toward mapping the effective elastic thickness of planetary lithospheres from a spherical wavelet analysis of gravity and topography abstract the effective elastic thickness t e of the lithosphere controls the flexural response to transverse loading and can be used in conjunction with rheological models to remotely estimate surface heat flux of terrestrial planets in the vast majority of studies t e estimation is carried out in a two step process 1 the joint spectra admittance and or coherency of gravity anomalies free air and or bouguer and topography are calculated within finite size windows and 2 the spectra are inverted using a model for the loading of an infinite elastic plate or shell in recent years research in the spatio spectral analysis of cartesian grids and improvements in lithospheric loading models have allowed the mapping of t e on the earth at unprecedented resolution nevertheless the limitations imposed by working with cartesian data and models are hampering further advances in terrestrial t e studies the planetary community on the other hand has traditionally used spatio spectral methods that work directly on the sphere thereby avoiding the undesirable distortions and biases inherent in cartesian studies however the models and methods developed for the earth have never been applied to planetary data therefore also limiting further advances in the mapping of planetary t e this paper reviews the latest developments in t e studies and proposes to combine advances in both terrestrial and planetary studies to allow the mapping of t e of terrestrial planets using a spherical wavelet analysis of gravity and topography data we begin with a review of the recent literature on the challenges and debates concerning t e estimation from joint gravity and topography spectra we then briefly review the implementation of the continuous planar and spherical wavelet transforms cpwt and cswt and demonstrate that both transforms possess exactly the same resolving power however the cswt does not suffer from effects associated with non periodic boundaries we further re derive in a consistent manner the expressions for the admittance and coherency from flexural equations for the loading of thin elastic plates and shells and show that they result in similar spectra except at the longest wavelengths where the shell membrane stresses dominate we then estimate global grids of earth s continental t e by inverting the planar and spherical admittance and coherency functions both separately and jointly using either free air or bouguer gravity anomalies the correspondence between the cartesian and spherical approaches and the similarity of t e results for the earth s continents indicate that the spherical methods are robust results obtained from the joint inversion of admittance and coherency show that simple lithospheric loading models fail to capture the complexity of the data with adverse effects on the estimated parameters finally we extend the analysis to the moon and other terrestrial planets and discuss limitations and future applications of the fully spherical techniques

particle size related mineral magnetic source sediment linkages in the rhode river catchment maryland usa characterization of both the source materials and the bottom sediments of an estuary by magnetic characters on a particle size basis allows the source of the bottom sediments to be determined and indicates a shift in sediment sources corresponding to changing land use patterns the major source of the sediments in the lower part of cores from the middle of the estuary is eroding shorelines soil derived particulates from the uplands dominate the upper part of the cores this change in source occurred in the early part of the 19th century the magnetic character of the most recent sediments suggests a progressive depletion through time of the upland soils in the finest fractions

crustal thickness and support of topography on venus united states national aeronautics and space administration nasa planetary geology and geophysics program grant

the dynamical equations of polar wander and the global characteristics of the lithosphere as extracted from rotational data abstract the initial value problem describing the linear responses of the spin axis of a layered viscoelastic planet from surface loading is studied by means of laplace transform techniques a complete solution of polar motion requires the usage of two classes of eigenspectra one arising from viscoelastic relaxation of the mantle due to surface forcing the other involving the gradual readjustment of the spin axis as a consequence of mantle viscoelasticity our analytical 4 layer model comprising an elastic lithosphere a two layer adiabatically stratified viscoelastic mantle and an inviscid core has been incorporated into this formalism in which rotational deformation and isostatic relaxation are taken into account for all times from employing both sets of rotational data polar variations from the 70 years of data from the international latitude service i l s and the non tidal deceleration of the length of the day l o d an estimate of the globally averaged lithosphere of between 130 and 200 km is obtained from the long wavelength flexural mode due to the degree two harmonic this range of values may have strong implications on the mode of continental evolution

constraints on the venusian crustal thickness variations in the isostatic stagnant lid approximation 1 the isostatic stagnant lid isl approximation is applied to the long wavelength venusian topography and geoid to place constraints on the thickness of the crust and lithosphere previous studies showed that a purely thermal isostasy model of the lithosphere the stagnant lid accounts for a significant portion of the topography and geoid anomalies here we assume that the remaining discrepancy between the observed and model geoid is due to crustal thickness variations and that the crust the lithosphere and the mantle are in a state of double isostatic equilibrium the lithosphere is isostatically floating on top of the mantle and the crust is isostatically floating on top of the lithosphere the addition of another variable the crustal thickness allows an exact fit to the observed topography and geoid this also makes the solution non unique an exact fit to topography and geoid can be achieved in a broad range of average lithospheric and crustal thicknesses additional constraints such as the gabbro eclogite phase transition and the existence of relatively young volcanism limit this range to some extent the inferred variations in the crustal thickness are less sensitive to model assumptions and generally agree with the results obtained in previous studies

east west faults due to planetary contraction abstract contraction expansion and despinning have been common in the past evolution of solar system bodies these processes deform the lithosphere until it breaks along faults their characteristic tectonic patterns have thus been sought for on all planets and large satellites with an ancient surface while the search for despinning tectonics has not been conclusive there is good observational evidence on several bodies for the global faulting pattern associated with contraction or expansion though the pattern is seldom isotropic as predicted the cause of the non random orientation of the faults has been attributed either to regional stresses or to the combined action of contraction expansion with another deformation despinning tidal deformation reorientation another cause of the mismatch may be the neglect of the lithospheric thinning at the equator or at the poles due either to latitudinal variation in solar insolation or to localized tidal dissipation using thin elastic shells with variable thickness i show that the equatorial thinning of the lithosphere transforms the homogeneous and isotropic fault pattern caused by contraction expansion into a pattern of faults striking east west preferably formed in the equatorial region by contrast lithospheric thickness variations only weakly affect the despinning faulting pattern consisting of equatorial strike slip faults and polar normal faults if contraction is added to despinning the despinning pattern first shifts to thrust faults striking north south and then to thrust faults striking east west if the lithosphere is thinner at the poles the tectonic pattern caused by contraction expansion consists of faults striking north south i start by predicting the main characteristics of the stress pattern with symmetry arguments i further prove that the solutions for contraction and despinning are dual if the inverse elastic thickness is limited to harmonic degree two making it easy to determine fault orientation for combined contraction and despinning i give two methods for solving the equations of elasticity one numerical and the other semi analytical the latter method yields explicit formulas for stresses as expansions in legendre polynomials about the solution for constant shell thickness though i only discuss the cases of a lithosphere thinner at the equator or at the poles the method is applicable for any latitudinal variation of the lithospheric thickness on iapetus contraction or expansion on a lithosphere thinner at the equator explains the location and orientation of the equatorial ridge on mercury the combination of contraction and despinning makes possible the existence of zonal provinces of thrust faults differing in orientation north south or east west which may be relevant to the orientation of lobate scarps

the large thaumasia graben on mars is it a rift 1 we investigate the morphology and topography of one of the largest fault bounded tectonic structures on mars a complex approximately n s trending system of troughs and scarps at the western border of the thaumasia plateau in the claritas region hereinafter referred to as thaumasia graben or tg it is located between 15 s and 38 s latitude and at 255 e longitude no detailed investigation of its morphotectonic setting has been performed yet the region is a complexly fractured area with a number of different fault sets including simple and complex graben the tg extends over more than 1000 km along its trend averaging 100 km in width and 1 6 km in depth crustal extension is accommodated by the formation of a system of asymmetric graben or halfgraben on the basis of fault orientation and trough depth the tg can be subdivided in a north south direction into three segments except for the northernmost segment the predominant master fault system is located along the eastern flank of the tg highlighting the overall asymmetric architecture fault length segments vary from 50 to 90 km with observable displacements of 1 3 2 2 km crustal extension inferred from gridded mola topography across scarp offsets varies along trend between 0 5 km and 4 km assuming a fault dip of 60 this is relatively moderate extension if compared to terrestrial continental rifts but consistent with extension measured across the tempe rift on mars we find that the thaumasia graben displays some characteristics which are common to terrestrial continental rifts whereas other properties are distinctively not rift like

characterisation of soils by mineral magnetic measurements processes of iron mineral authigenesis diagenesis and dissolution in interaction with primary inputs of iron minerals act to produce vertical differentiation of soil magnetic properties thus magnetic iron oxides in common with other iron forms may both respond to and reflect soil forming processes investigation of the degree of detectable and persistent magnetic differentiation within different soil materials can provide insights into the nature and direction of distinct sets of soil processes evidence of clear association between magnetic variation and discrete types of soil environment also has applied significance in several areas of environmental study for example the observed magnetic variation can be used to discriminate between individual soils and soil horizons for the purposes of soil surveying sediment tagging and tracing and empirical modelling of source sediment linkages this paper reports the use of mineral magnetic techniques to characterise the iron oxide assemblages within soils of varying type and provenance the effect of different pedogenic regimes have been investigated through measurement of a range of magnetic parameters including magnetic susceptibility frequency dependent susceptibility and anhysteretic and saturation remanences contrary to current pedological thought but in accord with other magnetically based studies e g mullins the presence of magnetite maghemite typically of superparamagnetic single domain grain size within soils has been found to be an extremely widespread phenomenon its contemporary neoformation within the soil environment is inferred however the input of artificially generated ferrimagnetic material is indicated for one of the magnetically enhanced soils examined here and the possibility of extraneous sources of magnetite in topsoils should be considered before pedogenic processes of magnetic enhancement are inferred from the data presented discrimination of industrially derived magnetic particles appears possible on the basis of their very low levels of frequency dependent susceptibility fd low anhysteretic remanence arm and dissociation from the finer clay sized not the formation but the active dissolution of ferrimagnetic minerals is indicated for soils affected by the processes of gleying and podsolisation eluvial horizons of podsolised profiles demonstrate almost total loss of detectable magnetic content variations in the form of the iron reprecipitated in the underlying illuvial layers may reflect differences in the pedological characteristics of these horizons within gleyed waterlogged soils processes of magnetite dissolution appear to be grain size specific preferential reduction of those grains of ultrafine superparamagnetic and fine single domain magnetic grain size is indicated where soil forms a major contributor to catchment sediment loads this has significance in the area of source sediment modelling soil derived from permanently wet or highly leached catchment areas is unlikely to contribute to peaks in the magnetic content of deposited sediments further only those erosional processes that operate at a faster rate than those of magnetic depletion will have the capacity to produce peaks in sediment ferrimagnetic concentrations such as have been observed within the historical magnetic record

impact basin relaxation as a probe for the thermal history of pluto we investigate viscoelastic impact basin relaxation on pluto for a variety of thermal evolution scenarios encompassing both convective and conductive ice shells basins smaller than 200 km in diameter do not relax appreciably while relaxation fractions can be up to 60 for large impact basins the main control on basin relaxation is the amount of radiogenic heat produced in the rocky core our results are insensitive to the formation time of the basin the ice reference viscosity adopted and the presence absence of a subsurface ocean other volatiles such as co2 or nh3 if present in the ice shell in sufficient quantities could increase the predicted relaxation fraction of basins relaxation causes extensional stresses interior to the basin the orientation of the resulting tectonic features is controlled by the effective elastic thickness beneath the basin future observations of the relaxation states and tectonics of impact basins are therefore likely to provide a key constraint on pluto s thermal history

bacterial magnetite and the magnetic properties of sediments in a swedish lake a comparison of the magnetic properties of lake sediments and catchment materials from pajep njakajaure north sweden demonstrates that high concentrations of single domain sd magnetite in the upper 70 cm of gyttja in the deepest part of the basin are not of detrital origin tem and light microscope examination revealed the existence of bacterial cells and magnetosomes in the upper sediments which are responsible for the presence of the sd magnetite most of the fossil magnetosomes appear to have been dissolved through reductive processes at lower depths although some are preserved in the lower sediments and carry a post depositional remanent magnetization pdrm the results highlight the complex effects of post depositional processes on mineral magnetic assemblages and natural remanent magnetization aquisition and demonstrate how mineral magnetic measurements may be used to identify magnetic grain size changes brought about by sediment diagenesis

tracer properties of eroded sediment and source material this paper examines the conservativeness of tracers through the sediment generation process this is done by comparing a selection of tracer properties of sediment eroded from large plots by simulated rainfall with the corresponding properties of the source materials within the plots sediment was generated using three simulated rainfall events for each of five selected erosion source types in the tarago catchment victoria australia as there were particle size and organic content differences between the source material and the generated sediment the measured tracer properties of the source material were corrected for these differences the possible role of analytical errors in this investigation was also addressed the geochemical property concentration of fe2o3 was not conservative for any of the process sources investigated concentration of al2o3 was not conservative for three of the four process sources investigated and the sum of molecular proportions of cao na2o k2o and al2o3 was not conservative for two of the four process sources investigated mineral magnetic properties irm850 and were also found to be not conservative although this may be the result of the complex relationship between particle size and mineral magnetic properties not being adequately accommodated in this analysis the radionuclide tracers 137cs and 210pbex were found to be conservative through the sediment generation process copyright 2002 john wiley sons ltd

source parameter inversion for recent great earthquakes from a decade long observation of global gravity fields we quantify gravity changes after great earthquakes present within the 10 year long time series of monthly gravity recovery and climate experiment grace gravity fields using spherical harmonic normal mode formulation the respective source parameters of moment tensor and double couple were estimated for the 2004 sumatra andaman earthquake the gravity data indicate a composite moment of 1 2 1023 n m with a dip of 10 in agreement with the estimate obtained at ultralong seismic periods for the 2010 maule earthquake the grace solutions range from 2 0 to 2 7 1022 n m for dips of 12 24 and centroid depths within the lower crust for the 2011 tohoku oki earthquake the estimated scalar moments range from 4 1 to 6 1 1022 n m with dips of 9 19 and centroid depths within the lower crust for the 2012 indian ocean strike slip earthquakes the gravity data delineate a composite moment of 1 9 1022 n m regardless of the centroid depth comparing favorably with the total moment of the main ruptures and aftershocks the smallest event we successfully analyzed with grace was the 2007 bengkulu earthquake with m0 5 0 1021 n m we found that the gravity data constrain the focal mechanism with the centroid only within the upper and lower crustal layers for thrust events deeper sources i e in the upper mantle could not reproduce the gravity observation as the larger rigidity and bulk modulus at mantle depths inhibit the interior from changing its volume thus reducing the negative gravity component focal mechanisms and seismic moments obtained in this study represent the behavior of the sources on temporal and spatial scales exceeding the seismic and geodetic spectrum

the effects of particle breakage and abrasion on the magnetic properties of two soils as mineral magnetism is used as a tracer for sourcing river and dam sediments changes in the magnetic properties that may occur during transport between the source and sink must be considered abrasion and breakage of particles will occur during transport these processes were examined in simulation experiments with a granitic and a sedimentary soil the effects of these processes on the magnetic properties of a granitic and a sedimentary soil were examined using a simulated breakage abrasion experiment breakage and or abrasion had substantial effects on the magnetic properties of both soils all particle sizes were affected but the magnitude varied through the size range of derived particles the major effect was on the concentration of magnetic minerals with differences between the concentrations in particle sizes of the original material and those generated by the experiments being as much as 20 times the effect on the granite soil was to reduce the concentrations i e derived material was less than original material whereas for the sedimentary soil the derived particles had higher concentrations the effect on magnetic grain size as indicated by the magnetic ratios was less than the effect on the mass magnetic properties but still substantial for some ratios for some sizes 1998 john wiley sons ltd

the effects of particle breakage and abrasion from simulated fluvial transport on phosphorus sorption by two soils phosphorus sorption studies were carried out on particle size fractions of soils collected from the walls of gullies through a granitic and a sedimentary soil as well as on particle size classes derived from breakage and abrasion of the 500 to 1400 m components of these soils sorption of phosphorus by the particle size classes of the sedimentary soil was much greater than those of the granite soil and this also applied to the particles derived from breakage and abrasion for the original sedimentary soil sorption of phosphorus by the particle size components was strongly associated with the iron content and less strongly associated with the aluminium content and this also applied to the particles derived from breakage and abrasion for the granitic soil these relationships were much less precise a period of vigorous mixing after 165 hours of gentle mixing caused release of a proportion of the sorbed phosphorus from all particle sizes of the original granitic soil and for most of the breakage abrasion derived particles the released phosphorus was re sorbed during a subsequent 48 hour period of settling relationships were evident between labile p and sorbed p for the particle size classes of the soils and treatments tested bacause particle size lithology of the transported sediments and flow dynamics affect the distribution of phosphorus between water and sediments they can also be expected to effect bio availability of phosphorus particle breakage and abrasion during sediment transport is another factor likely to influence the bioavailability of p

cenozoic potassium rich mafic volcanism in the western u s a its relationship to deep subduction cenozoic potassium rich volcanism characterized by k 2 o na 2 o and sio 2 60 wt follows a northeast to southwest younging trend in the western u s a correlation of this trend with the outer limits of arc related magmatism based on variable dip subduction models suggests that potassium rich volcanism may be related to deep subduction rather than intraplate tectonics

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

the formation of valles marineris 2 stress focusing along the buried dichotomy boundary 1 although valles marineris is widely regarded as an extensional tectonic feature the source of stress responsible for its formation remains unknown this study argues that the tensile stresses that triggered valles marineris tectonism are a result of its location south of and subparallel to the buried crustal dichotomy boundary beneath tharsis the emplacement of the tharsis volcanic load straddling the pre existing topographic step of the crustal dichotomy boundary would have resulted in an abrupt change in the thickness of the load causing differential subsidence and extension across the boundary thin shell flexural models predict a narrow belt of focused tensile stresses south of the buried dichotomy boundary coinciding with the location of present day valles marineris the interaction of these boundary generated stresses with the competing stress fields associated with tharsis loading can explain the formation of noctis labyrinthus in the west and the deflection of the valles marineris troughs away from the buried boundary toward the east finite element models demonstrate that the magnitudes and vertical variations of stress at valles marineris are sensitive to the timing of loading and flexure in tharsis the incremental loading and flexure expected for a large volcanic rise results in the maximum tensile stress at valles marineris occurring at depth with tensile stresses through the majority of the lithospheric column dikes forming within this tensile stress belt would propagate through the full vertical extent of the lithosphere due to the stress release associated with the dilation of the dikes playing a crucial role in the formation of the valles marineris troughs

measurements of the elastic thickness under ancient lunar terrain abstract the part of a planet s gravity that is coherent with its topography provides information about the deflection of its crust after loading and hence the resistance of its lithosphere to bending at the time the load was emplaced we used observed line of sight accelerations from lunar prospector together with the accelerations we would have expected if anomalies in the gravity field were only caused by topography to estimate the admittance and coherence between topography and gravity over several regions of the lunar nearside we then compared our estimates to what we would expect if the lithosphere behaved as a floating elastic plate or shell assuming a linear relationship between topography and gravity we found in the region surrounding the southern highland crater clavius that the data can be modeled using a thin plate with t e 12 5 km and uncorrelated loads at the surface and base of the upper crust a spherical shell model with surface loading is less satisfactory to fit the admittance adequately requires topography with wavelengths over 400 km to be formed when t e 1 km and the remainder when t e 7 5 km by contrast the apparent lack of compensation around the youngest giant impact basins requires a plate with t e 80 km or a shell with t e 25 km our results indicate the thickness of the lunar lithosphere increased from 12 km in the pre nectarian to 25 km in the nectarian

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

sediment tracing in a reservoir catchment system using a magnetic mixing model magnetic mixing models are developed for specific susceptibility and a demagnetisation parameter which demonstrate how the magnetic properties of soils are altered by mixing these phenomena are used to interpret the composition of reservoir sediments in terms of the relative proportions of two types of source materials top soil and sub soil which are eroded from the catchment area and deposited in the reservoir the model provides a black box approach to the reservoir catchment system dependent on four simplifying assumptions which are the subject of current research application of the model to an afforested catchment suggests a marked change in the types of erosion processes associated with the maturation of the forestry plantation over a period of 50 yr

role of membrane stresses in the support of planetary topography the principal purpose of this paper is to examine whether membrane stresses can support topographic loads on planetary elastic lithospheres it is found that the ability of a spherical shell to support loads through membrane stresses is determined by the nondimensional parameter ed gr2 where d is the thickness of the elastic lithosphere is the density difference between the mantle and crust and r is the radius of the planetary body when this parameter is large membrane stresses can fully support topographic loads without flexure and when it is small the influence of membrane stresses can be neglected solutions of the equation governing the behavior of a spherical shell are obtained for a topographic load expressed in terms of spherical harmonics spherical harmonic expansions of the measured gravity and topography for mars and the moon are compared with the theory it is found that for mars the support of topography is primarily due to membrane stresses for n 8 and for the moon for n 17 for mars the data for 4 n 7 give 0 5 for the moon the data have considerable scatter that is attributed to the mascons but generally correlate with 0 5 if bending stresses are neglected the governing equation for the deflection of the spherical shell is legendre s equation a general solution is obtained for an axisymmetric load this solution is applied to the tharsis region on mars the 60 65 compensation of this region requires that 0 6 the well defined fracture pattern surrounding the tharsis region is attributed to tensional membrane stresses

isostatic compensation of equatorial highlands on venus abstract spherical harmonic models for venus global topography and gravity incorporating magellan data are used to test isostatic compensation models in five 30 30 regions representative of the main classes of equatorial highlands the power spectral density for the harmonic models obeys a power law scaling with spectral slope 2 brown noise for the topography and 3 kaula s law for the geoid similar to what is observed for earth the venus topography spectrum has lower amplitudes than earth s which reflects the dominant lowland topography on venus observed degree geoid to topography ratios gtrs on venus are significantly smaller than degree gtrs for uncompensated topography indicative of substantial compensation assuming a global airy compensation most of the topography is compensated at depths greater than 100 km suggesting a thick lithosphere on venus for each region considered we obtain a regional degree of compensation c from a linear regression of bouguer anomaly versus bouguer gravity data geoid anomaly n versus topography variation h data for each sample were compared in the least squares sense to theoretical correlations for pratt airy and thermal thinning isostasy models yielding regional gtr zero elevation crustal thickness h and zero elevation thermal lithosphere thickness y l 0 respectively we find the regional compensation to be substantial c 52 90 and the h n data correlations in the chosen areas can be explained by isostasy models applicable on the earth and involving variations in crustal thickness airy and or lithospheric thermal thinning thickness however a thick crust and lithosphere y l 0 300 km must be assumed for venus compensation mechanisms are distributed as follows for the high plateaus of ovda gtr 9 m km and thetis gtr 11 m km mainly airy isostasy with h 50 60 km for the chasmata area sample gtr 15 m km airy with perhaps a thermal component finally a very strong thermal component for the broad swells of beta gtr 32 m km and atla gtr 25 m km with the lithosphere thinned to 100 km aphrodite terra which shows a marked eastward increase in pratt and airy model parameter values could be a candidate for thermal isostasy decay from east to west

tracing movements of topsoil by magnetic measurements two case studies an array of magnetic measurements is used to trace the occurrence of magnetically enhanced topsoil in two different environmental settings the first is a cultivated slope section where the results confirm that movements of topsoil have occurred but that identification of specific erosional processes is problematic the second is a lake catchment system where measurements on soils and sediments allow a partial reconstruction of soil movements from different sources over the last 200 y the study highlights both the need to analyse the magnetic mineralogies of different particle size fractions and the difficulties that may be encountered in trying to discriminate between topsoil and subsoil material on the basis of demagnetization parameters alone

correction to localized gravity topography admittance and correlation spectra on mars implications for regional and global evolution 1 in the paper localized gravity topography admittance and correlation spectra on mars implications for regional and global evolution by patrick j mcgovern sean c solomon david e smith maria t zuber mark simons mark a wieczorek roger j phillips gregory a neumann oded aharonson and james w head journal of geophysical research 107 e12 5136 doi 10 1029 2002je001854 2002 the thickness of the lithosphere and lithospheric heat flow for a number of regions of mars and as functions of time were inferred on the basis of gravity topography admittance spectra observed admittances derived from spherical harmonic expansions localized with the scheme of simons et al 1997 were compared with those predicted from models for the flexural response to lithospheric loading e g turcotte et al 1981 gravity was calculated according to the finite amplitude scheme of wieczorek and phillips 1998 estimates for the thickness of the elastic lithosphere te at the time of loading for each region were converted to equivalent thermal gradient dt dz and heat flux q by means of an elastic plastic stressenvelope formalism mcnutt 1984 here we describe a correction required in the calculation of the modeled gravity anomalies we report new estimates of te load density rl dt dz and q from corrected model admittances and we discuss the implications of the new results 2 the source of the required correction is a difference in reference radius values as defined by mcgovern et al 2002 the planetary shape was taken to equal the radius from the center of mass of mars to the martian surface expressed as a spherical harmonic expansion and referenced to the mean equatorial radius req 3396 km

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

a post accretionary lull in large impacts on early mars the timing and number of large impact basins on early mars are poorly constrained gravity and topographic analyses support a lull in basin forming impacts following the main stage of accretion

sediment source tracing using environmental magnetism a new approach with examples from australia environmental magnetism can be used for sediment source tracing in situations such as stream junctions where two catchments deliver magnetically distinguishable well combined average source mixes to a trunk stream consistent mineral magnetic parameter relationships show that spatially and temporally constant magnetic mineral assemblages occur along reaches of natural streams for most of the confluence mixing situations examined it is possible to distinguish between tributaries using magnetic parameter relationships using these relationships relative tributary contributions to the resultant downstream mix can be quantified the method can be used for tracing suspended and bedload sediments so that the principal source catchments can be determined by a sequence of measurements at stream junctions along a drainage network there is considerable potential for using this new and easily applied method for studies of sediment delivery processes and sediment movement in fluvial environments

claritas rise mars pre tharsis magmatism claritas rise is a prominent ancient noachian center of tectonism identified through investigation of comprehensive paleotectonic information of the western hemisphere of mars this center is interpreted to be the result of magmatic driven activity including uplift and associated tectonism as well as possible hydrothermal activity coupled with its ancient stratigraphy high density of impact craters and complex structure a possible magnetic signature may indicate that it formed during an ancient period of mars evolution such as when the dynamo was in operation as tharsis lacks magnetic signatures claritas rise may pre date the development of tharsis or mark incipient development since some of the crustal materials underlying tharsis and older parts of the magmatic complex respectively could have been highly resurfaced destroying any remanent magnetism here we detail the significant characteristics of the claritas rise and present a case for why it should be targeted by the mars odyssey mars reconnaissance orbiter and mars express spacecrafts as well as be considered as a prime target for future tier scalable robotic reconnaissance