the shape and internal structure of the moon from the clementine mission global topographic and gravitational field models derived from data collected by the clementine spacecraft reveal a new picture of the shape and internal structure of the moon the moon exhibits a 16 kilometer range of elevation with the greatest topographic excursions occurring on the far side lunar highlands are in a state of near isostatic compensation whereas impact basins display a wide range of compensation states that do not correlate simply with basin size or age a global crustal thickness map reveals crustal thinning under all resolvable lunar basins the results indicate that the structure and thermal history of the moon are more complex than was previously believed

venus topography a harmonic analysis a model of venusian global topography has been obtained by fitting an eighteenth degree harmonic series to pioneer venus orbiter radar altimeter data the mean radius is 6051 45 0 04 km the corresponding mean density is 5244 8 0 5 kg m 3 the center of figure is displaced from the center of mass by 0 339 0 088 km towards 6 6 10 1 n 148 8 7 7 e the figure of venus is distinctly triaxial but the orientation and magnitudes of the principal topographic axes correlate rather poorly with the gravitational principal axes however the higher degree harmonics of topography and gravity are significantly correlated the topographic variance spectrum of venus is very similar in form to those of the moon mars and especially earth we suggest that this spectral similarity simply reflects a statistical balance between constructional and degradational geomorphic processes venus and earth are particularly similar and differ from the moon and mars in that the larger bodies both exhibit a significant low degree deficit relative to the extrapolated trend of the higher harmonics

deformation of the oceanic crust between the north american and south american plates fracture zone trends and magnetic anomalies in the atlantic ocean indicate that the north american plate must have moved with respect to the south american plate during the opening of the atlantic a comparison of plate tectonic flow lines with fracture zones identified from geosat and seasat altimeter data suggests that the north american south american plate boundary migrated northward from die guinea demarara shear margin to the vema fracture zone before chron 34 84 ma to north of the doldrums fracture zone before chron 22 51 9 ma and to north of the mercurius fracture zone between chron 32 72 5 ma and chron 13 35 5 ma the paleoridge offset through time identified from magnetic anomalies and the computed cumulative strike slip motion in the plate boundary area indicate that the triple junction may have been located between the mercurius and the fifteen twenty fracture zones after 67 ma chron 30 plate reconstructions indicate a late cretaceous phase of transtension followed by transpression in the tertiary for the tiburon barracuda ridge area south of the fifteen twenty fracture zone the ocean floor in this area is characterized by a series of ridges and troughs with large bouguer gravity anomalies up to 135 mgal we use smoothing spline estimation to invert bouguer anomalies for crustal layer structure our model results suggest that the moho is uplifted 2 4 km over short wavelengths 70 km at the barracuda and tiburon ridges and imply large anelastic strains the severely thinned crust at the two ridges implies that crustal extension must have taken place before they were uplifted we propose that the north south american plate boundary migrated to the latitude of the tiburon ridge bounded by the vema and marathon fracture zones before chron 34 84 ma post chron 34 crustal thinning during a transtensional tectonic regime may have been localized at preexisting structural weaknesses such as the vema marathon mercurius and fifteen twenty fracture zone troughs but reaching the fifteen twenty fracture zone and future barracuda ridge area only after chron 32 72 5 ma this interpretation concurs with our crustal structural model which shows stronger crustal thinning underneath the tiburon ridge than at the barracuda ridge subsequent transpression may have continued along the existing zones of weakness in the tertiary creating the presently observed crustal deformation and uplift of the moho accompanied by anelastic failure of the crust middle eocene upper oligocene turbidites on the slope of the tiburon ridge now located 800 m above the abyssal plain suggest that most of its uplift occurred at post oligocene times the unusually shallow moho underneath the tiburon and barracuda ridges represents an unstable density distribution which may indicate that compressive stresses are still present to maintain these anomalies and that the north american south american plate boundary may still be located in this area

the release and dispersal of pb and zn contaminated sediments within an arctic braided river system abstract this paper examines the release and dispersal of pb and zn contaminated mine tailings within the tunnelelv river ne greenland the tunnelelv is an arctic braided river system and results derived from this research provide interesting comparisons to conclusions gained from previous studies which have mainly concentrated on temperate river systems patterns of dispersion are shown to relate intimately to the macroscale morphology of the braided river valley and also to the vertical tendency of the channel network storage of fine contaminated sediments are shown to relate to the bar pool morphology of the channel attention is drawn to the performance and limitations of existing sediment dispersion models in relation to the complexity of the processes they are trying to model

gravity inferred crustal attributes of visible and buried impact basins on mars 1 the impact basins of mars reveal important insights on martian tectonic evolution they involve strongly disrupted depressed regions of crust with likely enhanced porosity and permeability that may locally concentrate water and other crustal fluids hence the crustal properties of impact basins can also be important in the hunt for water and related clues for life on mars we assess the crustal details of impact basins by separating the mars global surveyor free air anomalies into terrain correlated and terrain decorrelated components the separation is based on the correlation spectrum between the free air anomalies and the gravity effects evaluated from the topography mapped by the mars orbital laser altimeter mola for topographically visible multiring basins like isidis striking circular patterns of alternating terrain correlated free air maxima and minima mark the uncompensated components of the central mantle plug and surrounding rings the first vertical derivatives of these anomalies effectively estimate the basin ring locations and a transient cavity depth to diameter ratio of 0 09 that is consistent with the ratio observed for lunar nearside multiring basins for the isidis basin we obtain an excavation depth of roughly 66 km that reflects considerably disrupted crust for concentrating local fluids since the noachian impact furthermore the related crustal terrain decorrelated free air anomalies suggest up to 2 km of high density basin fill may cap the central basin subtle quasi circular depressions in the relatively featureless mola terrain of the northern hemisphere have identified potentially buried impact basins frey et al 2002 an altimetry depression in acidalia planitia and another in utopia are also associated with ringed patterns of terrain decorrelated free air anomalies that may mark the uncompensated mass effects of buried impact basins the gravity derived transient excavation depths for these inferred basins are roughly 41 and 20 km respectively while the related ring diameters d follow the ubiquitous d rule of planetary impact basins the crust of these buried basins is likely to contain water at higher levels than the crust of the equatorial basins that was substantially dewatered with the development of the great northern basin hence analyzing surface fractures faults and other crustal discontinuities that can tap the more saturated crust of these inferred buried basins may facilitate the hunt for water on mars

mineralogy of the mafic anomaly in the south pole aitken basin implications for excavation of the lunar mantle the mineralogy of south pole aitken basin spa the largest confirmed impact basin on the moon is evaluated using five color images from clementine although olivine rich material as well as basalts rich in clinopyroxene are readily identified elsewhere on the farside the dominant rock type observed across the interior of spa is of a very noritic composition this mineralogy suggests that lower crust rather than the mantle is the dominant source of the mafic component at spa the lack of variation in observed noritic composition is probably due to basin formation processes during which extensive melting and mixing of target materials are likely to occur

inversion of combined gravity and bathymetry data for crustal structure a prescription for downward continuation abstract we propose a new and improved recipe for inverting for crustal thickness variations from combined gravity and bathymetry data the new ingredients with respect to previous studies are the posing of this problem as an inverse problem and the use of a downward continuation filter which can be tailored to find the crustal thickness solution which satisfies a minimum slope or maximal smoothness criteria or a weighted combination of these desired solution features we explore several suggestions for determining the optimum smoothing parameters for a given crustal thickness inversion then we compare this new method to that used previously in marine gravity studies we find it to be an improved recipe for dealing with gravity data with observation errors of 3 5 mgal but not by much this recipe will be most useful in extracting more geological information from marine gravity data where apparent observation errors are 1 mgal e g from future global positioning satellite navigated studies

palaeolithic archaeology and the british quaternary sequence abstract studies within the last two decades culminating in the recent publication of the i g c p project 24 quaternary glaciations in the northern hemisphere sibrava et al 1986 have amplified changed or questioned much of the accepted sequence in britain during the middle and late pleistocene this review takes the chronology of events as now seen and relates it to the evidence for the palaeolithic period prior to that in the reach of radiocarbon dating it would indicate that there was considerable human activity in britain before the hoxnian stage and that acheulian hand axe industries of considerable refinement were present and that these industries occurred before or co existed with non hand axe clactonian industries only the latter can be demonstrated as having been present during the earlier part of the hoxnian interglacial acheulian industries occur in various forms from towards the close of this interglacial and during the long period before the ipswichian stage it is not possible to demonstrate a human presence during the ipswichian interglacial as represented by the type site and artifacts occur very sparsely if at all in sediments attributed to other warm periods or the period between the hoxnian and ipswichian stages levallois technique is not found as a significant element of flint industries until the latter part of this period during the first half of the devensian stage flint industries with distinctive hand axes and levallois flakes occur and can be described as mousterian of acheulian tradition

the evolution of impact basins cooling subsidence and thermal stress potentially important contributors to the topography and tectonics of multi ring impact basins are the thermal contraction and thermal stress that accompany the loss of heat emplaced during basin formation heat converted from impact kinetic energy and contributed from the uplift of isotherms during cavity collapse are important components in the energy budget of a newly formed basin that the subsequent cooling may have been an important factor in the tectonic evolution of the orientale basin is suggested by the deep central depression and by a surrounding region of extensive fissuring to test these concepts we develop models for the anomalous temperature distribution immediately following basin formation and we calculate the resulting elastic displacement and stress fields that then would accompany cooling of the basin region all models predict subsidence of the basin floor and a near surface stress field consistent with fissuring in addition the rates of cooling and of accumulation of thermal stress are in agreement with the inferred timing of fissure formation in orientale the sensitivity of the predicted displacements and stresses to the initial temperature field allows us to place bounds on the quantity and distribution of impact heat emplaced during basin formation in order to be consistent with the observed topography and the distribution of fissures in the orientale basin the buried heat deposited during the basin forming event was between 1032 and 1033 erg it is likely that most of this heat was concentrated within a distance of 100 200 km from the point of impact

the clementine mission to the moon scientific overview in the course of 71 days in lunar orbit from 19 february to 3 may 1994 the clementine spacecraft acquired just under two million digital images of the moon at visible and infrared wavelengths these data are enabling the global mapping of the rock types of the lunar crust and the first detailed investigation of the geology of the lunar polar regions and the lunar far side in addition laser ranging measurements provided the first view of the global topographic figure of the moon the topography of many ancient impact basins has been measured and a global map of the thickness of the lunar crust has been derived from the topography and gravity

ancient multiring basins on the moon revealed by clementine laser altimetry analysis of laser altimetry data from clementine has confirmed and extended our knowledge of nearly obliterated multiring basins on the moon these basins were formed during the early bombardment phase of lunar history have been filled to varying degrees by mare lavas and regional ejecta blankets and have been degraded by the superposition of large impact craters the mendel rydberg basin a degraded three ring feature over 600 kilometers in diameter on the lunar western limb is about 6 kilometers deep from rim to floor only slightly less deep than the nearby younger and much better preserved orientale basin 8 kilometers deep the south pole aitken basin the oldest discernible impact feature on the moon is revealed as a basin 2500 kilometers in diameter with an average depth of more than 13 kilometers rim crest to floor this feature is the largest deepest impact crater yet discovered in the solar system several additional depressions seen in the data may represent previously unmapped ancient impact basins

global distribution of lunar composition new results from lunar prospector 1 maps of thorium th feo the ratio of epithermal to thermal neutrons e t and fast neutrons fn from lunar prospector were studied to determine their global distribution on the moon these distributions are compared to that of the 750 nm lunar albedo from clementine to aid in their interpretation all distributions were parameterized using a spherical harmonic expansion out to order l 30 resultant harmonic coefficients generally decrease with increasing l value as a power law in l for all five variables the axes of all dipole components l 1 cluster closely about a centroid given by 14 1 latitude and 16 4 west longitude this location is very close to the symmetry axes of their quadrupole components l 2 which cluster about a centroid given by 24 6 latitude and 25 1 west longitude both centroids are near the center of a suggested procellarum basin given by whitaker 1981 at 23 latitude and 15 west longitude this suggestion is strengthened by a sharp decrease of the intensities of all three variables at 50 from the centroids which is close to the boundary of the putative procellarum basin the coincidence of the global concentration of heat producing elements through th and mare deposits on the lunar surface through feo t e and fn with the circular outline of a putative procellarum basin suggests that the events that were responsible for producing oceanus procellarum perhaps a single giant impact must figure importantly in shaping the global distribution of surface composition a second apparently older circular structure having its center near 5 latitude and 65 east longitude and a radius of 50 is also hinted at in the data

the deep structure of lunar basins implications for basin formation and modification we present models for the structure of the crust and upper mantle beneath lunar impact basins from an inversion of gravity and topographic data from the nearside of the moon all basin models display a thinner crust and an elevated moho beneath the central basin region compared to surrounding areas a signature of the processes of basin excavation and mantle uplift during collapse of the transient cavity there is a general decrease in the magnitude of apparent uplift of mantle material with increasing basin age we attribute this relation primarily to enhanced rates of ductile flow of crustal material early in lunar history when crustal temperatures were relatively high and the effective elastic lithosphere was thin the more relaxed topographic and moho relief associated with older basins on the central nearside may in particular be at least partly a consequence of the extensive subsurface heating associated with the formation of the large procellarum basin the deep structure of the youngest basins constrains the geometry of the cavity of excavation and the amount of crustal material ejected beyond the basin rim from the volumes of the topographic basin of mare basalt fill and of uplifted mantle material the volume of crustal material ejected beyond the basin rim for an orientale sized event was of the order of 107 km 3 a near constant thickness of nonmare crustal material beneath the central regions of young basins of various diameters and preimpact crustal thicknesses suggests that the transient cavity excavated to at least the base of the crust for the largest basins significant excavation into the mantle may have been impeded by an abrupt increase in strength at the lunar moho

small scale density variations in the lunar crust revealed by grail abstract data from the gravity recovery and interior laboratory grail mission have revealed that 98 of the power of the gravity signal of the moon at high spherical harmonic degrees correlates with the topography the remaining 2 of the signal which cannot be explained by topography contains information about density variations within the crust these high degree bouguer gravity anomalies are likely caused by small scale 10 s of km shallow density variations here we use gravity inversions to model the small scale three dimensional variations in the density of the lunar crust inversion results from three non descript areas yield shallow density variations in the range of 100 200 kg m 3 three end member scenarios of variations in porosity intrusions into the crust and variations in bulk crustal composition were tested as possible sources of the density variations we find that the density anomalies can be caused entirely by changes in porosity characteristics of density anomalies in the south pole aitken basin also support porosity as a primary source of these variations mafic intrusions into the crust could explain many but not all of the anomalies additionally variations in crustal composition revealed by spectral data could only explain a small fraction of the density anomalies nevertheless all three sources of density variations likely contribute collectively results from this study of grail gravity data combined with other studies of remote sensing data and lunar samples show that the lunar crust exhibits variations in density by 10 over scales ranging from centimeters to 100 s of kilometers

igneous processes and closed system evolution of the tharsis region of mars a quantitative petrologic model for the formation of the tharsis rise of mars has been developed that is consistent with global gravity and topography data partial melting of the mantle underlying the tharsis plateau results in the depletion of basaltic chemical components in the source region iron is partitioned preferentially into the basaltic liquid so that the density of the source region is lowered relative to surrounding unmodified mantle basalt is erupted to the surface and or intruded at shallow levels in the crust where it solidifies to low pressure mineral assemblages or perhaps glass these low pressure materials are less dense than their mantle equivalents hence the net volume of the tharsis crust mantle system is increased resulting in the prominent topographic rise with no net gain or loss of mass the distribution of densities with depth is quantitatively consistent with the isostatic models of sleep and phillips 1979 1985 typical values of parameters that are constrained by the gravity and topography data are 150 km crustal thickness 250 km elastic mantle thickness 26 partial melting in the mantle source region and 32 addition of intrusive material to the crust this closed system petrologic process is strictly constructional in nature but shallow intrusion of magma into the crust can cause uplift of overlying strata as advocated by r j phillips and n h sleep submitted manuscript 1987

new lunar meteorites impact melt and regolith breccias and large scale heterogeneities of the upper lunar crust we have analyzed nine highland lunar meteorites lunaites using mainly inaa several of these rocks are difficult to classify dhofar 081 is basically a fragmental breccia but much of its groundmass features a glassy fluidized texture that is indicative of localized shock melting also much of the matrix glass is swirly brown suggesting a possible regolith derivation we interpret dar al gani dag 400 as an extremely immature regolith breccia consisting mainly of impact melt breccia clasts we interpret dhofar 026 as an unusually complex anorthositic impact melt breccia with scattered ovoid globules that formed as clasts of mafic subophitic impact melt the presence of mafic crystalline globules in a lunar material even one so clearly impact heated suggests that it may have originated as a regolith our new data and a synthesis of literature data suggest a contrast in al2o3 incompatible element systematics between impact melts from the central nearside highlands where apollo sampling occurred and those from the general highland surface of the moon impact melts from the general highland surface tend to have systematically lower incompatible element concentration at any given al2o3 concentration than those from apollo 16 in the case of dhofar 026 both the bulk rock and a comparatively al poor composition 14 wt al2o3 7 g g sm extrapolated for the globules manifest incompatible element contents well below the apollo 16 trend impact melts from luna 20 57e distribute more along the general highland trend than along the apollo 16 trend siderophile elements also show a distinctive composition for apollo 16 impact melts ni ir averaging 1 8x chondritic in contrast lunaite impact melt breccias have consistently chondritic ni ir impact melts from luna 20 and other apollo sites show average ni ir almost as high as those from apollo 16 the prevalence of this distinctive ni ir ratio at such widely separated nearside sites suggests that debris from one extraordinarily large impact may dominate the megaregolith siderophile component of a nearside region 2300 km or more across highland polymict breccia lunaites and other kreep poor highland regolith samples manifest a strong anticorrelation between al2o3 and mg the magnesian component probably represents the chemical signature of the mg suite of pristine nonmare rocks in its most pure form unaltered by the major kreep assimilation that is so common among apollo mg suite samples the average composition of the ferroan anorthositic component is now well constrained at al2o3 29 30 wt implying about 17 19 wt modal mafic silicates in good agreement with the composition predicted for flotation crust over a ferroan magma ocean warren 1990

on the origin of mascon basins on the moon and beyond 1 mascon basins on the moon are large craters that display significant positive free air and bouguer gravity anomalies an important question is why is not every large crater a mascon as less than half have been previously determined to be we detrend the free air topographic and bouguer gravity anomalies and find that most large basins 28 of 41 display mascon characteristics e g strong positive bouguer anomalies narrower than the surface rims negative free air gravity annuli surrounding the central highs generally are absent in the bouguer gravity implicating surface topography we propose that beneath a forming large basin the relatively narrow transient crater drives mantle uplift while upward and inward collapse forms the surface topography furthermore the nonmascon basins are all ancient and heavily degraded indicating a postimpact evolutionary process our results suggest that mascon formation is the standard for large impacts on the moon and by extension on other terrestrial planets

a simple mechanical model of valhalla basin callisto the valhalla basin on callisto is a multiringed structu e that extends over much of the satellite s surface although its appearance differs in detail from lunar multiringed basins its origin may also be attributed to lithospheric fragmentation accompanying collapse of the transient crater formed by an impact event this paper explores the mechanics of the collapse process by treating the lithosphere as a thin elastic von mises plastic sheet plane geometry or shell spherical geometry flow of the underlying asthenosphere inward toward the crater cavity induces plastic failure of the lithosphere and produces a characteristic pattern of faults in the disrupted lithosphere the pattern and extent of faulting is a function of a single dimensionless parameter that involves the strength and thickness of the lithosphere the crater depth and diameter and the surface gravity of the planet the tectonic structures of valhalla correspond well with the failure pattern expected for a large crater produced in a thin circa 30 km weak strength 100 bar lithospheric shell

the gravity field of mars results from mars global surveyor observations of the gravity field of mars reveal a planet that has responded differently in its northern and southern hemispheres to major impacts and volcanic processes the rough elevated southern hemisphere has a relatively featureless gravitational signature indicating a state of near isostatic compensation whereas the smooth low northern plains display a wider range of gravitational anomalies that indicates a thinner but stronger surface layer than in the south the northern hemisphere shows evidence for buried impact basins although none large enough to explain the hemispheric elevation difference the gravitational potential signature of tharsis is approximately axisymmetric and contains the tharsis montes but not the olympus mons or alba patera volcanoes the gravity signature of valles marineris extends into chryse and provides an estimate of material removed by early fluvial activity

a unified lunar control network the near side the lunakhod 2 apollo 11 14 and 15 retroreflectors and the apollo 15 16 and 17 alsep antenna locations are the most accurately located positions on the moon the apollo 15 retroreflector and the apollo 15 16 and 17 alsep antennas have been identified on high resolution apollo panoramic pictures and their locations transferred to apollo mapping camera frames three apollo control networks have been computed two by the defense mapping agency aerospace center and one by the national ocean survey u s geological survey based on measurements of points on the apollo mapping camera frames transformations involving translation rotation and scale were determined that adjusted the coordinates of the points of the three control networks to the center of mass origin and the mean earth polar axis coordinate system defined by the lunar ranging retroreflector experiment the transformed dma 603 control network was the best fit to the alsep coordinates and was selected as a base to transform all points in d l meyer s dmaac telescopic network to the new origin and coordinate system new coordinates of 1156 of these points are given as are 10 points from a mariner 10 solution in the north polar region these coordinates are presented in the appendix and are available only in the microfiche version of this journal

a stress interpretation scheme applied to lunar gravity and topography data 1 we present an approach of the inverse gravimetric problem that allows the gravity to be directly related to the deviatoric stresses without any rheological assumptions in this approach a new set of parameters is considered 1 the density variations over equipotential surfaces and the height of interfaces above the corresponding equipotential surfaces and 2 the stress difference the method is applied to lunar topographic and gravimetric data that are interpreted in term of transversally isotropic deviatoric stress within the moon it also provides inference on density and crustal thickness variations the estimated lateral variation in deviatoric stress is about 500 bars within the crust and upper mantle in the crust because of topography the strongest stress differences take place on the far side with large lateral compressions beneath the south pole aitken basin vertical compression under the mascons of the nearside is the main feature within the upper mantle

the evolution of impact basins viscous relaxation of topographic relief we evaluate the hypothesis that viscous relaxation has been an important process for modifying the topographic profiles of ancient large impact basins on the moon we adopt a representative topographic profile of the orientale basin the youngest large impact basin on the moon as an estimate of the initial topography of older basins of similar horizontal dimensions and we predict the topographic profiles that would result from viscous relaxation according to a number of simple analytical representations of the rheological response of the moon to surface topography at wavelengths greater than the thickness of a high viscosity lithosphere both a decrease in viscosity with depth and the partial to complete isostatic compensation of topographic relief have pronounced effects on the wavelength dependent relaxation times and must be considered in modeling viscous relaxation for features as large as impact basins the effect of a decrease in viscosity with depth is to enhance the rate of viscous relaxation at long wavelengths while the rate of relaxation decreases substantially for the fraction of long wavelength topography which is isostatically compensated as an initial condition these models are applied to two pre nectarian basins on the moon the tranquillitatis basin on the lunar nearside and the much larger and older south pole aitken basin on the farside the topographic profile of tranquillitatis after correcting for the effect of mare basalt fill is consistent with significant viscous relaxation of relief prior to the oldest episode of mare volcanism preserved as a surface unit the large topographic relief of the larger farside basin on the contrary is not consistent with significant viscous relaxation and implies a mean crustal viscosity at least a factor of 10 higher than for the central nearside over the time interval during which substantial viscous relaxation of older nearside basins such as tranquillitatis probably occurred a difference in typical crustal temperature profiles between the farside and nearside is the most likely explanation of such a viscosity difference such a nearside farside asymmetry in near surface temperature may date from the time of crust mantle differentiation and may have persisted because of the different histories of late stage impact basin formation and mare volcanism on the two hemispheres

density and porosity of the lunar crust from gravity and topography 1 newly obtained gravity and topography data of the moon combined with a lithospheric flexure model that considers both surface and subsurface loading are used to place constraints on the density of the upper crust from a localized spectral admittance analysis subsurface loads are found to be relatively unimportant in the highlands and when subsurface loads are neglected the best fitting bulk densities for a number of highland regions are found to vary from 2590 to 2870 kg m 3 with a mean value of 2691 kg m 3 crustal rock densities estimated from geochemical considerations and global iron and titanium abundances imply somewhat greater densities which we interpret as porosity affecting the gravity derived bulk density estimates the average porosity in the upper few kilometers of crust is calculated to be about 7 7 which is consistent with porosity estimates of impact fractured meteorites and terrestrial impact craters

abundance and distribution of iron on the moon the abundance and distribution of iron on the moon is derived from a near global data set from clementine the determined iron content of the lunar highlands crust 3 percent iron by weight supports the hypothesis that much of the lunar crust was derived from a magma ocean the iron content of lower crustal material exposed by the south pole aitken impact basin on the lunar farside is higher 7 to 8 percent by weight and consistent with a basaltic composition this composition supports earlier evidence that the lunar crust becomes more mafic with depth the data also suggest that the bulk composition of the moon differs from that of the earth9s mantle this difference excludes models for lunar origin that require the earth and moon to have the same compositions such as fission and coaccretion and favors giant impact and capture

small scale lunar farside volcanism abstract we identified and mapped 28 mare basalt occurrences between the australe and south pole aitken basins on the southern lunar farside and determined their absolute model ages amas by performing crater size frequency distribution csfd measurements our study area can be subdivided into seven major mare basalt occurrences in and around bolyai roche v rosseland pauli and roche craters south of both rosseland and coblentz craters as well as mare patches between eotvos and roche craters the amas of the mare basalts in and around bolyai crater range from 2 1 ga to 3 5 ga two units varying drastically within short distances the mare patches south of coblentz crater contain nine units that have amas ranging from 2 1 ga to 3 8 ga the mare basalts in roche v crater show an ama of 2 2 ga we mapped seven volcanic units in rosseland crater and derived amas for five of these units the mare basalts in rosseland crater show the youngest amas found in our study area ranging from 1 5 ga to 2 9 ga the mare basalt occurrence south of rosseland crater shows significantly older ages with an ama of 3 3 ga the mare basalts in pauli and roche craters show amas from 1 7 ga to 3 1 ga the mare patches between eotvos and roche craters show a similar range of amas from 1 9 ga to 3 1 ga the amas of the mare basalts in our study show that the lunar farside was volcanically active for nearly as long as the lunar nearside 1 2 ga ago or at least longer than previously thought 2 5 ga ago and predicted by models of the ascent and eruption of lunar basalts in addition we calculated thicknesses and volumes of the investigated mare basalts with thicknesses between 21 m and 172 m and volumes from 0 1 km3 to 379 km3 the mare basalts in our study area show a wide range of dimensions similar to other mare basalts of the lunar near and farsides

subsurface morphology and scaling of lunar impact basins impact bombardment during the first billion years after the formation of the moon produced at least several tens of basins the gravity recovery and interior laboratory grail mission mapped the gravity field of these impact structures at significantly higher spatial resolution than previous missions allowing for detailed subsurface and morphological analyses to be made across the entire globe grail derived crustal thickness maps were used to define the regions of crustal thinning observed in centers of lunar impact basins which represents a less unambiguous measure of a basin size than those based on topographic features the formation of lunar impact basins was modeled numerically by using the isale 2d hydrocode with a large range of impact and target conditions typical for the first billion years of lunar evolution in the investigated range of impactor and target conditions the target temperature had the dominant effect on the basin subsurface morphology model results were also used to update current impact scaling relationships applicable to the lunar setting based on assumed target temperature our new temperature dependent impact scaling relationships provide estimates of impact conditions and transient crater diameters for the majority of impact basins mapped by grail as the formation of lunar impact basins is associated with the first approximately 700 myr of the solar system evolution when the impact flux was considerably larger than the present day our revised impact scaling relationships can aid further analyses and understanding of the extent of impact bombardment on the moon and terrestrial planets in the early solar system

the lunar crust global structure and signature of major basins new lunar gravity and topography data from the clementine mission provide a global bouguer anomaly map corrected for the gravitational attraction of mare fill in mascon basins most of the gravity signal remaining after corrections for the attraction of topography and mare fill can be attributed to variations in depth to the lunar moho and therefore crustal thickness the large range of global crustal thickness 20 120 km is indicative of major spatial variations in melting of the lunar exterior and or significant impact related redistribution the 61 km average crustal thickness constrained by a depth to moho measured during the apollo 12 and 14 missions is preferentially distributed toward the farside accounting for much of the offset in center of figure from the center of mass while the average farside thickness is 12 km greater than the nearside the distribution is nonuniform with dramatic thinning beneath the farside south pole aitken basin with the global crustal thickness map as a constraint regional inversions of gravity and topography resolve the crustal structure of major mascon basins to half wavelengths of 150 km in order to yield crustal thickness maps with the maximum horizontal resolution permitted by the data the downward continuation of the bouguer gravity is stabilized by a three dimensional minimum slope and curvature algorithm both mare and non mare basins are characterized by a central upwarped moho that is surrounded by rings of thickened crust lying mainly within the basin rims the inferred relief at this density interface suggests a deep structural component to the surficial features of multiring lunar impact basins for large 300 km diameter basins moho relief appears uncorrelated with diameter but is negatively correlated with basin age in several cases it appears that the multiring structures were out of isostatic equilibrium prior to mare emplacement suggesting that the lithosphere was strong enough to maintain their state of stress to the present

acoustic fluidization and the scale dependence of impact crater morphology a phenomenological bingham plastic model has previously been shown to provide an adequate description of the collapse of impact craters this paper demonstrates that the bingham parameters may be derived from a model in which acoustic energy generated during excavation fluidizes the rock debris surrounding the crater experimental support for the theoretical flow law is presented although the bingham yield stress cannot be computed without detailed knowledge of the initial acoustic field the bingham viscosity is derived from a simple argument which shows that it increases as the 3 2 power of crater diameter consistent with observation crater collapse may occur in material with internal dissipation q as low as 100 comparable to laboratory observations of dissipation in granular materials crater collapse thus does not require that the acoustic field be regenerated during flow

galileo multispectral imaging of the north polar and eastern limb regions of the moon multispectral images obtained during the galileo probe s second encounter with the moon reveal the compositional nature of the north polar regions and the northeastern limb mare deposits in these regions are found to be primarily low to medium titanium lavas and as on the western limb show only slight spectral heterogeneity the northern light plains are found to have the spectral characteristics of highlands materials show little evidence for the presence of cryptomaria and were most likely emplaced by impact processes regardless of their age

gravity field and internal structure of mercury from messenger radio tracking of the messenger spacecraft has provided a model of mercury s gravity field in the northern hemisphere several large gravity anomalies including candidate mass concentrations mascons exceed 100 milli galileos mgal mercury s northern hemisphere crust is thicker at low latitudes and thinner in the polar region and shows evidence for thinning beneath some impact basins the low degree gravity field combined with planetary spin parameters yields the moment of inertia c mr2 0 353 0 017 where m and r are mercury s mass and radius and a ratio of the moment of inertia of mercury s solid outer shell to that of the planet of cm c 0 452 0 035 a model for mercury s radial density distribution consistent with these results includes a solid silicate crust and mantle overlying a solid iron sulfide layer and an iron rich liquid outer core and perhaps a solid inner core

characteristics of lunar mare deposits in smythii and marginis basins implications for magma transport mechanisms an analysis of 34 lunar lava flows and ponds in the eastern limb smythii and marginis basins was undertaken to examine and model the first stages of secondary crustal formation and assess processes involved in magma transport and eruption in order to isolate the characteristics of single eruptive episodes we focused on discrete mare ponds adjacent to the major mafia mean values for areas and volumes of deposits estimated to be good candidates for single eruptive phases are large approximately 950 1000 km 2 and 200 km 3 respectively these eruptive volumes are commensurate with the largest known terrestrial eruptions flood basalts the lack of geomorphological structures indicative of shallow magma reservoirs indicates that deep probably subcrustal source regions are prevalent with respect to crustal thickness relationships the magnitude and frequency of eruptive events are observed to be greatest in areas of thinnest crust specifically regions of major maria mare smythii mare marginis occur in areas of thinnest crust while isolated ponds occur where the crust is relatively thicker this is consistent with the correlation observed globally between crustal thickness and the magnitude and frequency of eruptive events ages of volcanic flows and pyroclastic events range from early imbrian to imbfian eratosthenian but are concentrated most heavily between 3 80 3 60 ga suggesting a period of peak volcanism beginning around 3 85 ga and lasting approximately 200 ma however the existence of dark halo crater clusters in non mare units within the region suggests the presence of cryptomaha which would indicate an earlier onset of volcanism and a volume of mare matehal potentially greater than that currently exposed on the surface typical nearest neighbor distances suggest deposits derive from reservoirs 100 km in diameter the observations made here are consistent with a magma transport model in which plumes rising diapirically stall at a density boundary under the lunar crust and propagate dikes to the surface through overpressufization

the materials of the lunar procellarum kreep terrane a synthesis of data from geomorphological mapping remote sensing and sample analyses major features of the moon s procellarum kreep terrane include subdued relief and extensive resurfacing with mare basalt consistent with high concentrations of th and other heat producing elements at depth we relate the chemistry of sampled materials to the geomorphology th surface concentrations determined by the lunar prospector 2 pixels and feo and tio2 concentrations derived from clementine ultraviolet visible spectral data on the basis of geologic maps each pixel was classified as mare terra or mixed near the periphery of the terrane terra pixel compositions are relatively feldspathic in the interior they mainly represent imbrium basin rim or ejecta deposits and are mainly incompatible trace element rich norites and presumably represent materials from a thick section tens of kilometers of the pre imbrium crust of the terrane excavated by the imbrium event although imbrium ejecta are the principal source of surface terra materials the imbrium event did not create the th rich procellarum kreep terrane broad continuous expanses of mare pixels are observed with little interruption from protruding terra or terra penetrating craters the mare basalt dominated regoliths of these areas have a wide range of tio2 concentrations 18 leading to the conclusion that the high th concentrations are in the mare basalts and are not present in the regoliths as terra derived materials volcanic glasses and impact glasses of mare basalt composition collected from the procellarum kreep terrane support this conclusion

copernicus crater central peak lunar mountain of unique composition olivine is identified as the major mafic mineral in a central peak of copernicus crater information on the mineral assemblages of such unsampled lunar surface material is provided by near infrared reflectance spectra 0 7 to 2 5 micrometers obtained with earth based telescopes the composition of the deep seated material comprising the copernicus central peak is unique among measured areas other lunar terra areas and the wall of copernicus exhibit spectral characteristics of mineral assemblages comparable to the feldspathic breccias returned by the apollo missions with low calcium orthopyroxene being the major mafic mineral