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

curiosity at gale crater mars characterization and analysis of the rocknest sand shadow the rocknest aeolian deposit is similar to aeolian features analyzed by the mars exploration rovers mers spirit and opportunity the fraction of sand 150 micrometers in size contains 55 crystalline material consistent with a basaltic heritage and 45 x ray amorphous material the amorphous component of rocknest is iron rich and silicon poor and is the host of the volatiles water oxygen sulfur dioxide carbon dioxide and chlorine detected by the sample analysis at mars instrument and of the fine grained nanophase oxide component first described from basaltic soils analyzed by mers the similarity between soils and aeolian materials analyzed at gusev crater meridiani planum and gale crater implies locally sourced globally similar basaltic materials or globally and regionally sourced basaltic components deposited locally at all three locations

a continuous 770 year record of volcanic activity from east antarctica a 100 m ice core from site g 15 accumulation rate 0 1 m water yr 1 mean annual temperature 38 c on the mizuho plateau dronning maud land east antarctica has been analysed using the dielectric profiling dep technique the capacitance and conductance of the core were measured at ac frequencies 20 hz 300 khz the high frequency conductivity profile shows variations that are primarily related to the strong acids derived from volcanic activity the tambora 1815 eruption can be identified with the aid of an approximate chronology based on the firn densification rate other historic eruptions can then be recognised beyond about 300 years historical observations are very few however if a constant overall accumulation rate is assumed a well known eruption of 1259 a d can be found near the bottom of the core other peaks in the conductivity profile can then be assigned dates accurate to within a few years using the conductivity profile it is possible to estimate the relative acid deposition fluxes produced by the main eruptions with reasonable accuracy the estimated acid deposisition fluxes realtive to the tambora 1815 eruption of agung 1963 is 27 krakatoa 1883 25 the signal of 1601 28 and that of 1259 53

large wind ripples on mars a record of atmospheric evolution wind blowing over sand on earth produces decimeter wavelength ripples and hundred meter to kilometer wavelength dunes bedforms of two distinct size modes observations from the mars science laboratory curiosity rover and the mars reconnaissance orbiter reveal that mars hosts a third stable wind driven bedform with meter scale wavelengths these bedforms are spatially uniform in size and typically have asymmetric profiles with angle of repose lee slopes and sinuous crest lines making them unlike terrestrial wind ripples rather these structures resemble fluid drag ripples which on earth include water worked current ripples but on mars instead form by wind because of the higher kinematic viscosity of the low density atmosphere a reevaluation of the wind deposited strata in the burns formation about 3 7 billion years old or younger identifies potential wind drag ripple stratification formed under a thin atmosphere

mineralogy of the msl curiosity landing site in gale crater as observed by mro crism orbital data acquired by the compact reconnaissance imaging spectrometer for mars crism and high resolution imaging science experiment instruments on the mars reconnaissance orbiter mro provide a synoptic view of compositional stratigraphy on the floor of gale crater surrounding the area where the mars science laboratory msl curiosity landed fractured light toned material exhibits a 2 2 m absorption consistent with enrichment in hydroxylated silica this material may be distal sediment from the peace vallis fan with cement and fracture fill containing the silica this unit is overlain by more basaltic material which has 1 m and 2 m absorptions due to pyroxene that are typical of martian basaltic materials both materials are partially obscured by aeolian dust and basaltic sand dunes to the southeast exhibit differences in mafic mineral signatures with barchan dunes enhanced in olivine relative to pyroxene containing longitudinal dunes this compositional difference may be related to aeolian grain sorting

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

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

chemistry mineralogy and grain properties at namib and high dunes bagnold dune field gale crater mars a synthesis of curiosity rover observations the mars science laboratory curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active bagnold dune field the bagnold sands are rounded to subrounded very fine to medium sized 45 500 m with 6 distinct grain colors in contrast to sands examined by curiosity in a dust covered inactive bedform called rocknest and soils at other landing sites bagnold sands are darker less red better sorted have fewer silt sized or smaller grains and show no evidence for cohesion nevertheless bagnold mineralogy and rocknest mineralogy are similar with plagioclase olivine and pyroxenes in similar proportions comprising 90 of crystalline phases along with a substantial amorphous component 35 15 yet bagnold and rocknest bulk chemistry differ bagnold sands are si enriched relative to other soils at gale crater and h 2o s and cl are lower relative to all previously measured martian soils and most gale crater rocks mg ni fe and mn are enriched in the coarse sieved fraction of bagnold sands corroborated by visible near infrared spectra that suggest enrichment of olivine collectively patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in martian soils 1 amorphous components in the sand sized fraction represented by bagnold that are si enriched hydroxylated alteration products and or h 2o or oh bearing impact or volcanic glasses and 2 amorphous components in the fine fraction 40 m represented by rocknest and other bright soils that are fe s and cl enriched with low si and adsorbed and structural h 2o

terrestrial analogs to wind related features at the viking and pathfinder landing sites on mars 1 features in the mojave desert and iceland provide insight into the characteristics and origin of martian wind related landforms seen by the viking and pathfinder landers the terrestrial sites were chosen because they exhibit diverse wind features that are generally well understood these features have morphologies comparable to those on mars and include origins by deposition and erosion with erosional processes modifying both soils and rocks duneforms and drifts are the most common depositional features seen at the martian landing sites and indicate supplies of sand sized particles blown by generally unidirectional winds erosional features include lag deposits moat like depressions around some rocks and exhumed soil horizons they indicate that wind can deflate at least some sediments and that this process is particularly effective where the wind interacts with rocks the formation of ripples and wind tails involves a combination of depositional and erosional processes rock erosional features or ventifacts are recognized by their overall shapes erosional flutes and characteristic surface textures resulting from abrasion by windblown particles the physics of saltation requires that particles in ripples and duneforms are predominantly sand sized 60 2000 m the orientations of duneforms wind tails moats and ventifacts are correlated with surface winds above particle threshold such winds are influenced by local topography and are correlated with winds at higher altitudes predicted by atmospheric models

gusev crater wind related features and processes observed by the mars exploration rover spirit 1 wind related features observed by the rover spirit in gusev crater mars include patches of soil on the surface some of which are organized into bed forms windblown grains include dust inferred to be 2 mm in diameter microscopic imager data show the sands and granules to be rounded and relatively spherical typical of grains transported long distances by the wind the interior of bed forms exposed by rover operations suggests the infiltration of dust among the grains indicating that these sands are not currently experiencing saltation orientations of 1520 features such as bed forms and ventifacts along spirit s traverse from the landing site the columbia memorial station to west spur in the columbia hills suggest primary formative winds from the north northwest which correlate with measurements of features seen in orbiter images and is consistent with afternoon winds predicted by atmospheric models a secondary wind from the southeast is also suggested which correlates with predictions for nighttime early morning winds wind abrasion is indicated by ventifacts in the form of facets and grooves cut into rocks the orientations of which also indicate prevailing winds from the north northwest orientations of many aeolian features in the west spur area however have more scatter than elsewhere along the traverse which is attributed to the influence of local topography on the patterns of wind active dust devils observed on the floor of gusev from the columbia hills demonstrate that dust is currently mobile sequential images of some dust devils show movement as rapid as 3 8 m s consistent with wind velocities predicted by atmospheric models for the afternoon when most of the dust devils were observed sands accumulated on the rover deck in the same period suggest that some sands in the columbia hills experience active saltation two toned rocks having a light band coating at their bases are considered to represent partial burial by soils and subsequent exposure while perched rocks could represent materials lowered onto other rocks by deflation of supporting soils measurements of the heights of the light bands and the perched rocks range from 1 cm to 27 cm indicating local deflation by as much as 27 cm

structural analysis of sheath folds with horizontal x axes northeast canada abstract early proterozoic supracrustal rocks occur below a thick nappe of archaean basement gneiss in the melville peninsula where sheath folds are exposed in a wide zone of middle proterozoic dynamothermal metamorphism outcrop patterns of truncated isoclinal sheath folds resemble cylindrical folds except in relatively small areas around the paraboloidal caps bulk extension axes are parallel to strike in the belt as shown by isoclinal sheath folds with horizontal central axes x axes as well as similarly aligned mullion structure and rotated scapolite prisms extension axes converge from northeast to southwest in the apparent flow direction

mineralogy of an active eolian sediment from the namib dune gale crater mars the mars science laboratory rover curiosity is using a comprehensive scientific payload to explore rocks and soils in gale crater mars recent investigations of the bagnold dune field provided the first in situ assessment of an active dune on mars the chemistry and mineralogy chemin x ray diffraction instrument on curiosity performed quantitative mineralogical analyses of the 150 m size fraction of the namib dune at a location called gobabeb gobabeb is dominated by basaltic minerals plagioclase fo56 olivine and two ca mg fe pyroxenes account for the majority of crystalline phases along with minor magnetite quartz hematite and anhydrite in addition to the crystalline phases a minimum 42 wt of the gobabeb sample is x ray amorphous mineralogical analysis of the gobabeb data set provides insights into the origin s and geologic history of the dune material and offers an important opportunity for ground truth of orbital observations chemin s analysis of the mineralogy and phase chemistry of modern and ancient gale crater dune fields together with other measurements by curiosity s science payload provides new insights into present and past eolian processes on mars

the mars science laboratory msl bagnold dunes campaign phase i overview and introduction to the special issue the bagnold dunes in gale crater mars are the first active aeolian dune field explored in situ on another planet the curiosity rover visited the bagnold dune field to understand modern winds aeolian processes rates and structures to determine dune material composition provenance and the extent and type of compositional sorting and to collect knowledge that informs the interpretation of past aeolian processes that are preserved in the martian sedimentary rock record the curiosity rover conducted a coordinated campaign of activities lasting 4 months interspersed with other rover activities and employing all of the rover s science instruments and several engineering capabilities described in 13 manuscripts and summarized here the major findings of the bagnold dunes campaign phase i include the following the characterization of and explanation for a distinctive meter scale size of sinuous aeolian bedform formed in the high kinetic viscosity regime of mars thin atmosphere articulation and evaluation of a grain splash model that successfully explains the occurrence of saltation even at wind speeds below the fluid threshold determination of the dune sands basaltic mineralogy and crystal chemistry in comparison with other soils and sedimentary rocks and characterization of chemically distinctive volatile reservoirs in sand sized versus dust sized fractions of mars soil including two volatile bearing types of amorphous phases

constraints on ripple migration at meridiani planum from opportunity and hirise observations of fresh craters 1 observations of fresh impact craters by the opportunity rover and in high resolution orbital images constrain the latest phase of granule ripple migration at meridiani planum to have occurred between 50 ka and 200 ka opportunity explored the fresh resolution crater cluster and concepcion crater that are superposed on and thus younger than the ripples these fresh craters have small dark pebbles scattered across their surfaces which are most likely fragments of the impactor suggesting that the dark pebbles and cobbles observed by opportunity at meridiani planum are a lag of impactor derived material either meteoritic or secondary impactors from elsewhere on mars two larger fresh rayed craters in meridiani planum bracket ripple migration secondaries from ada crater are clearly superposed on and secondaries from an unnamed 0 84 km diameter crater have been modified and overprinted by the ripples three methods were used to estimate the age of these craters and thus when the latest phase of ripple migration occurred the inactivity of the ripples over the past 50 ka at meridiani is also consistent with other evidence for the stability of the ripples the lack of observed eolian bed forms in craters that formed in the past 20 years and little evidence for much dune motion in the past 30 yr on mars observations of crater morphology and their interaction with the ripples allow the development of a general time scale for craters in meridiani planum over the past million years

mahli at the rocknest sand shadow science and science enabling activities 1 during martian solar days 57 100 the mars science laboratory curiosity rover acquired and processed a solid sediment sample and analyzed its mineralogy and geochemistry with the chemistry and mineralogy and sample analysis at mars instruments an aeolian deposit herein referred to as the rocknest sand shadow was inferred to represent a global average soil composition and selected for study to facilitate integration of analytical results with observations from earlier missions during first time activities the mars hand lens imager mahli was used to support both science and engineering activities related to sample assessment collection and delivery here we report on mahli activities that directly supported sample analysis and provide mahli observations regarding the grain scale characteristics of the rocknest sand shadow mahli imaging confirms that the rocknest sand shadow is one of a family of bimodal aeolian accumulations on mars similar to the coarse grained ripples interrogated by the mars exploration rovers spirit and opportunity in which a surface veneer of coarse grained sediment stabilizes predominantly fine grained sediment of the deposit interior the similarity in grain size distribution of these geographically disparate deposits support the widespread occurrence of bimodal aeolian transport on mars we suggest that preservation of bimodal aeolian deposits may be characteristic of regions of active deflation where winnowing of the fine sediment fraction results in a relatively low sediment load and a preferential increase in the coarse grained fraction of the sediment load the compositional similarity of martian aeolian deposits supports the potential for global redistribution of fine grained components combined with potential local contributions

columbia hills mars aeolian features seen from the ground and orbit 1 abundant wind related features occur along spirit s traverse into the columbia hills over the basaltic plains of gusev crater most of the windblown sands are probably derived from weathering of rocks within the crater and possibly from deposits associated with ma adim vallis windblown particles act as agents of abrasion forming ventifacts and are organized in places into various bed forms wind related features seen from orbit results from atmospheric models and considerations of topography suggest that the general wind patterns and transport pathways involve 1 winter nighttime winds that carry sediments from the mouth of ma adim vallis into the landing site area of spirit where they are mixed with locally derived sediments and 2 winter daytime winds that transport the sediments from the landing site southeast toward husband hill similar patterns occur in the summer but with weaker winds reversals of daytime flow out of gusev crater and nighttime wind flow into the crater can account for the symmetry of the bed forms and bimodal orientations of some ventifacts

compositional variations in sands of the bagnold dunes gale crater mars from visible shortwave infrared spectroscopy and comparison with ground truth from the curiosity rover during its ascent up mount sharp the mars science laboratory curiosity rover traversed the bagnold dune field we model sand modal mineralogy and grain size at four locations near the rover traverse using orbital shortwave infrared single scattering albedo spectra and a markov chain monte carlo implementation of hapke s radiative transfer theory to fully constrain uncertainties and permitted solutions these predictions evaluated against in situ measurements at one site from the curiosity rover show that x ray diffraction measured mineralogy of the basaltic sands is within the 95 confidence interval of model predictions however predictions are relatively insensitive to grain size and are nonunique especially when modeling the composition of minerals with solid solutions we find an overall basaltic mineralogy and show subtle spatial variations in composition in and around the bagnold dunes consistent with a mafic enrichment of sands with cumulative aeolian transport distance by sorting of olivine pyroxene and plagioclase grains furthermore the large variations in fe and mg abundances 20 wt at the bagnold dunes suggest that compositional variability may be enhanced by local mixing of well sorted sand with proximal sand sources our estimates demonstrate a method for orbital quantification of composition with rigorous uncertainty determination and provide key constraints for interpreting in situ measurements of compositional variability within martian aeolian sandstones

mineralogical characterization of mars science laboratory candidate landing sites from themis and tes data abstract data from the mars global surveyor thermal emission spectrometer tes and the mars odyssey thermal emission imaging system themis instruments are used to assess the mineralogic and dust cover characteristics of landing regions proposed for the mars science laboratory msl mission candidate regions examined in this study are eberswalde crater gale crater holden crater mawrth vallis miyamoto crater nili fossae trough and south meridiani planum compositional units identified in each region from tes and themis data are distinguished by variations in hematite olivine pyroxene and high silica phase abundance whereas no units are distinguished by elevated phyllosilicate or sulfate abundance though phyllosilicate minerals have been identified in all sites using near infrared observations these minerals are not unambiguously detected using either tes spectral index or deconvolution analysis methods for some of the sites small phyllosilicate outcrop sizes relative to the tes field of view likely hinder phyllosilicate mineral detection porous texture and or small particle size 15 possibly up to 40 of a high silica phase such as amorphous silica or zeolite high silica phase abundance over phyllosilicate bearing surfaces in mawrth vallis is higher than that of surrounding surfaces by 10 15 with the exception of these high silica surfaces in mawrth vallis regions examined in this study exhibit similar bulk mineralogical compositions to that of most low albedo regions on mars the msl scientific payload will thus be able to provide important information on surface materials typical of low albedo regions in addition to investigating the origin of phyllosilicate and or sulfate deposits with the exception of gale crater all of the landing sites have relatively low dust cover compared to classic high albedo regions tharsis arabia and elysium and to previous landing sites in gusev crater utopia planitia and chryse planitia

apxs derived chemistry of the bagnold dune sands comparisons with gale crater soils and the global martian average we present apxs data for the active bagnold dune field within the gale impact crater msl mission we derive an apxs based average basaltic soil abs composition for mars based on past and recent data from the msl and mer missions this represents an update to the taylor and mclennan 2009 average martian soil and facilitates comparison across martian datasets the active bagnold dune field is compositionally distinct from the abs with elevated mg ni and fe suggesting mafic mineral enrichment and uniformly low levels of s cl and zn indicating only a minimal dust component a relationship between decreasing grain size and increasing felsic content is revealed the bagnold sands possess the lowest s cl of all martian unconsolidated materials gale soils exhibit relatively uniform major element compositions similar to meridiani planum and gusev crater basaltic soils mer missions however they show minor enrichments in k cr mn and fe which may signify a local contribution the lithified eolian stimson formation within the gale impact crater is compositionally similar to the abs and bagnold sands which provide a modern analogue for these ancient eolian deposits compilation of apxs derived soil data reveals a generally homogenous global composition for martian soils but one that can be locally modified due to past or extant geologic processes that are limited in both space and time

recent aeolian dune change on mars previous comparisons of martian aeolian dunes in satellite images have not detected any change in dune form or position here we show dome dunes in the north polar region that shrank and then disappeared over a period of 3 04 mars years 5 7 earth years while larger neighboring dunes showed no erosion or movement the removal of sand from these dunes indicates that not only is the threshold wind speed for saltation exceeded under present conditions on mars but that any sand that is available for transport is likely to be moved dunes that show no evidence of change could be crusted indurated or subject to infrequent episodes of movement

mineralogy and stratigraphy of the gale crater rim wall and floor units the curiosity rover has detected diverse lithologies in float rocks and sedimentary units on the gale crater floor interpreted to have been transported from the rim to understand their provenance we examine the mineralogy and geology of gale s rim walls and floor using high resolution imagery and infrared spectra while no significant differences in bedrock spectral properties were observed within most thermal emission imaging system and compact reconnaissance imaging spectrometer for mars crism scenes some crism scenes of rim and wall rocks showed olivine bearing bedrock accompanied by fe mg phyllosilicates hydrated materials with 2 48 m absorptions in gale s eastern walls are spectrally similar to the sulfate unit in mount sharp aeolis mons sedimentary strata on the gale floor southwest of the landing site likely coeval with the bradbury units explored by curiosity also are hydrated and or have fe mg phyllosilicates spectral properties of these phyllosilicates differ from the al substituted nontronite detected by crism in mount sharp suggesting formation by fluids of different composition geologic mapping of the crater floor shows that the hydrated or hydroxylated materials are typically overlain by spectrally undistinctive erosionally resistant cliff forming units additionally a 4 km impact crater exposes 250 m of the gale floor including finely layered units no basement rocks are exposed thus indicating sedimentary deposits 250 m beneath strata studied by curiosity collectively the data indicate substantial sedimentary infill of gale crater including some materials derived from the crater rim lowermost thin layers are consistent with deposition in a lacustrine environment interbedded hydrated hydroxylated units may signify changing environmental conditions perhaps in a drying or episodically dry lake bed

martian aeolian activity at the bagnold dunes gale crater the view from the surface and orbit the first in situ investigation of an active dune field on another planetary surface occurred in 2015 2016 when the msl curiosity rover investigated the bagnold dunes on mars hirise images show clear seasonal variations that are in good agreement with atmospheric model predictions of intra annual sand flux and migration directions that together indicate that the campaign occurred during a period of low wind activity curiosity surface images show that limited changes nevertheless occurred with movement of large grains particularly on freshly exposed surfaces two occurrences of secondary grain flow on the slip face of namib dune and a slump on a freshly exposed surface of a large ripple these changes are seen at sol to sol time scales grains on a rippled sand deposit and unconsolidated dump piles show limited movement of large grains over a few hours during which mean friction speeds are estimated at 0 3 0 4 m s 1 overall the correlation between changes and peak rems winds is moderate with high wind events associated with changes in some cases but not in others suggesting that other factors are also at work the distribution of rems 1 hz wind speeds show a tail up to the 20 m s 1 showing that even higher speed winds occur non aeolian triggering mechanisms are also possible the low activity period at the dunes documented by curiosity provides clues to processes that dominated in the martian past under conditions of lower obliquity

paleoclimate of mars as captured by the stratigraphic record in gale crater a kilometers thick sedimentary sequence in gale crater exhibits stratigraphic changes in lithology that are consistent with transitions in aqueous and climatic conditions purported to be global in scale the sequence is divided into two formations where the lower formation exhibits a net transition in mineralogy from clay sulfate to sulfate oxide assemblages and is separated from the overlying upper formation by an erosional unconformity superposition and crater counts suggest strata in the lower formation lie along the noachian hesperian time stratigraphic boundary whereas beds in the upper formation which lack signatures indicative of clay minerals or sulfates are thinner more regularly spaced and clearly younger the observed stratigraphic trends are consistent with the rocks at gale crater recording a global transition from a climate favorable to clay mineral formation to one more favorable to forming sulfates and other salts

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

planet wide sand motion on mars prior to mars reconnaissance orbiter data images of mars showed no direct evidence for dune and ripple motion this was consistent with climate models and lander measurements indicating that winds of sufficient intensity to mobilize sand were rare in the low density atmosphere we show that many sand ripples and dunes across mars exhibit movement of as much as a few meters per year demonstrating that martian sand migrates under current conditions in diverse areas of the planet most motion is probably driven by wind gusts that are not resolved in global circulation models a past climate with a thicker atmosphere is only required to move large ripples that contain coarse grains

winds measured by the rover environmental monitoring station rems during the mars science laboratory msl rover s bagnold dunes campaign and comparison with numerical modeling using marswrf abstract a high density of rems wind measurements were collected in three science investigations during msl s bagnold dunes campaign which took place over 80 sols around southern winter solstice ls 90 and constituted the first in situ analysis of the environmental conditions morphology structure and composition of an active dune field on mars the wind characterization investigation was designed to fully characterize the near surface wind field just outside the dunes and confirmed the primarily upslope downslope flow expected from theory and modeling of the circulation on the slopes of aeolis mons in this season the basic pattern of winds is upslope from the northwest heading up aeolis mons during the daytime 09 00 17 00 or 18 00 and downslope from the southeast heading down aeolis mons at night 20 00 to some time before 08 00 between these times the wind rotates largely clockwise giving generally westerly winds mid morning and easterly winds in the early evening the timings of these direction changes are relatively consistent from sol to sol however the wind direction and speed at any given time shows considerable intersol variability this pattern and timing is similar to predictions from the marswrf numerical model run at a resolution of 490 m in this region although the model predicts the upslope winds to have a stronger component from the e than the w misses a wind speed peak at 09 00 and under predicts the strength of daytime wind speeds by 2 4 m s the namib dune lee investigation reveals blocking of northerly winds by the dune leaving primarily a westerly component to the daytime winds and also shows a broadening of the 1 hz wind speed distribution likely associated with lee turbulence the namib dune side investigation measured primarily daytime winds at the side of the same dune in support of aeolian change detection experiments designed to put limits on the saltation threshold and also appears to show the influence of the dune body on the local flow though less clearly than in the lee using a vertical grid with lower resolution near the surface reduces the relative strength of nighttime winds predicted by marswrf and produces a peak in wind speed at 09 00 improving the match to the observed diurnal variation of wind speed albeit with an offset in magnitude the annual wind field predicted using this grid also provides a far better match to observations of aeolian dune morphology and motion in the bagnold dunes however the lower overall wind speeds than observed and disagreement with the observed wind direction at 09 00 suggest that the problem has not been solved and that alternative boundary layer mixing schemes should be explored which may result in more mixing of momentum down to the near surface from higher layers these results demonstrate a strong need for in situ wind data to constrain the setup and assumptions used in numerical models so that they may be used with more confidence to predict the circulation at other times and locations on mars

ripple migration and dune activity on mars evidence for dynamic wind processes 1 in this report we show evidence of widespread ripple migration over the stoss side of dark barchan dunes in nili patera on mars the measured average migration of 1 7 meters in less than 4 terrestrial months clearly indicates that active sand saltation is occurring in the study area in addition we document widespread changes in the dune base ground surface contact and in the slip face structures showing that not only the ripples but the whole dunes are actually migrating in the present day atmospheric setting these results provide unequivocal evidence of recent aeolian activity and suggest that other dunes and ripples on mars may also be active

wind blown sandstones cemented by sulfate and clay minerals in gale crater mars gale crater contains mount sharp a 5km thick stratigraphic record of mars early environmental history the strata comprising mount sharp are believed to be sedimentary in origin but the specific depositional environments recorded by the rocks remain speculative we present orbital evidence for the occurrence of eolian sandstones within gale crater and the lower reaches of mount sharp including preservation of wind blown sand dune topography in sedimentary strata a phenomenon that is rare on earth and typically associated with stabilization rapid sedimentation transgression and submergence of the land surface the preserved bedforms in gale are associated with clay minerals and elsewhere accompanied by typical dune cross stratification marked by bounding surfaces whose lateral equivalents contain sulfate salts these observations extend the range of possible habitable environments that may be recorded within gale crater and provide hypotheses that can be tested in situ by the curiosity rover payload

determining olivine composition of basaltic dunes in gale crater mars from orbit awaiting ground truth from curiosity 1 the successful landing of the mars science laboratory curiosity rover in gale crater mars presents a rare opportunity for validation of a spectral index developed for determining olivine chemistry from orbital midinfrared remote sensing data here a spectral index is developed using laboratory emissivity data of 13 synthetic mg fe olivines utilizing this spectral index a prediction of olivine composition fo55 5 is made from orbital data for a ne sw trending dune field near the curiosity rover this dune field will be crossed during the mission as the rover travels toward a 5 km high sediment stack mount sharp that contains orbitally detected clays and sulfates curiosity can use its instrument suite chemmin alpha particle x ray spectrometer chemcam when it reaches the dunes to verify or refute the olivine chemistry prediction presented here the ability to validate the developed spectral index using the rover s ground truth instruments will strengthen olivine chemistry mapping across the martian surface using this spectral index

spatial grain size sorting in eolian ripples and estimation of wind conditions on planetary surfaces application to meridiani planum mars the landscape seen by the mars exploration rover mer opportunity at meridiani planum is dominated by eolian wind blown ripples with concentrated surface lags of hematitic spherules and fragments these ripples exhibit profound spatial grain size sorting with well sorted coarse grained crests and poorly sorted generally finer grained troughs these ripples were the most common bed form encountered by opportunity in its traverse from eagle crater to endurance crater field measurements from white sands national monument new mexico show that such coarse grained ripples form by the different transport modes of coarse and fine grain fractions on the basis of our field study and simple theoretical and experimental considerations we show how surface deposits of coarse grained ripples can be used to place tight constraints on formative wind conditions on planetary surfaces activation of meridiani planum coarse grained ripples requires a wind velocity of 70 m s at a reference elevation of 1 m above the bed from images by the mars orbiter camera moc of reversing dust streaks we estimate that modern surface winds reach a velocity of at least 40 m s and hence may occasionally activate these ripples the presence of hematite at meridiani planum is ultimately related to formation of concretions during aqueous diagenesis in groundwater environments however the eolian concentration of these durable particles may have led to the recognition from orbit of this environmentally significant landing site

pervasive aeolian activity along rover curiosity s traverse in gale crater mars the nasa mars science laboratory msl rover curiosity has safely landed near a 35 km long dark dune field in gale crater on mars this dune field crosses the landing site from the northeast to the southwest and lies along curiosity s traverse to aeolis mons here we present the first evidence of recent aeolian activity in the form of ripple and dune migration and further estimate wind directions within the dune field through analysis of ripple and dune morphologies and the mars regional atmospheric modeling system mrams we measured a minimum ripple migration rate of 0 66 m per earth year and dune migration rate of 0 4 m per earth year in the southwest portion of the field a strongly bidirectional ripple crestline orientation nearly orthogonal dune slipfaces and linear seif or oblique dunes indicate a bidirectional wind regime with winds mainly coming from the ene and from the northwest however mrams results indicate primary winds from the ene our constraints on the wind regime provide the unique opportunity to use ground measurements from msl to test the accuracy of winds predicted from orbital data