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

predicted diurnal variation of the deuterium to hydrogen ratio in water at the surface of mars caused by mass exchange with the regolith regolith on mars exchanges water with the atmosphere on a diurnal basis and this process causes significant variation in the abundance of water vapor at the surface while previous studies of regolith atmosphere exchange focus on the abundance recent in situ experiments and remote sensing observations measure the isotopic composition of the atmospheric water we are therefore motivated to investigate isotopic water exchange between the atmosphere and the regolith and determine its effect on the deuterium to hydrogen ratio d h of the atmosphere we model transport of water in the regolith and regolith atmosphere exchange by solving a transport equation including regolith adsorption condensation and diffusion the model calculates equilibrium fractionation between hdo and h 2o in each of these processes the fractionation in adsorption is caused by the difference in the latent heat of adsorption and that of condensation is caused by the difference in the vapor pressure together with a simple bulk aerodynamic boundary layer model we simulate the diurnal variation of the d h near the planetary surface we find that the d h can vary by 300 1400 diurnally in the equatorial and mid latitude locations and the magnitude is greater at a colder location or season the variability is mainly driven by adsorption and desorption of regolith particles and its diurnal trend features a drop in the early morning a rise to the peak value during the daytime and a second drop in the late afternoon and evening tracing the water vapor flow into and out from the regolith the predicted d h variation can be tested with in situ measurements as such our calculations suggest stable isotope analysis to be a powerful tool in pinpointing regolith atmosphere exchange of water on mars

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

hydrogeochemistry of maine seepage lakes and related groundwaters abstract southeastern maine contains numerous small seepage lakes no perennial surface inflows or outflows set in felsic glacial deposits eskers pitted outwash glacio marine deltaic terraces dating from the wisconsin glacial retreat ca 12 500 years b p the modern landscape is either forested or maintained as low blueberry heath by semi annual mowing and burning although local precipitation is currently moderately acidic volume weighted ph 4 5 spring waters issuing from the glacial deposits are only weakly acidic 6 1 na mg k the same as for upland granitic terrane in the same region springwater composition is temporally stable but geographically variable the most dilute springwaters drain blueberry barrens here chemical weathering is limited by available acidity as evidenced by the relatively high final phs 6 3 and low concentrations of strong oxy anions nitrate sulfate and dissolved inorganic carbon dic 100 cm year 1 for groundwater discharge lakes approximately 88 of si inputs to regional seepage lakes is retained in the sediments non marine sulfate is lowest in groundwater discharge lakes containing the highest concentrations of bc and f and featuring the shortest hydraulic residence times suggesting that s retention in lake sediments is currently less efficient than in the adjoining terrestrial soils and vegetation

water equivalent hydrogen estimates from the first 200 sols of curiosity s traverse bradbury landing to yellowknife bay results from the dynamic albedo of neutrons dan passive mode experiment abstract the dynamic albedo of neutrons dan experiment on the mars science laboratory msl rover curiosity is designed to detect neutrons to determine hydrogen abundance within the subsurface of mars mitrofanov i g et al 2012 space sci rev 170 559 582 http dx doi org 10 1007 s11214 012 9924 y litvak m l et al 2008 astrobiology 8 605 613 http dx doi org 10 1089 ast 2007 0157 while dan has a pulsed neutron generator for active measurements in passive mode it only measures the leakage spectrum of neutrons produced by the multi mission radioisotope thermoelectric generator mmrtg and galactic cosmic rays gcr dan passive measurements provide better spatial coverage than the active measurements because they can be acquired while the rover is moving here we compare dan passive mode data to models of the instrument s response to compositional differences in a homogeneous regolith in order to estimate the water equivalent hydrogen weh content along the first 200 sols of curiosity s traverse in gale crater mars weh content is shown to vary greatly along the traverse these estimates range from 0 5 0 1 wt to 3 9 0 2 wt for fixed locations usually overnight stops investigated by the rover and 0 6 0 2 wt to 7 6 1 3 wt for areas that the rover has traversed while continuously acquiring dan passive data between fixed locations estimates of weh abundances at fixed locations based on passive mode data are in broad agreement with those estimated at the same locations using active mode data localized meter scale anomalies in estimated weh values from traverse measurements have no particular surface expression observable in co located images however at a much larger scale the hummocky plains and bedded fractured units are shown to be distinct compositional units based on the hydrogen content derived from dan passive measurements dan passive weh estimates are also shown to be consistent with geologic models inferred from other msl instruments which indicate that fluvial lacustrine activity occurred at certain locations e g yellowknife bay

water and chlorine content in the martian soil along the first 1900 m of the curiosity rover traverse as estimated by the dan instrument the presence of hydrated phases in the soil and near surface bedrock of gale crater is thought to be direct evidence for water rock interaction in the crater in the ancient past layered sediments over the gale crater floor are thought to have formed in past epochs due to sediment transport accumulation and cementation through interaction with fluids and the observed strata of water bearing minerals record the history of these episodes the first data analysis of the dynamic albedo of neutrons dan investigation on board the curiosity rover is presented for 154 individual points of active mode measurements along 1900 m of the traverse over the first 361 martian solar days in gale crater it is found that a model of constant water content within subsurface should be rejected for practically all tested points whereas a two layer model with different water contents in each layer is supported by the data a so called direct two layer model water content increasing with depth yields acceptable fits for odometry ranges between 0 and 455 m and beyond 638 m the mean water h2o abundances of the top and bottom layers vary from 1 5 to 1 7 wt and from 2 2 to 3 3 wt respectively while at some tested spots the water content is estimated to be as high as 5 wt the data for odometry range 455 638 m support an inverse two layer model water content decreasing with depth with an estimated mean water abundance of 2 1 0 1 wt and 1 4 0 04 wt in the top and bottom layers respectively

equatorial locations of water on mars improved resolution maps based on mars odyssey neutron spectrometer data abstract we present a map of the near subsurface hydrogen distribution on mars based on epithermal neutron data from the mars odyssey neutron spectrometer the map s spatial resolution is approximately improved two fold via a new form of the pixon image reconstruction technique we discover hydrogen rich mineralogy far from the poles including 10 wt water equivalent hydrogen weh on the flanks of the tharsis montes and 40 wt weh at the medusae fossae formation mff the high weh abundance at the mff implies the presence of bulk water ice this supports the hypothesis of recent periods of high orbital obliquity during which water ice was stable on the surface we find the young undivided channel system material in southern elysium planitia to be distinct from its surroundings and exceptionally dry there is no evidence of hydration at the location in elysium planitia suggested to contain a buried water ice sea finally we find that the sites of recurring slope lineae rsl do not correlate with subsurface hydration this implies that rsl are not fed by large near subsurface aquifers but are instead the result of either small

neutron background environment measured by the mars science laboratory s dynamic albedo of neutrons instrument during the first 100 sols 1 the dynamic albedo of neutrons dan instrument on board mars science laboratory has been operating successfully since the landing and has been making measurements regularly along curiosity s traverse at the surface dan measures thermal e 0 4 ev and epithermal neutrons 0 4 ev e 1 kev while operating in two different modes active and passive the active mode uses a pulsed neutron generator png to study the geological characteristics of the subsurface in the passive mode dan measures the background neutron environment this paper presents results of measurements in the passive mode from landing through to sol 100 and provides an interpretation of the data based on extensive monte carlo simulations the main observations are summarized as follows 1 the thermal neutron counts vary strongly along the rover traverse while the epithermal counts do not show much variation 2 the neutrons from the multi mission radioisotope thermoelectric generator mmrtg are a larger contributor to the dan passive data than the galactic cosmic ray gcr induced neutrons 3 for the mmrtg neutrons both the thermal and the epithermal counts increase as a function of the subsurface water content 4 on the other hand for the gcr induced neutrons the thermal counts increase but the epithermal counts decrease as a function of the subsurface water content and 5 relative contributions by the mmrtg and gcr to the dan thermal neutron counts at the rocknest site where the rover was stationed from sol 59 to sol 100 are estimated to be 60 and 40 respectively

likely frost events at gale crater analysis from msl rems measurements abstract we provide indirect evidence for the formation of frost at the surface of gale crater by analyzing the highest confidence data from simultaneous measurements of relative humidity and ground temperature during the first 1000 sols of the mars science laboratory msl mission we find that except for sol 44 frost events could have occurred only between sols 400 and 710 corresponding to the most humid and coldest time of the year from early fall to late winter in particular measurements at dingo gap during sols 529 535 at an unnamed place during sols 554 560 at kimberley during sols 609 617 and at an unnamed place during sols 673 676 showed the largest likelihood of the occurrence of frost events at these four locations the terrain is composed of fine grained and loosely packed material with thermal inertia values of 200 si units much lower than the 365 50 si units value found at the landing ellipse this is important because terrains with exceptionally low thermal inertia favor the formation of frost by lowering minimum daily ground temperatures an order of magnitude calculation to determine the thickness of the frost layer at these four locations results in values of tenths of m while the precipitable water content is a few pr m therefore surface frost events can have important implications for the local water cycle at gale crater in addition frost is the most likely type of water that can be temporarily found in bulk amounts on the surface of mars at low latitudes and therefore can cause weathering influencing the geology of gale crater

the geochemical character of upland waters of northeast new south wales the water chemistry of 18 small reservoirs in the new england tablelands of northeast new south wales was strongly influenced by catchment geology cluster analysis distinguished three types of waters one group strongly dominated by mg2 and hc03 and also having high ca2 k ph and total conductivity was characteristic of catchments underlain by alkali olivine basalt a second group dominated by na and hc03 and having a relatively low conductivity and ph was characteristic of waters draining granitic rocks of adamellite composition a third less welldefined group similar to group two waters but having high conductivity drained catchments underlain by acid igneous rocks with a slightly more basic geochemistry and also mixed igneous and sedimentary catchments ratios of major cations in waters were highly determined by ratios in igneous catchment rocks mg r 0 983 na r 0 917 ca r 0 801 k r 0 390 the importance of marine salt varied from 7 of ions for waters draining basalts to as high as 65 for dilute water draining a granitic catchment the leaching of accumulated cyclic salt from the soil was inferred to be the principal source of these ions for all but the waters draining the younger basalts the presence of relict sea salts in the soils of the acid igneous and sedimentary rock is believed to be due to elevated accession during arid periods of the cretaceous and early tertiary present day cyclic salt accession connate salts and anthropogenic sources were unimportant ion sources the waters deviated substantially from the world average freshwater and also from the world water chemistry model of gibbs the average chemical composition of the

results from the dynamic albedo of neutrons dan passive mode experiment yellowknife bay to amargosa valley sols 201 753 abstract the mars science laboratory curiosity rover dynamic albedo of neutrons dan experiment detects neutrons for the purpose of searching for hydrogen in the shallow subsurface of mars dan has two modes of operation active and passive in passive mode the instrument detects neutrons produced by galactic cosmic ray interactions in the atmosphere and regolith and by the rover s multi mission radioisotope thermoelectric generator dan passive data from yellowknife bay to amargosa valley sols 201 through 753 are presented and analyzed here water equivalent hydrogen weh estimates from this portion of curiosity s traverse range from 0 0 wt up to 15 3 wt typical uncertainties on these weh estimates are 0 5 wt but in some cases can be as high as 4 0 wt depending on the specific circumstances of a given measurement here we also present a new way of reporting results from the passive mode of the experiment the dan passive geochemical index dpgi this index is sensitive to some key geochemical variations but it does not require assumptions about the abundances of high thermal neutron absorption cross section elements which are needed to estimate weh dpgi variations in this section of the traverse indicate that the shallow regolith composition is changing on both the local meters and regional 100 s of meters scales this variability is thought to be representative of the diverse composition of source regions for sediments within the crater floor kolmogorov smirnov tests on the populations of weh estimates and dpgi values demonstrate there are statistically significant differences between nearly all of the geologic units investigated along the rover s traverse we also present updated previous dan passive results from bradbury landing to john klein that make use of revised dan active mode results for calibration however no qualitative changes in the interpretations made in tate et al 2015b are incurred

three stage rupture process of the 28 december 1994 sanriku oki earthquake we investigated the rupture process of the 28 december 1994 sanriku oki earthquake mw 7 7 using broadband seismograms recorded at local distances the earthquake rupture nucleated at the eastern end of the aftershock area as it propagated towards the west a major subevent occurred near the center of the aftershock area about 26 s after the initial rupture releasing most of the seismic energy of this earthquake about 24 s later another subevent followed at the western end of the aftershock area emitting large high frequency waves the whole rupture time is about 55 sec the three stage rupture process is very similar to the earlier stage rupture process of the 1968 tokachi oki earthquake mw 8 2 the difference is that the rupture of the tokachi oki earthquake further propagated towards the north in the following stage instead of terminating at the western end the occurrence of the sanriku oki earthquake is critical to the validity of the characteristic earthquake so far believed to exist in this part of the plate boundary

mars science laboratory dynamic albedo of neutrons passive mode data and results from sols 753 to 1292 pahrump hills to naukluft plateau abstract the dynamic albedo of neutrons instrument dan onboard the mars science laboratory msl uses 3he proportional counters to detect neutrons escaping the martian surface this neutron leakage flux can be used to estimate the amount of hydrogen in the shallow martian regolith during sols 753 through 1292 of the msl mission the rover traversed from pahrump hills to the naukluft plateau and acquired slightly less than 2000 h of neutron count rate data covering 3 km of traverse and 125 waypoints along that traverse here we present an analysis of these data including new procedures to leverage the oversampling of the instrument within its own spatial footprint water equivalent hydrogen weh estimates and dan passive geochemical index dpgi values the average water equivalent hydrogen estimate for this region of the traverse is 1 6 wt with a standard deviation of 1 1 wt these results show that curiosity transitioned into a relatively lower weh content region as it left the plains of gale crater and began ascending the hills at the base of mt sharp we also show that the weh populations of the geologic units investigated during this time murray and stimson formations are statistically different both from each other and the previously studied aeolis palus sediments smooth hummocky bedded fractured eolian rugged and striated light toned additionally dan passive weh estimates agree with measurements from other msl instruments in this region and are consistent with decreasing phyllosilicate abundance with increasing elevation

apparent thermal inertia and the surface heterogeneity of mars abstract thermal inertia derivation techniques generally assume that surface properties are uniform at horizontal scales below the footprint of the observing instrument and to depths of several decimeters consequently surfaces with horizontal or vertical heterogeneity may yield apparent thermal inertia which varies with time of day and season to investigate these temporal variations we processed three mars years of mars global surveyor thermal emission spectrometer observations and produced global nightside and dayside seasonal maps of apparent thermal inertia these maps show broad regions with diurnal and seasonal differences up to 200 j m 2 k 1 s 1 2 at mid latitudes 60 s to 60 n and 600 j m 2 k 1 s 1 2 or greater in the polar regions we compared the seasonal mapping results with modeled apparent thermal inertia and created new maps of surface heterogeneity at 5 resolution delineating regions that have thermal characteristics consistent with horizontal mixtures or layers of two materials the thermal behavior of most regions on mars appears to be dominated by layering with upper layers of higher thermal inertia e g duricrusts or desert pavements over fines prevailing in mid latitudes and upper layers of lower thermal inertia e g dust covered rock soils with an ice table at shallow depths prevailing in polar regions less common are regions dominated by horizontal mixtures such as those containing differing proportions of rocks sand dust and duricrust or surfaces with divergent local slopes other regions show thermal behavior that is more complex and not well represented by two component surface models these results have important implications for mars surface geology climate modeling landing site selection and other endeavors that employ thermal inertia as a tool for characterizing surface properties

local variations of bulk hydrogen and chlorine equivalent neutron absorption content measured at the contact between the sheepbed and gillespie lake units in yellowknife bay gale crater using the dan instrument onboard curiosity data gathered with the dynamic albedo of neutron dan instrument onboard rover curiosity were analyzed for variations in subsurface neutron flux and tested for possible correlation with local geological context a special dan observation campaign was executed in which 18 adjacent dan active measurements were acquired every 0 75 1 0 m to search for the variations of subsurface hydrogen content along a 15 m traverse across geologic contacts between the sheepbed and gillespie lake members of the yellowknife bay formation it was found that several subunits in sheepbed and gillespie lake could be characterized with different depth distributions of water equivalent hydrogen weh and different chlorine equivalent abundance responsible for the distribution of neutron absorption elements the variations of the average weh at the top 60 cm of the subsurface are estimated at up to 2 3 chlorine equivalent neutron absorption abundances ranged within 0 8 1 5 the largest difference in weh and chlorine equivalent neutron absorption distribution is found between sheepbed and gillespie lake

hydrogen and chlorine abundances in the kimberley formation of gale crater measured by the dan instrument on board the mars science laboratory curiosity rover the dynamic albedo of neutron dan instrument on board the mars science laboratory curiosity rover acquired a series of measurements as part of an observational campaign of the kimberley area in gale crater these observations were planned to assess the variability of bulk hydrogen and neutron absorbing elements characterized as chlorine equivalent concentration in the geologic members of the kimberley formation and in surface materials exposed throughout the area during the traverse of the kimberley area curiosity drove primarily over the smooth hummocky unit a unit composed primarily of sand and loose rocks with occasional stops at bedrock of the kimberley formation during the kimberley campaign dan detected ranges of water equivalent hydrogen weh and chlorine equivalent concentrations of 1 5 2 5 wt and 0 6 2 wt respectively results show that as the traverse progressed dan observed an overall decrease in both weh and chlorine equivalent concentration measured over the sand and loose rocks of the smooth hummocky unit dan measurements of weh and chlorine equivalent concentrations in the well exposed sedimentary bedrock of the kimberley formation show fluctuations with stratigraphic position the kimberley campaign also provided an opportunity to compare measurements from dan with those from the sample analysis at mars sam and the alpha particle x ray spectrometer apxs instruments dan measurements obtained near the windjana drill location show a weh concentration of 1 5 wt consistent with the concentration of low temperature absorbed water measured by sam for the windjana drill sample a comparison between dan chlorine equivalent concentrations measured throughout the kimberley area and apxs observations of corresponding local surface targets and drill fines shows general agreement between the two instruments

water abundance of dunes in gale crater mars from active neutron experiments and implications for amorphous phases we report the water abundance of bagnold dune sand in gale crater mars by analyzing active neutron experiments using the dynamic albedo of neutrons instrument we report a bulk water equivalent hydrogen abundance of 0 68 0 15 wt which is similar to measurements several kilometers away and from those taken of the dune surface thus the dune is likely dehydrated throughout furthermore we use geochemical constraints including bulk water content to develop compositional models of the amorphous fraction for which little information is known we find the amorphous fraction contains 26 to 64 wt basaltic glass and up to 24 wt rhyolitic glass suggesting at least one volcanic source for the dune material we also find a range of hydrated phases may be present in appreciable abundances either from the incorporation of eroded aqueously altered sediments or the direct alteration of the dune sand

evolved gas analyses of sedimentary rocks and eolian sediment in gale crater mars results of the curiosity rover s sample analysis at mars instrument from yellowknife bay to the namib dune the sample analysis at mars instrument evolved gas analyzer sam ega has detected evolved water h2 so2 h2s no co2 co o2 and hcl from two eolian sediments and nine sedimentary rocks from gale crater mars these evolved gas detections indicate nitrates organics oxychlorine phase and sulfates are widespread with phyllosilicates and carbonates occurring in select gale crater materials coevolved co2 160 248 2373 820 gc co2 g and co 11 3 320 130 gc co g suggest organic c is present in gale crater materials five samples evolved co2 at temperatures consistent with carbonate 0 32 0 05 0 70 0 1 wt co3 evolved no amounts to 0 002 0 007 0 06 0 03 wt no3 evolution of o2 suggests oxychlorine phases chlorate perchlorate 0 05 0 025 1 05 0 44wt clo4 are present while so2 evolution indicates the presence of crystalline and or poorly crystalline fe and mg sulfate and possibly sulfide evolved h2o 0 9 0 3 2 5 1 6 wt h2o is consistent with the presence of adsorbed water hydrated salts interlayer structural water from phyllosilicates and possible inclusion water in mineral amorphous phases evolved h2 and h2s suggest reduced phases occur despite the presence of oxidized phases nitrate oxychlorine sulfate carbonate sam results coupled with chemin mineralogical and apxs elemental analyses indicate that gale crater sedimentary rocks have experienced a complex authigenetic diagenetic history involving fluids with varying ph redox and salt composition the inferred geochemical conditions were favorable for microbial habitability and if life ever existed there was likely sufficient organic c to support a small microbial population

mineralogy of a mudstone at yellowknife bay gale crater mars sedimentary rocks at yellowknife bay gale crater on mars include mudstone sampled by the curiosity rover the samples john klein and cumberland contain detrital basaltic minerals calcium sulfates iron oxide or hydroxides iron sulfides amorphous material and trioctahedral smectites the john klein smectite has basal spacing of similar to 10 angstroms indicating little interlayer hydration the cumberland smectite has basal spacing at both similar to 13 2 and similar to 10 angstroms the larger spacing suggests a partially chloritized interlayer or interlayer magnesium or calcium facilitating h2o retention basaltic minerals in the mudstone are similar to those in nearby eolian deposits however the mudstone has far less fe forsterite possibly lost with formation of smectite plus magnetite late noachian early hesperian or younger age indicates that clay mineral formation on mars extended beyond noachian time

effects of silicate weathering on water chemistry in forested upland felsic terrane of the usa the authors use data from the us epa national surface water survey nsws the usgs bench mark station monitoring program and the national acid deposition program nadp to evaluate the role of weathering in supplying base cations to surface waters in forested upland felsic terrane of the northeastern northcentral and northwestern idaho batholith us multivariate regression reveals differential effects of discharge on individual base cations and silica but no secular trend in the ca na denudation rate over 24 yr 1965 1988 for the wild river catchment in the white mountains because the turn over time for na in the soil exchange complex is only ca 1 5 yr the long term behavior of the ratios ca na and si na in waters leaving this catchment indicates that weathering is compensating for base cation export in every subregion ca and mg concentrations in lakes are statistically linked to nonmarine na but the median ca na ratio is greater than the ratio in local plagioclase the authors attribute this inequality to nonstoichiometric weathering of calcium in juvenile formerly glaciated terrane not to leaching of exchangeable cations by so sub 4 because intraregional and cross regional statistical analysis reveals no effect of atmospherically derived sulfate ion the median base cation denudation rates meq m supmore minus 2 yr sup minus 1 for these american lake regions are maine granites 108 western adirondack felsic gneiss 85 vermilion batholith 42 idaho batholith 52 the regional rates are high enough to compensate for present wet deposition of acidifying anions except in some vulnerable lake watersheds in the western adirondacks less

differentiation in impact melt sheets as a mechanism to produce evolved magmas on mars abstract asteroid bombardment contributed to extensive melting and resurfacing of ancient 3 5 ga mars evidence from the largest impact structures on earth and the moon suggests that vertically thick impact melt sheets experience chemical differentiation recently observed materials in gale crater are enriched in alkalis up to 14 wt na2o k2o and silica up to 67 wt sio2 with low mgo

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