observations at the mars pathfinder site do they provide unequivocal evidence of catastrophic flooding after mars pathfinder landed at the mouth of ares valus a large channel that drains into the chryse planitia basin the mission reports unanimously supported the interpretation that the lander site is the locus of catastrophic flooding by noting that all aspects of the scene are consistent with this interpretation however alternatives cannot be ruled out by any site observations as all aspects of the scene are equally consistent with other interpretations of origin namely ice and mass flow processes subsequently modified by wind erosion the authors discuss alternative explanations for the geologic history of the channel based on a regional view of the circum chryse channels from viking images our best broad scale information to date and the local view from the recent pathfinder landing site mega indicators of channel origin the regional geomorphology geology and planetary climatic conditions taken together suggest some combination of flood mass flow glacial and eolian processes the macro indicators of channel origin sedimentologic are also not indicative of one process of emplacement either as single criteria or taken cumulatively finally the micro indicators of channel origin geochemical and mineralogic composition do not provide very tight constraints on the deposits possible origins other than that water was in some way involved

ventifacts at the pathfinder landing site about half of the rocks at the mars pathfinder ares vallis landing site appear to be ventifacts rocks abraded by windborne particles comparable resolution images taken by the imager for mars pathfinder imp camera and the viking landers show that ventifacts are more abundant at the pathfinder site the ventifacts occur in several forms including rocks with faceted edges finger like projections elongated pits flutes grooves and possible rills the trends of elongated pits flutes grooves and rills cluster at 280 330 clockwise from north and generally dip 10 30 away from their trend direction these orientations are indicative of southeast to northwest winds and differ from the trend of wind tails at the landing site the direction of local wind streaks and predictions of the global circulation model all of which indicate northeast to southwest winds the disparity between these data sets strongly suggests that local circulation patterns have changed since the abrasion of the ventifacted rocks the greater number of ventifacts at the pathfinder site compared to either of the viking sites is most easily explained as being due to a larger supply of abrading particles composed of either sand sized grains or indurated dust aggregates and higher surface roughness which should increase the momentum of saltating grains the pathfinder ventifacts may have formed shortly after the deposition of outflow channel sediments nearly 2 gry ago when a large local supply of abrading particles should have been abundant and atmospheric conditions may have been more conducive to rock abrasion from saltating grains based on how ventifacts form on earth the several ventifact forms seen at the pathfinder site and their presence on some rocks but not on others are probably due to local airflow conditions original rock shape exposure duration rock movement and to a lesser extent rock lithology the abundance of ventifacts at the pathfinder site together with other evidence of weathering indicates that unaltered rock surfaces are rare on mars

distribution of rocks on the gusev plains and on husband hill mars 1 the population of rocks larger than 15 cm in diameter was measured at 36 locations imaged by the spirit rover over 4 km of the traverse across the gusev plains and husband hill in gusev crater on mars the rock population observed on plains surfaces is consistent with impact fragmentation of rubbly fractured volcanics and reveals little evidence for modification by secondary processes or weathering interpretation of counts from husband hill suggest an influence by bedrock for rocks larger than 0 5 m across but the distribution of smaller rocks is consistent with ejecta possessing contributions from pre plains impact events results indicate plains surfaces experienced only tens of centimeters of eolian erosion deposition since the hesperian whereas meters rather than tens of meters of erosion modified husband hill since the early hesperian

an aerodynamic roughness length map derived from extended martian rock abundance data many boundary layer processes simulated within a mars general circulation model mgcm including the description of the processes controlling dust rising from the martian surface are highly sensitive to the aerodynamic roughness length z0 on the basis of rock size frequency distributions inferred from different martian landing sites and earth analog sites we have first established that lognormal modeled rock size frequency distributions are able to reproduce correctly the observed martian rock populations we have validated the hypothesis that the rock abundance of a given area could be estimated at a first order from its thermophysical properties namely its thermal inertia i and its albedo we have demonstrated the possibility of using rock abundance to estimate the roughness density on mars and to retrieve subsequently the aerodynamic roughness length by using semi empirical relationships based on terrestrial wind tunnel and field measurements by combining our methodology with remote sensing measurements of the thermal emission spectrometer aboard mars global surveyor we have derived a global map of the aeolian aerodynamic roughness length with a 1 8 1 8 resolution over the entire martian surface contrary to what is often assumed the martian aeolian aerodynamic roughness length is spatially highly heterogeneous at the fullest resolution the martian aerodynamic roughness length varies from 10 3 cm to 2 33 cm about 84 of the martian surface seems to be characterized by an aeolian aerodynamic roughness length value lower than 1 cm the spatially uniform value that most of the mgcms simulations have assumed recently since the aerodynamic roughness length z0 is a key parameter in deriving the erosion threshold wind velocities we anticipate a significant impact of our findings on the efficiencies for lifting dust in future mgcms

surficial deposits at gusev crater along spirit rover traverses the mars exploration rover spirit has traversed a fairly flat rock strewn terrain whose surface is shaped primarily by impact events although some of the landscape has been altered by eolian processes impacts ejected basaltic rocks that probably were part of locally formed lava flows from at least 10 meters depth some rocks have been textured and or partially buried by windblown sediments less than 2 millimeters in diameter that concentrate within shallow partially filled circular impact depressions referred to as hollows the terrain traversed during the 90 sol martian solar day nominal mission shows no evidence for an ancient lake in gusev crater

constraints on the geologic history of home plate materials provided by clast morphology and texture 1 we quantified and classified the size shape roundness and texture of 333 loose surface particles clasts along the spirit rover traverse from martian solar days 750 to 1889 these data provided clues to origin transport mechanisms association with geologic units and other alteration processes clasts average 15 mm in size and 0 73 sphericity and display a low degree of roundness textures include vesicular smooth and rough flat faceted and granular platy clasts characteristics are comparable to those for clasts outside the home plate region mapped geologic units around home plate are characterized by distinctive clast morphologic parameters and only minor adjustments were made to unit boundaries and definitions mapped by others no new units are suggested by the data consistent roundness values seen from unit to unit coupled with the correlation between unit boundaries and clast characteristics in and outside home plate indicate that no appreciable transport has occurred subsequent to fragmentation from outcrop and emplacement rather clasts have been emplaced through volcanic activity and or impact and have been subjected to weathering processes since that time we interpret vesicular and flat faceted clasts texture types 1 3 to be derived from mitcheltree ridge basalts and the presence of these clasts to provide a general outline of the original extent of this unit platy granular textured clasts texture type 5 are derived from the upper home plate unit

quantitative morphologic analysis of boulder shape and surface texture to infer environmental history a case study of rock breakdown at the ephrata fan channeled scabland washington boulder morphology reflects both lithology and climate and is dictated by the combined effects of erosion transport and weathering at present morphologic information at the boulder scale is underutilized as a recorder of environmental processes partly because of the lack of a systematic quantitative parameter set for reporting and comparing data sets we develop such a parameter set incorporating a range of measures of boulder form and surface texture we use standard shape metrics measured in the field and fractal and morphometric classification methods borrowed from landscape analysis and applied to laser scanned molds the parameter set was pilot tested on three populations of basalt boulders with distinct breakdown histories in the channeled scabland washington 1 basalt outcrop talus 2 flood transported boulders recently excavated from a quarry and 3 flood transported boulders extensively weathered in situ on the ephrata fan surface size and shape data were found to distinguish between flood transported and untransported boulders size and edge angles 120 of flood transported boulders suggest removal by preferential fracturing along preexisting columnar joints and curvature data indicate rounding relative to outcrop boulders surface textural data show that boulders which have been exposed at the surface are significantly rougher than those buried by fan sediments past signatures diagnostic of flood transport still persist on surface boulders despite ongoing overprinting by processes in the present breakdown environment through roughening and fracturing in situ further use of this quantitative boulder parameter set at other terrestrial and planetary sites will aid in cataloging and understanding morphologic signatures of environmental processes

characteristics of pebble and cobble sized clasts along the curiosity rover traverse from bradbury landing to rocknest 1 we have assessed the characteristics of clasts along curiosity s traverse to shed light on the processes important in the genesis modification and transportation of surface materials pebble to cobble sized clasts at bradbury landing and subsequently along curiosity s traverse to yellowknife bay reflect a mixing of two end member transport mechanisms the general clast population likely represents material deposited via impact processes including meteorite fragments ejecta from distant craters and impactites consisting of shocked and shock melted materials from within gale crater which resulted predominantly in larger angular clasts a subset of rounded pebble sized clasts has likely been modified by intermittent alluvial or fluvial processes the morphology of this rounded clast population indicates that water was a more important transporting agent here than at other mars sites that have been studied in situ finally we identified populations of basalt clasts and porphyritic clasts of undetermined composition by their morphologic and textural characteristics basalts are confirmed by geochemical data provided by chemcam

the compositions of coexisting pyroxenes and garnet in the system cao mgo al2o3 sio2 at 900 1 100 c and high pressures the compositions of coexisting orthopyroxene clinopyroxene and garnet in the cao mgo al2o3 sio2 system are fixed at any givenp andt reversed hydrothermal experiments over thep t range 15 40 kb 900 l 100 c indicate that the garnet composition is nearly constant at py86gr14 the alcontent and ca ca mg values of the pyroxenes vary significantly however t p wt al2o3 frac ca ca mg times 100 c kbar in opx in cpx in opx in cpx 900 15 3 55 2 92 0 72 47 05 900 30 1 62 0 92 0 81 47 30 1 100 20 1 11 0 92 1 22 45 20 1 100 40 1 26 0 88 0 81 45 64 the significant variation of a12o3 content with pressure supports its use as a geobarometer the ca ca mg values of coexisting orthoand clino pyroxene have been used as a geothermometer however the present results show that the presence of a12o3 in the pyroxenes decreases significantly the mutual solubility of the pyroxenes which may cause errors of up to 200 c if the a12o3 effect is ignored

erosion rates on mars and implications for climate change constraints from the pathfinder landing site the observation that the mars pathfinder landing site looks very similar to its appearance after it was deposited by catastrophic floods around 1 8 3 5 ga allows quantitative constraints to be placed on the rate of change of the site since that time the abundance of erosional features such as an exhumed former soil horizon sculpted wind tails ripplelike and other tag deposits and ventifacts fluted and grooved rocks all suggest the site has undergone net deflation or loss of 3 7 cm of material the presence of barchan dunes and ventifacts argues for erosion by saltating crystalline sand size particles entrained in the wind most ventifacts probably formed soon after the catastrophic flood which likely introduced a large fresh supply of sand size particles distributed across the rocky plain the strongest winds blew toward the northwest during this time resulting in the sculpting of ventifacts deflation of the surface collections of dunes within big crater and other lows and possibly preferentially eroding small crater rims the predominant wind direction changed to blow toward the southwest similar to today these winds further deflated the surface completed the deposition of sand size material in dunes and ultimately trapped these dunes in lows the erosional features observed by pathfinder indicate extremely low long term deflation rates of 0 01 0 04 nm yr since the end of the hesperian 1 8 3 5 ga similar to less precise rates of 1 nm yr based on the preservation of craters at the viking 1 and pathfinder landing sites short term redistribution rates deposition and removal of atmospheric dust at the pathfinder landing site and preexisting dust and sand at other locations on mars are up to 10 5 nm yr estimates of erosion rates on mars show a rapid decrease by 3 6 orders of magnitude from 10 2 10 4 nm yr in noachian terrains characterized by rimless flat floored craters and valley networks to the exceedingly slow rates 10 2 10 nm yr operating during the hesperian and amazonian noachian erosion rates comparable to low continental denudation rates on earth are consistent with erosion by running water and perhaps a more clement climate the rapid decrease in erosion rates is consistent with a major climatic change during the noachian at the tail end of heavy bombardment and a cold dry desiccating climate similar to today s since that time

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

dark inclusions in allende leoville and vigarano evidence for nebular oxidation of cv3 constituents dark lithic inclusions are known to occur in several cv3 chondrites we report petrologic chemical and oxygen isotopic data on examples from allende leoville and vigarano the allende inclusions comprise a petrographic sequence ranging from a type which contains chondrules and refractory inclusions and resembles cv3 or co3 chondrites to a type which contains porous aggregates of iron rich olivine oxygen isotopic compositions correlate with the sequence chondrule rich inclusions have compositions similar to the host meteorite bulk values whereas olivine aggregate rich inclusions have more 16o depleted compositions chemical compositions on the other hand do not correlate with the petrographic sequence the dark inclusions are all systematically enriched in iron and depleted in potassium and sodium relative to their host meteorites the inclusions appear to be fragments of cv3 parent bodies which were processed to different degrees prior to their incorporation as clasts into allende leoville and vigarano the processing homogenized olivine compositions presumably through heating and also involved oxygen exchange with 16o poorer surroundings either parent body metamorphism or nebular heating might have produced the petrographic and isotopic sequences however the most 16o depleted inclusions also have layered silicate rims surrounding them which are better attributed to gas solid reactions than parent body processes in particular andradite is abundant in the rims which implies that the rims grew under conditions significantly more oxidizing than those likely to have occurred on a cv3 parent body at least part of the processing therefore appears to have taken place prior to final accumulation of the material when the fragments were dispersed in the nebula the evidence for coupled oxidation and 16o depletion in the nebula suggests that other features of the cv3 group such as the oxidized and reduced subgroups ferrous rims on forsteritic olivines and coarse grained rims on chondrules may have been established by similar gas solid reactions prior to the final assembly of the meteorites

earth mineralogical model gibbs free energy minimization computation in the system mgofeosio2 abstract a thermodynamic database which is consistent with most available phase equilibrium experiments and calorimetric and physical measurements on the solids in the system mgo feo sio 2 is established for the phases with the compositions mg fe sio 3 garnet perovskite pyroxene and ilmenite mg fe 2 sio 4 olivine and phases sio 2 stishovite and coesite and mg fe o periclase and wustite the data are systematized by using the high temperature birch murnaghan equation of state which includes the pressure and temperature dependent bulk modulus k and temperature dependent thermal expansion of the solids the systematized thermodynamic data contains heat capacity c p data which is internally consistent with the data on k volume and temperature such a systematized database is used to calculate by the method of minimization of gibbs free energy the mineralogical composition of the peridotitic pyrolitic and chondritic mgo feo sio 2 mantles the model corresponds closely to the seismological prem preliminary earth reference model in predicting the major seismic discontinuities however such discontinuities resulting from reactions or phase transformation are not as sharp as the seismic ones calculated adiabatic geothermal gradient starting at 6 gpa and 1500 k reaches a temperature of 2046 k at the core mantle pressure 135 gpa in a pyrolite mantle the model earth parameters in the lower mantle are prem parameters in bracket k s 308 306 to 687 656 gpa 70 69 to 121 118 km 2 s 2

low abundance materials at the mars pathfinder landing site an investigation using spectral mixture analysis and related techniques abstract recalibrated and geometrically registered multispectral images from the imager for mars pathfinder imp were analyzed using spectral mixture analysis sma and related techniques sma models a multispectral image scene as a linear combination of endmember spectra and anomalous materials which do not fit the model are detected as model residuals while most of the imp data studied here are modeled generally well using bright dust gray rock and shade image endmembers additional anomalous materials were detected through careful analysis of root mean square rms error images resulting from sma for example analysis of sma fraction and rms images indicates spectral differences within a previously monolithologic dark soil class a type of dark soil that has high fractional abundances in rock fraction images gray rock soil was identified other anomalous materials identified included a previously noted black rock lithology a class of possibly indurated compacted or partially cemented soils intermediate soil and a unit referred to as anomalous patches on at least one rock the black rock lithology has a strong 900 1000 nm absorption and modeling of the derived image endmembers using a laboratory reference endmember modeling rem approach produced best fit model spectra that are most consistent with the presence of high ca pyroxenes and or olivine crystalline ferric oxide minerals or mixtures of these materials as important components of the black rock endmember more unique mineralogic identifications could not be obtained using our initial rem analyses both intermediate soil and anomalous patches units exhibit a relatively narrow 860 950 nm absorption that is consistent with the presence of either low ca pyroxenes or a cementing crystalline ferric oxide mineral

size frequency distributions of rocks on the northern plains of mars with special reference to phoenix landing surfaces 1 the size frequency distributions of rocks 1 5 m diameter fully resolvable in high resolution imaging science experiment hirise images of the northern plains follow exponential models developed from lander measurements of smaller rocks and are continuous with rock distributions measured at the landing sites dark pixels at the resolution limit of mars orbiter camera thought to be boulders are shown to be mostly dark shadows of clustered smaller rocks in hirise images an automated rock detector algorithm that fits ellipses to shadows and cylinders to the rocks accurately measured within 1 2 pixels rock diameter and height by comparison to spacecraft of known size of 10 million rocks over 1500 km2 of the northern plains rock distributions in these counts parallel models for cumulative fractional area covered by 30 90 rocks in dense rock fields around craters 10 30 rock coverage in less dense rock fields and 0 10 rock coverage in background terrain away from craters above 1 5 m diameter hirise resolves the same population of rocks seen in lander images and thus size frequency distributions can be extrapolated along model curves to estimate the number of rocks at smaller diameters extrapolating sparse rock distributions in the phoenix landing ellipse indicate 1 chance of encountering a potentially hazardous rock during landing or that could impede the opening of the solar arrays extrapolations further suggest rocks large enough to depress the ground ice table and small enough to be picked up or pushed by the robotic arm should be present within reach for study after landing

the chemical composition of martian soil and rocks returned by the mobile alpha proton x ray spectrometer preliminary results from the x ray mode the alpha proton x ray spectrometer apxs on board the rover of the mars pathfinder mission measured the chemical composition of six soils and five rocks at the ares vallis landing site the soil analyses show similarity to those determined by the viking missions the analyzed rocks were partially covered by dust but otherwise compositionally similar to each other they are unexpectedly high in silica and potassium but low in magnesium compared to martian soils and martian meteorites the analyzed rocks are similar in composition to terrestrial andesites and close to the mean composition of earth s crust addition of a mafic component and reaction products of volcanic gases to the local rock material is necessary to explain the soil composition

geology of the gusev cratered plains from the spirit rover transverse 1 the cratered plains of gusev traversed by spirit are generally low relief rocky plains dominated by impact and eolian processes ubiquitous shallow soil filled circular depressions called hollows are modified impact craters rocks are dark fine grained basalts and the upper 10 m of the cratered plains appears to be an impact generated regolith developed over intact basalt flows systematic field observations across the cratered plains identified vesicular clasts and rare scoria similar to original lava flow tops consistent with an upper inflated surface of lava flows with adjacent collapse depressions crater and hollow morphometry are consistent with most being secondaries the size frequency distribution of rocks 0 1 m diameter generally follows exponential functions similar to other landing sites for total rock abundances of 5 35 systematic clast counts show that areas with higher rock abundance and more large rocks have higher thermal inertia plains with lower thermal inertia have fewer rocks and substantially more pebbles that are well sorted and evenly spaced similar to a desert pavement or lag eolian bed forms ripples and wind tails have coarse surface lags and many are dust covered and thus likely inactive deflation of the surface 5 25 cm likely exposed two toned rocks and elevated ventifacts and transported fines into craters creating the hollows this observed redistribution yields extremely slow average erosion rates of 0 03 nm yr and argues for very little long term net change of the surface and a dry and desiccating environment similar to today s since the hesperian or 3 ga

degassing of mantle derived co2 and he from springs in the southern colorado plateau region neotectonic connections and implications for groundwater systems groundwaters of the southern colorado plateau arizona transition zone region are a heterogeneous mixture of chemically diverse waters including meteoric epigenic fluids karst aquifer waters and deeply sourced endogenic fluids we investigate the composition of travertine depositing co 2 rich springs to determine the origin transport and mixing of these various components the san francisco mountain recharge area has little surface flow instead waters discharge through major springs hundreds of kilometers away about 70 9340 l s of the total recharge 13 500 l s discharges 100 km to the north in the incised aquifer system at grand canyon most of this water 85 8070 l s emerges through two travertine depositing karst spring systems blue springs 6230 l s and havasu springs 1840 l s about 30 of recharge 4150 l s flows to the south and discharges along nw striking faults in the arizona transition zone forming the base flow for the verde river geochemical data define regional mixing trends between meteoric recharge and different endogenic end members that range from bicarbonate waters to sulfate waters water quality in the region is dictated by the percentage and character of the endogenic inputs that cause a measurable degradation of groundwater quality for water supply sources for the high co 2 include dissolution of limestone and dolostone c carb and external carbon c external c external is computed as the bicarbonate alkalinity dissolved inorganic carbon dic minus the c carb c external dic c carb c external is deconvolved using carbon isotopes into biogenically derived sedimentary carbon c organic and deep co 2 inputs c endogenic measured 13 c values are 17 to 3 versus pee dee belemnite pdb assuming 13 c carb 2 13 c organic 28 and 13 c endogenic 5 water chemistry mixing models indicate that an average of 42 of the total dic comes from dissolution of carbonate rocks 25 from organic carbon including soil respired co 2 and 33 from deep endogenic sources helium isotope values 3 he 4 he in gases dissolved in spring waters in the southern colorado plateau region range from 0 10 to 1 16 r a relative to air indicating that a significant component of the deeply derived fluid is from the mantle mean of 5 asthenospheric or 10 subcontinental lithospheric mantle source measured co 2 3 he ratios of 2 10 9 to 1 4 10 13 are adjusted by removing the proportion of co 2 from c carb and c organic to give values 10 for all but four samples various mixing models using co 2 3 he suggest that the mantle derived components of the co 2 load are highly variable from spring to spring and may make up an average of 10 of the total co 2 load of the regional springs fluid rock interactions involving endogenic fluids are suggested by 87 sr 86 sr 18 o and other tracers the endogenic co 2 component multiplied by discharge for each spring yields an integrated annual flux of deeply derived co 2 to the groundwater system of 1 4 10 9 mol yr this co 2 emission from the colorado plateau region reflects a complex tectonic evolution involving laramide hydration of the lithosphere above the farallon slab addition of fluids from mid tertiary mantle tectonism during slab removal and ongoing fluid movement induced by neotectonic small scale asthenospheric convection

determination of the chemical composition of martian soil and rocks the alpha proton x ray spectrometer the alpha proton x ray spectrometer apxs for the mars pathfinder mission is designed to provide a complete and detailed analysis of chemical elements in martian soil and rocks near the landing site the apxs instrument is carried on the pathfinder microrover which will provide transportation to places of interest on the martian surface it consists of a complex sensor head mounted on a simple but sophisticated apxs deployment mechanism adm outside the warm electronics box web of the microrover and the instrument electronics mounted inside the web the adm permits the instrument sensor head to be placed against soil and rock samples in arbitrary positions ranging from horizontal to vertical in order to perform in situ analysis the possibility to transport the apxs to an arbitrary location preselected on earth and to perform in situ analysis there constitutes one of the most exciting aspects of the pathfinder mission the principle of the apxs technique is based on three interactions of alpha particles from a radioisotope source with matter simple rutherford backscattering production of protons from p reactions on light elements and generation of characteristic x rays upon recombination of atomic shell vacancies created by a bombardment measurement of the intensities and energy distributions of these three components yields information on the abundance of chemical elements in the sample in terms of sensitivity and selectivity data are partly redundant and partly complementary alpha backscattering is superior for light elements c o while proton emission is mainly sensitive to na mg al si s and x ray emission is more sensitive to heavier elements na to fe and beyond a combination of all three measurements enables determination of all elements with the exception of h and he present at concentration levels above typically a fraction of 1

an oxygen buffer for some peraluminous granites and metamorphic rocks the mineral assemblage biotite garnet muscovite magnetite quartz and its subsets are common in many peraluminous granites schists and gneisses if the biotite and garnet are reasonably iron rich then the system is a useful buffer for oxygen fugacity available thermochemical data indicate that in temperature oxygen fugacity space the buffer curve is located between the hematite magnetite curve and the quartz magnetite fayalite curve in a region that previously had no buffer curve applicable to peraluminous rocks the buffer equation partially taking into account the departures of biotite garnet and muscovite compositions from their end member formulae is logfo2 10 29 262847 t 0 148 p l r atog x3l 3log y 3log ff 2log 4lni 4log xgi 1l 650 t examples of applications are given for three peraluminous granitic rocks and three pelitic schists the calculated oxygen fugacity values corrected for mineral compositions generally agree with published estimated values based on the compositions of coexisting iron and titanium oxide phases

characteristics of pebble and cobble sized clasts along the curiosity rover traverse from sol 100 to 750 terrain types potential sources and transport mechanisms abstract we combine the results of orbitally derived morphologic and thermal inertia data with in situ observations of abundance size morphologic characteristics and distribution of pebble to cobble sized clasts along the curiosity rover traverse our goals are to characterize rock sources and transport history and improve our ability to predict upcoming terrain there are ten clast types with nine types interpreted as sedimentary rocks only type 3 clasts had morphologies indicative of significant wear through transport thus most clast types are indicative of nearby outcrops or prior presence of laterally extensive sedimentary rock layers consistent with the erosional landscape a minor component may reflect impact delivery of more distant material types 1 and 4 are heavily cemented sandstones likely associated with a caprock layer types 5 and 6 and possibly 7 are pebble rich sandstones with varying amounts of cement leading to varying susceptibility to erosion wear type 3 clasts are rounded pebbles likely transported and deposited alluvially then worn out of pebbly sandstone conglomerate types 9 and 10 are poorly sorted sandstones with type 9 representing fragments of square top type layers and type 10 deriving from basal or other mt sharp layers types 2 8 and 9 are considered exotics there are few clear links between clast type and terrain surface roughness particularly in identifying terrain that is challenging for the rover to navigate orbital data may provide a reasonable prediction of certain end member terrains but the complex interplay between variables that contribute to surface characteristics makes discriminating between terrain types from orbital data problematic prediction would likely be improved through higher resolution thermal inertia data

impact fragmentation of lonar crater india implications for impact cratering processes in basalt impact fragmentation is an energetic process that has affected all planetary bodies to understand its effects in basalt we studied lonar crater which is a rare terrestrial simple impact crater in basalt and analogues to kilometer scale simple craters on mars the lonar ejecta consists of basaltic fragments with sizes ranging from silt to boulder the cumulative size and mass frequency distributions of these fragments show variation of power index for different size ranges suggesting simple and complex fragmentation the general shape of the fragments is compact platy bladed and elongated with an average edge angle of 100 the size distribution of cobble to boulder sized fragments is similar to the fracture spacing distribution in the upper crater wall indicating the provenance of those large fragments its consistency with a theoretical spallation model suggests that the large fragments were ejected from near surface of the target whereas the small fragments from deeper level the petrophysical properties of the ejecta fragments reflect the geophysical heterogeneity in the target basalt that significantly reduced the original size of spall fragments the presence of fe mg phyllosilicates smectites both in the ejecta and wall indicates the role of impact in excavating the phyllosilicates from the interior of basaltic target affected by aqueous alteration the seismic images reveal a thickness variation in the ejecta blanket segregation of boulders fractures and faults in the bedrock beneath the crater rim the fracturing fragmentation and fluvial degradation of lonar crater have important implications for mars

overview of the mars pathfinder mission and assessment of landing site predictions chemical analyses returned by mars pathfinder indicate that some rocks may be high in silica implying differentiated parent materials rounded pebbles and cobbles and a possible conglomerate suggest fluvial processes that imply liquid water in equilibrium with the atmosphere and thus a warmer and wetter past the moment of inertia indicates a central metallic core of 1300 to 2000 kilometers in radius composite airborne dust particles appear magnetized by freeze dried maghemite stain or cement that may have been leached from crustal materials by an active hydrologic cycle remote sensing data at a scale of generally greater than 1 kilometer and an earth analog correctly predicted a rocky plain safe for landing and roving with a variety of rocks deposited by catastrophic floods that are relatively dust free

general geology and geomorphology of the mars pathfinder landing site the mars pathfinder mpf spacecraft landed on relatively young late hesperian early amazonian 3 1 0 7 ga plains in chryse planitia near the mouth of ares vallis images returned from the spacecraft reveal a complex landscape of ridges and troughs large hills and crater rims rocks and boulders of various sizes and shapes and surficial deposits indicating a complex multistage geologic history of the landing site after the deposition of one or more bedrock units depositional and erosional fluvial processes shaped much of the present landscape multiple erosional events are inferred on the basis of observations of numerous channels different orientations of many streamlined tails from their associated knobs and hills and superposition of lineations and streamlines medium and small scale features interpreted to be related to late stage drainage of floodwaters are recognized in several areas at the landing site streamlined knobs and hills seen in viking orbiter images support this inference as they seem to be complex forms partly erosional and partly depositional and may also indicate a series of scouring and depositional events that in some cases further eroded or partially buried these landforms although features such as these are cited as evidence for catastrophic flooding at ares vallis some of these features may also be ascribed to alternative primary or secondary depositional processes such as glacial or mass wasting processes close inspection of the landing site reveals rocks that are interpreted to be volcanic in origin and others that may be conglomeratic if such sedimentary rocks are confirmed fluvial processes have had a greater significance on mars than previously thought for the last several hundred million to few billion years eolian processes have been dominant dunes and dune like features ventifacts and deflation and exhumation features around several rocks probably are the most recent landforms the relatively pristine nature of the overall landscape at the mpf site suggests weathering and erosion processes on mars are exceptionally slow

the imager for mars pathfinder experiment the imager for mars pathfinder imp a stereoscopic multispectral camera is described in terms of its capabilities for studying the martian environment the camera s two eyes separated by 15 0 cm provide the camera with range finding ability each eye illuminates half of a single ccd detector with a field of view of 14 4 14 0 and has 12 selectable filters the 18 optics have a large depth of field and no focussing mechanism is required a mechanical shutter is avoided by using the frame transfer capability of the 512 512 ccd the resolving power of the camera 0 98 mrad pixel is approximately the same as the viking lander cameras however the signal to noise ratio for imp greatly exceeds viking approaching 350 this feature along with the stable calibration of the filters between 440 and 1000 nm distinguishes imp from viking specially designed targets are positioned on the lander they provide information on the magnetic properties of wind blown dust measure the wind vectors and provide radiometric standard reflectors for calibration also eight low transmission filters are included for imaging the sun directly at multiple wavelengths giving imp the ability to measure dust opacity and potentially the water vapor content several experiments beyond the requisite color panorama are described in detail contour mapping of the local terrain multispectral imaging of the surrounding rock and soil to study local mineralogy viewing of three wind socks measuring atmospheric opacity and water vapor content and estimating the magnetic properties of wind blown dust this paper is intended to serve as a guide to understanding the scientific integrity of the imp data that will be returned from mars starting on july 4 1997

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

overview of the mars pathfinder mission launch through landing surface operations data sets and science results mars pathfinder successfully landed at ares vallis on july 4 1997 deployed and navigated a small rover about 100 m clockwise around the lander and collected data from three science instruments and ten technology experiments the mission operated for three months and returned 2 3 gbits of data including over 16 500 lander and 550 rover images 16 chemical analyses of rocks and soil and 8 5 million individual temperature pressure and wind measurements path finder is the best known location on mars having been clearly identified with respect to other features on the surface by correlating five prominent horizon features and two small craters in lander images with those in high resolution orbiter images and in inertial space from two way ranging and doppler tracking tracking of the lander has fixed the spin pole of mars determined the precession rate since viking 20 years ago and indicates a polar moment of inertia which constrains a central metallic core to be between 1300 and 2000 km in radius dark rocks appear to be high in silica and geochemically similar to anorogenic andesites lighter rocks are richer in sulfur and lower in silica consistent with being coated with various amounts of dust rover and lander images show rocks with a variety of morphologies fabrics and textures suggesting a variety of rock types are present rounded pebbles and cobbles on the surface as well as rounded bumps and pits on some rocks indicate these rocks may be conglomerates although other explanations are also possible which almost definitely require liquid water to form and a warmer and wetter past air borne dust is composed of composite silicate particles with a small fraction of a highly magnetic mineral interpreted to be most likely maghemite explanations suggest iron was dissolved from crustal materials during an active hydrologic cycle with maghemite freeze dried onto silicate dust grains remote sensing data at a scale of a kilometer or greater and an earth analog correctly predicted a rocky plain safe for landing and roving with a variety of rocks deposited by catstrophic floods which are relatively dust free the surface appears to have changed little since it formed billions of years ago with the exception that eolian activity may have deflated the surface by 3 7 cm sculpted wind tails collected sand into dunes and eroded ventifacts fluted and grooved rocks pathfinder found a dusty lower atmosphere early morning water ice clouds and morning near surface air temperatures that changed abruptly with time and height small scale vortices interpreted to be dust devils were observed repeatedly in the afternoon by the meteorology instruments and have been imaged

results from the mars pathfinder camera images of the martian surface returned by the imager for mars pathfinder imp show a complex surface of ridges and troughs covered by rocks that have been transported and modified by fluvial aeolian and impact processes analysis of the spectral signatures in the scene at 440 to 1000 nanometer wavelength reveal three types of rock and four classes of soil upward looking imp images of the predawn sky show thin bluish clouds that probably represent water ice forming on local atmospheric haze opacity 0 5 haze particles are about 1 micrometer in radius and the water vapor column abundance is about 10 precipitable micrometers

morphologies of rocks within and near the rock garden at the mars pathfinder landing site this paper considers the morphology of several rocks and rock fragments within and near the rock garden at the mars pathfinder landing site we have analyzed stereo images taken both by the lander imp camera and by the rover forward cameras the rocks were found to differ in their roundness angularity and in their densities of millimeter to centimter sized pits and flute like features on the rock facets no correlation between rock roundness and the degree of rock pitting was found indicating that rounding and pitting formed by different processes pits are either gas bubbles implying the rocks are volcanic or resulted from eolian abrasion deflation putting no constraints on the nature of the rocks or both if pits are of eolian origin variations in the density of pits on different rocks imply that either the rock surfaces have been exposed for different times or the susceptibility of different rocks to pitting varies significantly from rock to rock implying differences in composition and or lithology the densities of pits and flutes on the rocks show anti correlation this may be connected to their formation but probably is mostly related to issues of observation and definition of what is a pit and what is a flute flute like features may be a result of eolian abrasion but in this case the spatial closeness of fluted rocks and those having delicately pitted textures requires explanation other mechanisms producing flute like features such as collisions in the deposit forming flows and the breaking of rock in impact cratering should not be ignored our observations agree with the conclusion of golombek et al this issue that deflational exhumation in this area was minor the observed relatively large rocks typically do not show a concentration of small rock fragments at their feet this implies diurnal thermal cycles are very ineffective at destructing rocks the rock half dome may be a conglomerate as suggested by smith et al 1997a for this and several other rocks but this hypothesis remains to be proven impact craters of a few meters to a few tens meters in diameter may have played a role in the local geology

characteristics of the pathfinder apxs sites implications for the composition of martian rocks and soils an integrated study of spectral elemental abundance and image data from the pathfinder alpha proton x ray spectrometer apxs measurement sites has led to a better understanding of the nature of martian surface materials this rigorous analysis provides a new level of detail that forms the basis for the results reported here and that can be used by future scientists trying to understand rocks and soils on mars each apxs site has been precisely located by analyzing stereo imager for mars pathfinder imp and rover camera images to determine the position of the apxs during deployment rover and imp images are used to assess local geology namely the presence of pebbles clods and aeolian features in soils and surface textures and dust concentrations on rocks imp spectra using the latest calibrations for radiance and reflectance are analyzed at a number of different illumination geometries for each apxs site the three dimensional orientation of the sites has been determined and then used to compute the true sunlight incidence and viewing emission angles where suitable photometric coverage is available reflectances are fit to the hapke irvine function this is then used to adjust spectral reflectances to a normalized illumination geometry common to all rocks and soils comparing all the data sets shows a positive correlation among red blue reflectance ratio so3 content and dust abundance on rocks indicating that rocks are coated with varying amounts of sulfur rich red dust other elements such as silicon and iron are poor tracers for dust because their abundances within soil are similar to those within rock rock apxs targets that are bluer poorer in sulfur and have minimal dust coverage face toward the northeast the direction in which winds may be capable of efficiently removing loose material under current martian conditions the imp spectral properties of the soils show poor correlations with apxs elemental abundances on the basis of currently released apxs data bulk soils at the pathfinder landing site are richer in silica and sulfur than the viking landing sites suggesting a different composition the apxs soils with the most apparent pebbles are the poorest in sio2 indicating that either the pebbles are more mafic than the apxs rocks or the pebble free soil component is inherently enriched in sio2 compared to viking soils the mixture of materials at the apxs sites is a reflection of the overall complexity of martian surface materials a detailed understanding of which should drive the choice of future instruments and missions

the al 2 o 3 contents of enstatite in equilibrium with garnet in the system mgo al 2 o 3 sio 2 at 15 40 kbar and 900 1 600 c forty six reversed determinations of the al2o3content of enstatite in equilibrium with garnet were made in the p t range 15 40 kbar 900 1 600 c in the mgo al2o3 sio2 system starting materials were mixtures of synthetic pyrope al free enstatite and pyrope enstatite 5 12 al2o3 al2o3 contents in reversal run pairs closely approached common values from both the high and low al sides most experiments were done in a piston cylinder device using a nacl medium some runs at very high temperatures were made in pyrex nacl or pyrex talc assemblies the measured enstatite compositions expressed as mole fractions of mg2 mgal alsi3 o12 x opy en were fitted by a monte carlo method to the equilibrium condition begin gathered delta h 970 0 970 delta s 970 0 hfill mathop smallint limits 1 p delta v 970 0 dp mathop smallint limits 970 t delta s t 0 dt rt ln x opy en 0 hfill end gathered where the best fit parameters of h s and v 1 bar 970 k for the reaction pyrope opy are 2 040 cal mol 2 12 eu and 9 55 cc mol in addition to the determination of al2o3 contents of enstatite the univariant reaction pyrope forsterite enstatite spinel was reversibly located in the range 1 100 1 400 c a best fit line passes through 22 22 5 and 25 kbar at 1 040 1 255 and 1 415 c respectively our results for the univariant reaction are in agreement with previous studies of macgregor 1974 and haselton 1979 however comparison of the experimentally determined curve with thermochemical calculations suggests that there may be a small error in the tabulated h f 970 1 0 value for enstatite a value of 8 32 rather than 8 81 kcal mole charlu et al 1975 is consistent with the present data application of garnet enstatite spinel forsterite equilibria to natural materials is fraught with difficulties the effects of nonternary components are poorly understood and the low solubilities of al2o3 in enstatite under most geologically reasonable conditions make barometric or thermometric calculations highly sensitive more detailed studies including reversed determinations in low friction assemblies are sorely needed before the effects of important diluents such as fe ca and cr can be fully understood

an evaluation of shape indices as palaeoenvironmental indicators using quartzite and metavolcanic clasts in upper cretaceous to palaeogene beach river and submarine fan conglomerates the feasibility of using quantitative shape measurements to discriminate between clast populations from different depositional settings was evaluated using samples from 11 fluvial six submarine fan and four beach conglomerates from south west california these origins had been established previously by facies analysis quartzite and metavolcanic clasts were characterized by the following indices modified wentworth roundness rw maximum projection sphericity p oblate prolate index opi and long l intermediate i and short s axial ratios these indices were compared with those documented previously for modern gravels the results show that certain indices are useful palaeoenvironmental indicators despite inherited differences in shape due to texture provided that multiple sites are sampled and a statistical approach is used statistically the most effective shape indices are p and s l which give good results with the zingg classification i l vs s i better results are also obtained using quartzite clasts the opi is useful for discriminating between beach and river conglomerates which consist largely of oblate and prolate clasts respectively the relative abundance of blade shaped clasts is a useful index of sediment maturity being greatest for river clast samples and smallest for submarine fan clast samples the latter are dominated by spherical particles no correlation between palaeoenvironment and rw is observed hence the abundance of disc shaped clasts in the beach conglomerates studied is attributed to selective transport in suspension and sediment by passing during fluvial transport prior to deposition in the surf zone selective transport of rollers spheres and rods by traction in a shallow marine setting prior to redeposition by mass transport may be responsible for the dominance of spherical particles in submarine fan conglomerates

characterization of the martian surface deposits by the mars pathfinder rover sojourner sojourner the mars pathfinder rover discovered pebbles on the surface and in rocks that may be sedimentary not volcanic in origin surface pebbles may have been rounded by ares flood waters or liberated by weathering of sedimentary rocks called conglomerates conglomerates imply that water existed elsewhere and earlier than the ares flood most soil like deposits are similar to moderately dense soils on earth small amounts of dust are currently settling from the atmosphere

aeolian features and processes at the mars pathfinder landing site the mars pathfinder landing site contains abundant features attributed to aeolian or wind processes these include wind tails drift deposits duneforms of various types ripplelike features and ventifacts the first clearly seen on mars many of these features are consistant with formation involving sand size particles although some features such as dunes could develop from saltating sand size aggregates of finer grains the discovery of ventifact flutes cut in rocks strongly suggests that at least some of the grains are crystalline rather than aggregates excluding the ventifacts the orientations of the wind related features correlate well with the orientations of bright wind steaks seen on viking orbiter images in the general area they also correlate with wind direction predictions from the nasa ames general circulation model gcm which show that the strongest winds in the area occur in the northern hemisphere winter and are directed toward 209

fabric shape and the interpretation of sedimentary fabric data abstract the concept of fabric shape provides a powerful means of visualizing and analyzing data on sedimentary fabric the shape of a fabric is defined in terms of the ratios between eigenvalues s1 s2 and s3 derived using the orientation tensor method a continuum of all possible orthorhombic fabric shapes can be clearly represented on equilateral ternary diagrams originally developed for the presentation of particle shape data two indices are of particular value in scaling these diagrams fabric isotropy i s3 s1 and fabric elongation e 1 s2 s1 together these indices uniquely define the shape of any orthorhombic fabric and provide a rational and quantitative basis for reconstructing depositional and de ormational processes equilateral ternary diagrams provide a more versatile and powerful basis for analyzing fabric data than other eigenvalue diagrams now in use use of the diagrams in reconstructing processes of sediment transport and deposition is illustrated using fabric data from subglacial tills and a variety of slope deposits

morphology and texture of particles along the spirit rover traverse from sol 450 to sol 745 1 we quantified and classified the shape roundness size and texture of 935 loose surface particles along the spirit rover traverse from sols 450 745 to assess origin transport and other alteration mechanisms that altered particles during and after formation variation in particle morphologic parameters along traverse is consistent with crossing mapped geologic unit boundaries texture is divided into four types vesicular smooth and flat faceted rough and flat faceted and very rough sphericity and roundness are intermediate and low respectively comparable to particles moved by high energy transport or to crushed particles this indicates intermittent high energy emplacement or modification of a single lithology rather than systematic continuous low energy abrasion or wear over time comparison with particle morphology at other mars landing sites is consistent with the hypothesis that no secondary systematic transport or wide scale chemical alteration was active at a significant enough level to alter macromorphology in particular particle morphology at the mars pathfinder site shows stronger evidence of abrasion than along the spirit traverse suggesting mars pathfinder particles have undergone abrasion processes that particles in this study area have not additionally morphology indices have correlation coefficients near zero indicating that a fluvial transport mechanism is likely not responsible for morphology morphology and texture are instead related to origin and composition rather than subsequent modification morphology and texture support a volcanic origin possibly without modification but most likely altered primarily by ballistic impact implying that the spirit landing site and traverse may be utilized in the future as a standard site for characterization of impact derived morphology

geotraverse from xanthe terra to chryse planitia viking 1 lander region mars high resolution 1 500 000 scale geologic mapping of a 300 km wide and 1500 km long strip or geotraverse across the transition from the xanthe terra cratered highlands to the chryse planitia lowlands encompasses an area on the margin of the chryse basin unaffected by outflow channels it thus characterizes the transition where it has been relatively unmodified by erosion and the stratigraphy of pre outflow units is well preserved two types of highland lowland boundary are identified 1 a topographic boundary and 2 a geologic morphologic boundary the topographic boundary occurs well within the cratered highlands and separates a lower standing surface with characteristics transitional to cratered highlands from the true highland surface of xanthe terra the lower transitional highland surface or transition zone is partially inundated by plains forming materials interpreted to be plains type lava flows of late noachian early hesperian age similar to later basin fill material forming hesperian aged lowland ridged plains the geologic boundary between this transitional surface and ridged lowland plains surface is identified with the traditional highland lowland boundary as mapped in previous studies mapping in this study identifies a moat like region between this geologic boundary and the basin interior is filled with an easily eroded material erosion of the moat filling deposit along the outer margins of the chryse basin accounts for the streamlined tables formed during outflow channeling throughout the margins of chryse planitia the geology of the central basin interior where the viking 1 lander is located is consistent with the presence of fluvial sediments derived from both the adjacent highlands and remobilized from the marginal moat filling unit and deposited near the termini of the maja and kasei valles outflow channels because the plains forming lavas overlie much of the proximal portions of the highlands and moat filling sediments ring the margins of the basin materials eroded from the transition zone and deposited toward the basin interior by later outflow channels may be similar to interior plains lavas and marginal moat filling deposits if the transitional highland surface is typical of the basin elsewhere true highland rocks are likely to be a small component of any outflow channel sediments even in settings near the basin margin rock populations and sediments at the proposed mars pathfinder site located near the geologic boundary further east could contain a significant portion of materials typical of lowlands in addition to some highland materials

quantitative morphology of rocks at the mars pathfinder landing site 1 we adapt and test a standard terrestrial technique of assessing morphology quantitatively for use with sites on mars based on two dimensional equations and particle outlines whereby images of particles obtained remotely may yield dimensionless numerical shape and roundness values consistent with previous knowledge of the lithology and sedimentary transport history our test site was the particle rich rock garden at the mars pathfinder landing site a location where the primary geologic processes and lithology have been determined by other means a total of 575 particles were assessed in terms of size sphericity elongation and roundness qualitative roundness was determined for 460 particles particles are mostly pebble to cobble sized and have an average sphericity of 0 75 elongation of 0 63 and relative roundness of 0 083 69 of particles are subangular or subrounded particle sphericity is unimodal with a size sphericity profile matching trends for terrestrial populations of similar lithology and elongations nearly identical to those for particles at vikings 1 and 2 this matches the predictions for a site with the single overall lithology implied from other analyses roundness data indicate one or possibly two particle populations representing the primary processes that likely affected particle roundness most strongly impact and catastrophic flooding finally we tested a hypothesis suggesting that darker smaller more angular particles comprise a population transported through impact cratering while larger less dark more rounded particles are associated with catastrophic flood transport the opposite result is seen larger particles throughout the rock garden are more angular than smaller ones

chemical multispectral and textural constraints on the composition and origin of rocks at the mars pathfinder landing site rocks at the mars pathfinder site are probably locally derived textures on rock surfaces may indicate volcanic sedimentary or impact generated rocks but aeolian abration and dust coatings prevent unambiguous interpretation multispectral imaging has resolved four spectral classes of rocks gray and red which occur on different surfaces of the same rocks pink which is probably soil crusts and maroon which occurs as large boulders mostly in the far field rocks are assigned to two spectral trends based on the position of peak reflectance the primary spectral trend contains gray red and pink rocks maroon rocks constitute the secondary spectral trend the spatial pattern of spectral variations observed is oriented along the prevailing wind direction the primary spectral trend arises from thin ferric coatings of aeolian dust on darker rocks the secondary spectral trend is apparently due to coating by a different mineral probably maghemite or ferrihydrite a chronology based on rock spectra suggests that rounded maroon boulders constitute the oldest petrologic unit a flood deposit succeeded by smaller cobbles possibly deposited by impact and followed by aeolian erosion and deposition nearly linear chemical trends in alpha proton x ray spectrometer rock compositions are interpreted as mixing lines between rock and adhering dust a conclusion supported by a correlation between sulfur abundance and red blue spectral ratio extrapolations of regression lines to zero sulfur give the composition of a presumed igneous rock the chemistry and normative mineralogy of the sulfur free rock resemble common terrestrial volcanic rocks and its classification corresponds to andesite igneous rocks of this composition may occur with clastic sedimentary rocks or impact melts and breccias however the spectral mottling expected on conglomerates or breccias is not observed in any apxs analyzed rocks interpretation of the rocks as andesites is complicated by absence of a 1 m pyroxene absorption band plausible explanations include impact glass band masking by magnetite or presence of calcium and iron rich pyroxenes and olivine which push the absorption band minimum past the imager s spectral range the inferred andesitic composition is most similar to terrestrial anorogenic icelandites formed by fractionation of tholeiitic basaltic magmas early melting of a relatively primitive martian mantle could produce an appropriate parent magma supporting the ancient age of pathfinder rocks inferred from their incorporation in hesperian flood deposits although rocks of andesitic composition at the pathfinder site may represent samples of ancient martian crust inferences drawn about a necessary role for water or plate tectonics in their petrogenesis are probably unwarranted

sedimentary history and mass flow structures of chryse and acidalia planitiae mars geologic mapping and crater counting in chryse and acidalia planitiae cap reveal five major sedimentary deposits of hesperian to early amazonian age including 1 a mass flow deposited during the early hesperian near deuteronilus mensae northeast of the map region that may have resulted from the carving of kasei valles 3000 km southwest of the exposed part of the deposit 2 knobby plains material consisting of channel likely from simud and tiu valles and possibly ares and shalbatana valles and mass wasting deposits in central and eastern cap 3 material largely from maja and ares valles emplaced in at least western and southern cap outcrops in southern chryse planitia developed thermokarst 4 a thin mass flow covering much of southern chryse planitia that emanated from simud and tiu valles and 5 a thick extensive perhaps 3500 km across mass flow deposit in central and northern cap derived from accumulation and backflow of the preceding thin mass flow or perhaps melting of polar deposits other possible deposits may not be recognizable owing to burial by younger materials or a lack of morphologic signature various associated landforms appear to be consistent with the mass flow interpretations including lobate and linear scarps along deposit edges fractures related to desiccation of thick sediments troughs and ridges near the edges of the deposit indicative of secondary mass movement and deformation pitted domes and fissure fed flows possibly formed by sedimentary mud eruptions and longitudinal channel grooves perhaps formed by roller vortices no convincing evidence for paleoshorelines or stagnant ice sheets is found in cap these findings suggest that mass flow and hyperconcentrated flooding may have been the predominant processes of outflow channel dissection in cap elsewhere in the northern plains similar landforms are prevalent the mass flow interpretation does not require either multiple episodes of extraordinarily high water discharge rates achieved by freeing huge volumes of water from the crust repetitive recycling of immense volumes of water into highland aquifers at the heads of chryse channels or profound climate change mars pathfinder will most likely land on and inspect the surface of the thin mass flow that originated from the canyons of simud and tiu valles

high temperature phase equilibria in a solar composition gas abstract using recent additions to thermochemical data on minerals and information on their solid solution behavior new equilibrium phase diagrams have been computed in a system of solar gas composition si al mg ca fe ni ti na k c h o s n in the pressure and temperature ranges of 1 to 10 6 bar and 1153 to 1773 k respectively these calculations show that fe ni alloy condenses before all silicates included here except melilite down to a pressure of 2 10 4 bar below which plagioclase and clinopyroxene condense first orthopyroxene condenses next followed by ilmenite pressure temperature variation of the chemical composition of melilite clinopyroxene orthopyroxene metal alloy and plagioclase may be used for cosmothermometry and cosmobarometry for equilibrium assemblages the major transition from the refractory oxides and melilite the meteorite inclusion assemblage to an assemblage of fe ni alloy olivine plagioclase and pyroxenes planet forming takes place within a narrow interval of pressure and temperature small fluctuations of either pressure or temperature across this narrow region result in drastic changes in types and modes of minerals which may explain the wide mineralogical varieties of meteorites

debris flow origin for the simud tiu deposit on mars a late hesperian smooth plains deposit on mars interpreted as a debris flow extends more than 2000 km from hydraotes chaos through simud and tiu valles and into chryse planitia the simud tiu deposit widens out to 1000 km and embays streamlined landforms and knobs made up of sedimentary and perhaps volcanic deposits that were carved by earlier channeling activity morphologic features of the simud tiu deposit observed in viking and pathfinder images are generally consistent with a debris flow origin but some of the deposit s salient features are not readily explained by catastrophic flooding or ice flow internal depressions appear to be bounded by linear scarps along flow margins where differential shearing may have occurred and in areas where flow spreading may have produced zones of extensional breakup and thinning within the flow possible flow lobes within the deposit may have formed by successive flow surges within the flow unit the pathfinder landing site is on the simud tiu deposit and the observations there are consistent with debris flow the low longitudinal ridges at the site may have formed by clast interactions as the flow ground to a halt imbricated planar rocks on the ridges such as in the rock garden also may have been emplaced by debris or ice flow however stream energy calculations at ares vallis and channel geology indicate that flooding probably was incapable of emplacing the meter size boulders observed at the pathfinder site dewatering of pressurized zones in the debris flow or underlying material may be responsible for mud eruptions that formed a couple of patches of low pancakelike shields up to 5 km in diameter and for probable water flows that formed two small rille channels a few kilometers long local irregular grooves may be cracks that resulted from later desiccation and contraction of the flow material the debris flow unit apparently coalesced from outflows of water fluidized debris originating from beneath chaotic and hummocky terrains within and along the margins of simud and tiu valles the deposit is onlapped from the north by another flow deposit originating from acidalia planitia if the simud tiu debris flow had entered a standing body of water a turbidity current may have arisen from the debris flow and then backflowed over the debris flow to account for the acidalia deposit

spectral evidence of volcanic cryptodomes on the northern plains of mars abstract the composition and detailed morphology of dome shaped features located in western arcadia planitia and just west of utopia planitia were examined in this study utilizing data from mars reconnaissance orbiter and mars odyssey sensors the domes have diameters averaging 1 5 km and heights averaging 160 m and are generally dark toned although some are lighter toned or have split dark and light toned surfaces the domes are surrounded by annular deposits comprising with increasing distance from the domes dark toned aprons light toned aureoles and dark toned aureoles compact reconnaissance imaging spectrometer for mars crism data over several areas in the western arcadia region show that spectra from the flanks of several domes have 1 and 2 m absorption features consistent with the presence of olivine and a high ca pyroxene nominally augite modified gaussian model mgm analysis of these spectra indicates fe rich olivine compositions the tops of domes and the aprons surrounding many domes have negative sloping flat spectra in the near infrared which is consistent with tachylite rich glassy compositions high resolution imaging science experiment hirise images over several domes indicate that relatively high thermal inertia values associated with the tops of domes can be attributed to boulder strewn surfaces hirise images also reveal that light toned aureoles around domes consist of crenulated ground resembling brain terrain textures previously described for ice rich concentric crater fill elsewhere on the northern plains the plains surrounding the domes also display lineations that are interpreted to be lava channels or tubes the combination of volcanic and ice related features are consistent with the domes having formed as cryptodomes in the near sub surface we suggest that the domes could be basaltic in composition if the magmas were degassed and or highly crystallized and thus more viscous than typical basaltic magmas the intrusion of these magmas into an ice rich horizon would have produced a pervasively jointed chilled margin on the domes which once the domes were exposed would have mechanically weathered to form the dark aprons the domes could have served as local centers for ice accumulation during periods of high orbital obliquity which ultimately would have led to the formation of the brain terrain surrounding the features the domes represent late stage volcanic products on the northern plains of mars and associated features provide more evidence for the role that ice accumulation and modification has played in recent martian history

martian fluvial conglomerates at gale crater observations by the mars science laboratory mast camera mastcam in gale crater reveal isolated outcrops of cemented pebbles 2 to 40 millimeters in diameter and sand grains with textures typical of fluvial sedimentary conglomerates rounded pebbles in the conglomerates indicate substantial fluvial abrasion chemcam emission spectra at one outcrop show a predominantly feldspathic composition consistent with minimal aqueous alteration of sediments sediment was mobilized in ancient water flows that likely exceeded the threshold conditions depth 0 03 to 0 9 meter average velocity 0 20 to 0 75 meter per second required to transport the pebbles climate conditions at the time sediment was transported must have differed substantially from the cold hyper arid modern environment to permit aqueous flows across several kilometers

mineralogy composition and alteration of mars pathfinder rocks and soils evidence from multispectral elemental and magnetic data on terrestrial analogue snc meteorite and pathfinder samples major element multispectral and magnetic properties data were obtained at ares vallis during the mars pathfinder mission to understand the compositional mineralogical and process implications of these data we obtained major element mineralogical and magnetic data for well crystalline and nanophase ferric minerals terrestrial analogue samples with known geologic context and snc meteorites analogue samples include unaltered palagonitic and sulfatetic tephra from mauna kea volcano hydrolytic and acid sulfate alteration steam vent material from kilauea volcano hydrolytic alteration and impactites from meteor crater relithification salient results for mars pathfinder include 1 band depths bd530b and bd600 and the reflectivity ratio r800 r750 are consistent with the dominant ferric mineral being nanophase ferric oxide associated with an unknown amount of h2o and occurring in composite particles along with subordinate amounts of other ferric minerals hematite and hematite plus nanophase goethite are most consistent with the data but maghemite akaganeite schwertmannite and nanophase lepidocrocite are also possible interpretations ferric oxides that are consistently not favored by the data as sole alteration products are jarosites and well crystalline goethite and lepidocrocite 2 the strength of the ferric adsorption edge r750 r445 implies the fe3 fe2 values for pathfinder rock and soil are within the ranges 0 7 3 and 3 20 respectively 3 ferrous silicates are indicated for subsets of pathfinder rocks and soils one subset has a band minimum near 930 nm that can attributed to low ca pyroxene alternatively the band could be a second manifestation of certain ferric oxides including nanophase goethite maghemite akaganeite and schwertmannite another subset has a negative spectral slope from 800 to 1005 nm which could result from the high energy wing of a high ca pyroxene and or olivine band a mixture of bright and dark materials and for rocks thin coatings of bright dust on dark rocks 4 chemical data on pathfinder rocks and soils are consistent with two component mixtures between an andesitic rock with low mgo and so3 concentrations soil free rock and a global basaltic soil with high mgo and so3 concentrations rock free soil pathfinder rock free soil can be modeled as a chemical mixture of snc meteorites and the pathfinder soil free rock 5 pathfinder soil cannot be obtained by chemical alteration of pathfinder rocks by any of the hydrolytic and acid sulfate alteration processes we studied presumably global mixing has obscured and possibly erased the elemental signatures of chemical alteration 6 the strongly magnetic phase in palagonitic and sulfatetic tephra is titanomagnetite and possibly its oxidation product titanomaghemite fe ti spinels the saturation magnetization of the tephra samples 0 5 2 0 am2 kg is at or below the low end of the range inferred for martian dust 4 2 am2 kg implying that lithogenic fe ti spinels are a possible candidate for the martian strongly magnetic phase 7 the predominantly palagonitic spectral signature and magnetic nature of martian soil and dust are consistent with glassy precursors with imbedded fe ti spinel particles comparison with lunar glass production rates suggests that production of sufficient quantities of glassy materials on mars by volcanic and impact processes is sufficient to account for these observations

mineral equilibrium in fractionated nebular systems we investigated the equilibrium mineral assemblages in chemically fractionated nebular systems using a computer routine that finds the set of minerals and gases which minimizes the gibbs free energy of a system with stipulated elemental abundances diagrams are presented showing the equilibrium mineralogy as a function of temperature 400 2300 k for unfractionated solar material and five fractionated systems the fractionated systems were defined by mixing in various proportions the following four volatility components that solar material can be divided into refractory dust carbonaceous matter ices and h2 gas dust enrichment is seen to increase temperatures of condensation evaporation and the fe2 content of mafic minerals and to permit existence of stable melt phases enrichment of dust and organic matter produces mineral assemblages that are similar in many ways to those of enstatite chondrites but with mafic minerals that are far more reduced fe2 poor than those in primitive enstatite chondrites enrichment of dust organics and ices leads to highly ferrous mineralogies even at the highest temperatures but does not predict the stability of hydrous phases above 450 k

boulder abundances and size frequency distributions on oxia planum mars scientific implications for the 2020 esa exomars rover abstract this paper presents the abundances and the size frequency distributions sfd of boulders identified on a sector of the prime landing site for the exomars 2020 rover in oxia planum region by means of a hirise image boulders 1 75 m across have been identified and subdivided according to the two main oxia planum geological units the noachian clay rich formation nc and the amazonian volcanic deposit av the spatial density of boulders 1 75 m over the entire study area is 6 75 10 4 m2 with a size frequency that is best fit both with power law and exponential law curves with indices of 4 9 0 1 0 2 and 1 29 0 04 0 06 respectively significant differences were found by analysing separately the av and nc geological units the data collected in the av unit are well fitted with a power law curve with an index equal to 4 8 0 2 and with an exponential law curve with an index of 1 24 0 05 0 06 whilst in the nc unit such indices are 5 5 0 3 0 4 and 1 70 0 09 0 12 power law and exponential law curve respectively the spatial density of boulders in the av unit is 7 0 times larger than in the nc one this may be due primarily to the distinct mechanical properties of the two units that may result in a different production rate or preservation of the boulders secondly the av unit overlies the nc unit possibly resulting in more impacts and or different weathering processes throughout the ages this study provides a quantitative evaluation of the abundances of boulders 1 75 m across on oxia planum it is therefore a reference for the exomars 2020 mission both during the landing phase and the rover traverse to specific areas of interest the landing ellipse presents much higher abundances of boulders 1 75 m than all previous martian rover landing areas this is particularly evident when the rougher av unit is taken into account contrarily the nc unit shows a much more comparable value but still slightly higher to the mars pathfinder landing site we provide illustrative navigating scenarios for both the nc and the av units as well

characteristics of terrestrial basaltic rock populations implications for mars lander and rover science and safety abstract we analyzed the morphometry of basaltic rock populations that have been emplaced or affected by a variety of geologic processes including explosive volcanic eruptions as a proxy for impact cratering catastrophic flooding frost shattering salt weathering alluvial deposition and chemical weathering morphometric indices for these rock populations were compared to an unmodified population of rocks that had broken off a solidified lava flow to understand how different geologic processes change rock shape we found that a majority of rocks have an sphericity described as either a disc or sphere in the zingg classification system and posit that this is a function of cooling fractures in the basalt zingg 1935 schweiz miner petrogr mitt 15 39 140 angularity roundness is the most diagnostic morphometric index but the corey shape factor csf oblate prolate index opi and deviation from compactness d also sometimes distinguished weathering processes comparison of our results to prior analyses of rock populations found at the mars pathfinder spirit and curiosity landing sites support previous conclusions the observation that the size frequency distribution of terrestrial rock populations follow exponential functions similar to lander and orbital measurements of rocks on mars which is expected from fracture and fragmentation theory indicates that these distributions are being dominantly controlled by the initial fracture and fragmentation of the basalt