dust devil speeds directions of motion and general characteristics observed by the mars express high resolution stereo camera abstract a total of 205 dust devils were detected in 23 high resolution stereo camera hrsc images taken between january 2004 and july 2006 with the esa mars express orbiter in which average dust devil heights were 660 m and average diameters were 230 m for the first time dust devil velocities were directly measured from orbit and range from 1 to 59 m s the observed dust devil directions of motion are consistent with data derived from a general circulation model gcm in some respects hrsc dust devil properties agree favorably with data from the nasa mars exploration rover spirit dust devil analyses the spatial distribution of the active dust devils detected by hrsc supports the conjecture that the ascending branch of the hadley circulation is responsible for the increase in dust devil activity especially observed during southern summer between 50 and 60 s latitude combining the dust lifting rate of 19 kg km2 sol derived from the spirit observations with the fewer in number but larger in size dust devils from various other locations observed by hrsc we suggest that dust devils make a significant contribution to the dust entrainment into the atmosphere and to the martian dust cycle

tertiary paleoweatherings and silcretes in the southern paris basin abstract the southern border of the paris basin has undergone successive weathering events during the tertiary fluviatile and lacustrine deposits are scattered being mainly confined to several north south trending grabens these are generally devoid of fossils which would allow them to he dated a discontinuous blanket of weathering products is the main record of this long period of continental evolution these weathered materials result mainly from alteration of the cretaceous flint bearing chalk and are composed of corroded flints enclosed in brown and red mottled kaolinitic clays in places the succession of cretaceous layers has been preserved in the paleoprofiles testifying of in situ paleoprofiles but most profiles are the result of reworking as shown by the mixture of materials coming from different stratigraphic horizons these paleoweathered materials led to various residual and sedimentary deposits from flint breccia along the graben scarps to flint gravels clay deposits and lacustrine limestones in the grabens these weathering products correspond to warm and humid climatic periods their reworking results from a renewal of tectonic activities combined with a period of drier climate a later silicification process has affected the weathering cover and the tertiary deposits of the graben as well extensive pedogenic silcrete crusts with typical columnar structures developed on the plateaux this period of silicification corresponds to a climate with a marked dry season which led to the development of glacis massive silicification preserving the primary sedimentary structures developed in the grabens this was sub contemporaneous with the pedogenic silcretes which lie over them and which were developed at their expense the significance of the massive silicification is not yet clear nor the geochemical mechanism of their formation in the process primary clay minerals are destroyed and silica must have been fixed while aluminium was leached out of the profile the silcretes are covered by lacustrine limestones and calcretes which accumulated in the lowest parts of the paleolandscape and toward the centre of the basin they seal the silcrete development and are dated from upper eocene a period of very dry climates as shown by thick gypsum deposits in the center of the basin no remnants from oligocene miocene times are preserved in the region studied during late miocene the disruption of these landscapes took place because a very low sea level led to the renewal of erosion as a result residual landforms with siliceous crusts now cap the higher elevations

sutton alaska earthquake of 1984 evidence for activity on the talkeetna segment of the castle mountain fault system a magnitude 5 7 mb 5 2 ms earthquake occurred on 14 august 1984 14 km north of sutton in the vicinity of the mapped trace of the talkeetna segment of the castle mountain fault system the focal mechanism of the earthquake and the spatial distribution of well controlled aftershock hypocenters indicate that the shock involved dextral slip at 13 to 20 km depth on the talkeetna fault segment the depth of the shocks is consistent with the lack of observed surface breakage the sutton earthquake sequence plus recent small shocks recorded by the southern alaska seismograph network provide definitive evidence that the talkeetna segment of the fault system is active

recent high latitude icy mantle in the northern plains of mars characteristics and ages of emplacement 1 martian high latitude zones are covered with a smooth layered ice rich mantle containing characteristic polygonal patterns the mantle is especially uniform and homogeneous in the northern plains we performed a survey of decameter scale mantle textures and circular features including impact craters in the northern lowlands down to 50 n latitude strongly altered and mantled craters of impact and non impact origin form a population of subtle circular features below the mantle pits of non impact origin are numerous in some regions at lower latitudes impact craters superposed on the mantle are small and very sparse the inferred mean crater retention age of the mantle is 0 1 ma the spatial distribution of young craters suggests an age difference between the highest latitudes younger and some lower latitude regions older latitudinal trends in polygon textures agree with impact crater evidence for a latitudinal age progression of mantle properties

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

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

active dust devils in gusev crater mars observations from the mars exploration rover spirit 1 a full dust devil season was observed from spirit from 10 march 2005 sol 421 first active dust devil observed to 12 december 2005 sol 691 last dust devil seen this corresponds to the period ls 173 2 to 339 5 or the southern spring and summer on mars thermal emission spectrometer data suggest a correlation between high surface temperatures and a positive thermal gradient with active dust devils in gusev and that spirit landed in the waning stages of a dust devil season as temperatures decreased 533 active dust devils were observed enabling new characterizations they ranged in diameter from 2 to 276 m with most in the range of 10 20 m in diameter and occurred from about 0930 to 1630 hours local true solar time with the maximum forming around 1300 hours and a peak occurrence in southern late spring ls 250 horizontal speeds of the dust devils ranged from 1 to 21 m s while vertical wind speeds within the dust devils ranged from 0 2 to 8 8 m s these data when combined with estimates of the dust content within the dust devils yield dust fluxes of 3 95 10 9 to 4 59 4 kg m2 s analysis of the dust devil frequency distribution over the inferred dust devil zone within gusev crater yields 50 active dust devils km2 sol suggesting a dust loading into the atmosphere of 19 kg km2 sol this value is less than one tenth the estimates by cantor et al 2001 for regional dust storms on mars

aeolian behavior of dust in a simulated martian environment the behavior of aeolian dust particles 1 2 microns m in diameter was analyzed in a simulated martian environment three main areas have been investigated 1 characterizing spectral and aeolian properties of martian particles and natural wind blown terrestrial dust in order to identify a suitable surrogate martian dust 2 emplacement of the material in the simulated martian environment and 3 experimental procedures and testing in the martian surface wind tunnel marswit the first phase of the study involved choosing a terrestrial dust that closely resembled martian dust data accumulated from various sources suggest that martian dust is derived from the weathering of basaltic parent material nontronite clay being a good candidate composition a commercial clay carbondale red clay crc was determined to be an appropriate surrogate martian dust using a compressed air dust ejection system an air entrained dust cloud was generated which settled to cover the test section in the marswit this method best replicated the natural acrodynamic settling process presumed to exist on mars low pressure experiments were performed in the marswit facility located at the nasa ames research center moffett field california two separate wind tunnel floors were used for these experiments one provided an aerodynamically smooth surface flow and the other was an aerodynamically rough surface flow initial and momentary particle movement was recorded at friction velocities as low as 2 m s however the dust never reached fluid saltation threshold because individual particles less than 10 m typically do not saltate but pass into suspension an estimated dust flux of 3 7 x 10 7 g cm 2 s was determined for a friction velocity of 2 m s this flux could suspend about 10 000 metric tons of dust per second over the surface of mars the dust behavior on the smooth surface was markedly different than on the rough surface under martian conditions application of the processes described above to the martian environment suggests that on rocky surfaces dust suspension would first occur whereas smooth plains would require higher wind speeds for dust entrainment

mars dust devil track survey in argyre planitia and hellas basin dust devils and dust devil tracks have been frequently observed in viking orbiter and mars orbiter camera moc images but the parameters that control their distribution have been poorly constrained here we investigate the abundance of dust devil tracks in two large study areas argyre planitia and hellas basin using a survey of over 3000 moc narrow angle na images we report the effect of season elevation and surface properties on track distribution using measurements of dust devil track density the number of dust devil tracks per square kilometer in both areas dust devil tracks occur predominantly in summer and are rarely observed in winter the lifetime of dust devil tracks is inferred to be short i e less than a few months there is no unambiguous correlation of abundance with elevation rather the spatial distribution follows albedo patterns suggesting that dust availability controls the abundance of dust devil tracks we estimate the total dust lifting potential of dust devils using the average dust devil track density for argyre and hellas and conclude that unless the average dust devil track is greater than 20 m wide longer than 2 km and more than 40 mm deep they cannot account for the estimated global sedimentation rate in addition by comparing 2 mars years of observations we find no evidence of an increase in dust devil track density prior to the global dust storm that occurred in june 2001 we conclude that dust devils did not trigger this storm

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

deflation erosion rates for the parva member dorsa argentea formation and implications for the south polar region of mars 1 the origins of the surficial materials in the geologic units surrounding the martian southern polar region have been poorly constrained on the basis of pre mars global surveyor mgs data and studies mgs studies suggest that these units are the remnant of volatile loss from an originally massive volatile rich debris blanket or the result of fluidized slurries resulting from magma volatile interactions or impact shaking we use mars orbiter laser altimeter data to examine a region adjacent to the south polar layered terrain at 72 79 s and 230 275 e generally equivalent to the mapped parva member of the dorsa argentea formation daf the pedestal and ghost impact crater morphologies in this area suggest that extensive deposits of loosely consolidated materials have been removed from this region the parva member is thus likely to be the remaining debris blanket from the deflated remnant of an unprotected deposit that was originally similar to the buried daf deposits in the adjacent cavi member crater counts indicate that the parva member is of hesperian age and overlies an older noachian surface likely the highland cratered terrain npl1 if regional deflation began in the hesperian and continues through today the region has been exposed to erosion rates of 1 3 1 6 10 7 m yr however if deflation started later than the assumed times or ceased in the amazonian when deposition of the polar layered deposits began erosion rates as high as 2 5 2 10 7 m yr might have existed these erosion rates are within the range of published martian nonbedrock erosion rates of 10 8 10 5 m yr

formation of recent martian debris flows by melting of near surface ground ice at high obliquity the observation of small gullies associated with recent surface runoff on mars has renewed the question of liquid water stability at the surface of mars the gullies could be formed by groundwater seepage from underground aquifers however observations of gullies originating from isolated peaks and dune crests question this scenario we show that these landforms may result from the melting of water ice in the top few meters of the martian subsurface at high obliquity our conclusions are based on the analogy between the martian gullies and terrestrial debris flows observed in greenland and numerical simulations that show that above freezing temperatures can occur at high obliquities in the near surface of mars and that such temperatures are only predicted at latitudes and for slope orientations corresponding to where the gullies have been observed on mars

outwash plains and thermokarst on mars abstract the spatial distribution of different types of rampart craters on mars suggests a hemispheric asymmetry in the distribution of ground ice the northern plains especially major topographic depressions near the terminations of outflow channels have high percentages of rampart craters two of these basins acidalia and utopia planitiae received extraordinarily large amounts of water and sediment from the chryse and elysium outflow channels in both regions the analysis of high resolution viking pictures 12 m pixel indicates a concentration of kilometer scale depressions that are similar in size and form to thermokarstic features in yakutia siberia and parts of the arctic coastal plain of north america accordingly we infer that 1 utopia planitia and acidalia planitia may contain thick laterally continuous ice rich sedimentary deposits related to outflow channel forming floods and 2 these areas of mars may have experienced thermokarstic processes similar to modern thermokarstic processes in some periglacial regions of earth

scalloped terrains in the peneus and amphitrites paterae region of mars as observed by hirise abstract the peneus and amphitrites paterae region of mars displays large areas of smooth geologically young terrains overlying a rougher and older topography these terrains may be remnants of the mid latitude mantle deposit which is thought to be composed of ice rich material originating from airfall deposition during a high obliquity period less than 5 ma ago within these terrains there are several types of potentially periglacial features in particular there are networks of polygonal cracks and scalloped shaped depressions which are similar to features found in utopia planitia in the northern hemisphere this area also displays knobby terrain similar to the so called basketball terrains of the mid and high martian latitudes we use recent high resolution images from the high resolution imaging science experiment hirise along with data from previous mars missions to study the small scale morphology of the scalloped terrains and associated polygon network and knobby terrains we compare these with the features observed in utopia planitia and attempt to determine their formation process while the two sites share many general features scallops in peneus amphitrites paterae lack the diverse polygon network i e there is little variation in the polygon sizes and shapes and large curvilinear ridges observed in utopia planitia this points to a more homogeneous ice content within the substrate in the peneus amphitrites paterae region and implies that scallop formation is independent of polygon formation this work shows that as in utopia planitia sublimation of interstitial ice is a likely process explaining the formation of the scalloped depressions in the region of peneus amphitrites paterae therefore we provide a simplified scallop formation model based on sublimation of interstitial ice as proposed for utopia planitia we also show that the differences in scallop morphologies between the two regions may be explained by differences in near surface ice content sublimation rates and age of formation of the scalloped terrains

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

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

metastability of liquid water on mars abstract a simple model of local heat transport on mars demonstrates that transient melting of ice may occur in depressions and gullies nearly anywhere on the planet where thin ice is illuminated by normal incidence insolation an experiment has been performed to confirm the model of evaporation rate at low pressure reduction of radiative cooling due to gully geometry is shown to be important since appropriate meteorological topographic and optical conditions may occur on slopes nearly anywhere on the planet hydrological features such as gullies would likely form only where such ice might accumulate notably in sheltered locations at high latitudes it is suggested that cold trapping of winter condensation could concentrate a sufficient amount of ice to allow seasonal melting in gullies

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

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

thermokarst processes and the origin of crater rim gullies in utopia and western elysium planitia abstract we have identified a number of gullies that could be aqueous in origin near or at the rim of several impact craters in utopia planitia and western elysium planitia 30 0 59 0 n 241 0 291 0 w based on the sharpness of their incisions and the general absence of superposed craters we ascribe a relatively recent origin to the gullies scalloped depressions are commonplace throughout the region as well as on the crater walls rims and floors near the areas of gully issuance occasionally the depressions cross cut the gully debris aprons suggesting that the formation of some depressions is even more recent than that of the gullies previous research has proposed that the depressions are collapse basins formed by thermokarst processes on earth thermokarst landforms occur in areas of low gradient topography where the permanently frozen ground permafrost is ice rich and has undergone a change in thermal equilibrium this change can be triggered by long term or episodic cyclic climate change and accompanying rises in mean temperatures towards 0 c as well as by rises in seasonally sustained summer temperatures well above 0 c in order to explain the origin of the rim or near rim gullies we invoke high obliquity and the possibility that this region of mars experienced obliquity driven rises in temperature atmospheric pressure and humidity sufficient to keep surface water and near surface ground ice stable for extended periods of time we propose that gully formation is closely related to local freeze thaw processes that in turn generate a thermokarst landscape of which the gullies are a part this geological and climatological scenario comprises the following steps 1 an inundation of meltwater at high obliquity due to the thawing of an atmospherically deposited snowpack or ice sheet and the subsequent saturation of the underlying regolith to tens of metres of depth 2 loss of water on the surface perhaps as obliquity decreases slightly followed by the progressive freezing of the saturated regolith this creates an aggrading mass of ice rich regolith 3 obliquity induced temperature rises that engender the thaw drainage and partial evaporation of the near surface ice rich regolith 4 localised formation of thermokarst collapse basins alases as water is evacuated from these basins 5 formation of gullies near or at some impact crater rims as the result of meltwater migration from nearby alases through the thawed regolith to the areas of gully issuance although the plains materials in this region are in part very old possibly hesperian or even noachian the mantling deposits and their deformation by thermokarst processes appears to be relatively young this suggests that recent climatic conditions could have been episodically warmer and wetter than had been previously thought