planetary surface dating from crater size frequency distribution measurements partial resurfacing events and statistical age uncertainty abstract we describe the procedure to fit a cumulative production function polynomial to a partial crater size frequency distribution the technique is of particular use in deriving ages for surfaces which have undergone partial resurfacing events namely erosional or depositional events which have affected a limited diameter range of the crater population we demonstrate its use in obtaining times for both the surface formation and the resurfacing event we give a practical outline of the method for making age measurements from crater counts and how to identify resurfacing effects in the results we discuss the conversion of production function polynomials between common presentations and the statistical uncertainty of the determined ages with respect to the non linear chronology function and a minor refinement of data binning

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

fluid lava flows in gusev crater mars 1 rocks on the floor of gusev crater are basaltic in composition as determined from measurements by the mars exploration rover spirit on the basis of compositional data models of the basaltic lavas at the time of their emplacement suggest viscosities of 2 3 to 50 pa s dependent on the number of phenocrysts and vesicles that were present which would be more fluid than terrestrial tholeiitic lavas and comparable to mare lavas on the moon or archean high mg basalts on earth morphological data and crater counts derived from the high resolution stereo camera on mars express and other orbiters suggest that the lavas flooded gusev crater at about 3 65 b y and postdate older floor materials such as putative sediments emplaced by ma adim vallis

hydrated silicate minerals on mars observed by the mars reconnaissance orbiter crism instrument phyllosilicates a class of hydrous mineral first definitively identified on mars by the omega observatoire pour la mineralogie l eau les glaces et l activitie instrument preserve a record of the interaction of water with rocks on mars global mapping showed that phyllosilicates are widespread but are apparently restricted to ancient terrains and a relatively narrow range of mineralogy fe mg and al smectite clays this was interpreted to indicate that phyllosilicate formation occurred during the noachian the earliest geological era of mars and that the conditions necessary for phyllosilicate formation moderate to high ph and high water activity were specific to surface environments during the earliest era of mars s history here we report results from the compact reconnaissance imaging spectrometer for mars crism of phyllosilicate rich regions we expand the diversity of phyllosilicate mineralogy with the identification of kaolinite chlorite and illite or muscovite and a new class of hydrated silicate hydrated silica we observe diverse fe mg oh phyllosilicates and find that smectites such as nontronite and saponite are the most common but chlorites are also present in some locations stratigraphic relationships in the nili fossae region show olivine rich materials overlying phyllosilicate bearing units indicating the cessation of aqueous alteration before emplacement of the olivine bearing unit hundreds of detections of fe mg phyllosilicate in rims ejecta and central peaks of craters in the southern highland noachian cratered terrain indicate excavation of altered crust from depth we also find phyllosilicate in sedimentary deposits clearly laid by water these results point to a rich diversity of noachian environments conducive to habitability

a total electron content space weather study of the nighttime weddell sea anomaly of 1996 1997 southern summer with topex poseidon radar altimetry this paper reports on a total electron content space weather study of the nighttime weddell sea anomaly overlooked by previously published topex poseidon climate studies and of the nighttime ionosphere during the 1996 1997 southern summer to ascertain the morphology of spatial tec distribution over the oceans in terms of hourly geomagnetic longitudinal and summer winter variations the topex tec magnetic and published neutral wind velocity data are utilized to understand the underlying physical processes the tec results are combined with inclination and declination data plus global magnetic field line maps to investigate spatial and temporal tec variations geographic magnetic latitudes and local times are computed as results show the nighttime weddell sea anomaly is a large 1 600 2 22 million km2 estimated for a steady ionosphere space weather feature extending between 200 e and 300 e geographic it is an ionization enhancement peaking at 50 s 60 s 250 e 270 e and continuing beyond 66 s it develops where the spacing between the magnetic field lines is wide medium easterly declination is large medium 20 50 and inclination is optimum 55 s its development and hourly variations are closely correlated with wind speed variations there is a noticeable 43 reduction in its average area during the high magnetic activity period investigated southern summer nighttime tecs follow closely the variations of declination and field line configuration and therefore introduce a longitudinal division of four indian western eastern pacific atlantic northern winter nighttime tecs measured over a limited area are rather uniform longitudinally because of the small declination variation topex maps depict the expected strong asymmetry in tec distribution about the magnetic dip equator

analysis of tec data from the topex poseidon mission 1 topex poseidon mission has provided an extensive database of vertical tec over the ocean since august 1992 data from nearly 10 years of topex tec observations were analyzed to study the tec climatology first tec data were binned by season geomagnetic activity and solar activity to create longitudinally averaged tec maps in magnetic latitude and local time these maps show the annual and semiannual anomalies well known from climatological studies of nmf2 but lack the seasonal anomaly because of the longitudinally averaged binning the equatorial anomaly is the most prominent feature in the maps and they show strong tec variations with solar activity but relatively weak variations with geomagnetic activity in our three kp bins compared with the low solar activity conditions f10 7 120 the tec values for f10 7 120 are much larger and the equatorial anomaly lasts longer into the night up to midnight during geomagnetically active periods the tec maps generally show a noticeable increase at low latitudes for f10 7 120 but this effect is barely detectable for f10 7 120 finally three longitudinal bins indian pacific and atlantic were added in order to see how the tec morphology varies with longitude the tec measurements display strong longitudinal variations that closely follow the longitudinal variation of the magnetic declination in the southern pacific where the declination is positive and large the diurnal tec variations significantly differ from those in the other longitude sectors where the magnetic declination is negative in the southern hemisphere also at noon the phase of the longitudinal tec variation is typically opposite to that at midnight

large scale traveling ionospheric disturbances impacting equatorial ionization anomaly development in the local morning hours of the halloween superstorms on 29 30 october 2003 this study investigates the development of eia like features during the halloween superstorms these features are similar to a well developed equatorial ionospheric anomaly eia and therefore suggest superfountain effects we tracked eia like features in the early morning sector of 29 30 october 2003 and at around midday on 30 october their plasma environment was studied with field aligned plasma density vertical plasma drift electron temperature and vertical plasma flow profiles coupled thermosphere ionosphere plasmasphere ctip simulations reproduced storm generated equatorward wind surges when these eia like features appeared early morning on 29 30 october there was no forward fountain circulation only large scale traveling ionospheric disturbances tids and strong equatorward winds were present these provide observational evidence that large scale tids created large plasma depletions over the dip equator and with the aid of equatorward winds some large enhancements at 30 n geomagnetic resulting in the development of early morning eia like features we identified tid signatures in the equatorial and midlatitude ionosonde and magnetometer data and studied eia like features at around midday on 30 october utilizing non field aligned topex tec 2000 ut and published champ tec 2030 ut 2200 ut line plots according to our analysis the eia like features seen in the tec data were created by large scale tids at 2000 and 2030 ut and by the combined effects of large scale tids and forward superfountain at 2200 ut ctip simulations demonstrate the crucial role of the neutral winds mechanical or direct effects in the development of high plasma densities at low midlatitudes

geologic evolution of the eastern eridania basin implications for aqueous processes in the southern highlands of mars the terra sirenum region of mars is thought to have hosted the eridania paleolake during the late noachian early hesperian and it offers an insight into the regional aqueous history of mars we focus on four basins including atlantis simois caralis and an unnamed basin they are hypothesized to have hosted isolated lakes after the drainage of the eridania lake we produced a geologic map and derived model absolute ages of our main mapped units the map and model ages enable us to interpret the geologic history of the region the basin floors are covered by light toned materials containing fe mg phyllosilicates across most of the region the electris unit covers the highlands and is eroded into mesas the deposition of this unit corresponds to air fall and or fluvial mechanisms that transported the material into the basins and accumulated it on the plateaus and basin floors and rims the deposits on the basin floors were later degraded into light toned knobs that are rich in fe mg phyllosilicates on the rim of the simois and the unnamed basins a sequence of al phyllosilicates on top of fe mg phyllosilicates has been observed these al phyllosilicate rich materials may have been formed by pedogenic leaching the presence of chloride in the area suggests that a playa environment prevailed during the last stage of water presence or after desiccation of the lakes in the early amazonian the last aqueous activity cemented the postlacustrine air fall deposits in the basins and shows that liquid water was present in terra sirenum long after the noachian

hirise views enigmatic deposits in the sirenum fossae region of mars hirise images together with other recent orbital data from mars define new characteristics of enigmatic hesperian aged deposits in sirenum fossae that are mostly 100 200 m thick drape kilometers of relief and often display generally low relief surfaces new characteristics of the deposits previously mapped as the electris deposits include local detection of meter scale beds that show truncating relationships a generally light toned nature and a variably blocky weakly indurated appearance boulders shed by erosion of the deposits are readily broken down and contribute little to talus thermal inertia values for the deposits are 200 j m 2 k 1 s 1 2 and they may incorporate hydrated minerals derived from weathering of basalt the deposits do not contain anomalous amounts of water or water ice deflation may dominate degradation of the deposits over time and points to an inventory of fine grained sediment together with constraints imposed by the regional setting on formation processes these newly resolved characteristics are most consistent with an eolian origin as a loess like deposit comprised of redistributed and somewhat altered volcanic ash constituent sediments may be derived from airfall ash deposits in the tharsis region an origin directly related to airfall ash or similar volcanic materials is less probable and emplacement by alluvial fluvial impact lacustrine or relict polar processes is even less likely

seismic velocity models for heat zones in athabasca tar sands recent laboratory and field studies indicate that the p wave velocity in athabasca tar sands decreases when temperature increases during steam injection in this paper we derive time variant velocity models from seismic traveltime inversions of both reflection and borehole data prior to steam injection three dimensional 3 d reflector velocity depth models are established using image ray con versions of traveltimes to depth the changes in velocity due to steam injection are modeled by inverting traveltime data from seismic monitor surveys after steam injection and comparing these results to velocities computed prior to steam injection velocity models are essentially deter mined by traveltimes from the 3 d seismic reflection survey the surface to wellbore data traveltimes show the ex pected delay caused by steam injection but do not significantly alter the velocity model produced by reflec tion traveltimes for seismic monitor surveys low velocity zones show a very good correlation with zones of temperature increase at injector well positions the results indicate that velocity models obtained from seismic traveltimes may prove useful in detecting steam fronts in tar sands

evoluton of polygonal fracture patterns in lava flows cooling induced fractures also known as columnar joints divide basaltic lava flows into prismatic columns with polygonal cross sections the regularity and symmetry of the fracture patterns have long fascinated naturalists in view of the recent selection of two candidate nuclear waste sites in areas where polygonally fractured volcanic rocks are located a better understanding of the fracture patterns is required field data indicate that the tetragonal networks at flow surfaces evolve systematically to hexagonal networks as the joints grow inward during solidification of lava this evolution occurs by the gradual change of most orthogonal intersections to nonorthogonal intersections of about 120 degrees the surface features and intersection geometries of columnar joints show that joint segments at any given level form sequentially yet harmoniously

storm enhanced plasma density and polar tongue of ionization development during the 15 may 2005 superstorm we investigate the ionosphere s global response to the 15 may 2005 superstorm in terms of storm evolution and ionospheric electrodynamics our aim is to study the global distribution of plasma and the resultant large scale ionospheric features including the equatorial ionization anomaly eia storm enhanced density sed and polar tongue of ionization toi we have combined multi instrument ionospheric data solar and terrestrial magnetic data and polar convection maps results reveal the prompt penetration of the interplanetary electric field to the polar region and then to the equator with a dusk to dawn polarity during the initial phase and with a dawn to dusk polarity during the main phase this drove during the initial phase a weak eastward equatorial electrojet eej in the american sector at nighttime and a weak westward eej in the indian australian sector at daytime during the main phase these eejs intensified and changed polarities sed and polar toi development was observed prior to and during the initial phase at evening premidnight hours over north america and during the main phase in the south at afternoon evening hours in the australian sector during the main phase and early in the recovery phase the eia sed structure was well formed in the asian longitude sector then polar toi development was absent in the north because of the long distance from the magnetic pole but was supported in the south because of the closeness of daytime cusp and magnetic pole thus the eia sed toi structure developed twice but each time in a different longitude sector and with different characteristics

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

duration of the ma adim vallis gusev crater hydrogeologic system mars abstract ma adim vallis and gusev crater aeolis subquadrangle of mars formed a complex hydrogeologic system through time crater statistics over five geologic units coupled with morphologic and geologic observations show that this system was active over a period ranging from 0 7 to about 2 billion years these results make the floor of gusev crater one of the most prominent martian depositional features the last aqueous sedimentary deposition could have occurred during early amazonian

the effect of atmospheric pressure on the dispersal of pyroclasts from martian volcanoes a planetary global circulation model developed by the laboratoire de meteorologie dynamique lmd was used to simulate explosive eruptions of ancient martian volcanoes into paleo atmospheres with higher atmospheric pressures than that of present day mars atmospheric pressures in the model were varied between 50 mbar and 2 bars in this way it was possible to investigate the sensitivity of the volcanic plume dispersal model to atmospheric pressure it was determined that the model has a sensitivity to pressure that is similar to its sensitivity to other atmospheric parameters such as planetary obliquity and season of eruption higher pressure atmospheres allow volcanic plumes to convect to higher levels meaning that volcanic pyroclasts have further to fall through the atmosphere changes in atmospheric circulation due to pressure cause pyroclasts to be dispersed in narrower latitudinal bands compared with pyroclasts in a modern atmosphere atmospheric winds are generally slower under higher pressure regimes however the final distance traveled by the pyroclasts depends greatly on the location of the volcano and can either increase or decrease with pressure the directionality of the pyroclast transport however remains dominantly east or west along lines of latitude augmentation of the atmospheric pressure improves the fit between possible ash sources arsia and pavonis mons and the medusae fossae formation a hypothesized ash deposit

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

mineralogy of the nili fossae region with omega mars express data 2 aqueous alteration of the crust 1 nili fossae is a region with fresh exposures of old material omega spectral data have revealed a strong diversity of minerals in the nili fossae region including mafic minerals and phyllosilicates phyllosilicates are found to be primarily fe rich smectites a type of clay minerals these phyllosilicates are observed only on the noachian crust in four types of locations three are without any signatures other than phyllosilicates on 1 smooth layered deposits 2 massive exhumed material and 3 crater ejecta and one type of location is associated with olivine 4 over an altered mafic unit this diversity suggests a widespread liquid water activity and a variety of alteration processes the formation of phyllosilicates underwent considerable reduction if not cessation by the time of formation of syrtis major lava flows in the hesperian period phyllosilicates are spatially and chronologically disconnected from the fluvial and depositional landforms observed in the nili fossae region observations suggest that these landforms formed after the extensive formation of phyllosilicates during short periods of time and or temperatures close to freezing

theoretical study of the ionospheric weddell sea anomaly using sami2 1 the ionospheric weddell sea anomaly wsa was first reported more than five decades ago based on ionosonde data near the antarctica peninsula the wsa is an ionospheric structure characterized by a larger nighttime electron density than daytime density recent satellite observations indicate that the wsa can extend from south america and antarctica to the central pacific the major physical mechanisms that have been suggested for the wsa formation are an equatorward neutral wind an electric field the photoionization and the downward diffusion from the plasmasphere on the basis of the theoretical modeling performed in this study using the sami2 model an equatorward neutral wind is identified as the major cause of the wsa while the downward flux from the plasmasphere provides an additional plasma source to enhance or maintain the density of the anomalous structure

a large sedimentary basin in the terra sirenum region of the southern highlands of mars abstract different lines of evidence point to hydrological cycling in the martian past the extent duration and magnitude of this cycling remains unclear as well as the magnitude of aqueous processes on the surface here we provide geomorphic and mineralogic evidence of a large inter crater sedimentary basin located in the terra sirenum region which was once covered by a body of liquid water with an areal extent of at least 30 000 km 2 and a depth of approximately 200 m the topographic basin which is modified by a number of large impact craters is partly controlled by ancient impact and tectonic structures as a result of evaporation of the large body of water salt flats formed in the lowest topographic reaches of the basin hydrated phyllosilicates occur in close proximity to the salt flats and in the ejecta and rim materials of small impact craters with stratigraphic relations that suggest that they underlie the evaporite deposits crater statistics place the maximum age of aqueous activity during the late noachian epoch the relatively pristine mineral deposits in the basin have a high potential to yield information of the geochemistry and water activity during the ancient noachian period when conditions were seemingly more conducive to life

geomorphology of ma adim vallis mars and associated paleolake basins 1 ma adim vallis one of the largest valleys in the martian highlands appears to have originated by catastrophic overflow of a large paleolake located south of the valley heads ma adim vallis debouched to gusev crater 900 km to the north the landing site for the spirit mars exploration rover support for the paleolake overflow hypothesis comes from the following characteristics 1 with a channel width of 3 km at its head ma adim vallis originates at two eastern and western gaps incised into the divide of the 1 1 m km2 enclosed eridania head basin which suggests a lake as the water source 2 the sinuous course of ma adim vallis is consistent with overland flow controlled by preexisting surface topography and structural control is not evident or required to explain the valley course 3 the nearly constant 5 km width of the inner channel through crater rim breaches the anastomosing course of the wide western tributary the migration of the inner channel to the outer margins of bends in the valley s lower reach a medial sedimentary bar 200 m in height and a step pool sequence are consistent with modeled flows of 1 5 106 m3 s peak discharges were likely higher but are poorly constrained by the relict channel geometry 4 small direct tributary valleys to ma adim vallis have convex up longitudinal profiles suggesting a hanging relationship to a valley that was incised quickly relative to the timescales of tributary development 5 the eridania basin had adequate volume between the initial divide and the incised gap elevations to carve ma adim vallis during a single flood 6 the eridania basin is composed of many overlapping highly degraded and deeply buried impact craters the floor materials of the six largest craters have an unusually high internal relief 1 km and slope 0 5 1 5 among degraded martian craters which are usually flat floored long term fluvial sediment transport appears to have been inhibited within these craters and the topography is inconsistent with basaltic infilling 7 fluvial valleys do not dissect the slopes of these deeper crater floor depressions unlike similar slopes that are dissected at higher levels in the watershed these characteristics 6 7 suggest that water mantled at least the lower parts of the eridania basin floor throughout the period of relatively intense erosion early in martian history the lake level increased and an overflow occurred near the close of the noachian age determined using 5 km crater counts initially the eridania basin debouched northward at two locations into the intermediate basin a highly degraded impact crater 500 km in diameter as this intermediate basin was temporarily filled with water erosion took place first along the lower northern reach of ma adim vallis debouching to gusev crater the western overflow point was later abandoned and erosion of the intermediate basin interior was concentrated along the eastern pathway subsequent air fall deposition impact gardening tectonism and limited fluvial erosion modified the eridania basin region so evidence for a paleolake is restricted to larger landforms that could survive post noachian degradation processes

martian layered fluvial deposits implications for noachian climate scenarios 1 fluvial deposits in a basin north of holden crater exhibiting a sinuous anabranching pattern are of deltaic or fan origin channel width and meander wavelength indicate persistent flow magnitudes of about 700 m3 s if these flows were produced by quasi periodic climate episodes involving typical terrestrial style precipitation the deposit required thousands to millions of years to accumulate however a scenario of deposition during a few short episodes of constant heavy precipitation resulting from large impacts cannot be excluded

planetary surface dating from crater size frequency distribution measurements spatial randomness and clustering we describe a quantitative procedure to measure the degree of clustering in an observed crater population relative to a series of randomly distributed populations we split the population by according to crater size to be able to identify clustering at different scales and find that a clustering analysis based on the mean 2nd closest neighbour distance measure more closely corresponds to visual interpretations of the spatial configuration than the mean closest neighbour distance standard deviation of adjacent area is found in certain cases to be an even more sensitive measure the technique is demonstrated for two sites on mars we were able to make use of a case where the spatial distribution was less clustered than random to reveal the transition between a crater population superimposed on a lava flow and that belonging to an underlying unit in general this type of analysis may give a better insight into the post formation modification of studied units enabling a more precise classification of which sizes of craters derive from the original accumulation population and which from areas resurfaced by later modification events consequentially improving the accuracy of dating resurfacing events clustering analysis is thus an additional tool for understanding the structure of a crater population and the effects causing an observed population to differ from an ideal one

a decade of shear wave splitting in the earth s crust what does it mean what use can we make of it and what should we do next it is 10 years since shear wave splitting throught to be diagnostic of some form of seismic anisotropy was first positively identified in the earth s crust from the beginning it was argued that the splitting was probably associated with the presence of stress aligned cracks inclusions in the crust and that this would provide the opportunity for monitoring the in situ geometry of cracks and stress in a variety of different circumstances and in a variety of different applications

amazonian aged fluvial system and associated ice related features in terra cimmeria mars abstract the martian climate throughout the amazonian is widely believed to have been cold and hyper arid very similar to the current conditions however ubiquitous evidence of aqueous and glacial activity has been recently reported including channels that can be tens to hundreds of kilometres long alluvial and fluvial deposits ice rich mantles and glacial and periglacial landforms here we study a 340 km long fluvial system located in the terra cimmeria region in the southern mid latitudes of mars the fluvial system is composed of an upstream catchment system with narrow glaciofluvial valleys and remnants of ice rich deposits we observe depositional features including fan shaped deposits and erosional features such as scour marks and streamlined islands at the downstream section of this fluvial system is an outflow channel named k r n valles which displays a unique braided alluvial fan and terminates on the floor of the ariadnes colles basin our observations point to surface runoff of ice snow melt as the water source for this fluvial activity according to our crater size frequency distribution analysis the entire fluvial system formed during early to middle amazonian between 1 8 0 2 0 2 ga to 510 40 40 ma hydraulic modelling indicates that the k r n valles and consequently the alluvial fan formation took place in geologically short term event s we conclude that liquid water was present in terra cimmeria during the early to middle amazonian and that mars during that time may have undergone several episodic glacial related events

comment on quantitative measurements of shear wave polarizations at the anza seismic network southern california implications for shear wave splitting and earthquake prediction by richard c aster peter m shearer and jon berger

variability of rock texture and morphology correlated with the clay bearing units at mawrth vallis mars 1 the clay units at mawrth vallis have been well characterized in hyperspectral data however a similar study of high spatial resolution high resolution imaging science experiment hirise data has not been previously conducted here the textures of the clay units are described and related to mineralogy across the central mawrth vallis region the nontronite bearing rocks appear tan in hirise color data and are polygonally fractured with polygons 2 5 m across in some cases the fractures appear wider and or have darker fill or the rocks are a darker brown the montmorillonite bearing rocks appear blue with regular polygons 0 5 1 5 m across sometimes there are larger polygons surrounded by regular polygons a square fracture pattern or the color appears yellow or mottled blue yellow kaolinite rich rocks are the brightest outcrops and are nonpolygonally fractured regions with spectra consistent with hydrated silica or the ferrous mineral component do not have unique textures hydrated silica bearing rocks appear yellow or mottled with a regular polygonal texture or yellow with hummocky appearance with no polygons it is also possible that dust sand on the surface alters the montmorillonite spectrum to appear like that of hydrated silica the ferrous component may be expressed as mottled coloring or as a bright fracture fill the nontronite and montmorillonite bearing units have remarkably consistent textures in this region allowing them to be uniquely identified in the mawrth vallis region in nonhyperspectral data sets such as ctx and hirise the morphology of the polygons in these two units suggests that their formation is likely dominated by desiccation and controlled by composition

clay minerals in delta deposits and organic preservation potential on mars clay rich sedimentary deposits are often sites of organic matter preservation and have therefore been sought in mars exploration however regional deposits of hydrous minerals including phyllosilicates and sulphates are not typically associated with valley networks and layered sediments that provide geomorphic evidence of surface water transport on early mars the compact reconnaissance imaging spectrometer for mars crism has recently identified phyllosilicates within three lake basins with fans or deltas that indicate sustained sediment deposition eberswalde crater holden crater and jezero crater here we use high resolution data from the mars reconnaissance orbiter mro to identify clay rich fluvial lacustrine sediments within jezero crater which has a diameter of 45 km the crater is an open lake basin on mars with sedimentary deposits of hydrous minerals sourced from a smectite rich catchment in the nili fossae region we find that the two deltas and the lowest observed stratigraphic layer within the crater host iron magnesium smectite clay jezero crater holds sediments that record multiple episodes of aqueous activity on early mars we suggest that this depositional setting and the smectite mineralogy make these deltaic deposits well suited for the sequestration and preservation of organic material

analysis of polygonal cracking patterns in chloride bearing terrains on mars indicators of ancient playa settings the ancient southern highlands on mars 3 5 gyr old contain 600 regions that display spectral evidence in the infrared for the presence of chloride bearing materials many of these locations were previously reported to display polygonal cracking patterns we studied more than 80 of the chloride bearing terrains using high resolution 0 25 0 5 m pixel images as well as near infrared spectral data to characterize the surface textures and the associated cracking patterns and mineralogies our study indicates that 75 of the studied locations display polygonal cracks that resemble desiccation cracks while some resemble salt expansion thrust polygons furthermore we detect spectrally the presence of smectites in association with 30 of the studied fractured terrains we note that smectites are a special class of swelling clay minerals that can induce formation of large desiccation cracks as such we suggest that the cracking patterns are indicative of the presence of smectite phyllosilicates even in the absence of spectral confirmation our results suggest that many chloride bearing terrains have a lacustrine origin and a geologic setting similar to playas on earth such locations would have contained ephemeral lakes that may have undergone repeated cycles of desiccation and recharging by a near surface fluctuating water table in order to account for the salt phyllosilicates associations these results have notable implications for the ancient hydrology of mars we propose that the morphologies and sizes of the polygonal cracks can be used as paleoenvironmental as well as lithological indicators that could be helpful in planning future missions

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

topography of mars from global mapping by hrsc high resolution digital terrain models and orthoimages characteristics and performance abstract we report on the results of the mars express high resolution stereo camera hrsc experiment pertaining to one of its major aims mapping the surface of mars by high resolution digital terrain models dtm up to 50 m grid spacing and orthoimages up to 12 5 m resolution we introduce the specifications and characteristics of these data products and give an overview of the procedures that have been developed and are applied for their derivation we also address the performance characteristics of the mapping project related to different aspects of internal accuracy accuracy with respect to the global reference system and regional aspects using adaptive processing techniques for terrain reconstruction and a revised approach to the improvement of orientation data a mean precision of the resulting 3d points of about 12 m is obtained exceeding the mean ground resolution of the stereo images using mars orbiter laser altimeter mola data the hrsc models are firmly tied to the global reference system at the scale of the hrsc dtm grid spacing in the lateral dimension and to within few meters vertically hrsc high resolution dtms are typically generated using a grid size of about 2 times the mean ground resolution but usually not larger than 3 times the mean ground resolution and not smaller than 3 times the precision of the integrated 3d points derived from stereo image analysis statistically every grid cell is based on at least one measured 3d point thus horizontal dtm resolution is well established with regard to the precision and density of the derived 3d points while the concurrent aim of a detailed terrain representation at maximum possible resolution is pursued comparison with the dtm derived from mola data allows us to identify specific advancements related to this updated view of martian topography we also address the mapping performance of hrsc in comparison to mola with respect to latitude and to different surface types and morphologies finally comparison with mola highlights typical complementarities of the two different approaches for mapping planetary surfaces

distribution and formation of chlorides and phyllosilicates in terra sirenum mars 1 the terra sirenum region of mars located in the noachian southern highlands is mineralogically diverse providing unique insight into ancient aqueous processes analyses of remote sensing data over the region indicate the presence of both fe or mg rich phyllosilicates and a spectrally unique deposit interpreted to be rich in chloride salts the stratigraphic relationships indicate that the phyllosilicates are part of the ancient highland crust and that the salts were deposited at a later time in some instances there is clear morphological evidence that salts were mobilized and deposited by near surface waters

the fracture criticality of crustal rocks summary the shear wave splitting observed along almost all shear wave ray paths in the earth s crust is interpreted as the effects of stress aligned fluid filled cracks microcracks and preferentially oriented pore space once away from the free surface where open joints and fractures may lead to strong anisotropy of 10 per cent or greater intact ostensibly unfractured crustal rock exhibits a limited range of shear wave splitting from about 1 5 to 4 5 per cent differential shear wave velocity anisotropy interpreting this velocity anisotropy as normalized crack densities a factor of less than two in crack radius covers the range from the minimum 1 5 per cent anisotropy observed in intact rock to the 10 per cent observed in heavily cracked almost disaggregated near surface rocks this narrow range of crack dimensions and the pronounced effect on rock cohesion suggests that there is a state of fracture criticality at some level of anisotropy between 4 5 and 10 per cent marking the boundary between essentially intact and heavily fractured rock when the level of fracture criticality is exceeded cracking is so severe that there is a breakdown in shear strength the likelihood of progressive fracturing and the dispersal of pore fluids through enhanced permeability the range of normalized crack dimensions below fracture criticality is so small in intact rock that any modification to the crack geometry by even minor changes of conditions or minor deformation particularly in the presence of high pore fluid pressures may change rock from being essentially intact below fracture criticality to heavily fractured above fracture criticality this recognition of the essential compliance of most crustal rocks and its effect on shear wave splitting has implications for monitoring changes in any conditions affecting the rock mass these include monitoring changes in reservoir evolution during hydrocarbon production and enhanced oil recovery and in monitoring changes before and after earthquakes amongst others

extensive linear ridge networks in nili fossae and nilosyrtis mars implications for fluid flow in the ancient crust 1 we have undertaken high resolution mapping of the distribution physical characteristics orientation and stratigraphic occurrence of 4000 linear ridge segments in two study areas the nilosyrtis highlands and the nili fossae region covering 1 105 km2 ridges are typically hundreds of meters in length meters in width and up to tens of meters in height ridges form intersecting networks of anastomosing and bifurcating segments and consequently have variable orientations ridges are expressed in altered and brecciated basement materials on the floors and rims of impact craters deeply eroded by fluvial and other processes the ridge bearing basement is the lowest exposed stratigraphic unit and is overlain by a relatively unaltered mafic cap rock ridges are observed to terminate at the contact of these two units we interpret the ridges to represent a complex of fractures faults shear zones clastic and melt bearing dikes and pseudotachylytes that have been variably indurated by fluid percolation and mineralization the fluid conduits were hardened relative to the host rock and are expressed as ridges due to differential erosion the orientations of the exhumed ridges record the state of stress in the crust at the time of formation in nili fossae a significant population of ridges is aligned with the orientations of the nili fossae graben indicating that their emplacement may be related to crustal loading of the isidis basin after the impact event the association of ridges with the hydrated mineral bearing basement suggests that in the postimpact environment the fractures served as conduits of preferential fluid flow which were cemented by mineral precipitation

stratigraphy in the mawrth vallis region through omega hrsc color imagery and dtm abstract the mawrth vallis region contains an extensive at least 300 km 400 km and thick 300 m finely layered at meter scale clay rich unit detected by omega we use omega hrsc dtms derived from stereoscopic imagery hrsc color imagery and high resolution imagery such as moc ctx and hirise to characterize the geometry and the composition of the clay rich unit at the regional scale our results show that the clay bearing unit can be divided into sub units on the basis of differences in color and composition in false color visible imagery alternating white bluish and orange red colored units correspond to a compositional succession of respectively al and fe or mg phyllosilicate rich material geological cross sections are presented along the principal outcrops of the region in order to define the stratigraphy of these sub units this method shows that the dips of the sub units are frequently close to the slopes of the present topography except for scarps visible at the dichotomy boundary inside impact craters walls and outcrops inside mawrth vallis in addition to the al and fe or mg phyllosilicate rich sub units an altered surface is identified as the lower basement unit we propose two possible end member scenarios to explain the derived stratigraphy 1 alteration of volcaniclastic aeolian or aqueous layered deposits of various compositions by groundwater resulting in distinct altered rocks or 2 alteration coeval with the deposition of sediments under varying chemical conditions in wet pedodiagenetic environment

characterization of phyllosilicates observed in the central mawrth vallis region mars their potential formational processes and implications for past climate mawrth vallis contains one of the largest exposures of phyllosilicates on mars nontronite montmorillonite kaolinite and hydrated silica have been identified throughout the region using data from the compact reconnaissance imaging spectrometer for mars crism in addition saponite has been identified in one observation within a crater these individual minerals are identified and distinguished by features at 1 38 1 42 1 91 and 2 17 2 41 m there are two main phyllosilicate units in the mawrth vallis region the lowermost unit is nontronite bearing unconformably overlain by an al phyllosilicate unit containing montmorillonite plus hydrated silica with a thin layer of kaolinite plus hydrated silica at the top of the unit these two units are draped by a spectrally unremarkable capping unit smectites generally form in neutral to alkaline environments while kaolinite and hydrated silica typically form in slightly acidic conditions thus the observed phyllosilicates may reflect a change in aqueous chemistry spectra retrieved near the boundary between the nontronite and al phyllosilicate units exhibit a strong positive slope from 1 to 2 m likely from a ferrous component within the rock this ferrous component indicates either rapid deposition in an oxidizing environment or reducing conditions formation of each of the phyllosilicate minerals identified requires liquid water thus indicating a regional wet period in the noachian when these units formed the two main phyllosilicate units may be extensive layers of altered volcanic ash other potential formational processes include sediment deposition into a marine or lacustrine basin or pedogenesis

a large paleolake basin at the head of ma adim vallis mars at 8 to 15 kilometers wide ma9adim vallis is one of the largest valleys in the martian highlands although a groundwater source was previously suggested the channel originates at a spillway in the divide of a 3 000 000 square kilometer closed drainage basin the interior morphology of this source basin including likely shoreline features following topographic contours suggests that ma9adim vallis was created through catastrophic overflow of a 1 100 000 square kilometer highland lake the size constant levels and interior morphology of three regional paleolake basins require a warmer paleoclimate and a long term recharged stable highland water table more than 3 5 billion years ago

potential desiccation cracks on mars a synthesis from modeling analogue field studies and global observations potential desiccation polygons pdps are polygonal surface patterns that are a common feature in noachian to hesperian aged phyllosilicate and chloride bearing terrains and have been observed with size scales that range from cm wide by current rovers to 10s of meters wide the global distribution of pdps shows that they share certain traits in terms of morphology and geologic setting that can aid identification and distinction from fracturing patterns caused by other processes they are mostly associated with sedimentary deposits that display spectral evidence for the presence of fe mg smectites al rich smectites or less commonly kaolinites carbonates and sulfates in addition pdps may indicate paleolacustrine environments which are of high interest for planetary exploration and their presence implies that the fractured units are rich in smectite minerals that may have been deposited in a standing body of water a collective synthesis with new data particularly from the hirise camera suggests that desiccation cracks may be more common on the surface of mars than previously thought a review of terrestrial research on desiccation processes with emphasis on the theoretical background field studies and modeling constraints is presented here as well and shown to be consistent with and relevant to certain polygonal patterns on mars

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

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

scarp bounded benches in gorgonum chaos mars formed beneath an ice covered lake 1 level bench like platforms edged with scarps facing the interior of the martian gorgonum chaos basin may have formed in conjunction with an ancient ice covered lake these benches however lack the typical features of shorelines associated with wave and current transport and erosion such as crescentic embayments spits barrier islands and wave cut cliffs rather the basin facing platform edges are commonly rounded and cumulate in planform often evenly encircling buttes protruding above the level of the benches the benches are postulated to have been formed by outward growth in a quiescent environment possibly by deformative lateral flow of sediment below the ice water interface in a perennially frozen lake due to the weight of the ice overburden

extensive surface pedogenic alteration of the martian noachian crust suggested by plateau phyllosilicates around valles marineris 1 thousands of phyllosilicate rich outcrops mainly iron or magnesium rich are exposed on noachian terrains in the martian southern highlands we analyzed 90 crism observations and more than a hundred hirise images located on the plateaus surrounding valles marineris we mapped an extensive al and fe mg phyllosilicate rich formation covering at least 197 000 km2 for which we introduce the name plateau phyllosilicates tens of meters in thickness this light toned formation crops out at various elevations on top of the noachian units npl1 and npl2 as flat exposures on plateaus and along scarps such as valley walls chasma walls pit walls and impact crater rims the fe mg phyllosilicate rich lower member of the formation is composed of fe mg smectites nontronite saponite and vermiculite the al phyllosilicate rich upper member of the formation contains al smectites montmorillonite beidellite and locally kaolinite and or halloysite we suggest that the plateau phyllosilicates were mainly formed by pedogenesis related to the weathering of the noachian bedrock by percolation of meteoric water or melted snow under a temperate and subarid climate during the noachian epoch in an alkaline to neutral environment kaolinite and or halloysite may have formed in areas of more intense drainage at the surface under slightly acidic environments during the noachian and hesperian epochs fluvial activity and deuteric alteration may have locally contributed to the genesis of phyllosilicates this study suggests that the alteration of the noachian basement of the plateaus surrounding valles marineris was widespread during the noachian epoch and was still active during the hesperian epoch even though the water availability was limited

evidence for amazonian highly viscous lavas in the southern highlands on mars we have identified small scale volcanic edifices two cones and three domes with associated flows within terra sirenum a region situated in the martian southern highlands based on thermal morphological and morphometrical properties and the determination of absolute model ages we conclude that these features were formed by volcanic activity of viscous lavas in the mid amazonian epoch relatively recently in martian history if our hypothesis is correct this small volcanic field represents rare evidence of young volcanic activity in the martian highlands in which martian equivalents of terrestrial lava domes and coulees might be present on earth such landforms are usually formed by highly viscous evolved lavas i e andesitic to rhyolitic for which observational evidence is sparse on mars hence this field might be one of only a few where martian evolved lavas might be investigated in detail

the evolution of lacustrine environments on mars is mars only hydrologically dormant abstract this study surveys the evolution of martian impact crater paleolakes through time by establishing their age comparing their locations and describing the formation of lacustrine sedimentary structures and features over time we explore their meaning in terms of global climate changes but also on local and regional scales we observe a co location between recent impact crater paleolakes and regions where gcm modeling shows that mars is currently experiencing days above triple point and below boiling point of water some source areas show morphologies that could be consistent with ancient glacier features in the argyre basin darwin crater region in locations that are also consistent with gcm models of past snow precipitation on mars we propose that at least for some paleolakes our results are best explained by recent and abundant aqueous activity on mars with some meteorological contribution these results are supported by other recent findings on martian meteorite ages by the analysis of new mgs data showing recent volcanic and fluvial activity and by climate modeling they point toward the possibility that mars currently is only hydrologically dormant and that there is a potential for hydrological activity to be generated again in the future following changes in the planet s orbital parameters

martian cratering 8 isochron refinement and the chronology of mars abstract this paper reviews and refines the technique of dating martian surfaces by using impact crater isochrons defined as size distributions of impact craters on undisturbed martian surfaces of specified ages in the 1970s this system identified not only abundant ancient martian volcanic surfaces but also extensive lava plains with ages of a few 108 y old this dating was initially controversial but confirmed in the 1980s and 90s by martian meteorites the present update utilizes updated estimates of the mars moon cratering ratio the most important calibration factor improves treatment of gravity and impact velocity scaling effects combines aspects of the crater size distribution data from earlier work by both neukum and hartmann and for the first time applies a correction for loss of small meteoroids in the martian atmosphere from popova et al 2003 meteorit planet sci 38 905 925 the updated isochrons are not radically different from the previous 2002 iteration but fit observed data better and give somewhat older model ages for features dated from small craters diameter d 100 m crater counts from young lava flows in various areas give good fits to the new isochrons over as much as 3 orders of magnitude in d confirming the general isochron shape and giving crater retention ages in the range of some 106 to some 108 y interpreted as lava flow ages more complex older units are also discussed uncertainties are greatest if only small craters d 100 m are used suggestions by other workers of gross uncertainties due to local secondary craters and deposition exhumation are discussed they do not refute our conclusions of significant volcanic fluvial and other geologic activity in the last few percent of martian geologic time or the importance of cratering as a tool for studying processes such as exhumation indeed crater count data suggest certain very recent episodes of deposition exhumation and ice flow possibly associated with obliquity cycles of 10 7 y timescale evidence from ancient surfaces suggests higher rates of volcanism fluvial activity glaciation and other processes in noachian hesperian time than in amazonian time

exploring gusev crater with spirit review of science objectives and testable hypotheses 1 gusev crater was selected as the landing site for the mars exploration rover mer spirit mission located at the outlet of ma adim vallis and 250 km south of the volcano apollinaris patera gusev is an outstanding site to achieve the goals of the mer mission the crater could have collected sediments from a variety of sources during its 3 9 ga history including fluvial lacustrine volcanic glacial impact regional and local aeolian and global air falls it is a unique site to investigate the past history of water on mars climate and geological changes and the potential habitability of the planet which are central science objectives of the mer mission because of its complex history and potential diversity gusev will allow the testing of a large spectrum of hypotheses with the complete suite of mer instruments evidence consistent with long lived lake episodes exist in the landing ellipse area they might offer a unique opportunity to study for the first time martian aqueous sediments and minerals formed in situ in their geological context we review the geological history and diversity of the landing site the science hypotheses that can be tested during the mer mission and the relevance of gusev to the mer mission objectives and payload

a study on the nighttime midlatitude ionospheric trough constellation observing system for meteorology ionosphere and climate cosmic electron density profiles are used to investigate the nighttime midlatitudeionospheric trough mit we find that at midnight the longitudinally deepest mit occursto the west of the geomagnetic pole in both the northern and southern hemispheres duringthe equinox seasons and local summer the deepest mit could be ascribable to theenhanced depletion caused by horizontal neutral wind in the early evening the eastwardneutral wind prevails in the midlatitude f region which blows the plasma downwardwhere the declination is eastward in the northern hemisphere but westward in thesouthern hemisphere both lying to the west of the geomagnetic pole the downward driftwould enhance the plasma depletion for more molecular composition at lower altitude in addition we find for the first time that the location of nighttime mit minimumoscillated with a periodicity of 9 days and an amplitude of about 1 1 5 geomagneticlatitude during 2007 2008 associated with the recurrent high speed solar wind ourresults shed new light on the empirical description and numerical simulation of mit

hydrous minerals on mars as seen by the crism and omega imaging spectrometers updated global view 1 the surface of mars has preserved the record of early environments in which its basaltic crust was altered by liquid water these aqueous environments have survived in the form of hydrological morphologies and alteration minerals including clays and hydrated salts because these minerals probe on earth aqueous environments compatible with biotic activity understanding their formation processes on mars is of great exobiological relevance and also offers insight into earth s now erased ancient water environments using remote sensing we conducted a large scale investigation of the distribution composition age and geomorphic settings of hydrous minerals on mars providing a sharpened global view of the early aqueous environments and their evolution with time aqueous alteration seems to have produced clays on a planetary scale but these are found to be restricted to the oldest observable terrains on mars 4 gyr however very diverse aqueous environments have also been found which suggest widespread complex aqueous settings from the surface to kilometric depths and spanning over 1 gyr by building a robust statistical sample of detections the global trends inferred here attempt to provide a broad view of our current understanding of hydrous minerals on mars and provide context for more localized in depth analyses collectively these trends suggest that at least transient conditions have existed on mars which may have been favorable for pre biotic to biotic activity

eridania basin an ancient paleolake floor as the next landing site for the mars 2020 rover abstract the search for traces of past martian life is directly connected to ancient paleolakes where ponding water or low energy water fluxes were present for long time intervals the eridania paleolakes system located along the 180 meridian is one of the largest lacustrine environments that were once present on mars morphological features suggest that it was constituted by connected depressions filled by water to maximum depths of 2400 m and a volume of at least 562 000 km3 we focused our attention on the northern side of the eridania basin where high albedo uneven patches of material characterized by the absence of dust are present based on omega and crism orbital imaging spectroscopy data a large clay bearing unit has been identified there in particular a set of aqueous minerals in present in the stratigraphy being visible through erosional windows in the first several tens of meters of the sedimentary sequence below this capping unit a thin al rich clay stratum attributable to al smectite and or kaolins is present this overlies a fe rich clay stratum attributable to the nontronite smectite at the base of the mineralogic sequence a stratum that could be either a zeolite or more likely a hydrated sulfate is present in addition small deposits of alunite a rare phase on mars and jarosite are here found at several locations such stratigraphy is interpreted as originating from a surface weathering process similar to terrestrial abiotic pedogenesis nonetheless possible exobiologic processes can be also invoked to explain it nasa s spirit rover landed on gusev crater in 2004 near the mouth of the ma adim vallis which connects this crater with the considered paleolakes system the eridania site provides the unique opportunity to complete the measurements obtained in gusev crater while investigating the exposed mineralogical sequence in its depositionary setting in addition the extremely favorable landing parameters such as elevation slope roughness rock distribution thermal inertia and dust coverage support this location as a possible landing site for the nasa mars 2020 rover

constraints on the history of open basin lakes on mars from the composition and timing of volcanic resurfacing 1 abundant evidence exists for valley network related fluvial activity near the noachian hesperian transition on mars and areally significant quantities of volcanic ridged plains were emplaced during this period as well thus it is worthwhile to explore the hypothesis that lava water interaction occurred on the surface of mars at this time we analyzed the morphology physical properties composition and surface ages of thirty open basin lakes topographic lows with both an inlet valley and an outlet valley that were also resurfaced by volcanic flows hyperspectral imaging data from the compact reconnaissance imaging spectrometer for mars crism and observatoire pour la mineralogie l eau les glaces et l activite omega instruments indicate that of the 30 basins 12 exhibit the spectral properties of basaltic lithologies with diagnostic absorptions of olivine high calcium pyroxene and low calcium pyroxene an olivine high calcium pyroxene mixture is the most commonly identified mineral assemblage consistent with other hesperian aged volcanic units therefore our mineralogical results for over a third of the open basin lake floors analyzed support prior interpretations that the basins were resurfaced by volcanic flows supporting evidence for resurfacing by volcanic flows is also given by the observed morphology and physical properties e g surface roughness thermal inertia of the resurfaced open basin lake floors in these 30 examples however no evidence was found for lava water interaction the ages of emplacement derived through counts of superposed craters of all 30 of the open basin lake volcanic resurfacing units show that resurfacing began in the late noachian near the noachian hesperian boundary was concentrated in the hesperian and continued into the early amazonian the lack of geologic features indicative of lava water interaction suggests that the basins were likely to have been mostly devoid of water at the time of the latest phase of volcanic resurfacing we conclude that there is no geologic evidence that suggests the fluvial activity associated with the studied paleolakes was coeval with the emplacement of the observed volcanic resurfacing units several of which date to the late noachian early hesperian

ma adim vallis revisited through new topographic data evidence for an ancient intravalley lake abstract based on a comprehensive study of the recent topographic map usgs mc 23 se i 2119 usgs 1991 topographical map of aeolis plus geomorphic and digital elevation we have constructed a geometric model of ma adim vallis the sedimentary history of the valley was determined by the damming of the valley by two impact craters one by the southern crater over gusev rim and the second located 120 km upstream the presence of an intravalley lake system is inferred from independent sedimentary analysis and from geomorphic evidence for valley benches peripheral and parallel topographic contour intervals of the putative intravalley lake shores suggest that the lake was covered by a thick ice sheet the longitudinal profile of the valley floor shows a peculiar reverse slope located 300 km upstream from the southern gusev crater rim we conclude that this is an accumulation of sedimentary deposits adjacent to the crater rampart which defined the northern boundary of the lake when the water level reached the lowest point of the west bank which is 0 4 km below the top of the rim of gusev crater it began to floor the surrounding plateau as the intravalley lake level raised its ice cover formed a wide lateral bench later this ponded water was funneled into gusev crater through the breaching of the southern gusev rampart by an impact crater the paleolacustrine sediments transported by the lake water that channeled through the rampart debris slope mantled the floor of gusev crater the sublacustrine sediments are promising targets for future missions and of high priority in the search for past life

the daytime f layer trough and its relation to ionospheric magnetospheric convection the daytime f layer trough is studied by means of an extensive network of ground based ionospheric sounders in the northern hemisphere under conditions of solar maximum near winter solstice the trough is observed to be a continuous band having an instantaneous extent of thousands of kilometers consisting of depletions in the daytime electron density often by an order of magnitude it lies in regions of sunward ionospheric magnetospheric convection an afternoon sector corresponding to the dusk cell a morning sector corresponding to the dawn cell and morphology and activity dependence consistent with convection as detected in the diurnal distributions of f0f2 the trough is a persistent feature at high latitudes appearing on each day of a 31 day period of continuous observation and although highly variable from day to day is apparent in the monthly medians the afternoon trough which is detected independently by at least five and as many as 17 stations on each day is generally continuous and stationary for a duration of many hours in magnetic latitude magnetic local time coordinates the trough contracts during quiet conditions so as to lie above 70 magnetic latitude but expands during disturbed conditions so as to extend from 75 to 52 magnetic latitude the trough has a pronounced dependence on longitude appearing principally in the afternoon in eastern magnetic longitudes but in the morning in western magnetic longitudes an effect so prevalent that it produces large east west local time asymmetries in the diurnal distributions of median daytime f layer electron densities throughout a wide range of latitudes the longitudinal dependence is found to result from the relation between the two principal coordinate systems of the ionosphere magnetosphere interaction solar geomagnetic coordinates in which the convection pattern and the resultant daytime trough reside and solar terrestrial coordinates in which solar ion production and the undisturbed daytime f layer in general reside as a consequence of the fact that these coordinate systems vary with respect to one another with longitude the trough varies within the daytime f layer with longitude

chemistry of fracture filling raised ridges in yellowknife bay gale crater window into past aqueous activity and habitability on mars the chemcam instrument package on the curiosity rover was used to characterize distinctive raised ridges in the sheepbed mudstone yellowknife bay formation gale crater the multilayered fracture filling ridges are more resistant to erosion than the sheepbed mudstone rock in which they occur the bulk average composition of the raised ridges is enriched in mgo by 1 2 1 7 times average of 8 3 11 4 wt single shot maximum of 17 0 wt over that of the mudstone al2o3 is anticorrelated with mgo while li is somewhat enriched where mgo is highest some ridges show a variation in composition with different layers on a submillimeter scale in particular the mcgrath target shows similar high mgo resistant outer layers and a low mgo less resistant inner layer this is consistent with the interpretation that the raised ridges are isopachous fracture filling cements with a stratigraphy that likely reveals changes in fluid composition or depositional conditions over time overall the average composition of the raised ridges is close to that of a mg and fe rich smectite or saponite which may also be the main clay mineral constituent of the host mudstone these analyses provide evidence of diagenesis and aqueous activity in the early postdepositional history of the yellowknife bay formation consistent with a low salinity to brackish fluid at near neutral or slightly alkaline ph the fluids that circulated through the fractures likely interacted with the sheepbed mudstone and or other stratigraphically adjacent rock units of basaltic composition and leached mg from them preferentially

thermal contraction crack polygons on mars classification distribution and climate implications from hirise observations morphology is shown to be consistent with thermal contraction cracking of an ice rich mantling unit consistent with observations of sediment wedge thermal contraction crack polygons forming in ice cemented sediment at the phoenix landing site polygon groups are distributed symmetrically in both northern and southern hemispheres suggesting strong climate controls on polygon morphology northern hemisphere polygonally patterned surfaces are found to decrease in age from low to high latitude spanning surface ages from 1 to 0 1 ma suggesting more recent deposition of ice rich material at high latitudes than at low latitudes six of the seven classes of polygons are interpreted to be capable of forming because of the combined effects of thermal contraction cracking and differential sublimation suggesting that sublimation and sand wedge polygons dominate martian high latitudes gully polygon systems present at midlatitudes suggest that small amounts of liquid water may have been involved in thermal contraction crack polygon processes producing composite wedge polygons no evidence is found for the presence of pervasive small scale ice wedge polygons

knob fields in the terra cimmeria terra sirenum region of mars stratigraphy mineralogy and morphology abstract we investigate the stratigraphy morphology and mineralogy of five major knob fields in the region between terra cimmeria and terra sirenum on mars based on hrsc ctx moc and hirise imagery together with hyperspectral data from crism the knob fields comprise ariadnes colles atlantis chaos and gorgonum chaos and further unnamed fields of mounds they have been mapped in previous studies as hesperian or amazonian units and are located within the shoreline of the proposed eridania lake the putative source of ma adim vallis the mounds contain mg fe bearing phyllosilicates and locally al rich phyllosilicates our geological mapping shows that the knob fields have a late noachian age which indicates later phyllosilicate formation than typically observed on mars the knob fields formed by alteration of the electris deposit an airfall deposit possibly rich in basaltic glass grant j a schultz p h 1990 icarus 84 166 195 in local depressions possibly in the eridania lake the spectroscopic detection of phyllosilicates here may indicate that liquid water persisted longer in this region than elsewhere on mars the knob fields are embayed by the hesperian ridged plains numerous valleys carve into the ridged plains and document that the aqueous history of this region continued into the hesperian and amazonian the study area is traversed by the sirenum fossae these graben appear to post date the aqueous activity in the study area except in the gorgonum basin where a lake developed after their formation

morphometry of great basin pluvial shore landforms implications for paleolake basins on mars 1 many basins with relict contributing valley networks and outlet valleys in the martian highlands indicate past flowing and ponded water on the surface these likely paleolakes motivate an investigation of pluvial shore landforms in the great basin region of the western united states as confident identification of strandlines on mars would facilitate analyses of its past hydrology and climate the purpose of this study is to characterize the scale of late pleistocene erosional and depositional shore landforms in an endorheic setting determine the preservation potential of similar forms from multiple epochs in early martian history and identify the data products that would be necessary to detect them we use differential global positioning system field surveys to measure the dimensions and elevations of shore landforms compare shore platform widths to theoretical maxima and note the minimum scale of landforms that have survived since the late noachian and early hesperian epochs on mars we find that due to impact gardening and aeolian erosion martian highland paleolakes like those in the pluvial great basin would likely not have well preserved shore landforms unless they were unusually large and formed in the late hesperian or later individual strandlines are often not equally well expressed around an entire basin so correlating shore landforms in plan view imaging and using their consistency in elevation as a hypothesis test for paleolakes can be challenging detection of younger shore landforms like those examined here would require meter resolution imaging and topography such as stereo digital elevation models

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

the summer evening anomaly and conjugate effects 1 the constellation observing system for meteorology ionosphere and climate cosmic gps occultation data have been analyzed in this study to provide a better understanding of the weddell sea anomaly wsa and to place it in the wider context of a general phenomenon that occurs near dusk in summer which we are calling the summer evening anomaly to better capture its global nature the terminator and the magnetically conjugate points for the terminator in the other hemisphere have been plotted on top of global maps of cosmic nmf2 and hmf2 for 2 months either side of the december and june solstices for 2006 2008 these plots show that there are distinct enhancements of nmf2 and increases in hmf2 as soon as the conjugate footprint of the field line on the winter terminator is seen at middle latitudes in the summer hemisphere this effect is most pronounced where the wsa is formed but it also occurs across the south pacific ocean in the southern summer and across much of the north atlantic ocean siberia and kamchatka during the northern summer an hmf2 increase occurs between the two terminators even at locations where there is no increase in nmf2 a similar but reversed effect occurs in hmf2 near dawn this behavior appears to be most consistent with upward and poleward ion drifts in the evening but neutral wind and downward precipitation may make important contributions to this effect

optimum field development with seismic reflection data petroleum engineers and production geologists generally build their reservoir models from smooth interpolation of petrophysical parameters obtained at well locations well information is usually accurate but is unevenly and sparsely distributed in heterogeneous formations these interpolated models can be erroneous with costly consequences on field development expenditures in addition the volume of reservoir rock physically investigated in a field by core analysis and wireline logging generally is on the order of one part per billion yet development geologists and petroleum engineers need to produce one or more detailed 3 d model s of the reservoir to estimate reserves design an effective drilling program and optimize resource recovery

topside ionospheric electron temperature and density along the weddell sea latitude it has been well known that the ionospheric electron density ne is greater in the summer nighttime than daytime around the weddell sea region which is named weddell sea anomaly wsa this paper for the first time reports unusual increases decreases of the daytime nighttime electron temperature te at about 830 km altitude over the wsa latitudes probed by tatiana 2 during december 2009 to january 2010 concurrent measurements at 660 830 km altitude observed by tatiana 2 detection of electro magnetic emissions transmitted from earthquake regions demeter and formosa satellite 3 constellation observing system for meteorology ionosphere and climate f3 c reveal the anticorrelation between te and ne along the wsa latitudes in the daytime and nighttime based on f3 c ne along the wsa latitudes observed at various local times the associated te values are computed the tatiana 2 and demeter observations as well as the computed results show that te yield the maximum values over the wsa region during daytime and over the indian and atlantic ocean area during nighttime the maxima or minima in f3 c ne and the computed te reveal eastward phase shifts

hirise imaging of impact megabreccia and sub meter aqueous strata in holden crater mars high resolution imaging science experiment hirise images of holden crater mars resolve impact megabreccia unconformably overlain by sediments deposited during two noachian age phases of aqueous activity a lighter toned lower unit exhibiting phyllosilicates was deposited in a long lived quiescent distal alluvial or lacustrine setting an overlying darker toned and often blocky upper unit drapes the sequence and was emplaced during later high magnitude flooding as an impounded uzboi vallis lake overtopped the crater rim the stratigraphy provides the first geologic context for phyllosilicate deposition during persistent wet and perhaps habitable conditions on early mars

seismic fracture anisotropy in the earth s crust an overview fluid filled fractures and microcracks are the most stress sensitive component of crustal rock and often determine the pathways and volume of crustal fluid movement if we are to comprehend the role of fractures and fluids in tectonic processes to formulate an accurate hypothesis for phenomena precursory to catastrophic seismic failure or to monitor hydrocarbon and geothermal reservoirs for the presence or absence of major fluid pathways we must understand how seismic waves interact with the fracture crack and microcrack structures within the rock mass a salient feature of fracture related rock structure is the effective seismic anisotropy of aligned fractures and microcracks with the advent of large volume digital seismic data sets it is feasible to use polarized shear waves to explore the anisotropic fracture properties of the crust crustal fracture structures which may be monitored by polarized shear waves range in dimensions from the 10 100 km scale of crustal stress orientation and preseismic stress buildup through the 100 1000 m scale of fluid reservoir structure and characterization and the 1 10 scale of mining and geoengineering rock strain monitoring to millimeter and micrometer or possibly smaller fluid filled inclusions determining the elastic response of the intact rock mass to focus developments in seismic anisotropic studies of crustal fracture phenomena the american geophysical union and the society of exploration geophysicists sponsored a chapman conference on seismic anisotropy in the earth s crust held may 31 to june 4 1988 at the lawrence berkeley laboratory of the university of california this was the third international workshop on seismic anisotropy 3iwsa nineteen conference papers are presented in this special section of the journal of geophysical research

planetary surface dating from crater size frequency distribution measurements multiple resurfacing episodes and differential isochron fitting abstract the analysis of crater size frequency distributions and absolute densities forms the basis of current approaches for estimating the absolute and relative ages of planetary surfaces users of the neukum system of crater dating have conventionally used a cumulative presentation of the data but because of the recent proliferation of interest in identifying resurfacing ages it is worth emphasising the utility of the differential presentation of crater data in identifying resurfacing events and particularly in distinguishing the signature of short lived events such as volcanic flows from long acting processes such as aeolian erosion the work describes some additional considerations for making isochron fits to differentially plotted crater populations with respect to the removal of a binning bias for incrementally differentially plotted data the hartmann approach has not typically employed the fitting of isochrons but differential fitting would be a natural choice for this system and is implemented in the craterstats software a revised calculation of the martian epoch boundary times in both chronology systems is provided

compositional investigation of the proposed chloride bearing materials on mars using near infrared orbital data from omega mex 1 several hundred occurrences of chloride bearing salt deposits have been proposed in terrains within the southern highlands of mars on the basis ofthermal emission imaging system and thermal emission spectrometerinfrared observations the spectral identification of chloride salts by remote sensing is challenging because they are transparent over much of the thermal infrared portion of the spectrum further ambiguity arises from the diverse geologic settings in which the putative chloride bearing materials are found in order to better constrain the composition of these unique compositional units we perform a global survey of these materials in the near infrared nir domain with theobservatoire pour la mineralogie l eau les glaces et l activite omega imaging spectrometer the spectral signatures of the deposits are consistent with although not specific of chlorides we do not observe olivine to be associated with the deposits which confirms that sulfides are an unlikely alternative candidate our systematic search reveals the global lack of association with hydrated minerals phyllosilicates sulfates hydrated silica except for a few deposits noteworthy in northwestern terra sirenum where a small fraction of chloride material overlaps fe mg rich clay bearing terrains even in these locations the morphology and crosscutting relationships of the deposits suggest two separate episodes of mineralization first phyllosilicates then chlorides followed by subsequent formation of sulfates our study shows that local groundwater upwelling seems to be the most frequent source for the water involved in the formation of chloride rather than surface runoff

distribution classification and ages of martian impact crater lakes paleolakes in impact craters on mars are characterized at global scale using the viking orbiter data we identified 179 paleolakes in impact structures formed by the influx of water and sediment derived from valley networks and channels that can be classified into three different fluviolacustrine systems closed open and lake chain systems we show the hydrogeologic implications for each of the three systems and their significance in terms of duration of fluviolacustrine activity this study provides a catalog of areographic physical and physiographic data for each of the studied impact crater lakes associated with the description of the sedimentary structures observed it also identifies environments where life and or precursors to life could have found favorable conditions to evolve