gravity field of the moon from the gravity recovery and interior laboratory grail mission spacecraft to spacecraft tracking observations from the gravity recovery and interior laboratory grail have been used to construct a gravitational field of the moon to spherical harmonic degree and order 420 the grail field reveals features not previously resolved including tectonic structures volcanic landforms basin rings crater central peaks and numerous simple craters from degrees 80 through 300 over 98 of the gravitational signature is associated with topography a result that reflects the preservation of crater relief in highly fractured crust the remaining 2 represents fine details of subsurface structure not previously resolved grail elucidates the role of impact bombardment in homogenizing the distribution of shallow density anomalies on terrestrial planetary bodies

apollo 16 regolith breccias characterization and evidence for early formation in the mega regolith all of the apollo 16 regolith breccias 8 specimens have been characterized in terms of their petrography grain size distribution porosity major and trace element composition noble gas contents and ferromagnetie resonance properties these breccias vary signkqcantly with respect to their density and porosity with the more dense breccias showing significant shock damage the regolith breccias resemble the soils in grain size distribution and in the relative proportions of major petrological components except agglutinates many of the breecias are compositionally different from the apollo 16 soils in that they lack an important marie component present in the soils although some groupings occur the petrologic and chemical compositions of the regolith breedas do not correlate with the station location of the samples all but one of the breceias show some evidence of irradiation at the lunar surface solar gases measurable fmr agglutinates and analyses made on grain size separates from two disaggregated breedas indicate that this irradiation occurred before compaction when the breccia material was finely disseminated on the surface however the concentrations of surface irradiation parameters solar gases fmr agglutinates for most breedas are far less than seen in any lunar soils or in regolith breccias from other apollo missions several breedas also contain unusually high trapped 4oar 36ar ratios of 8 12 and a significant fission xe component in excess of that expected from in situ production these observations suggest that the surface irradiation of these breedas occurred as early as 4 x 109 years ago we conclude that most of the apollo 16 regolith breedas were not formed from any known apollo 16 soil they appear to be well comminuted material that contains ancient regolith developed during the late stage heavy bombardment of the moon when large impacts were much more common relative to small impacts so that regoliths did not have time to significantly mature before being diluted by fresh ejecta and buffed this ancient megaregolith is significantly different from more recent lunar regolith but may be similar to asteroidal regoliths from which some brecciated meteorites have formed

summary of the results from the lunar orbiter laser altimeter after seven years in lunar orbit in june 2009 the lunar reconnaissance orbiter lro spacecraft was launched to the moon the payload consists of 7 science instruments selected to characterize sites for future robotic and human missions among them the lunar orbiter laser altimeter lola was designed to obtain altimetry surface roughness and reflectance measurements the primary phase of lunar exploration lasted one year following a 3 month commissioning phase on completion of its exploration objectives the lro mission transitioned to a science mission after 7 years in lunar orbit the lola instrument continues to map the lunar surface the lola dataset is one of the foundational datasets acquired by the various lro instruments lola provided a high accuracy global geodetic reference frame to which past present and future lunar observations can be referenced it also obtained high resolution and accurate global topography that were used to determine regions in permanent shadow at the lunar poles lola further contributed to the study of polar volatiles through its unique measurement of surface brightness at zero phase which revealed anomalies in several polar craters that may indicate the presence of water ice in this paper we describe the many lola accomplishments to date and its contribution to lunar and planetary science

laboratory study of loose saturated and unsaturated decomposed granitic soil weathered soils are used extensively as fill materials in slope construction in tropical and subtropical cities such as hong kong the mechanical behavior of loose decomposed fill materials particularly in the unsaturated state has not often been investigated and is not yet fully understood the objective of this study was to understand the mechanical behavior of loose unsaturated decomposed granitic soil and to study the effects of the stress state the stress path and the soil suction on the stress strain relationship shear strength volume change and dilatancy via three series of stress path triaxial tests on both saturated and unsaturated specimens it was found that loose and saturated decomposed granitic soil behaves like clean sands during undrained shearing strain softening behavior is observed in loose saturated specimens in unsaturated specimens sheared at a constant water content a hardening stress strain relationship and volumetric contractions are observed in the considered range of net mean stresses the suction of the soil contributed little to the apparent cohesion the angle of friction appeared to be independent of the suction in unsaturated specimens subjected to continuous wetting suction reduction at a constant deviator stress the volumetric behavior changed from dilative to contractive with increasing net mean stress and the specimen failed at a degree of saturation far below full saturation it was revealed that the dilatancy of the unsaturated soil depends on the suction the state and the stress path

the shape of 433 eros from the near shoemaker laser rangefinder measurements from the near earth asteroid rendezvous near shoemaker laser rangefinder nlr indicate that asteroid 433 eros is a consolidated body with a complex shape dominated by collisions the offset between the asteroid s center of mass and center of figure indicates a small deviation from a homogeneous internal structure that is most simply explained by variations in mechanical structure regional scale relief and slope distributions show evidence for control of topography by a competent substrate impact crater morphology is influenced by both gravity and structural control small scale topography reveals ridges and grooves that may be generated by impact related fracturing

zonal and vertical structure of the madden julian oscillation abstract a statistical study of the three dimensional structure of the madden julian oscillation mjo is carried out by projecting dynamical fields from reanalysis and radiosonde data onto space time filtered outgoing longwave radiation olr data mjo convection is generally preceded by low level convergence and upward motion in the lower troposphere while subsidence cooling and drying prevail aloft this leads to moistening of the boundary layer and the development of shallow convection followed by a gradual and then more rapid lofting of moisture into the middle troposphere at the onset of deep convection after the passage of the heaviest rainfall a westerly wind burst region is accompanied by stratiform precipitation where lower tropospheric subsidence and drying coincide with continuing upper tropospheric upward motion the evolution of the heating field leads to a temperature structure that favors the growth of the mjo the analysis also reveals distinct differences in the vertical structure

dawn arrives at ceres exploration of a small volatile rich world on 6 march 2015 dawn arrived at ceres to find a dark desiccated surface punctuated by small bright areas parts of ceres surface are heavily cratered but the largest expected craters are absent ceres appears gravitationally relaxed at only the longest wavelengths implying a mechanically strong lithosphere with a weaker deep interior ceres dry exterior displays hydroxylated silicates including ammoniated clays of endogenous origin the possibility of abundant volatiles at depth is supported by geomorphologic features such as flat crater floors with pits lobate flows of materials and a singular mountain that appears to be an extrusive cryovolcanic dome on one occasion ceres temporarily interacted with the solar wind producing a bow shock accelerating electrons to energies of tens of kilovolts

global structure of asteroid 433 eros 1 models of asteroid formation and evolution suggest a variety of internal structures ranging from gravitationally bound accumulations of debris to fully rigid monolithic bodies the near shoemaker spacecraft has provided detailed imaging and gravity data relevant to the characteristics of structural features and global mass properties a long ridge coplanar with a degraded trough ridge system and an approximately parallel surface facet suggest exploitation of a nearly global fabric by both compressive and extensional failure at significantly different times

mass and local topography measurements of itokawa by hayabusa the ranging instrument aboard the hayabusa spacecraft measured the surface topography of asteroid 25143 itokawa and its mass a typical rough area is similar in roughness to debris located on the interior wall of a large crater on asteroid 433 eros which suggests a surface structure on itokawa similar to crater ejecta on eros the mass of itokawa was estimated as 3 58 0 18 1010 kilograms implying a bulk density of 1 95 0 14 grams per cubic centimeter for a volume of 1 84 0 09 107 cubic meters and a bulk porosity of 40 which is similar to that of angular sands when assuming an ll low iron chondritic meteorite composition combined with surface observations these data indicate that itokawa is the first subkilometer sized small asteroid showing a rubble pile body rather than a solid monolithic asteroid

vesta s shape and morphology vesta s surface is characterized by abundant impact craters some with preserved ejecta blankets large troughs extending around the equatorial region enigmatic dark material and widespread mass wasting but as yet an absence of volcanic features abundant steep slopes indicate that impact generated surface regolith is underlain by bedrock dawn observations confirm the large impact basin rheasilvia at vesta s south pole and reveal evidence for an earlier underlying large basin veneneia vesta s geology displays morphological features characteristic of the moon and terrestrial planets as well as those of other asteroids underscoring vesta s unique role as a transitional solar system body

compaction behaviour of clay this paper presents an experimental study of the compaction behaviour of non active clay one dimensional static compaction tests were carried out at high and medium water content with matric suction monitoring using trento high capacity tensiometers at lower water contents a transistor psychrometer was used to measure post compaction suction samples were compacted on the dry side of optimum to cover a wide range of compaction water contents and vertical stresses three water content regions were identified in the compaction plane depending on whether post compaction suction increased decreased or remained constant as the degree of saturation was increased at constant water content hydraulic paths of specimens subjected to loading unloading cycles at constant water content have clearly shown that post compaction suction may increase as the degree of saturation increases this non intuitive behaviour was demonstrated to be associated with the coupling between mechanical and water retention behaviour to this end a coupled mechanical water retention model was formulated irreversible one dimensional mechanical paths were modelled by a boundary surface in the space average skeleton vertical stress modified suction and void ratio irreversible hydraulic wetting paths were modelled by a boundary surface in the space suction degree of saturation and void ratio this study was completed by investigating the pore size distribution of compacted samples through mip tests

the violent collisional history of asteroid 4 vesta vesta is a large differentiated rocky body in the main asteroid belt that accreted within the first few million years after the formation of the earliest solar system solids the dawn spacecraft extensively imaged vesta s surface revealing a collision dominated history results show that vesta s cratering record has a strong north south dichotomy vesta s northern heavily cratered terrains retain much of their earliest history the southern hemisphere was reset however by two major collisions in more recent times we estimate that the youngest of these impact structures about 500 kilometers across formed about 1 billion years ago in agreement with estimates of vesta asteroid family age based on dynamical and collisional constraints supporting the notion that the vesta asteroid family was formed during this event

influence of compaction procedure on the mechanical behaviour of an unsaturated compacted clay part 2 shearing and constitutive modelling the influence of compaction pressure compaction water content and type of compaction static or dynamic on subsequent soil behaviour was investigated by conducting controlled suction triaxial tests on samples of unsaturated compacted speswhite kaolin compaction pressure influences initial state by determining the initial position of the yield surface thus affecting among other things the shape of stress strain curves during shearing compaction pressure also influences to a limited degree the positions of the normal compression lines for different values of suction but it has no effect on critical state relationships the effect of compaction pressure can probably be modelled solely in terms of initial state if an anisotropic elastoplastic model incorporating rotational hardening is employed whereas the parameters defining the slopes and intercepts of the normal compression lines for different values of suction require adjustment with variation of compaction pressure if a conventional isotropic

phobos grooves and impact craters a stereographic analysis abstract phobos parallel grooves were first observed on viking images 38 years ago and since then they have been greatly debated leading to several formation hypotheses nevertheless none of them have been favoured and widely accepted in this work we provide a different approach assuming that phobos grooves can be the expression of fracture planes and deriving their spatial distribution and orientation on 3d reconstructions we point out that any origin related only to craters at phobos surface should be ruled out since the majority of the grooves is unrelated to any craters now present at its surface this raises the intriguing possibility that such grooves if expression of fracture planes are remnant features of an ancient parent body from which phobos could have originated such scenario has never been considered for phobos though this origin was already proposed for the formation of 433 eros grooves buczkowski d l barnouin jha o s prockter l m 2008 icarus 193 39 if this idea holds true the observed groove distribution could be explained as the result of possible major impacts on the larger parent body which were inherited by the phobos shard

isostatic compensation of the lunar highlands the lunar highlands are isostatically compensated at large horizontal scales but the specific compensation mechanism has been difficult to identify with topographic data from the lunar orbiter laser altimeter and gravity data from the gravity recovery and interior laboratory we investigate support of highland topography poor correlation between crustal density and elevation shows that pratt compensation is not important in the highlands using spectrally weighted admittance we compared observed values of geoid to topography ratio gtr with those predicted by isostatic models observed gtrs are 25 8 7 5 5 7 m km for the nearside highlands and 39 3 5 7 6 2 m km for the farside highlands these values are not consistent with flexural compensation of long wavelength topography or airy isostasy defined under an assumption of equal mass in crustal columns instead the observed gtr values are consistent with models of airy compensation in which isostasy is defined under a requirement of equal pressures at equipotential surfaces at depth the gravity and topography data thus reveal that long wavelength topography on the moon is most likely compensated by variations in crustal thickness implying that highland topography formed early in lunar history before the development of a thick elastic lithosphere

mars pathfinder spectral measurements of phobos and deimos comparison with previous data the imager for mars pathfinder imp acquired four spectra of parts of the sub mars hemispheres of phobos and deimos the measured region of phobos is expected to be a mixture of the two spectral units identified on that satellite from phobos 2 data and the imp spectra of phobos are intermediate to the two units as expected the derived geometric albedo is consistent with the value for that part of phobos determined from viking imagery the imp spectrum of deimos is generally consistent with previous measurements acquired from the ground and from the hubble space telescope hst but the signal to noise ratio is lower than that of the phobos data the spectral contrast between the two moons is similar to that seen in hst and phobos 2 data mars pathfinder measurements therefore substantiate recent results which indicate that phobos and deimos are not as previously believed analogous to c type asteroids they also provide some indications for an absorption near 700 nm perhaps like that seen in other low albedo asteroids both martian moons are redder than most asteroids and most closely resemble two analog materials believed to have undergone very dissimilar histories primitive d like asteroids and highly space weathered mafic rich assemblages such as are present in lunar mare soils

results from the ism experiment the imaging spectrometer ism operating in the near infrared is the first ever flown in space for planetary observation with a spectral range of 0 76 3 14 m its main goals were to obtain information on the mineralogical composition of the surfaces of mars and phobos and on the composition spatial and temporal variations of the martian atmosphere the infrared imaging spectrometer ism acquired 40 000 spectra of mars and phobos here we present the first results on the surface mineralogy of mars and phobos and the atmospheric composition of mars

loss of water from phobos a quantitative model of the migrational history of any free water in the martian satellite phobos is presented results include predicted depths of retained ice and current water fluxes as a function of latitude regolith porosity and effective pore size it is found that despite phobos small size low albedo and proximity to the sun ice may be present within the sounding depth of the grunt experiment on the soviet phobos mission at least at mid to high latitudes implications for other experiments on the phobos mission are also discussed

isostatic equilibrium in spherical coordinates and implications for crustal thickness on the moon mars enceladus and elsewhere miller institute for basic research in science at the university of california berkeley nasa gravity recovery and interior laboratory guest scientist program

experimental observations of the stress regime in unsaturated compacted clay when laterally confined construction processes often involve reformation of the landscape which will inevitably encompass compaction of artificially placed soils a common application of fill materials is their use as backfill in many engineering applications for example behind a retaining wall the post construction behaviour of clay fills is complex with respect to stresses and deformation when the fills become saturated over time heavily compacted fills swells significantly more than the lightly compacted fills this will produce enhanced lateral stresses if the fill is laterally restrained the work presented in this paper examines how the stress regime in unsaturated clay fills changes with wetting under laterally restrained conditions specimens of compacted kaolin with different initial conditions were wetted to various values of suction under zero lateral strain at constant net overburden pressure which allowed the concept of k0 the ratio between the net horizontal stress and the net vertical stress to be examined

yield states and stress strain relationships in a natural plastic clay reply natural clays are commonly anisotropic due to their mode of deposition and lightly overconsolidated because of a variety of subsequent geological processes they exhibit marked changes in stiffness when they yield yield stresses from individual tests can be generalized into a yield surface for the clay if displacements during loading are taken into account by calculating specific volumes v 1 e throughout the tests this paper describes tests on 76 mm diameter triaxial samples of natural plastic lake agassiz clay from winnipeg the samples were carefully trimmed reconsolidated to approximately their in situ stresses and loaded in stress controlled tests along various stress paths in p q stress space the tests produced well defined yield envelopes in p q p v and q v plots and in corresponding plots where the stresses were normalized with respect to the vertical preconsolidation pressure vc comparison of one dimensional yielding states with results from k0 triaxial tests that were continu

an improved jpl mars gravity field and orientation from mars orbiter and lander tracking data abstract the mars gravity field resolution is mostly determined by the lower altitude mars reconnaissance orbiter mro tracking data with nearly four years of additional mro and mars odyssey tracking data since the last jpl released gravity field mro110c and lander tracking from the mer opportunity rover the gravity field and orientation of mars have been improved the new field mro120d extends the maximum spherical harmonic degree slightly to 120 improves the determination of the higher degree coefficients as demonstrated by improved correlation with topography and reduces the uncertainty in the corresponding mars orientation parameters by up to a factor of two versus previously combined gravity and orientation solutions the new precession solution is 7608 3 2 1 mas yr and is consistent with previous results but with a reduced uncertainty by 40 the love number solution k2 0 169 0 006 also shows a similar result to previous studies

abundance and distribution of ultramafic microbreccia in moses rock dike quantitative application of mapping spectroscopy moses rock dike is a tertiary diatreme containing serpentinized ultramafic microbreccia sum located on the colorado plateau in utah field evidence indicates that sum was emplaced first followed by breccias derived from the permian strata exposed in the walls of the diatreme and finally by complex breccias containing basement and mantle derived rocks sum is primarily found dispersed throughout the matrix of the diatreme we examined the nature of sum abundance and spatial distribution using data collected remotely by the airborne imaging spectometer ais the minerals serpentine gypsum and illite as well as desert varnish and the lithologies sum and various sandstones were identified from the ais data six end members sum two types of sandstone gypsiferous soil clay rich soil desert varnish were chosen to represent the dominant lithologies of the surface in moses rock dike region spectra of these end members were used in an intimate mixing model to deconvolve the ais spectral data into surface abundance coefficients for each component using a nonnegative least squares inverse algorithm the results of this calculation of surface composition are consistent with field observations and investigations sum distribution and abundance in the matrix of the diatreme were examined in detail and two distinct styles of sum dispersion were observed one style is characterized by high to moderate sum abundance surrounded by halos of lesser sum abundance the dispersion halos grade steeply into regions of the matrix with little to no sum the second style is characterized by moderate sum abundances and broad dispersion halos with sum distributed across the entire width of the diatreme these dispersion styles are consistent with emplacement of the dike as a fluidized solid volatile system where sum which is emplaced early becomes reincorporated into the turbulent flow of the diatreme by abrasion and comminution by paniculate matter carried along in the eruption this eroded material is then dispersed throughout the matrix by eddy diffusion the first style represents an early arrested phase of the eruption sequence while the second style represents a more mature phase distributions of the second style probably indicate the location of channels where flow was concentrated during later stages of eruption since both styles are observed at the same level of erosion this indicates that the duration of eruption varied along strike at moses rock dike

grail gravity constraints on the vertical and lateral density structure of the lunar crust we analyzed data from the gravity recovery and interior laboratory grail mission using a localized admittance approach to map out spatial variations in the vertical density structure of the lunar crust mare regions are characterized by a distinct decrease in density with depth while the farside is characterized by an increase in density with depth at an average gradient of 35 kg m 3 km 1 and typical surface porosities of at least 20 the apollo 12 and 14 landing site region has a similar density structure to the farside permitting a comparison with seismic velocity profiles the interior of the south pole aitken sp a impact basin appears distinct with a near surface low density porous layer 2 3 times thinner than the rest of the farside this result suggests that redistribution of material during the large sp a impact likely played a major role in sculpting the lunar crust

propagation of the madden julian oscillation through the maritime continent and scale interaction with the diurnal cycle of precipitation the convectively active part of the madden julian oscillation mjo propagates eastward through the warm pool from the indian ocean through the maritime continent the indonesian archipelago to the western pacific the maritime continent s complex topography means the exact nature of the mjo propagation through this region is unclear model simulations of the mjo are often poor over the region leading to local errors in latent heat release and global errors in medium range weather prediction and climate simulation using 14 northern winters of trmm satellite data it is shown that where the mean diurnal cycle of precipitation is strong 80 of the mjo precipitation signal in the maritime continent is accounted for by changes in the amplitude of the diurnal cycle additionally the relationship between outgoing long wave radiation olr and precipitation is weakened here such that olr is no longer a reliable proxy for precipitation the canonical view of the mjo as the smooth eastward propagation of a large scale precipitation envelope also breaks down over the islands of the maritime continent instead a vanguard of precipitation anomalies of 2 5 mm day 1 over 10 6 km 2 jumps ahead of the main body by approximately 6 days or 2000 km hence there can be enhanced precipitation over sumatra borneo or new guinea when the large scale mjo envelope over the surrounding ocean is one of suppressed precipitation this behaviour can be accommodated into existing mjo theories frictional and topographic moisture convergence and relatively clear skies ahead of the main convective envelope combine with the low thermal inertia of the islands to allow a rapid response in the diurnal cycle which rectifies onto the lower frequency mjo hence accurate representations of the diurnal cycle and its scale interaction appear to be necessary for models to simulate the mjo successfully

gravity field expansion in ellipsoidal harmonic and polyhedral internal representations applied to vesta abstract a 20th degree ellipsoidal harmonic gravity field of vesta is determined by processing radiometric doppler and range data from the dawn mission the gravity field shows sensitivity up to degree 18 and the coefficients are globally determined on average to degree 15 gravity anomalies are mapped to the brillouin ellipsoid 304 289 247 km which is a substantially closer fit to the surface than the reference ellipsoid 290 290 265 km used to map the conventional spherical harmonic series especially near the poles two models of internal structure are subsequently explored in which density variations are permitted in the uppermost layer i e crust in order to explain vesta s local gravitational signature these models include the case of a two layer model with an average crustal thickness of 55 5 km and a three layer model with an average crustal thickness of 22 4 km for both two layer and three layer scenarios the bouguer gravity anomaly is minimized for a crustal density of 2970 kg m 3 the remaining bouguer anomalies can be explained by lateral crustal density variation of 2310 3440 kg m 3 and 2660 3240 kg m 3 for the 22 4 km and 55 5 km crustal thickness models respectively the general trend of the estimated lateral crustal densities for the two cases is very similar with a wider range for the 22 4 km case due to a thinner crust this indicates that a thick crust e g 55 5 km would be more favorable for minimizing the range of lateral crustal density variations consideration of independent geochemical and petrological constraints suggests that a three layer model is a more appropriate representation of vesta s internal structure despite the fact that two layer models provide a satisfactory fit to gravity data alone in detail it is found that densities derived from gravity data assuming three layer models and those derived from the howardite eucrite diogenite meteorites and estimates of plausible bulk vesta composition show an excellent level of mutual consistency

drainage pits in cohesionless materials implications for the surface of phobos viking orbiter images show grooves and chains of pits crossing the surface of phobos many of which converge toward the large crater stickney or its antipode although it has been proposed that the pits and grooves are chains of secondary craters their morphology and geometric relations suggest that they are the surface traces of fractures in the underlying solid body of phobos several models have been proposed to explain the pits of which the most plausible are gas venting and drainage of regolith into open fractures the latter mechanism is best supported by the image data and is the mechanism studied in this investigation drainage pits and fissures are modeled experimentally by using two rigid substrate plates placed edge to edge and covered by uniform thicknesses of dry fragmental debris simulated regolith fracture extension is simulated by drawing the plates apart allowing drainage of regolith into the newly created void a typical drainage experiment begins with a shallow depression on the surface of the regolith above the open fissure increased drainage causes local drainage pits to form continued drainage causes the pits to coalesce forming a cuspate groove the resulting experimental patterns of pits and grooves have pronounced similarities to those observed on phobos characteristics such as lack of raised rims linearity of grooves and chains of pits uniform spacing of pits and progression from discrete pits to cuspate grooves are the same in the experiments and on phobos in contrast gas venting pits occur in irregular chains and have raised rims these experiments thus indicate that the phobos grooves and pits formed as drainage structures the pit spacing in an experiment is measured at the time that the maximum number of pits forms prior to groove development the average pit spacing is compared to the regolith thickness for each material regression line fits indicate that the average spacing of drainage pits in unconsolidated noncohesive regolith is nearly equal to the thickness of regolith and appears to gbe independent of the angle of repose within the resolution of our experiments this provides a simple means of estimating regolith thickness where drainage pits are present on phobos two locations differing by 90 degrees in longitude have average pit spacings that suggest regolith thicknesses of 290 and 300 m suggesting that large areas of phobos have a nearly uniform regolith thickness of approximately 300 m

topographic power spectra of cratered terrains theory and application to the moon impact cratering produces characteristic variations in the topographic power spectral density psd of cratered terrains which are controlled by the size frequency distribution of craters and the spectral content shape of individual features these variations are investigated here in two parallel approaches first a cratered terrain model based on monte carlo emplacement of craters and benchmarked by an analytical formulation of the one dimensional psd is employed to generate topographic surfaces at a range of size frequency power law exponents and shape dependencies for self similar craters the slope of the psd varies inversely with that of the production function leveling off to 0 at high surface topography dominated by the smallest craters and maintaining a roughly constant value 2 at low surface topography dominated by the largest craters the effects of size dependent shape parameters and various crater emplacement rules are also considered second we compare the model derived predictions for the behavior of the psd with values of calculated along transects from the lunar orbiter laser altimeter lola at small scales 115 m to 1 km model predictions agree well with the psd slope over the observed range of lunar size frequency distributions differences between global psd slopes at subkilometer and kilometer scales reflect a scale separation in roughness consistent with prior observations using a variety of surface roughness parameters understanding the statistical markers left by the impact cratering process on the lunar surface is useful for distinguishing between competing geological processes on planetary surfaces throughout the solar system

observational evidence of crystalline iron oxides on mars visible to near ir 0 4 1 0 mu m spectral reflectance observations of mars during the 1988 opposition were performed at mauna kea observatory using a circular variable filter spectrometer at a spectral resolution r lambda delta lambda approx 80 on august 13 and 14 1988 ut 41 regions 500 600 km in diameter were observed on mars the data have been reduced both to reflectance relative to solar analog mars 16 cyg b and to relative reflectance spot spot the spectra show the strong near uv reflectance dropoff characteristic of mars as well as absorptions at 0 62 0 72 mu m and 0 81 0 94 mu m both seen here clearly for the first time these absorption features are interpreted as fe sup 3 electronic transition bands that indicate the presence of crystalline ferric oxide or hydroxide minerals on the martian surface comparison of these data with laboratory spectra obtained by other workers supports the conclusion that a single iron oxide phase most likely hematite could account for all of the observed spectral behavior of the martian surface soils and airborne dust in the 0 4 1 0 mu m region this possibility must be reconciled with data from other possible spectral analogs and other wavelength regions as well as geochemical and mineral stability considerations to arrive at amore more complete understanding of the role of ferric minerals in martian surface mineralogy and weathering less

additional evidence about an early intense flux of c asteroids and the origin of phobos abstract the preponderance of cm clasts among the foreign fragments in polymict meteoritic breccias including basaltic achondritic hosts indicates collisions of cm carbonaceous parent bodies believed to be c class asteroids with noncarbonaceous asteroids after differentiation of some of the latter this supports the suggestion developed in an earlier paper that a flux of predominantly c like asteroids was scattered around the solar system as jupiter approached its present mass together with the low density measured for phobos this supports a hypothesis of origin for phobos and certain other satellites as captured carbonaceous c like asteroids

the density and porosity of meteorites from the vatican collection abstract we have developed a nondestructive technique to measure the densities and porosities of large 50 g to several kilogram meteorite samples and have begun a systematic measurement program starting with meteorites from the vatican observatory collection our technique utilizes a modified archimedean method 40 m glass spheres substituting for the fluid to determine bulk density and an unusually large he pycnometer to determine grain density from these the porosity is calculated we report here our first results for 89 samples nearly doubling the published database on porosities of meteorite hand samples including porosities of 35 different meteorites these include several types not previously reported eight iron meteorites six stony iron meteorites an enstatite chondrite the ci carbonaceous chondrite orgueil and the shergottite nakhlatite chassignite snc meteorite nakhla

enceladus s and dione s floating ice shells supported by minimum stress isostasy enceladus gravity and shape have been explained in terms of a thick isostatic ice shell floating on a global ocean in contradiction of the thin shell implied by librations here we propose a new isostatic model minimizing crustal deviatoric stress and demonstrate that gravity and shape data predict a 38 4km thick ocean beneath a 23 4km thick shell agreeing with but independent from libration data isostatic and tidal stresses are comparable in magnitude south polar crust is only 7 4km thick facilitating the opening of water conduits and enhancing tidal dissipation through stress concentration enceladus resonant companion dione is in a similar state of minimum stress isostasy its gravity and shape can be explained in terms of a 99 23km thick isostatic shell overlying a 65 30km thick global ocean thus providing the first clear evidence for a present day ocean within dione

efficient early global relaxation of asteroid vesta abstract the asteroid vesta is a differentiated planetesimal from the accretion phase of solar system formation although its present day shape is dominated by a non hydrostatic fossil equatorial bulge and two large mostly unrelaxed impact basins vesta may have been able to approach hydrostatic equilibrium during a brief early period of intense interior heating we use a finite element viscoplastic flow model coupled to a 1d conductive cooling model to calculate the expected rate of relaxation throughout vesta s early history we find that given sufficient non hydrostaticity the early elastic lithosphere of vesta experienced extensive brittle failure due to self gravity thereby allowing relaxation to a more hydrostatic figure soon after its accretion vesta reached a closely hydrostatic figure with 40 200 my after formation depending on the assumed depth of megaregolith the veneneia and rheasilvia giant impacts which generated most non hydrostatic topography must have therefore occurred 40 200 my after formation based on crater retention ages topography and relation to known impact generated features we identify a large region in the northern hemisphere that likely represents relic hydrostatic terrain from early vesta the long wavelength figure of this terrain suggests that before the two late giant impacts vesta had a rotation period of 5 02 h 6 3 faster than present while its spin axis was offset by 3 0 from that of the present the evolution of vesta s figure shows that the hydrostaticity of small bodies depends strongly on its age and specific impact history and that a single body may embody both hydrostatic and non hydrostatic terrains and epochs

radar images of asteroid 4179 toutatis delay doppler images of the earth crossing asteroid 4179 toutatis achieve resolutions as fine as 125 nanoseconds 19 meters in range and 8 3 millihertz 0 15 millimeter per second in radial velocity and place hundreds to thousands of pixels on the asteroid which appears to be several kilometers long topographically bifurcated and heavily cratered the image sequence reveals toutatis to be in an extremely slow non principal axis rotation state

the mercury gravity field orientation love number and ephemeris from the messenger radiometric tracking data abstract the mercury gravity field spin pole axis rotation period love number and ephemeris have been determined using the complete four years of messenger tracking data from march 2011 to april 2015 the pole location and obliquity 1 99 0 12 arcmin is consistent with previous determinations since messenger was in a highly elliptical orbit with periapsis in the far northern hemisphere the gravity resolution over the surface of mercury varies greatly from harmonic degree n 12 at the south pole to n 154 in a small region near the north pole which was covered with exceptionally low periapsis data near the end of mission the gravity field mess160a is determined to n 160 and shows notable improvement in the correlation with topography three different constraint methods are used to generate the gravity field the nominal method is a kaula power law of 5 10 5 n2 to constraint the coefficients one alternate constraint uses surface acceleration measurements which only constrains the unobserved portion of the gravity field the other constraint method sets the gravity uncertainties using the harmonic spectrum of the gravity derived from topography the mercury tidal love number solution k2 0 53 0 03 is larger than previous results but within suggested error bounds in addition the technique for estimating the mercury ephemeris is discussed

photometric properties of phobos surface materials from viking images abstract clear filter viking images and an accurate numerical model of the shape of phobos have been used to determine this satellite s photometric properties a global average hapke function derived from disk resolved data confirms previous indications that phobos has a strong opposition surge photometrically corrected images were mosaicked into an albedo map most of the resulting normal reflectances are in the range 0 06 0 10 and the brightest region on phobos is the northeast rim of the crater stickney the portion of that rim with the highest concentration of grooves globally there are three albedo classes reasonably separated geographically 1 bright material is to the east and south of stickney corresponding approximately to the locations on phobos having the highest bluest visible near ir ratio murchie et al 1991 2 the darkest material is to stickney s west correlating with material having an intermediate visible nir ratio murchie et al s bluish gray unit 3 intermediate albedo material dominates the anti stickney hemisphere corresponding to material with a lower visible nir ratio murchie et al s reddish gray unit a search for variations in phase behavior across phobos surface shows few such effects overall limited to isolated areas 1 stickney s floor darkens with increasing phase faster than average phobos this crater floor is both slightly more backscattering and significantly rougher than the global average the latter effect may be related to the slumping hinted at in low resolution images of stickney 2 we confirm that in many cases the contrast between the bright rims of small craters and grooves and their surroundings drops noticeably with increasing phase phase angles in use 10 50 however these bright rims overall display a diversity of photometric behavior and are the most heterogeneous areas on phobos in terms of regolith properties 3 we confirm that dark deposits in the floors of smaller craters darken faster with increasing phase than their surroundings cf goguen et al 1978 and find that these deposits are more backscattering than average phobos isolated regions with unusual phase behavior occur on phobos but not on deimos thomas et al 1996 the variable photometric properties of phobos isolated craters and grooves and the association of global albedo features with stickney reinforce interpretations that phobos regolith is emplaced and modified by discrete cratering events and is not mixed horizontally by extensive downslope creep as is apparently the case on deimos

titan s gravity field and interior structure after cassini since its arrival at saturn in 2004 cassini performed nine flybys devoted to the determination of titan s gravity field and its tidal variations here we present an updated gravity solution based on the final data set collected during the gravity dedicated passes before cassini s plunge into saturn s atmosphere the data set includes an additional flyby t110 march 2015 primarily devoted to imaging titan s north polar lakes carried out with the low gain antenna this flyby was particularly valuable because the closest approach occurred at a high latitude 75 n over an area not previously sampled previously published gravity results iess et al 2012 indicated that titan is subject to large eccentricity tides in response to the time varying perturbing potential exerted by saturn the magnitude of the response quadrupole field expressed in the tidal love number k 2 was used to infer the existence of an internal ocean the new gravity field determination provides an improved estimate of k 2 of about 0 62 accurate to a level of a few percent the value is higher than the simplest models of titan suggest and the interpretation is unclear possibilities include a high density ocean as high as 1300 kg m 3 a partially viscous response of the deeper region or a dynamic contribution to the tidal response the new solution includes higher degree and order harmonic coefficients up to 5 and offers an improved map of gravity anomalies the geoid is poorly correlated with the topography implying strong compensation in addition the updated geoid and its associated uncertainty could be used to refine the gravity altimetry correlation analysis and for improved interpretation of radar altimetric data

color heterogeneity of the surface of phobos relationships to geologic features and comparison to meteorite analogs multispectral observations of phobos by the vsk videospectrometric tv cameras and krfm combined radiometer and photometer for mars uv visible spectrometer on phobos 2 have provided new determinations of the satellite s spectral reflectance properties at greater spatial and spectral resolutions and over a greater geographic range than have previously been available images of the ratio of visible and nir reflectances covering the longitude range 30o 250ow were constructed from 0 40 0 56 pm and 0 781 1 tm vsk images eight channel 0 3 0 6 pm spectra obtained by the krfm instrument package were used to provide greater spectral resolution of parts of these images the data were calibrated using instrumental parameters measured on ground and in flight and the calibrations were refined and tested using previous spectral measurements of phobos and telescopic spectra of mars which is visible in the background in both data sets the average color ratio of phobos was found to be 0 97 0 14 consistent with previously obtained measurements however the surface is heterogeneous with at least four recognizable spectral units whose absolute color ratios were determined to within 10 a red unit with a color ratio of 0 7 0 8 a reddish gray unit with a color ratio of 0 8 1 0 a bluish gray unit with a color ratio of 1 0 1 1 and a blue unit with a color ratio of 1 1 1 4 the red unit occurs in the interiors of several dark floored craters and as adjacent patches the blue unit composes the interior of stickney as well as a lobate deposit superposed on the crater s rim and extending to the southwest the blue lobe is surrounded by a broad bluish gray aureole that breaks up into patchy outliers in its distal portions intervening surfaces are reddish gray the red reddish gray and bluish gray units were sampled by the krfm spectrometer and the bluish gray unit was found to have a distinct 0 3 0 6 grn spectrum the spatial distributions of the color ratio units and their reflectance systematics are inconsistent with mars shine or particle size differences alone being responsible for color variations but lateral optical or compositional heterogeneity is supported by the units different uv visible spectra the redder and bluer color units are interpreted to have been excavated by impacts from an optically and or compositionally heterogeneous interior overlain by a reddish gray surficial layer the location of the blue lobe emanating from stickney correlates with the location of one of the morphologic classes of grooves as predicted by ejecta reimpact models of groove origin the large color ratio of blue material is inconsistent with a carbonaceous chondfite composition but is comparable to that of an assemblage of mafic minerals like that forming black chondrites qualitative and quantitative comparison of the color ratio and uv visible spectral properties of bluish gray material with those of meteorites indicates that black chondfites are this matefial s closest spectral analog the uv visible spectra of reddish gray and red materials most resemble spectra of black chondrites but are also comparable to spectra of some carbonaceous chondrites

thermodynamics based constitutive framework for unsaturated soils 2 a basic triaxial model following the theoretical framework established in part 1 a basic elastoplastic unsaturated soil model is formulated the model is a combination of a soil skeleton model and an swcc soil water characteristic curve model for simplicity the model deals only with isotropic soils in triaxial compression space under a constant pore air pressure the paper shows that the central element in the model that differentiates itself from a saturated model is its dual plastic hardening which not only reflects the evolution of the internal structure of the soil skeleton but is also associated with the evolution of the solid fluid interactive structure for more flexible shear stress strain responses the non associated flow rule the alpha model by collins kelly based on a thermodynamic analysis is adopted the present model introduces six new material constants which can be calibrated following a systematic procedure the model successfully simulates the multiple series laboratory tests reported by sivakuma

phobos regolith and ejecta blocks investigated with mars orbiter camera images four flybys of phobos by the mars global surveyor spacecraft in 1998 allowed imaging at resolutions 2 7 m better than obtained for any other satellite or asteroid except earth s moon the images show the interior and vicinity of the large crater stickney there are 2000 identifiable ejecta blocks the largest about 85 m across the great majority of these blocks come from stickney as part of low velocity ejecta spread eastward by the influence of phobos s rapid rotation they appear to have experienced only a few meters at most of burial or modification since emplacement the images also show materials of different albedos within stickney that mark downslope motion of regolith the number of craters on the steep slopes of stickney that are subject to the downslope motion suggests that 4 km have been degraded to the point that they are no longer recognizable

near photometry of asteroid 253 mathilde abstract near s multispectral imager msi recorded over 300 images of asteroid 253 mathilde during a flyby on june 27 1997 images were acquired at 0 70 m at solar phase angles from 40 to 136 these data combined with telescopic observations at phase angles from 1 to 16 were used to derive a photometric model for mathilde the photometric properties of mathilde were then compared with those of similar small bodies we find that 1 mathilde has a geometric albedo of 0 047 0 005 at 0 55 m making it the darkest minor planet yet observed by spacecraft 2 mathilde is remarkably homogeneous in reflectance across the surface normal reflectance ranges from 0 041 to 0 053 a distribution at the low end of the range of reflectance measurements of carbonaceous chondrites 0 03 0 11 and in the middle of the range of albedo measurements of c type asteroids 0 03 0 06 3 typical reflectance contrasts on mathilde occur at the level of 6 from the mean as compared to phobos which exhibits variation at the level of 20 from the mean 4 as a whole mathilde is more backscattering than phobos and mathilde may have a less porous regolith or a different distribution of regolith grain sizes than phobos

behavior of deep convective clouds in the tropical pacific deduced from isccp radiances abstract we analyze the properties of deep convection over the equatorial pacific and its relationship to sea surface temperature sst and surface wind divergence using isccp radiance data for july 1983 and january 1984 deep convective clouds dcc are diagnosed with both a combined visible infrared threshold method and an infrared only threshold method the visible channel is important in diagnosing deep convection in different regions with different surface and atmospheric properties because of the existence of large scale variations of dcc top altitudes the itcz and spcz exhibit changes in these two months that are characteristic of both the el nino and seasonal cycles deep convection is latitudinally confined to a much smaller spatial scale than that suggested by maps of outgoing longwave radiation diurnal variations of dcc cover and associated mesoscale cirrus anvil cloud cac cover are out of phase with deep convection peaking in the early morning throughout the equatorial pacific the diurna

television observations of phobos in february and march 1989 the phobos 2 spacecraft took 37 television images of the moon phobos from a distance of 190 1 100 km these images complement the data from the mariner 9 and viking missions by providing higher resolution coverage of a large region west of the crater stickney 70 160 w and by providing disk resolved measurements of surface brightness at a greater range of phase angles and wavelengths the data are being used to update the three dimensional model of phobos to provide improved determinations of its density and orbital dynamics and to study its surface colour composition and texture here we present preliminary findings which include different integrated photometric behaviour in visible and near infrared bands observation of a region immediately west of stickney which is relatively free of large grooves the prevalence of bright rims on grooves and younger craters and low bulk density

the diurnal cycle of tropical convection the diurnal cycle of tropical convection is investigated with global cloud imagery constructed from 11 m radiance measurements taken aboard six satellites four harmonics of the diurnal cycle are resolved in the cloud imagery with about 50 km horizontal resolution to isolate deep convective activity from other processes which cause diurnal fluctuations in longwave radiance an index of deep convective activity is constructed by thresholding to brightness temperatures less than 230 k significant diurnal amplitude of deep convection is found only over tropical landmasses over the tropical oceans the diurnal cycle is weak and is barely discernible from the background red spectrum of convective variance nonetheless oceanic convection exhibits a systematic diurnal fluctuation with maximum intensity in the early morning nocturnal subsidence along the cloud free equator is postulated to play a role in forcing diurnal variation in the intertropical convergence zones other mechanisms are also implied to contribute as a similar early morning maximum in deep convection is seen even where no adjoining cloud free regions occur the diurnal cycle of deep convection is found to be organized on planetary scales predominantly in nonmigrating modes i e modes with phase speeds not equal to that of the sun the nonmigrating modes are postulated to be produced by the nonuniform distribution of convective centers the nonmigrating zonally symmetric component is found to be especially large while the role of this mode in forcing diurnal variations of the tropospheric circulation e g the hadley cell is questionable its role in modulating the ionospheric electric potential is well established discrepancies with the traditional notion that cloud to ground lightning is the dominant mechanism by which the earth is negatively charged are discussed in particular the probable role of nonlightning producing clouds e g the stratiform portion of convective complexes in diurnally modulating the negative charge on earth is discussed

coupling of hydraulic and mechanical behaviour in unsaturated compacted clay an experimental study was carried out to investigate the shear strength of a compacted non active clay speswhite kaolin a total of 33 statically compacted specimens were prepared at vertical stresses of 300 600 and 1200 kpa and water contents ranging from 0 24 to 0 34 this made it possible to explore a broad range of initial compaction induced conditions and hence to examine whether differences in water retention characteristics and shear strength are due to differences in initial compaction induced state or are to be attributed to fundamentally different microfabrics a shearbox was modified to allow the direct measurement of negative pore water pressure using trento high suction tensiometers tests were carried out at constant water content by monitoring suction changes in these tests it was possible to investigate the transition from unsaturated to saturated states in the first stage of the test the specimen was compressed at constant water content the specimen was therefore wetted in the s

a fractal interpretation of topography and geoid spectra on the earth moon venus and mars global spectra are available for topography and geoid on the earth venus mars and the moon if the spectral energy density has a power law dependence on wave number a fractal is defined the topography spectrum for the earth is a well defined fractal with d 1 5 this corresponds to brown noise with the amplitude proportional to the wave length although there is more scatter for the other planetary bodies the data for mars and the moon correlate well with the data for the earth venus topography also exhibits a brown noise behavior but with a smaller amplitude the power law dependence of the earth s geoid is known as kaula s law we show that uncompensated brown topography gives a geoid with a power law dependence that is in quite good agreement with kaula s law however the required amplitude is only 8 of the observed topography a similar result is found for the other bodies with the ratio of the amplitude of topography required to explain the geoid to the observed topography increasing to 72 for the moon

near infrared spectral reflectance of mineral mixtures systematic combinations of pyroxenes olivine and iron oxides near infrared spectral reflectance data are presented for systematic variations in weight percent of two component mixtures of ferromagnesian and iron oxide minerals mixtures were chosen for application to the study of the dark materials on mars but the results are equally applicable to mafic and ultramafic assemblages elsewhere in the solar system olivine spectral features are greatly reduced in contrast by admixture of other phases but remain distinctive even for low olivine contents clinopyroxene and orthopyroxene mixtures show resolved pyroxene absorptions near 2 m the addition of limonite greatly modifies pyroxene and olivine reflectance but does not fully eliminate distinctive spectral characteristics using only spectral data in the 1 m region it is difficult to differentiate orthopyroxene and limonite goethite in a mixture additional spectral coverage or other evidence may be required for a unique interpretation all composite mineral absorptions observed in this study are either weaker than or intermediate in strength to the end member absorptions and have bandwidths greater than or equal to those for the end members in general spectral properties in an intimate mixture combine in a complex nonadditive manner with features demonstrating a regular but usually nonlinear variation as a function of end member phase proportions

potential anomalies on a sphere applications to the thickness of the lunar crust a new technique for calculating potential anomalies on a sphere due to finite amplitude relief has been developed we show that by raising the topography to the nth power and expanding this field into spherical harmonics potential anomalies due to topography on spherical density interfaces can be computed to arbitrary precision using a filter for downward continuing the bouguer anomaly we have computed a variety of crustal thickness maps for the moon assuming both a homogeneous as well as a dual layered crust the crustal thickness maps for the homogeneous model give plausible results but this model is not consistent with the seismic data petrologic evidence and geoid to topography ratios all of which suggest some form of crustal stratification several dual layered models were investigated and it was found that only models with both upper and lower crustal thickness variations could satisfy the gravity and topography data these models predict that the entire upper crust has been excavated beneath the major nearside multiring basins additionally significant amounts of lower crustal material was excavated from these basins especially beneath crisium this model also predicts that mantle material should not have been excavated during the south pole aitken basin forming event and that lower crustal material should be exposed at the surface in this basin

constraints on vesta s interior structure using gravity and shape models from the dawn mission abstract we use the shape and gravity field of vesta determined from observations of the dawn spacecraft to place constraints on the asteroid s interior structure we compute a three layer interior structure model by minimizing the power of the residual gravity anomaly the densities of the mantle and crust are based on constraints derived from the howardite eucrite diogenite hed meteorites vesta s present day shape is not in hydrostatic equilibrium the rheasilvia and veneneia impact basins have a large effect on vesta s shape and are the main source of deviation from hydrostatic shape constraining a pre giant impact rotation rate and orientation of the spin axis from an ellipsoidal fit to the parts of vesta unaffected by the giant impacts and using the theory of figure we can constrain the shape of the core our solution for vesta s crust mantle interface reveals a belt of thick crust around rheasilvia and veneneia the thinnest crust is in the floor of the two basins and in the vestalia terra region our solution does not reveal an uplift of the crust mantle boundary to the surface in the largest basins this together with the lack of olivine detected by the visible and infrared spectrometer vir data in rheasilvia and veneneia indicates that vesta s presumed olivine mantle was either not brought to the surface by these large impacts or was covered by ejecta from subsequent impacts

harmonic and statistical analyses of the gravity and topography of vesta abstract we examine the gravity and topography of the asteroid 4 vesta as recently revealed by the dawn mission the observed gravity is highly correlated with the observed topography and suggests little lateral variation in density the variance spectra of both gravity and topography follow power laws which are very similar to those seen for the moon mars venus and earth a significant way in which vesta differs from these larger silicate bodies is that both gravity and topography are significantly anisotropic with more north south variation than east west variation rapid rotation plausibly contributes to this anisotropy but only at harmonic degree two the remainder of the anisotropy appears related to the large impacts which formed the rheasilvia and veneneia basins we note that as usual gravitational inverse problems are non unique while the observed gravity and topography of vesta do not preclude existence of a metallic core they certainly do not require it

barrier effect of the indo pacific maritime continent on the mjo perspectives from tracking mjo precipitation abstractexplanations for the barrier effect of the indo pacific maritime continent mc on the mjo should satisfy two criteria first they should include specific features of the mc namely its intricate land sea distributions and elevated terrains second they should include mechanisms for both the barrier effect and its overcoming by some mjo events guided by these two criteria a precipitation tracking method is applied to identify mjo events that propagate across the mc mjo c and those that are blocked by the mc mjo b about a half of mjo events that form over the indian ocean propagate through the mc most of them 75 become weakened over the mc the barrier effect cannot be explained in terms of the strength horizontal scale or spatial distribution of mjo convection when it approaches the mc from the west a distinction between mjo b and mjo c is their precipitation over the sea versus land in the mc region mjo c events rain much more over the sea than over land whereas rainfall over

radar observations and shape model of asteroid 16 psyche abstract using the s band radar at arecibo observatory we observed 16 psyche the largest m class asteroid in the main belt we obtained 18 radar imaging and 6 continuous wave runs in november and december 2015 and combined these with 16 continuous wave runs from 2005 and 6 recent adaptive optics ao images drummond et al 2016 to generate a three dimensional shape model of psyche our model is consistent with a previously published ao image hanus et al 2013 and three multi chord occultations our shape model has dimensions 279 232 189 km 10 deff 226 23 km and is 6 larger than but within the uncertainties of the most recently published size and shape model generated from the inversion of lightcurves hanus et al 2013 psyche is roughly ellipsoidal but displays a mass deficit over a region spanning 90 of longitude there is also evidence for two 50 70 km wide depressions near its south pole our size and published masses lead to an overall bulk density estimate of 4500 1400 kgm 3 psyche s mean radar albedo of 0 37 0 09 is consistent with a near surface regolith composed largely of iron nickel and 40 porosity its radar reflectivity varies by a factor of 1 6 as the asteroid rotates suggesting global variations in metal abundance or bulk density in the near surface the variations in radar albedo appear to correlate with large and small scale shape features our size and psyche s published absolute magnitude lead to an optical albedo of pv 0 15 0 03 and there is evidence for albedo variegations that correlate with shape features

simultaneous estimation of the masses of mars phobos and deimos using spacecraft distant encounters the masses of mars and its satellites phobos and deimos have been estimated from the mariner 9 and viking 1 and 2 orbiter tracking data these spacecraft were sensitive to the gravitational force of mars as well as to its satellites although the satellite masses are eight orders of magnitude smaller than mars their regular effect on the orbits of the spacecraft is evident in the tracking data and has enabled us to derive their masses simultaneously with that of mars our method for estimating the satellite masses uses the many distant encounters of the spacecraft with these small bodies rather than the few close encounters used in previous studies the mass estimate for phobos leads to a mean density of 1530 100 kg m 3 based on a volume of 5748 190 km 3 thomas 1993 while the mass estimate of deimos leads to a poorly constrained mean density of 1340 828 kg m 3 based on a volume of 1017 130 km 3 thomas 1993 our analysis confirms within the bounds of error the anomalously low density of phobos using an independent method and data set if the result is valid within several times the estimated error lc0 then factors other than composition i e porosity a thick regolith and or a significant interior ice content are required to explain the observed mass of this body

galileo encounter with 951 gaspra first pictures of an asteroid galileo images of gaspra reveal it to be an irregularly shaped object 19 by 12 by 11 kilometers that appears to have been created by a catastrophic collisional disruption of a precursor parent body the cratering age of the surface is about 200 million years subtle albedo and color variations appear to correlate with morphological features brighter materials are associated with craters especially along the crests of ridges have a stronger 1 micrometer absorption and may represent freshly excavated mafic materials darker materials exhibiting a significantly weaker 1 micrometer absorption appear concentrated in interridge areas one explanation of these patterns is that gaspra is covered with a thin regolith and that some of this material has migrated downslope in some areas

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

the surface roughness of europa derived from galileo stereo images abstract we assess the surface roughness of europa by reevaluating galileo stereo images roughness provides important information about surface textures which are related to geologic processes operating at a variety of scales roughness also sets important performance requirements for various remote sensing instruments on board the upcoming icy satellite missions to the jovian system in this study roughness is derived for different geologic terrains on europa which have been distinguished through geomorphological mapping for each terrain type we derive the scale dependent root mean square roughness and corresponding hurst exponents we investigate the scale between 30 m and 5 km and show that europa s surface can mostly be described by a monofractal behavior over these baselines i e surface roughness follows power laws with breakpoints located at a few hundred meters hurst exponents are higher below the breakpoints with typical values between 0 4 and 0 8 and lower above typically between 0 2 and 0 6 this behavior is mostly controlled by ridges which are dominating the topography on europa at unity scale 1 m roughness is extrapolated to be around 0 4 0 7 m with strong exceptions on chaos terrain where values over 1 2 m can be achieved assuming that no further breakpoints are present below the resolution of the digital terrain models used in this study

constraints on ceres internal structure and evolution from its shape and gravity measured by the dawn spacecraft ceres is the largest body in the asteroid belt with a radius of approximately 470 km in part due to its large mass ceres more closely approaches hydrostatic equilibrium than major asteroids pre dawn mission shape observations of ceres revealed a shape consistent with a hydrostatic ellipsoid of revolution the dawn spacecraft framing camera has been imaging ceres since march 2015 which has led to high resolution shape models of the dwarf planet while the gravity field has been globally determined to a spherical harmonic degree 14 equivalent to a spatial wavelength of 211 km and locally to 18 a wavelength of 164 km we use these shape and gravity models to constrain ceres internal structure we find a negative correlation and admittance between topography and gravity at degree 2 and order 2 low admittances between spherical harmonic degrees 3 and 16 are well explained by airy isostatic compensation mechanism different models of isostasy give crustal densities between 1 200 and 1 400 kg m3 with our preferred model giving a crustal density of 1 287 70 87 kg m3 the mantle density is constrained to be 2 434 5 8 kg m3 we compute isostatic gravity anomaly and find evidence for mascon like structures in the two biggest basins the topographic power spectrum of ceres and its latitude dependence suggest that viscous relaxation occurred at the long wavelengths 246 km our density constraints combined with finite element modeling of viscous relaxation suggests that the rheology and density of the shallow surface are most consistent with a rock ice salt and clathrate mixture

work input analysis for soils with double porosity and application to the hydromechanical modeling of unsaturated expansive clays a mechanical approach for unsaturated expansive soils considering double porosity has been developed based on the porous media theory in this approach the adsorbed and the capillary water as well as the micropores and macropores are two distinct phases an interaggregate stress considered as the work conjugate of the macrostructural strain increment has been defined both physicochemical and capillary effects of the pore water have been introduced at the macroscopic level other work conjugate variables relevant for the constitutive modeling of double porosity unsaturated media have also been identified consisting of the modified suction as conjugate of the increment of the macrostructural degree of saturation and the microstructural effective stress as conjugate of the microstructural volumetric strain increment a hydromechanical model for unsaturated expansive clays taking into account the interaction between the micro and the macrostructures in expansive clays can thus be built based on the bou

interannual variations of outgoing ir associated with tropical circulation changes during 1974 78 abstract interannual variability of outgoing ir in the tropical pacific ocean is studied using measurements derived from the noaa scanning radiometer in addition to the usual mean maps seasonal anomaly maps are constructed from june july august 1974 december 1977 january february 1978 these ir anomalies are closely related to changes in convective cloudiness patterns time series representing the equatorial eastern pacific sea surface temperature sst anomalies and monthly anomalies at various locations are also plotted during this period a warming event occurs in which ssts in the eastern pacific rapidly become anomalously warm dramatic changes in outgoing ir occur simultaneously with this sst increase the region of convergence over indonesia shifts eastward and connects to a well developed intertropical convergence zone itcz the south pacific convergence zone spcz is also connected to the indonesian convergence zone but develops more slowly and does not reach its maximum strength unt

formation of phobos and deimos via a giant impact abstract although the two moons of mars phobos and deimos have long been thought to be captured asteroids recent observations of their compositions and orbits suggest that they may have formed from debris generated by one or more giant impacts of bodies with 0 01 target mass recent studies have both analytically estimated debris produced by giant impacts on mars and numerically examined the evolution of circum mars debris disks we perform a numerical study smoothed particle hydrodynamics simulation of debris retention from giant impacts onto mars particularly in relation to a borealis scale giant impact e 3 10 29 j capable of producing the borealis basin we find that a borealis scale impact is capable of producing a disk of mass 5 10 20 kg 1 4 of the impactor mass sufficient debris to form at least one of the martian moons according to recent numerical studies of martian debris disk evolution while a borealis scale impact may generate sufficient debris to form both phobos and deimos further studies of the debris disk evolution are necessary our results can serve as inputs for future studies of martian debris disk evolution

topography of the northern hemisphere of mercury from messenger laser altimetry laser altimetry by the messenger spacecraft has yielded a topographic model of the northern hemisphere of mercury the dynamic range of elevations is considerably smaller than those of mars or the moon the most prominent feature is an extensive lowland at high northern latitudes that hosts the volcanic northern plains within this lowland is a broad topographic rise that experienced uplift after plains emplacement the interior of the 1500 km diameter caloris impact basin has been modified so that part of the basin floor now stands higher than the rim the elevated portion of the floor of caloris appears to be part of a quasi linear rise that extends for approximately half the planetary circumference at mid latitudes collectively these features imply that long wavelength changes to mercury s topography occurred after the earliest phases of the planet s geological history

the decay of the spectrum of the gravitational potential and the topography for the earth summary the spectrum of the earth s gravitational potential and topography as represented by spherical harmonic expansions to degree 180 have been computed modelling the decay in the form of al values of a and for several degree l ranges were computed for degree range 5 180 was 2 54 for the potential and 2 16 for equivalent rock topography the potential decay was somewhat slower than that i e 3 implied by kaula s rule however at high degree ranges the values were larger 3 20 for degrees 101 180 agreeing better with recent determinations from terrestrial gravity data and geoid undulations implied by satellite altimetric data the values imply that the potential decays faster at higher l values the values of for topography were fairly uniform around 2 which agrees with a suggestion made by vening meinesz in 1951 we also found that the value for the earth s potential agrees well with the value implied by the topography with airy isostatic compensation with the depth of compensation equal to 30 km however the magnitude of the power implied by the topographic isostatic potential was approximately one third of the observed potential

mechanical behaviour of unsaturated kaolin with isotropic and anisotropic stress history part 1 wetting and compression behaviour over the last 40 years considerable progress has been made in understanding the complex behaviour of unsaturated soils research using constitutive modelling has extended the critical state framework and the concept of yielding in saturated soils to encompass unsaturated soils experiencing suction however validation testing of the framework for unsaturated soils has shown disagreement with the basic propositions the main reason for this disparity is the anisotropic properties of the soil specimens tested as a result of preparation using one dimensional compaction the paper describes the detailed testing carried out to justify this statement as part of the work presented samples of unsaturated kaolin were prepared using isotropic compression the suctions in these samples were reduced to predefined values by wetting under low isotropic loading the pore size distributions the pressure volume relationships and yielding under subsequent isotropic loading are compared with tests on samples prepared by

long wavelength topographic relaxation for self gravitating planets and implications for the time dependent compensation of surface topography the support of planetary surface topography is controlled by the thickness of the elastic lithosphere and thus has implications for the thermomechanical structure of shallow planetary interiors previous analyses of the support of long wavelength topography have generally utilized elastic formulations which preclude consideration of the time evolution of lithospheric stresses and thermal state here we formulate a viscoelastic model for the support of topography on a spherical planet our stress relaxation model employs a multilayer linear viscoelastic rheology and includes the effect of self gravitation in these models we approximate internal rheology with an olivine flow law and we estimate the internal thermal structure assuming simple conductive cooling we analyze how relief at the surface and internal density interfaces evolves with time in response to a surface or internal load our analysis demonstrates that crustal compensation is strongly dependent on planetary radius with a tendency for a large terrestrial planet like earth to reach complete airy isostasy at long wavelengths within a time scale controlled by the mantle viscosity the correlation of degree of compensation with planetary radius is consistent with previous work turcotte et al 1981 which showed that membrane stress can support significant long wavelength gravity anomalies applied to the moon the degree of compensation associated with loading of 100 ma lithosphere is less than 0 3 and the load love numbers are greater than 0 6 for all harmonics including degree 2 even after 109 years of relaxation this conclusion does not change significantly even with a moderately low viscosity for the crust the tendency for a small body like the moon to support long wavelength stresses may be relevant in understanding the anomalously large degree 2 terms in the lunar shape the results also suggest that major impact basins would not be compensated throughout lunar geological history 4 b y even if the surfaces on which the basins were initially formed were relatively young i e 100 300 ma the fact that the south pole aitken basin is largely compensated suggests that the lateral variations in thermal and or mechanical structure induced by impact processes play significant roles in the compensation of this structure

the spectra of the topography of the earth venus and mars the global topography of the terrestrial bodies has been more or less determined from past planetary missions and from ground measurements and the behaviour of their spectra studied over the low frequencies only except the earth s case we here perform new spherical harmonic analysis of the topography of the earth venus and mars by using existing sometimes recently made available data sets to the highest possible degree and order so as to establish the decay of these spectra over a larger range of frequencies than before study the limit of validity of the used data sets and provide some new inputs to further geophysical analysis

relationship between soil structure and mechanical behavior for an expansive unsaturated clay to investigate the soil structure and mechanical behavior of an unsaturated expansive clay soil triaxial and mercury intrusion tests have been performed and are presented in this paper also an optical test system was developed for studying the internal structure evolution of the unsaturated expansive soil during shear loading tests the research results show a linear relationship between the cohesion intercept and the degree of saturation of the unsaturated clay for the test data for the tested soil the pore size distribution curves were found to be bimodal the measurement results from mercury intrusion tests confirm that the micropores of guangxi expansive soils of this study remain constant and that the macropores vary with the dry density of soil samples comparing the volumetric strain curves with the soil particle area curves some correlation and dependence on the macropore variation of soil samples during shear loading tests can be shown to exist key words soil structure mechanical behavior

geophysical implications of the long wavelength topography of the saturnian satellites 1 we use limb profiles to quantify the long wavelength topography of the saturnian satellites the degree 2 shapes of mimas enceladus and tethys are not consistent with hydrostatic equilibrium we derive 2 d topographic maps out to spherical harmonic degree 8 there is a good correlation with topography derived from stereo techniques if uncompensated topography at degree 3 and higher is large enough to be detectable during close spacecraft flybys if not properly accounted for this topography may bias estimates of a satellite s degree 2 gravity coefficients which are used to determine the moment of inertia we also derive a one dimensional variance spectrum a measure of how roughness varies with wavelength for each body the short wavelength spectral slope is 2t o 2 5 similar to silicate bodies however unlike the terrestrial planets each satellite spectrum shows a reduction in slope at longer wavelengths if this break in slope is due to a transition from flexural to isostatic support the globally averaged elastic thickness te of each satellite may be derived we obtain te values of 5 km 1 5 5 km 5 km and 5 km for tethys dione rhea and iapetus respectively for europa we obtain te 1 5 km these estimates are generally consistent with estimates made using other techniques for enceladus intermediate wavelengths imply te 0 5 km but the variance spectrum at wavelengths greater than 150 km is probably influenced by long wavelength processes such as convection or shell thickness variations impact cratering may also play a role in determining the variance spectra of some bodies citation nimmo f b g bills and p c thomas 2011 geophysical implications of the long wavelength topography of the saturnian satellites j geophys res 116 e11001 doi 10 1029 2011je003835

morphology of asteroid 4179 toutatis as imaged by chang e 2 spacecraft 1 close observations by the chang e 2 spacecraft reveal that the surface of asteroid 4179 toutatis is characterized by abundant impact craters with most of them being degraded by surface resetting the less degraded large crater with a diameter of 800 m at the south pole is estimated to be produced by an impactor with a diameter of 50 m from strength crater scaling relations from the analysis of large impact events on highly porous targets we argue that toutatis is likely a rubble pile body and its two lobes are contact binaries the fact that toutatis suffered plenty of impacts with seismic shaking resetting the initial surface features but not resulting in catastrophic disruption is probably because of the material s high attenuation of shock wave

microporosity structure of coarse granular soils to date the microporosity structures of coarse soils with various coarse fines contents are still not fully understood in this study the pore size distributions psds of five types of soil varying from gravel to clay were characterized using mercury intrusion porosimetry the soil with a coarse content below 70 i e fines content above 30 is found to have a fines controlled microstructure which is sensitive to water content changes such soil forms a dual porosity structure due to compaction in which both intraaggregate pores and interaggregate pores are dominant after saturation the dual porosity structure evolves into a unimodal porosity structure dominated by the intraaggregate pores during drying such soil exhibits a significant reduction of total volume the soil with a coarse content above 70 instead has a coarse controlled microstructure which is stable upon water content changes such soil maintains dual porosity structures no matter if the soil is compacted saturated or dried as an example of application the measured psds are used to predict the soil water characteristic curves swccs for the test soils and the predictions are consistent with the swccs measured in the laboratory

seasonal and static gravity field of mars from mgs mars odyssey and mro radio science abstract we present a spherical harmonic solution of the static gravity field of mars to degree and order 120 gmm 3 that has been calculated using the deep space network tracking data of the nasa mars missions mars global surveyor mgs mars odyssey ody and the mars reconnaissance orbiter mro we have also jointly determined spherical harmonic solutions for the static and time variable gravity field of mars and the mars k 2 love numbers exclusive of the gravity contribution of the atmosphere consequently the retrieved time varying gravity coefficients and the love number k 2 solely yield seasonal variations in the mass of the polar caps and the solid tides of mars respectively we obtain a mars love number k 2 of 0 1697 0 0027 3 the inclusion of mro tracking data results in improved seasonal gravity field coefficients c 30 and for the first time c 50 refinements of the atmospheric model in our orbit determination program have allowed us to monitor the odd zonal harmonic c 30 for 1 5 solar cycles 16 years this gravity model shows improved correlations with mola topography up to 15 larger at higher harmonics l 60 80 than previous solutions

diurnal cycle of deep convection in super clusters embedded in the madden julian oscillation 1 the diurnal cycle of deep convection in the convectively active phase cap and convectively suppressed phase csp of the madden julian oscillation mjo was investigated using global infrared equivalent blackbody temperature tbb data from october 2000 to april 2005 we particularly focused on super clusters scs that occurred during the cap of the mjo to analyze the behavior of scs and the csp of the mjo statistically we created composites of tbb for each case four regions were examined 1 the indian ocean io 2 the ocean area of the maritime continent mco 3 the land area of the maritime continent mcl and 4 the western pacific wp the amplitude phase of the diurnal cycle of deeper convection in scs was larger than similar to that of the csp of the mjo this result is consistent with that found in a previous study however the diurnal cycle of deep convection in the csp of the mjo had a clear maximum peak especially over the mcl but that in scs had a broader maximum peak of deep convection especially in oceanic regions although the diurnal phase was similar between scs and the csp of the mjo this result statistically suggests that the organization of a convective system affects the diurnal cycle of its deep convection as described in a previous case study we also demonstrated that the difference in the diurnal cycle of deep convection in the io and wp regions arose from sea surface temperature differences in those regions

the interior structure of ceres as revealed by surface topography abstract ceres the largest body in the asteroid belt 940 km diameter provides a unique opportunity to study the interior structure of a volatile rich dwarf planet variations in a planetary body s subsurface rheology and density affect the rate of topographic relaxation preferential attenuation of long wavelength topography 150 km on ceres suggests that the viscosity of its crust decreases with increasing depth we present finite element fe geodynamical simulations of ceres to identify the internal structures and compositions that best reproduce its topography as observed by the nasa dawn mission we infer that ceres has a mechanically strong crust with maximum effective viscosity 10 25 pa s combined with density constraints this rheology suggests a crustal composition of carbonates or phyllosilicates water ice and at least 30 volume percent vol low density high strength phases most consistent with salt and or clathrate hydrates the inference of these crustal materials supports the past existence of a global ocean consistent with the observed surface composition meanwhile we infer that the uppermost 60 km of the silicate rich mantle is mechanically weak with viscosity 21 pa s suggesting the presence of liquid pore fluids in this region and a low temperature history that avoided igneous differentiation due to late accretion or efficient heat loss through hydrothermal processes

the ceres gravity field spin pole rotation period and orbit from the dawn radiometric tracking and optical data abstract ceres gravity field and rotational parameters have been precisely measured using 1 5 years of radiometric doppler and range data and optical landmark tracking from the dawn spacecraft in orbit about the dwarf planet as was the case with dawn at vesta the gravity field orientation parameters landmark locations and ceres orbit are jointly estimated in a global solution even though dawn s radio science investigation at ceres was complicated by additional thrusting for attitude control the resulting spherical harmonic gravity field has a half wavelength resolution of up to 82 km degree 18 near the equator which is similar harmonic resolution to that of vesta the gravity field is consistent with airy isostatic compensation and this model assumption limits ceres crustal density to be between 1200 and 1600 kg m 3 for two layer and three layer models with mean crustal thickness between 27 and 43 km the compensation depth is determined using admittance between gravity and gravity from topography and is superior to admittance between gravity and topography the gravitational mass of ceres is determined to better than 0 002 gm ceres 62 62736 0 00040 km 3 s 2 the spin pole location is improved by 10 over previous results with right ascension 291 427 and declination 66 760 uncertainty less than 0 001 and the rotation rate is improved by 100 over previous determinations from hubble space telescope hst images ceres heliocentric orbit has also been improved with about 17 months of precision range measurements reducing ephemeris uncertainties to about 10 m during the dawn timeframe