the age of the medusae fossae formation evidence of hesperian emplacement from crater morphology stratigraphy and ancient lava contacts abstract the medusae fossae formation mff covering about 2 1 10 6 km 2 with an estimated volume of 1 4 10 6 km 3 and straddling the equatorial region of mars east of tharsis has historically been mapped and dated as amazonian in age analysis of the mff using a range of new observations from recent mission data at multiple resolutions reveals evidence that the formation is older than previously hypothesized with parts of the mff having formed in the hesperian and parts having been reworked and reformed throughout the amazonian up to the present ancient outcroppings of the mff edged with jagged yardangs became a mold for embaying hesperian aged lavas the erosion of the mff left solidified lava casts in the embaying lava unit this lava edge morphology permits the identification of ancient contacts between the mff and hesperian aged lava terrain additionally the flanking fan of the hesperian aged apollinaris patera volcano embays the formation at its foot indicating that parts of the mff were formed in the hesperian erosion has erased and inverted many of the superposed craters in the region showing that very young amazonian ages derived from impact crater size frequency distributions are resurfacing ages and not emplacement ages we find abundant evidence that the formation is extremely mobile and continuously reworked we conclude that a significant part of the mff may have originally been emplaced in the hesperian these observations place new constraints on the mode of origin of the mff

sharad radar sounding of the vastitas borealis formation in amazonis planitia 1 amazonis planitia has undergone alternating episodes of sedimentary and volcanic infilling forming an interleaved sequence with an upper surface that is very smooth at the kilometer scale earlier work interprets the near surface materials as either young rough lava flows or ice rich sediment layers overlying a basement comprising the vastitas borealis formation and earlier hesperian plains sounding radar profiles across amazonis planitia from the shallow radar sharad instrument on the mars reconnaissance orbiter reveal a subsurface dielectric interface that increases in depth toward the north along most orbital tracks the maximum depth of detection is 100 170 m depending upon the real dielectric permittivity of the materials but the interface may persist at greater depth to the north if the reflected energy is attenuated below the sharad noise floor the dielectric horizon likely marks the boundary between sedimentary material of the vastitas borealis formation and underlying hesperian volcanic plains the sharad detected interface follows the surface topography across at least one of the large wrinkle ridges in north central amazonis planitia this conformality suggests that vastitas borealis sediments at least in this region were emplaced prior to compressional tectonic deformation the change in radar echo strength with time delay is consistent with a loss tangent of 0 005 0 012 for the column of material between the surface and the reflector these values are consistent with dry moderate density sediments or the lower end of the range of values measured for basalts while a component of distributed ice in a higher loss matrix cannot be ruled out we do not find evidence for a dielectric horizon within the vastitas borealis formation that might suggest an abrupt change from an upper dry layer to an ice rich lower deposit

rock physics transforms and scale of investigation abstractrock physics velocity porosity transforms are usually established on sets of laboratory and or well data with the latter data source being dominant in recent practice the purpose of establishing such transforms is to 1 conduct forward modeling of the seismic response for various geologically plausible what if scenarios in the subsurface and 2 interpret seismic data for petrophysical properties and conditions such as porosity clay content and pore fluid because the scale of investigation in the well is considerably smaller than that in reflection seismology an important question is whether the rock physics model established in the well can be used at the seismic scale we use synthetic examples and well data to show that a rock physics model established at the well approximately holds at the seismic scale suggest a reason for this scale independence and explore where it may be violated the same question can be addressed as an inverse problem assume that we have a rock physics tran

medusae fossae formation new perspectives from mars global surveyor 1 the nature and origin of the medusae fossae formation mff on mars has been debated since the return of the first viking images the mff s young age distinctive surface texture and lack of obvious source have prompted multiple hypotheses for its origin this study uses data from the mars global surveyor mgs mission to examine the mff at all available scales we discuss and quantify observations from mars orbiter laser altimeter mola topography and mars orbiter camera moc images to better constrain the origin of the mff topographic grid estimates yield a present extent of 2 1 106 km2 and a volume of 1 4 106 km3 however remnant yardang deposits observed far from the thicker lobes of mff material suggest that it may have once covered up to 5 106 km2 we do not find compelling evidence for extensive fluvial reworking of the mff however in several regions buried channels are apparent in the mff because the formation is draped over underlying topography layering is apparent at all scales from submeter to hundreds of meters with variable resistance to weathering continuity of layers appears to be local to regional but not likely formation wide yardangs form both parallel and bidirectional patterns with resistant layers and jointing probably influencing their orientations a comparative study of mff regional topography and surface expression indicates that the mff is quantitatively dissimilar to martian polar layered deposits the material is most likely a friable and irregularly consolidated air fall deposit of probable volcanic origin

shallow radar sharad sounding observations of the medusae fossae formation mars the sharad shallow radar sounding radar on the mars reconnaissance orbiter detects subsurface reflections in the eastern and western parts of the medusae fossae formation mff the radar waves penetrate up to 580 m of the mff and detect clear subsurface interfaces in two locations west mff between 150 and 155 e and east mff between 209 and 213 e analysis of sharad radargrams suggests that the real part of the permittivity is 3 0 which falls within the range of permittivity values inferred from marsis data for thicker parts of the mff the sharad data cannot uniquely determine the composition of the mff material but the low permittivity implies that the upper few hundred meters of the mff material has a high porosity one possibility is that the mff is comprised of low density welded or interlocked pyroclastic deposits that are capable of sustaining the steep sided yardangs and ridges seen in imagery the sharad surface echo power across the mff is low relative to typical martian plains and completely disappears in parts of the east mff that correspond to the radar dark stealth region these areas are extremely rough at centimeter to meter scales and the lack of echo power is most likely due to a combination of surface roughness and a low near surface permittivity that reduces the echo strength from any locally flat regions there is also no radar evidence for internal layering in any of the sharad data for the mff despite the fact that tens of meters scale layering is apparent in infrared and visible wavelength images of nearby areas these interfaces may not be detected in sharad data if their permittivity contrasts are low or if the layers are discontinuous the lack of closely spaced internal radar reflectors suggests that the mff is not an equatorial analog to the current martian polar deposits which show clear evidence of multiple internal layers in sharad data

origin and evolution of a cold based tropical mountain glacier on mars the pavonis mons fan shaped deposit 1 each of the large tharsis montes volcanoes in the equatorial region of mars has an unusual amazonian aged fan shaped deposit on its west northwestern flank on the basis of viking orbiter data the origin of these deposits has been variously ascribed to volcanic mass wasting tectonic and glacial processes using new mgs and odyssey data combined with recent developments in the study of cold based glaciers we reassess the geology and mode of origin for these deposits with particular emphasis on pavonis mons the deposits share three characteristic facies including 1 a ridged facies consisting of tens to 100 parallel concentric ridges around the margins of the deposits 2 a knobby facies composed of irregular hills and hummocks and 3 a smooth facies of broad lobate plains that superposes all other units within the deposits on the basis of morphology topography superposition relationships and close terrestrial analogs in the dry valleys of antarctica we interpret the pavonis fan shaped deposit as the depositional remains of a cold based glacier that formed on the northwestern flank in recent martian history we interpret the ridged facies as drop moraines formed around the margins of a retreating cold based glacier the knobby facies as a sublimation till derived from in situ down wasting of cold based glacial ice and the smooth facies as extant debris covered glacial ice in addition to the three main facies the fan shaped deposit at pavonis mons contains several unique features including arcuate scarps high relief flow like features and radial ridges which suggest that volcanism played a role during its formation using recent results from mars general circulation model simulations we outline a model of glacier formation involving atmospheric deposition of water ice on the northwestern flanks of the tharsis montes during periods of high mean obliquity reconstructed ice sheet profiles for each of the tharsis montes glaciers suggest that the ice sheets attained average thicknesses of 1 6 2 4 km values that are consistent with a cold based glacial origin analysis of crater size frequency distributions using new data indicates that the age of the glaciation lies within the late amazonian 10 200 ma thus our results suggest that multiple phases of tropical mountain glaciation occurred on mars within the past few hundred myr and that significant amounts of near surface equatorial ice may remain within the deposit today

226ra and222rn contents of galapagos rift hydrothermal waters the importance of low temperature interactions with crustal rocks abstract hydrothermal waters collected by alvin from the galapagos spreading center are enriched in 222 rn by factors of 50 200 over bottom waters the 226 ra in the same samples however is enriched by less than a factor of four over bottom waters enrichments of 222 rn result primarily from recoil from rock surfaces while 226 ra enrichments are dominantly produced by high temperature alteration of cooling ridge volcanics the abundances of both nuclides exhibit positive correlations with temperature the data extrapolate to bottom water temperatures and compositions demonstrating the importance of seawater mixing different vents however have different mixing lines and vents with high 222 rn have low 226 ra we propose these patterns result from variations in the extent of low temperature crustal interaction with the hydrothermal fluids low temperature crustal waters can maintain high steady state 222 rn contents due to the recoil additions to the fluids the 226 ra however is strongly adsorbed at low temperatures resulting in low concentrations of this nuclide in low temperature crustal waters thus physical mixing of a crustal water component with hydrothermal waters or variable crustal path lengths of the hydrothermal fluids can account for the variable mixing lines and 222 rn 226 ra values of the hot springs the 222 rn 226 ra value appears to be a sensitive indicator of low temperature crustal interaction values 100 have experienced extensive crustal interaction and are indicative of diffuse hydrothermal flow values between 1 and 10 are indicative of primary hydrothermal fluids which have not experienced significant interaction with the crust values of 222 rn 226 ra between 10 3 and 10 4 are indicative of interaction of the hydrothermal fluids with sediments such values are observed in water samples from the galapagos hydrothermal mounds

ignimbrites of amazonis planitia region of mars a series of postulated ignimbrite units is mapped in the amazonis memnonia and aeolis quadrangles of mars the units cover about 2 2 106 km2 within a broad but discontinuous and irregular belt trending east west along the highland lowland boundary the ignimbrites overlie parts of the western and southern aureole materials of olympus mons but are embayed in places by the lava plains of the lowlands stratigraphic relations between the basalt flows from the tharsis montes region and the ignimbrites are not clearly defined crater counts suggest that the younger ignimbrites postdate the lava flows crater counts per square kilometer for the ignimbrites range from 7 29 1 95 10 4 to 6 36 2 01 10 5 for craters larger than 1 km in diameter the ignimbrite materials form thick 100 m extensive relatively flat sheets that are smooth to grooved or gently undulating grooved surfaces appear to be yardangs and in most places are not alined with prevailing wind directions the seven mapped ignimbrite units are characterized by morphologic expression stratigraphic position and crater counts similarities to ignimbrites in the pancake range of central nevada include 1 rounded patches of smooth high albedo nonwelded material superposed on jointed low albedo welded material 2 local complementary joint sets in welded materials and 3 thick flow sheets of great areal extent that follow but subdue underlying topography four major eruptive centers occur in areas where units are thickest and where a dominant nnw sse structural trend is expressed locally by unit margins elongate collapse features and normal faulting a minimum volume of 3 85 106 km3 for the deposits has been calculated from thickness estimates based on shadow measurements and crater rim height relations

quantitative analysis of mars surface radar reflectivity at 20 mhz abstract the radar surface echoes taken from sharad observations are extracted to obtain a reflectivity map covering almost half of the martian surface and then compared to available roughness maps then we used a 2 step method based on a stochastic description of reflectivity in order to i separate the coherent incoherent components of the signal by means of a probability density function fitting of amplitude distributions and ii express these components with respect to roughness permittivity values by adapting common backscattering models to the nadir case scattering is found to be the most important process dominating reflectivity over the martian terrains reflectivity is best correlated with roughness maps derived from the slope parameter the stochastic behavior of reflectivity is confirmed by the excellent agreement of our models and demonstrates the low probability of retrieving permittivity from scattering surfaces the non stationary nature of most martian terrains is consolidated by a very good fit to k distributions justifying the use of the fractal theory for describing surface roughness on mars a few slightly rough regions exhibit both a coherent and incoherent component when surface correlation length is non significant within the resolution cell we show that the rms roughness at a decameters baseline can be derived with sub decimeter sensitivity without prior signal calibration improving the capabilities of sharad in determining surface roughness with a view to landing site selection sets of derived dielectric constants are obtained and analyzed with regard to the reference signal used for calibration given the very different implications of each set to the composition of martian terrains we emphasize the importance of good signal calibration as a major issue for sharad and the next interplanetary radar missions

mars mapping with delay doppler radar mars radar imaging results from arecibo 12 6 cm observations are presented the images were derived from delay doppler mapping using a coded long pulse technique to mitigate the effects of echo overspreading images of the depolarized echo are used to identify regions of high decimeter scale roughness some of the strongest echo features are located on the major shield volcanoes or on relatively young off shield flows such as the olympus and pavonis lava aprons the shields themselves have highly irregular radar signatures suggesting complex volcanic histories some mars radar features have twice the depolarized brightness of the roughest terrestrial lava flows apparently due to higher levels of multiple scattering from surfaces of spectacular roughness or from volume scattering low brightness smooth areas are associated with older surfaces such as fractured and highland terra as well as with terrain interpreted to be debris lobes ash flows and aureoles in particular a close connection was found between the 12 6 cm counterpart of the stealth feature and the medusae fossae formation postulated to be deep ignimbrite deposits marte valus is anomalous in being the only outflow channel showing strongly enhanced echoes which supports the idea that this channel and the elysium basin that it drained are filled with lava flows a weak radar feature was found for the south polar residual ice cap comparisons with goldstone 3 5 cm data show that the south polar enhancement is much weaker at 12 6 cm than at 3 5 cm indicating that the southern ice cap becomes optically thin at the longer wavelength a north polar enhancement has also been found which is comparable in strength to the 12 6 cm south polar feature

mapping medusae fossae formation materials in the southern highlands of mars abstract the medusae fossae formation mff is an extensive deposit 2 2 106 km2 bradley b a sakimoto s e h frey h zimbelman j r 2002 j geophys res 107 5058 of wind eroded material of widely debated origin which unconformably overlies a considerable area of the crustal dichotomy boundary on mars the mff shows a variety of layering patterns erosional styles and channel like forms and has been mapped into five main outcrops and three geological members according to exposure and stratigraphy scott d h tanaka k l 1986 usgs map i 1802 a greeley r guest j e 1987 map i 1802 b zimbelman j r crown d jenson d 1996 lunar planet sci xxvii abstract 1748 away from the three main lobes are numerous outliers of mff materials these have mainly been reported in the northern lowlands regions keszthelyi l jaeger w l and hirise team 2008 lunar planet sci xxxix abstract 2420 but few studies have examined the possibility of mff outliers on high ground south of the dichotomy boundary we have searched mars orbiter camera narrow angle moc na images for outliers in this region our observations show that there are many mff outliers on the southern highlands the characteristics of the outliers indicate materials which overlie the underlying terrain for they appear widely in dips craters and topographic lows the surfaces are typified by yardang fields and have a similar patchy and discontinuous nature to materials of the upper member of the mff most have consistent lineation orientations across the wider area which match the dominant orientation of yardangs in the main mff outcrops furthermore elevation data shows that the maximum minimum and mean elevations of these newly discovered outliers are closest to those of the upper member of the mff we therefore conclude that these deposits are mff outliers and that they probably represent remnant upper member material we suggest that there might be two possible explanations for these outliers 1 the mff had a much greater pre erosional extent than previously estimated or 2 materials from the main outcrops were eroded and then blown south to accrue in the highland areas where they were subsequently reworked we suggest that the topography of the region favors the first option we outline an overflowing layer cake deposition model in which layers of sediment stacked up against the dichotomy boundary until they reached the topographic level of the highlands further materials that went onto become upper member mff material and outliers were then deposited across a wider area including south of the dichotomy boundary severe erosion subsequently removed much of this material

the roughness of natural terrain a planetary and remote sensing perspective we examine the various methods and parameters in common use for quantifying and reporting surface topographic roughness it is shown that scale dependent roughness parameters are almost always required though not widely used we suggest a method of standardizing the parameters that are computed and reported so that topographic data gathered by different workers using different field techniques can be directly and easily intercompared we illustrate the proposed method by analyzing topographic data from 60 different surfaces gathered by five different groups and examine the information for common features we briefly discuss the implications of our analysis for studies of planetary surface roughness lander safety and radar remote sensing modeling and analysis

radar images of mars full disk images of mars have been obtained with the use of the very large array vla to map the radar reflected flux density the transmitter system was the 70 m antenna of the deep space network at goldstone california the surface of mars was illuminated with continuous wave radiation at a wavelength of 3 5 cm the reflected energy was mapped in individual 12 minute snapshots with the vla in its largest configuration fringe spacings as small as 67 km were obtained the images reveal near surface features including a region in the tharsis volcano area over 2000 km in east west extent that displayed no echo to the very low level of the radar system noise the feature called stealth is interpreted as a deposit of dust or ash with a density less than about 0 5 gram per cubic centimeter and free of rocks larger than 1 cm across the deposit must be several meters thick and may be much deeper the strongest reflecting geological feature was the south polar ice cap which was reduced in size to the residual south polar ice cap at the season of observation the cap image is interpreted as arising from nearly pure co 2 or h 2o ice with a small amount of martian dust less than 2 percent by volume and a depth greater than 2 to 5 m only one anomalous reflecting feature was identified outside of the tharsis region although the elysium region was poorly sampled in this experiment and the north pole was not visible from earth

geologic context of the mars radar stealth region in southwestern tharsis stealth is a region on mars that has no distinguishable radar return stealth was discovered in 1988 by muhleman et al 1991 in 3 5 cm earth based radar images and it was found to extend 2000 km along the martian equator west of arsia and pavonis montes stealth was proposed to be a deposit of unconsolidated granular material with a minimum thickness of several meters with the most likely explanation being that stealth is a volcanic tephra deposit muhleman et al 1991 1995 stealth overlies some of the youngest geologic units on mars including lava flows and a giant curvilinear ridged lobate unit on the west flank of arsia mons stealth also overlies part of a region of smooth and wind scoured materials called the medusae fossae formation examination of high resolution viking orbiter images suggests that stealth is the youngest of several discontinuous wind worked mantles of fine grained 1 cm sediment older deposits of fine sediment appear to be interbedded with lava flows and show evidence of aeolian deposition dunes and deposits in the lee of topographic obstacles and erosion yardangs and pedestal craters the geologic context supports a volcanic ash origin for stealth if stealth is composed of tephra then its extent and the nature of landforms in the region indicate that it resulted from multiple eruptions that occurred relatively late in martian history possible source vents include linear depressions flanked by constructive volcanic landforms that are located on the lower western slopes of arsia and pavonis montes

global permittivity mapping of the martian surface from sharad abstract sharad is a subsurface sounding radar aboard nasa s mars reconnaissance orbiter capable of detecting dielectric discontinuities in the subsurface caused by compositional and or structural changes echoes coming from the surface contain information on geometric properties at metre scale and on the permittivity of the upper layers of the martian crust a model has been developed to estimate the effect of surface roughness on echo power depending on statistical parameters such as rms height and topothesy such model is based on the assumption that topography can be characterized as a self affine fractal and its use allows the estimation of the dielectric properties of the first few metres of the martian soil a permittivity map of the surface of mars is obtained covering several large regions across the planet surface the most significant correspondence with geology is observed at the dichotomy boundary with high dielectric constant on the highlands side 7 to over 10 and lower on the lowlands side 3 to 7 other geological correlations are discussed

a numerical characterization workflow for assessing the strength and failure modes of heterogeneous oil sands understanding the strength and failure modes of overburden and reservoir are critical components in safety assessments for oil sands surface mining and in situ thermal recovery operations currentl

simulated electrical conductivity response of clogging mechanisms for managed aquifer recharge abstractmotivated by the need for improved understanding and monitoring of clogging during managed aquifer recharge we use numerical experiments to evaluate the effect of three different clogging mechanisms on electrical conductivity ec porosity specific surface area and electrical tortuosity of a simulated sediment pack the clogging experiments are designed to simulate effect of clogging due to a addition of finer grains b addition of nonconductive films and c addition of conductive films the simulations involved starting with a random grain pack of 43 porosity and subsequently reducing the porosity as would occur during clogging for each of the experiments we compute the ec response specific surface area and electrical tortuosity across the range of porosities the differences in ec response between a and b is minor however the sediment parameters measuring pore space configuration show very different responses i e specific surface area and tortuosity indicating ec is l

arecibo radar imagery of mars the major volcanic provinces abstract we present earth based radar images of mars obtained with the upgraded arecibo s band 12 6 cm radar during the 2005 2012 oppositions the imaging was done using the same long code delay doppler technique as for the earlier pre upgrade imaging but at a much higher resolution 3 km and for some regions a more favorable sub earth latitude this has enabled us to make a more detailed and complete mapping of depolarized radar reflectivity a proxy for small scale surface roughness over the major volcanic provinces of tharsis elysium and amazonis we find that vast portions of these regions are covered by radar bright lava flows exhibiting circular polarization ratios close to unity a characteristic that is uncommon for terrestrial lavas and that is a likely indicator of multiple scattering from extremely blocky or otherwise highly disrupted flow surfaces all of the major volcanoes have radar bright features on their shields although the brightness distribution on olympus mons is very patchy and the summit plateau of pavonis mons is entirely radar dark the older minor shields paterae and tholi are largely or entirely radar dark which is consistent with mantling by dust or pyroclastic material other prominent radar dark features include the fan shaped deposits possibly glacial associated with the three major tharsis montes shields various units of the medusae fossae formation a region south and west of biblis patera where stealth deposits appear to obscure tharsis flows and a number of dark halo craters with radar absorbing ejecta blankets deposited atop surrounding bright flows several major bright features in tharsis are associated with off shield lava flows these include the olympus mons basal plains volcanic fields east and south of pavonis mons the daedalia planum flows south of arsia mons and a broad expanse of flows extending east from the tharsis montes to echus chasma the radar bright lava plains in elysium are concentrated mainly in cerberus and include the fluvio volcanic channels of athabasca valles grjota valles and marte valles as well as an enigmatic region at the southern tip of the cerberus basin some of the cerberus bright features correspond to the distinctive platy ridged flows identified in orbiter images the radar bright terrain in amazonis planitia comprises two distinct but contiguous sections a northern section formed of lavas and sediments debouched from marte valles and a southern section whose volcanics may derive in part from local sources this south amazonis region shows perhaps the most complex radar bright structure on mars and includes features that correspond to platy ridged flows similar to those in cerberus

mars orbiter laser altimeter pulse width measurements and footprint scale roughness the mars orbiter laser altimeter mola measured the pulse width and energy of altimetric laser returns during the course of two mars years of operations as secondary science objectives mola obtains the footprint scale roughness and the bidirectional reflectivity of mars mola underwent extensive preflight calibration and pulse measurements were monitored continuously in flight but anomalous values of roughness have been inferred a calibration of pulse widths using inflight data yields a slope corrected roughness over 75 m diameter footprints that may be used for quantitative geomorphic surface characterization required for example for landing site selection the recalibration uses a total least squares estimation of pulse characteristics that generalizes the method of abshire et al 2000 this method utilizing the timing at voltage threshold crossings and the area between crossings accounts for observation errors and shows that surface roughness as small as 1 m can be resolved

mars nature and evolution of young latitude dependent water ice rich mantle 1 high resolution altimetry and imaging have revealed the presence of a meters thick sedimentary layer at middle to high northern and southern latitudes presently covering at least 23 of the planet the layer is interpreted to be water ice rich and to undergone degradation recently its activity very likely coincided with the last major obliquity excursion a few hundred thousand years ago the majority of the layer at higher latitudes however persisted for a much longer time in the late amazonian stratigraphic analysis suggests a complex history of successive episodes of deposition and removal repeated deposition and removal of the mantles are interpreted to be responsible for the unusual statistical properties of kilometer scale topography in the transitional mid latitude zones

hesperian age for western medusae fossae formation mars the medusae fossae formation mff on mars is an intensely eroded deposit north of the cratered highlands it is widely thought that mff materials were emplaced through ignimbrite eruptions recent geologic mapping of western mff identified outliers of mff materials well beyond the previously mapped western extent for the deposit including outliers close to gale crater we report counts of impact craters on the mff units that have implications for our understanding of the general history of mff and the uppermost layered materials on the gale crater mound

scale of experiment and rock physics trends because rock is heterogeneous at all scales it is often invalid to assign a single porosity permeability resistivity or velocity to a volume in the subsurface well data demonstrate that these properties can vary appreciably between two points just a foot apart the same happens at the pore scale consider for example a ct scan of a 1 3 mm berea sandstone cube figure 1 the porosity of this sample as calculated by counting the blue pore space pixels is 0 164

radar evidence for ice in lobate debris aprons in the mid northern latitudes of mars 1 subsurface radar sounding data indicate that lobate debris aprons found in deuteronilus mensae in the mid northern latitudes of mars are composed predominantly of water ice the position in time delay and the relatively low amount of signal loss of the apparent basal reflectors below the debris aprons indicate that aprons contain only a minor component of lithic material the current presence of large ice masses at these latitudes has important implications for the climate evolution of mars and for future targets for in situ exploration

roughness and near surface density of mars from sharad radar echoes 1 we present a technique for estimating mars topographic roughness on horizontal scales from about 10 m to 100 m using shallow radar sharad sounding data our results offer a view of surface properties complementary to mars orbiter laser altimeter mola pulse width or baseline roughness maps and can be compared to sharad peak echo properties to infer deviations from the average near surface density latitudinal averaging of sharad derived roughness over arabia and noachis terrae shows good agreement with mola derived roughness and provides clear evidence for latitude dependent mantling deposits previously inferred from image data in northwestern gordii dorsum we find that bulk density in at least the upper few meters is significantly lower than in other units of the medusae fossae formation we observe the same behavior indicative of low near surface density in wind eroded crater fill in the southern highlands combining surface properties analysis subsurface sounding and high resolution optical images we show that the pavonis mons fan shaped deposit differs significantly from lobate debris aprons which sharad has shown to be ice cored there are no internal radar reflections from the smooth facies portion of the pavonis mons fan shaped deposit and we suggest that these deposits are either quite thin or have little dielectric i e density contrast with the underlying terrain future application of these techniques can identify other low density units across mars assist in the mapping of regional volatile rich mantling units and provide new constraints on the physical properties of the polar layered terrain

venus topography and kilometer scale slopes during the first 8 months of the magellan mission the radar altimeter has made some three million measurements of the surface of venus covering the latitude range from 85 n to 80 s methods involving range correlation doppler filtering multi burst summation and range migration are used to focus the observations and to achieve high surface resolution results are presented as maps of the global distribution of topography meter scale roughness and power reflection coefficient the results are similar to those reported in previous experiments surface heights exhibit a unimodal distribution with more than 80 of the surface lying within 1 km of the 6051 84 km mean radius but the higher resolution of the magellan altimeter has disclosed several surprisingly steep features e g the southwest face of the maxwell montes the southern face of the danu montes and the chasmata to the east of thetis regio where average kilometer scale slopes of greater than 30 are not uncommon this conclusion is corroborated by close inspection of synthetic aperture radar imagery

sparse subsurface radar reflectors in hellas planitia mars abstract geomorphological features potentially related to subsurface ice such as scalloped depressions expanded craters pedestal craters and banded terrain are present in and around hellas planitia mars we present a radar survey of the region using the shallow radar sharad instrument on board the mars reconnaissance orbiter mro to identify candidate subsurface reflectors that may be due to the presence of potentially ice rich deposits we found that the majority of radar returns are likely from off nadir surface topography clutter arising from the rough topography of the region there is no widespread radar return from any subsurface interfaces however we identify a group of six reflectors adjacent to each other on a plateau in malea patera in which we have higher confidence landforms associated with a likely ice rich mantle are associated with the plateau but the thickness of this mantle does not correspond to the expected depth of the reflectors however layers beneath the mantle and marginal pitting at the edge of the plateau are similar to those associated with pedestal craters which may be ice rich and are a similar thickness to the expected depth of the reflectors malea patera has been interpreted to be a volcanic caldera so the reflectors may be associated with a volcanic deposit within the plateau although the evidence for this is inconclusive because this radar detection is localized and its origin ambiguous we cannot use it to make conclusions about the thickness of subsurface deposits in the hellas region as a whole the lack of widespread radar reflectors in this region as compared to the northern mid latitudes where extensive radar reflections have been mapped may be due in part to higher surface roughness which creates radar clutter that may obscure subsurface reflectors however on the southern rim of the basin and south of the basin the lack of reflectors may indicate that the possible ice rich deposits observed geomorphologically in this region are too thin to be resolved by sharad are dielectrically similar to the underlying unit or have a gradual vertical transition in ice content that is not reflective for the radar this would imply that recent climate processes may have favored widespread thick ice deposition or preservation in the northern hemisphere as compared to the southern hemisphere

kilometer scale roughness of mars results from mola data analysis the mars orbiter laser altimeter mola data are used to characterize the kilometer scale surface roughness of mars the median absolute value of the differential slope at a given baseline is proposed as a data derived measure of the surface roughness at this scale study of the scale dependence of roughness for the smoothest terrains gives an independent estimate of 20 cm for mola ranging accuracy the baseline lengths from 0 6 to 20 km are used and kilometer scale roughness is mapped for the entire surface the maps show that different geological units have distinctive roughness characteristics scale dependence of roughness for a number of geological units is presented and discussed the southern polar cap is rougher than the northern at kilometer and subkilometer scale which suggests differences in the sublimation condensation balance the vastitas borealis formation has a distinctive 3 km scale background surface topography which suggests a nonvolcanic origin for its upper layer young volcanic plains in amazonis planitia and the eastern part of elysium planitia are very similar to each other in their roughness characteristics and differ from other volcanic plains on mars which suggests a distinctive eruption style there are systematic latitudinal variations of roughness in both the southern highlands and the northern lowlands terrains at high latitude are smoother at short baselines the characteristic vertical scale related to this difference is several meters processes that could be responsible for formation of this trend include creep of ice rich near surface material at high latitudes treatment of the surface with repetitive deposition and sublimation of seasonal frost climate controlled deposition and or cementation of dust at high latitudes and repetitive sublimation and accumulation of subsurface ice at low latitudes with climate variations all mechanisms of origin could operate more effectively under different climate conditions relevant morphological observations favor mechanisms involving deposition of smooth blankets at high latitudes

etudes in computational rock physics alterations and benchmarking abstractwe tested computational benchmarking data for the absolute permeability electrical formation factor and elastic moduli based on the finney pack a physical dense random pack of identical spheres digitally rendered into a 3d rectangular coordinate system as the starting digital object it is altered by a changing the radius of each sphere and b geometrically inverting these new packs by swapping grains and pores porosity the absolute permeability electrical formation factor and elastic moduli are computed for all these alterations the direct grain based objects are relevant to clastic rock and the inverse objects are proxies for carbonates with moldic pores to corroborate these computational results we matched the permeability versus porosity formation factor versus porosity and elastic moduli versus porosity trends they form by established theoretical rock physics models these trends persisted when we reduced the scale of investigation by subsampling some of the digital objects

limits on inference of mars small scale topography from mola data 1 the surface roughness of mars at scales from 1 200 m is of interest for lander hazard and radar sounder clutter analysis but mola data are the only current source of global topographic information we use synthetic fractal profiles to determine the uncertainties associated with deriving self affine statistics from detrended segments of mola tracks the mean hurst exponent derived from such segments is an underestimate of the true value h for h 0 5 and an overestimate for h 100 m scales we suggest that any extrapolation be regarded as a lower bound on the true terrain statistics

estimation of the total electron content of the martian ionosphere using radar sounder surface echoes 1 the martian ionosphere s local total electron content tec and the neutral atmosphere scale height can be derived from radar echoes reflected from the surface of the planet we report the global distribution of the tec by analyzing more than 750 000 echoes of the mars advanced radar for subsurface and ionospheric sounding marsis this is the first direct measurement of the tec of the martian ionosphere the technique used in this paper is a novel transmission mode sounding of the ionosphere of mars in contrast to the active ionospheric sounding experiment ais on marsis which generally operates in the reflection mode this technique yields a global map of the tec for the martian ionosphere the radar transmits a wideband chirp signal that travels through the ionosphere before and after being reflected from the surface the received waves are attenuated delayed and dispersed depending on the electron density in the column directly below the spacecraft in the process of correcting the radar signal we are able to estimate the tec and its global distribution with an unprecedented resolution of about 0 1 deg in latitude 5 km footprint the mapping of the relative geographical variations in the estimated nightside tec data reveals an intricate web of high electron density regions that correspond to regions where crustal magnetic field lines are connected to the solar wind our data demonstrates that these regions are generally but not exclusively associated with areas that have magnetic field lines perpendicular to the surface of mars as a result the global tec map provides a high resolution view of where the martian crustal magnetic field is connected to the solar wind we also provide an estimate of the neutral atmospheric scale height near the ionospheric peak and observe temporal fluctuations in peak electron density related to solar activity

coherent and incoherent components in near nadir radar scattering applications to radar sounding of mars 1 we examine the relative importance of coherent and incoherent echo components in near nadir radar scattering from self affine surfaces the coherent component important only for observations at small incidence angles nadir looking sounders and altimeters is a function of both surface roughness and scattering area models for the incoherent component require a minimum scattering area for validity for smaller regions the radar echo is overestimated we propose a simple criterion for the horizontal scale that defines this shift in applicable scattering model and show the range of roughness parameters for which marsis sharad and possibly jimo radar sounder measurements may be modeled using the two approaches

cold based mountain glaciers on mars western arsia mons surface environmental conditions on mars are currently extremely cold and hyperarid most equivalent to polar deserts on earth coupling newly acquired mars data with fieldbased observations regarding the flow surface morphology and depositional history of polar glaciers in antarctica we show that the multiple facies of an extensive fan shaped deposit on the western flanks of arsia mons volcano are consistent with deposition from cold based mountain glaciers an outer ridged facies that consists of multiple laterally extensive arcuate and parallel ridges resting without disturbance on both well preserved lava flows and an impact crater is interpreted as drop moraines formed at the margin of an ablating and predominantly receding cold based glacier a knobby facies that consists of equidimensional knobs each to several kilometers in diameter is inward of the ridges this facies is interpreted as a sublimation till derived from in situ downwasting of ashrich glacier ice a third facies comprising distinctive convex outward lobes with concentric parallel ridges and aspect ratios elongated downslope likely represents rock glacier deposits some of which may still be underlain by a core of glacier ice taken together these surficial deposits show that the western flank of arsia mons was occupied by an extensive mountain glacial system accumulating on and emerging from the upper slopes of the volcano and spreading downslope to form a piedmont like fan

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

radar sounding evidence for buried glaciers in the southern mid latitudes of mars lobate features abutting massifs and escarpments in the middle latitudes of mars have been recognized in images for decades but their true nature has been controversial with hypotheses of origin such as ice lubricated debris flows or glaciers covered by a layer of surface debris these models imply an ice content ranging from minor and interstitial to massive and relatively pure soundings of these deposits in the eastern hellas region by the shallow radar on the mars reconnaissance orbiter reveal radar properties entirely consistent with massive water ice supporting the debris covered glacier hypothesis the results imply that these glaciers formed in a previous climate conducive to glaciation at middle latitudes such features may collectively represent the most extensive nonpolar ice yet recognized on mars