples could be relatively common on mars because development of durable well sorted sediments analogous to terrestrial aeolian quartz sand deposits is restricted by the lack of free quartz and limited hydraulic sediment processing

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

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

could mars be dark and altered there is a long known dichotomy in the martian albedo with an associated but mostly assumed mineralogical split as well the bright red regions are inferred to be weathered oxidized dust and the dark grey regions unaltered volcanic material a number of recent analyses suggest this division is unnaturally simplistic and the association of many dark regions with the former presence of water requires a re examination of the spectra in light of potential alteration minerals i present an alternate interpretation of the reflectance spectral characteristics of some dark regions on mars that includes dark layer silicates if their presence is confirmed on mars this will have implications for sequestration of current and past volatile inventories clues to the extent and type of geochemical weathering and potential zones where bacterial life forms may have emerged

mars global digital dune database and initial science results 1 a new mars global digital dune database mgd3 constructed using thermal emission imaging system themis infrared ir images provides a comprehensive and quantitative view of the geographic distribution of moderate to large size dune fields area 1 km2 that will help researchers to understand global climatic and sedimentary processes that have shaped the surface of mars mgd3 extends from 65 n to 65 s latitude and includes 550 dune fields covering 70 000 km2 with an estimated total volume of 3 600 km3 this area when combined with polar dune estimates suggests moderate to large size dune field coverage on mars may total 800 000 km2 6 times less than the total areal estimate of 5 000 000 km2 for terrestrial dunes where availability and quality of themis visible vis or mars orbiter camera narrow angle moc na images allow we classify dunes and include dune slipface measurements which are derived from gross dune morphology and represent the prevailing wind direction at the last time of significant dune modification for dunes located within craters the azimuth from crater centroid to dune field centroid referred to as dune centroid azimuth is calculated and can provide an accurate method for tracking dune migration within smooth floored craters these indicators of wind direction are compared to output from a general circulation model gcm dune centroid azimuth values generally correlate to regional wind patterns slipface orientations are less well correlated suggesting that local topographic effects may play a larger role in dune orientation than regional winds

geochemical indicators of separate sources for eolian sands in the eastern mojave desert california and western arizona low stabilized sand dunes cover much of the cactus and la posa plains in western arizona near the town of parker the provenance of the dunes is not well defined and it had been hypothesized that they were possibly related to extensive eolian sand deposits in the eastern mojave desert of california on the other side of the colorado river major oxide analyses of bulk sand samples collected from southeastern california and western arizona show clear chemical differences the mojave sands all have sio 2 10 wt and na 2 o k 2 o 5 wt whereas the colorado river and arizona sands have sio 2 81 wt al 2 o 3 6 wt and na 2 o k 2 o 4 wt these results show that the stabilized dunes near parker are chemically indistinguishable from colorado river sands the chemical differences between the southeastern california sands and the western arizona sands are supported by x ray diffraction results that indicate these two sand populations have significant differences in the relative abundance of quartz and feldspar our data also indicate a near source origin for the mojave sands whereas the colorado river and arizona sands have undergone more prolonged chemical weathering the major oxide results are consistent with published trace element studies by others that clearly distinguished between mature and immature sands in california and colorado the quartz feldspar ratio may be amenable to measurement by some advanced remote sensing instruments

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

analysis of surface compositions in the oxia palus region on mars from mars global surveyor thermal emission spectrometer observations 1 we examine the distribution of thermal emission spectrometer tes derived surface compositions in the oxia palus region on mars through high spatial resolution mapping and integration with mars orbiter camera and mars orbiter laser altimeter data sets we also fit the basalt and andesite weathered basalt interpretations of tes surface type 1 and type 2 materials into multiple working hypotheses to describe the origin of surface compositions a mixing transition from surface type 1 to type 2 is observed in low albedo regions of southern acidalia planitia and may represent either 1 an influx of basaltic sediment from the southern highlands deposited on and mixed with andesitic volcanics 2 an influx of water transported basaltic sediment from the southern highlands that was altered and later deposited as a thin sedimentary veneer or 3 different degrees of weathering of indigenous basalt marking the geographic extent of submarine alteration of basaltic crust tes spectra of low albedo intracrater materials reveal that surface type 1 compositions form a central core on crater floors while type 2 compositions form a surrounding arc on the dark downwind sides of crater walls intracrater floor materials are interpreted as eolian sediment and wall materials are interpreted as either eolian sediment or eroded material from in place crater wall lithologies surface type 1 and type 2 compositions are also observed in adjacent low albedo wind streaks however a mixing trend is not as evident the mars pathfinder landing site and ares and tiu valles source regions are sufficiently blanketed by fine grained dust to prohibit the analysis of surface rock compositions

water on early mars possible subaqueous sedimentary deposits covering ancient cratered terrain in western arabia and sinus meridiani western arabia and northern sinus meridiani 30 n 10 s 40 w 40 e are almost entirely covered by wind eroded horizontally bedded sedimentary layers that lap against local topographic features this portion of mars ancient cratered terrain is relatively low 1 km elevation and flat sloping westward 0 7 m km over 3 000 km the region lacks valley network channels we propose that at some time in early martian history this region was under water the water hypothesis is strengthened by the presence of 1 a shore like contact between smooth surfaced deposits and ancient cratered terrain in central sinus meridiani 2 polygonal structures in northern sinus meridiani and 3 sand which cannot be from airfall possibly reworked by wind from the underlying sedimentary units the september 1997 arrival of mars global surveyor s thermal emission spectrometer offers an opportunity to begin to test this hypothesis by searching for carbonate and evaporite minerals among the sediment covering the region

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

non active dunes in the acheron fossae region of mars between the viking and mars global surveyor eras comparison of a high resolution viking image 422b10 8 m pixel with a mars orbiter camera image sp2 502 06 5 6 m pixel of dunes in the acheron fossae region of mars 38 n 135 w reveals that the dunes moved 1 pixel during a span of almost 21 earth years very shallow illumination in the moc image indicates the dunes are 1 5 m high the images indicate that any movement of these martian dunes is 0 4 m yr a rate that is less than the documented movement of comparable dunes on earth by a factor of up to 200 the acheron fossae dunes occur within a region of low thermal inertia indicating that the dunes may be stabilized by a pervasive dust cover alternatively the saltation threshold was not exceeded significantly at this location in more than 20 years

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

inference of dust opacities for the 1977 martian great dust storms from viking lander 1 pressure data abstract a eddington radiative transfer algorithm is used to compute the thermal tidal heating of a dusty martian atmosphere for a given set of dust optical depth effective single scattering albedo and phase function asymmetry parameter the resulting thermal tidal forcing is used in a classical atmospheric tidal model to compute the amplitudes of the surface pressure oscillations at the viking lander 1 site for the two 1977 martian great dust storms parametric studies show that the dust opacities and optical parameters derived from the viking lander imaging data are roughly representative of the global dust haze needed to reproduce the tidal surface pressure amplitudes also observed at lander 1 except that the model inferred asymmetry parameter is smaller during the onset of a great storm the observed preferential enhancement during dust storm onset of the semidiurnal tide at viking lander 1 relative to its diurnal counterpart is shown to be due primarily to the elevation of the tidal heating source in a very dusty atmosphere although resonant enhancement of the main semidiurnal tidal mode makes an important secondary contribution

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

analysis of regional gullies within noachis terra mars a complex relationship between slope surface material and aspect abstract the precise mechanisms by which martian hillside gullies erode and their dependence on the local environment remain subjects of debate we studied three sharp rimmed craters in noachis terra and 37 gully profiles using context camera ctx mars orbiter laser altimeter mola and high resolution stereo camera hrsc data we analysed the gully topographic profiles of seven gullies and nine dry ravines we measured slope properties using hrsc elevation data and used thermal inertia to infer material types of the gully sites we compared these with three nearby noachian age craters possessing crater wall slope angles within the range of previously observed gully formations in line with previous findings on individual gullies we found that the slope angles of gullies in our study area consistently reflect the inherited slope angles of the host escarpment suggesting that traditional slope based evidence of fluvial activity in martian gullies needs to be placed in context of its local environment we also observed a direct relationship between gully morphology and local composition of surface units martian gully features and possibly method of erosion appeared heavily influenced by changes in underlying geology and presence of erodible sediment examples included gully shape changing in accordance with type of erodible sediment we suggest that the degraded rims of gully free noachian craters precluded slope angles high enough to trigger creation of precursors to alcoves through mass wasting lack of these hollows has probably prevented the accumulation of enough ice rich sediment for gullies to form in our analysis reveals that there is a complex interdependence between slope processes and the local environment and global martian gully models may not work at the local scale

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

the southern westerlies in central chile holocene precipitation estimates based on a water balance model for laguna aculeo 33 50 s central chile 32 35 s lies at the northern border of strong influence of the westerly circulation belt westerlies and is therefore characterized by a steep precipitation gradient in this region quantitative reconstructions of holocene precipitation are scarce hence the present study estimates precipitation changes based on lake level fluctuations of laguna aculeo 33 50 s 70 54 w the lake level curve has been reconstructed using a multi proxy study of lake sediments lake level changes have been simulated using a simple water balance model as a result palaeo precipitation could be estimated uncertainties concerning the input parameters and past conditions have limitated the precision of precipitation estimates the results suggest that during the beginning of the holocene when the lake level 1 5 m was low precipitation was 200 mm year before 8000 cal yr bp the lake frequently dried out between 8000 and 6000 cal yr bp precipitation appeared to be higher 150 300 mm year and after about 6000 cal yr bp precipitation increased dramatically 350 450 mm year around 3000 cal yr bp modern lake level and precipitation 450 550 mm year were generally established the dry conditions during the early and mid holocene are in good agreement with other records from central chile and northern patagonia the westerlies were probably deflected southward by the southeast pacific subtropical high pressure cell during the mid and early holocene subsequently the increase in moisture in central chile during the late holocene appears to be strongly related to intensified westerly activity and probably also to increased el nino activity

new dust opacity mapping from viking infrared thermal mapper data global dust opacity mapping for mars has been carried forward using the approach described by martin 1986 for viking ir thermal mapper data new maps are presented for the period from the beginning of viking observations until ls 210 in 1979 1 36 mars years this range includes the second and more extensive planet encircling dust storm observed by viking known as storm 1977b improvements in approach result in greater time resolution and smaller noise than the earlier work a strong local storm event filled the hellas basin at ls 170 prior to the 1977a storm dust is retained in equatorial regions following the 1977b storm far longer than in mid latitudes minor dust events appear to raise the opacity in northern high latitudes during northern spring additional mapping with high time resolution has been done for the periods of time near the major storm origins in order to search for clues to the mechanism of storm initiation the first evidence of the start of the 1977b storm is pushed back to ls 274 2 preceding signs of the storm in images by about 15 hours

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