radar observations of asteroid 1999 jm8 we report results of delay doppler observations of 1999 jm8 with the goldstone 8560 mhz 3 5 cm and arecibo 2380 mhz 13 cm radars over 18 days in july august 1999 the images place thousands of pixels on the asteroid and achieve range resolutions as fine as 15 m pixel the images reveal an asymmetric irregularly shaped object with a typical overall dimension within 20 of 7 km if we assume that 1999 jm8 s effective diameter is 7 km then the absolute magnitude 15 15 and the average goldstone radar cross section 2 49 km 2 correspond to optical and radar albedos of 0 02 and 0 06 establishing that 1999 jm8 is a dark object at optical and radar wavelengths the asteroid is in a non principal axis spin state that although not yet well determined has a dominant periodicity of 7 days however images obtained between july 31 and august 9 show apparent regular rotation of features from day to day suggesting that the rotation state is not far from principal axis rotation 1999 jm8 has regions of pronounced topographic relief prominent facets several kilometers in extent numerous crater like features between 100 m and 1 5 km in diameter and features whose structural nature is peculiar arecibo images provide the strongest evidence to date for a circular polarization ratio feature on any asteroid combined optical and radar observations from april 1990 to december 2000 permit computation of planetary close approach times to within 10 days over the interval from 293 to at least 2907 one of the longest spans for any potentially hazardous asteroid integration of the orbit into the past and future shows close approaches to earth mars ceres and vesta but the probability of the object impacting earth is zero for at least the next nine centuries

pb isotopic evidence for an early enriched crust on mars abstract martian meteorite nwa 7533 is a regolith breccia that compositionally resembles the martian surface measured by orbiters and landers nwa 7533 contains monzonitic clasts that have zircon with u pb ages of 4 428 ga the pb isotopic compositions of plagioclase and alkali feldspars as well as u pb isotopic compositions of chlorapatite in the monzonitic clasts of nwa 7533 have been measured by secondary ion mass spectrometry sims the u pb isotopic compositions measured from the chlorapatite in nwa 7533 yield an age of 1 357 81 ga 2 the least radiogenic pb isotopic compositions measured in plagioclase and k feldspar lie within error of the 4 428 ga geochron these data indicate that the monzonitic clasts in nwa 7533 are a product of a differentiation history that includes residence in a reservoir that formed prior to 4 428 ga with a value 238 u 204 pb of at least 13 4 1 7 2 and a value 232 th 238 u of 4 3 this value is more than three times higher than any other documented martian reservoir these results indicate either the martian mantle is significantly more heterogeneous than previously thought value of 1 14 vs 1 5 and or the monzonitic clasts formed by the melting of martian crust with a value of at least 13 4 therefore nwa 7533 may contain the first isotopic evidence for an enriched differentiated crust on mars

isotopic and ree studies of lunar basalt 12038 implications for petrogenesis of aluminous mare basalts we report sr nd and sm isotopic studies of lunar basalt 12038 one of the so called aluminous mare basalts a precise internal rb sr isochron yields a crystallization age of 3 35 0 09 ae and initial87sr 86sr 0 69922 2 2 error limits 1ae 109 years 87rb 0 0139ae 1 an internal sm nd isochron yields an age of 3 28 0 23ae and initial143nd 144nd 0 50764 28 present day143nd 144nd is less than the chondritic value i e nd 0 2 3 0 4 where nd is the deviation of143nd 144nd from chondritic evolution expressed as parts in 104 at the time of crystallization nd 3 2ae 1 5 0 6 we have successfully modeled the evolution of the sr and nd isotopic compositions and the ree abundances within the framework of our earlier model for apollo 12 olivine pigeonite and ilmenite basalts the isotopic and trace element features of 12038 can be modeled as produced by partial melting of a cumulate mantle source which crystallized from a lunar magma ocean with a chondrite normalized ree pattern of constant negative slope chondrite normalized la yb 2 2 for this hypothetical magma ocean pattern a plot of i sr versus nd for the apollo 12 basalts clearly shows the influence of varying proportions of olivine clinopyroxene orthopyroxene and plagioclase in the basalt source regions a small percentage of plagioclase 5 in the 12038 source apparently is responsible for low i sr and nd in this basalt aluminous mare basalts from mare crisium luna 24 and by inference mare fecunditatis luna 16 occupy locations on the i sr nd plot similar to that of 12038 implying that some basalts from three widely separated lunar regions came from plagioclase bearing source regions a summary of model calculations for mare basalts shows a record of lunar mantle solidification during the period when ree abundances in the lunar magma ocean increased from 20 chondritic to 100 chondritic although there is a general trend from olivine to clinopyroxene dominated source regions with progressive magma ocean evolution significant mineralogical heterogeneities in mantle composition apparently formed at any given stage of evolution as evidenced in particular by the three apollo 12 magma types

further evidence for a low u pb source in the moon uthpb smnd and arar isotopic systematics of lunar meteorite yamato 793169 abstract the coarse grained lunar meteorites yamato 793169 and asuka 881757 represent a new type of low ti mare basalt this paper reports the results of a u th pb sm nd and ar ar isotopic study of yamato 793169 performed as part of a consortium studies of lunar basaltic meteorites the isotopic study was carried out on a small sample 100 mg so that only three density fractions could be separated these fractions were leached with dilute acid in order to eliminate terrestrial pb contamination however the leaching procedure did not completely remove this contamination in some fractions and also apparently caused a fractionation of elements u th pb due to preferential leaching effects producing a secondary disturbance of the systematics furthermore the ar ar analyses indicate that the isotopic systematics in this meteorite might have been disturbed sometime later than 750 ma for these reasons the ages obtained using different isotopic systems disagree with each other and a precise formation age could not be obtained for this meteorite however using what results there are two reasonable interpretations can be made 1 the sm nd system yielded an age of 3 4 ga that could be interpreted as the formation age assuming that this system is possibly the least disturbed during the metamorphic event s that this meteorite experienced at least once and that all other isotopic systems and their corresponding ages were disturbed and 2 the u pb system yielded a nearly concordant age of 3 8 ga that could be interpreted as the formation age and the sm nd isotopic systematics were somehow disturbed we prefer the second interpretation for the reasons discussed below on a concordia diagram the cdt canon diablo troilite corrected u pb isotopic data yield a discordia line similar to the lunar catastrophic array indicating that the source of the meteorite formed during early lunar differentiation 4 4 ga and that the basalt was generated near 3 9 ga total ar ar age on plagioclase is 3 26 ga which seems to be too old if the formation age is 3 4 ga because low temperature fractions lost large amounts of radiogenic 40 ar during the late thermal event if we assume a formation age of 3 8 ga the estimated source 238 u 204 pb is 21 6 3 5 and nd is 3 9 0 3 these results indicate that the source of yamato 793169 is more depleted than apollo 12 and 15 lt basalts but less depleted than asuka 881757 therefore yamato 793169 may represent a new type of lt or vlt like mare basalt that is different from asuka 881757 the wide variety of lead and neodymium isotopic characteristics among lt and vlt mare basalts indicate that the lunar mantle was very heterogeneous with respect to trace element abundances

bias corrected population size distribution and impact hazard for the near earth objects abstract utilizing the largest available data sets for the observed taxonomic binzel et al 2004 icarus 170 259 294 and albedo delbo et al 2003 icarus 166 116 130 distributions of the near earth object population we model the bias corrected population diameter limited fractional abundances of the taxonomic complexes are a 0 2 c 10 d 17 o 0 5 q 14 r 0 1 s 22 u 0 4 v 1 x 34 in a diameter limited sample 30 of the neo population has jovian tisserand parameter less than 3 where the d types and x types dominate the large contribution from the x types is surprising and highlights the need to better understand this group with more albedo measurements combining the c d and x complexes into a dark group and the others into a bright group yields a debiased dark to bright ratio of 1 6 overall the bias corrected mean albedo for the neo population is 0 14 0 02 for which an h magnitude of 17 8 0 1 translates to a diameter of 1 km in close agreement with morbidelli et al 2002 icarus 158 2 329 342 coupling this bias corrected taxonomic and albedo model with the h magnitude dependent size distribution of stuart 2001 science 294 1691 1693 yields a diameter distribution with 1090 180 neos with diameters larger than 1 km as of 2004 june the spaceguard survey has discovered 56 of the neos larger than 1 km using our size distribution model and orbital distribution of stuart 2001 science 294 1691 1693 we calculate the frequency of impacts into the earth and the moon globally destructive collisions 10 21 j of asteroids 1 km or larger strike the earth once every 0 60 0 1 myr on average regionally destructive collisions with impact energy greater than 4 10 18 j 200 m diameter strike the earth every 56 000 6000 yr collisions in the range of the tunguska event 4 8 10 16 j occur every 2000 3000 yr these values represent the average time between randomly spaced impacts actual impacts could occur more or less closely spaced solely by chance as a verification of these impact rates the crater production function of shoemaker et al 1990 geological society of american special paper 247 has been updated by combining this new population model with a crater formation model to find that the observed crater production function on both the earth and moon agrees with the rate of crater production expected from the current population of neos

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

radar imaging and physical characterization of near earth asteroid 162421 2000 et70 we observed near earth asteroid 162421 2000 et70 using the arecibo and goldstone radar systems over a period of 12 days during its close approach to the earth in february 2012 we obtained continuous wave spectra and range doppler images with range resolutions as fine as 15 m inversion of the radar images yields a detailed shape model with an effective spatial resolution of 100 m the asteroid has overall dimensions of 2 6 km 2 2 km 2 1 km 5 uncertainties and a surface rich with kilometer scale ridges and concavities this size combined with absolute magnitude measurements implies an extremely low albedo 2 it is a principal axis rotator and spins in a retrograde manner with a sidereal spin period of 8 96 0 01 h in terms of gravitational slopes evaluated at scales of 100 m the surface seems mostly relaxed with over 99 of the surface having slopes less than 30 but there are some outcrops at the north pole that may have steeper slopes our precise measurements of the range and velocity of the asteroid combined with optical astrometry enables reliable trajectory predictions for this potentially hazardous asteroid in the interval 460 2813

origin of lead from green glass of apollo 15426 a search for primitive lunar lead a major obstacle in lunar u pb chronology is the elusiveness of the primary pb isotopic composition and u pb ratio and therefore the pb evolution for the early history of the moon in an attempt to seek the primitive lunar pb isotopic composition green glass from lunar clod 15426 49 was studied for u th pb systematics because it is extremely mg rich and known to be the most primitive among sampled lunar volcanic rocks green glass and yellow impact glass were handpicked washed with water then washed in an acid mixture 0 3 n hbr 0 2 n hf and the washes and residues were analyzed in contrast to the pb from apollo 17 orange glass pb from the surface of the green glass spherules is totally different from that of the spherule interior but is similar to lunar surface lead data for the interior pb yield a 207pb 206pb age of 3 41 ga because of the low pb concentration and high u pb ratio observed for the interior the initial pb was poorly defined nevertheless the data indicate that lunar pb evolved in an environment with 238u 204pb 19 55 which is considerably lower than those for mare basalts around 300 but higher than values for the earth 6 8

timing of crystallization of the lunar magma ocean constrained by the oldest zircon the primitive moon was covered with a thick layer of melt known as the lunar magma ocean whose crystallization resulted in the moon s surface as it is observed today dating of the oldest zircon so far in lunar rocks indicates that much of the magma was probably crystallized within 100 million years of the moon s formation

on the elusive isotopic composition of lunar pb highly radiogenic pb isotope compositions determined for volcanic glass beads from the apollo 14 soil sample 14163 are similar to those commonly determined for mare basalts and are correlated with chemical variations observed in the beads this indicates that pb unsupported by in situ u decay has a similar origin in both glass beads and mare basalt samples and is likely to reflect variations of 238u 204pb in the lunar mantle an alternative explanation that this pb is a result of late equilibration with the radiogenic pb present in soil is less likely as it would imply that all other characteristics of glass beads such as their chemistry must also be a consequence of equilibration near the lunar surface regardless of the origin of unsupported pb observed variations of pb isotope compositions in the glass beads and mare basalts appear to be a result of two component mixing between a primitive reservoir with a value similar to the earth s mantle and kreep with a value in excess of several thousand this range cannot be explained by the fractionation of major rock forming minerals from the crystallising lunar magma ocean and instead requires substantial extraction of sulphide late in the crystallisation sequence the proportion of sulphide required to produce the inferred range places limits on the starting of the moon prior to differentiation demanding a relatively high value of about 100 200 low indicated by several basalt samples and previously analysed volcanic glass beads can be explained by the preservation of an early but post ferroan anorthosite sulphide rich reservoir in the lunar mantle while a complete range of pb isotope compositions observed in the glass beads and mare basalts can be interpreted as mixing between this sulphide rich reservoir and kreep

direct measurement of ar diffusion profiles in a gem quality madagascar k feldspar using the ultra violet laser ablation microprobe uvlamp abstract controversy surrounding the mechanisms and controls on argon diffusion in k feldspar has led us to undertake direct diffusion measurements on a crystal with simple microtextures over a range of temperatures measurements of argon diffusion profiles in a gem quality iron rich orthoclase heated in a cold seal apparatus have been undertaken in situ using an ultra violet laser ablation microprobe uvlamp technique the results agree very closely with the previously determined bulk values for benson mines orthoclase activation energy e 43 8 1 kcal mol 1 and vacuum furnace cycle heating studies of k feldspars e 46 6 kcal mol 1 however instead of defining a single activation energy e and diffusion coefficient do the data yield two sets of parameters a low temperature 550 720 c array with an e of 47 2 2 5 kcal mol 1 198 2 10 5 kj mol 1 and a do of 0 0374 0 1123 0 0281 cm2 s 1 and a high temperature 725 1019 c array with an e of 63 8 3 4 kcal mol 1 268 0 14 3 kj mol 1 and a do of 55 0 225 5 44 2 cm2 s 1 the new results closely reproduce two sets of apparent activation energies previously measured in cycle heating studies of madagascar k feldspar 40 3 and 57 3 kcal mol 1 previous interpretations of the two arrays have included multiple domains with variable activation energies and fast track diffusion however the uv depth profile analyses indicate simple diffusion to the grain surface and importantly diffusion radii calculated by combining the uvlamp and cycle heating data are the same as the physical grain sizes used in the experiments around 1 mm vacuum furnace stepped heating experiments on slowly cooled k feldspars have been interpreted as showing diffusion radii of around 6 m and indicate complex populations of sub grains this study indicates that madagascar k feldspar and thus probably all gem quality k feldspars act as single diffusion domains and that short circuit or pipe diffusion was not an important loss mechanism an apparent diffusion compensation relationship in the stepped heating data for madagascar k feldspar implies that similar relationships seen in other k feldspars are a result of a range of diffusion mechanisms

origin of the lunar highlands mg suite an integrated petrology geochemistry chronology and remote sensing perspective the mg suite represents an enigmatic episode of lunar highlands magmatism that presumably represents the first stage of crustal building following primordial differentiation this review examines the mineralogy geochemistry petrology chronology and the planetary scale distribution of this suite of highlands plutonic rocks presents models for their origin examines petrogenetic relationships to other highlands rocks and explores the link between this style of magmatism and early stages of lunar differentiation of the models considered for the origin of the parent magmas for the mg suite the data best fit a process in which hot solidus temperature at 2 gpa 1600 to 1800 c and less dense 3100 kg m3 early lunar magma ocean cumulates rise to the base of the crust during cumulate pile overturn some decompressional melting would occur but placing a hot cumulate horizon adjacent to the plagioclase rich primordial crust and kreep rich lithologies at temperatures of 1300 c would result in the hybridization of these divergent primordial lithologies producing mg suite parent magmas as urkreep primeval kreep is not the petrologic driver of this style of magmatism outside of the procellarum kreep terrane pkt mg suite magmas are not required to have a kreep signature evaluation of the chronology of this episode of highlands evolution indicates that mg suite magmatism was initiated soon after primordial differentiation 10 m y alternatively the thermal event associated with the mantle overturn may have disrupted the chronometers utilized to date the primordial crust petrogenetic relationships between the mg suite and other highlands suites e g alkali suite and magnesian anorthositic granulites are consistent with both fractional crystallization processes and melting of distinctly different hybrid sources

the constitution and structure of the lunar interior the current state of understanding of the lunar interior is the sum of nearly four decades of work and a range of exploration programs spanning that same time period missions of the 1960s including the rangers surveyors and lunar orbiters as well as earth based telescopic studies laid the groundwork for the apollo program and provided a basic understanding of the surface its stratigraphy and chronology through a combination of remote sensing surface exploration and sample return the apollo missions provided a general picture of the lunar interior and spawned the concept of the lunar magma ocean in particular the discovery of anorthite clasts in the returned samples led to the view that a large portion of the moon was initially molten and that crystallization of this magma ocean gave rise to mafic cumulates that make up the mantle and plagioclase flotation cumulates that make up the crust smith et al 1970 wood et al 1970 this model is now generally accepted and is the framework that unifies our knowledge of the structure and composition of the moon the intention of this chapter is to review the major advances that have been made over the past decade regarding the constitution of the moon s interior much of this new knowledge is a direct result of data acquired from the successful clementine and lunar prospector missions as well as the analysis of new lunar meteorites as will be seen results from these studies have led to many fundamental amendments to the magma ocean model much of what we know from sample analyses has been previously summarized elsewhere and only their most important aspects will be discussed in this chapter the reader is referred to the relevant chapters in the books basaltic volcanism on the terrestrial planets basaltic volcanism study project 1981 the

pb pb ages of feldspathic clasts in two apollo 14 breccia samples pb pb isochron ages of ca 3 92 ga for three k feldspar rich clasts from apollo 14 breccias 14303 and 14083 were determinedusing secondary ion mass spectrometry sims these ages are interpreted t

hydrochemical characteristics of sabkha brines evaporite crystallization and microbial activity in al kharrar sabkha and their implication on future infrastructures in rabigh area red sea coastal plain of saudi arabia al kharrar sabkha area is characterized by a distinctive distribution of varied evaporite minerals and microbial activities the lowest topographic depressions are dominated with primary halite crystals in a high salinity brine 220 or microbial mats at a relatively low salinity value mg2 ca2 k or mg2 na ca2 k for cations and cl so4 2 hco3 for anions no distinct correlation is observed between the various cations anions alkalinity and tds with the exception of the positive relation between cl and tds the dominant brine type for most samples is nacl or mgnacl mg ca ratio in some water samples is high 12 14 23 66 which allows dolomitization of the early deposited carbonate minerals most water and brine samples are located in the field of recent or old marine water and of mgcl2 or cacl2 composition respectively the resultant crystallization pressure by evaporite minerals microbial activity and varied brine compositions are factors that increase the future corrosion for foundations in al kharrar sabkha area

the timing of basaltic volcanism at the apollo landing sites precise crystallisation ages have been determined for a range of apollo basalts from pb pb isochrons generated using secondary ion mass spectrometry sims analyses of multiple accessory phases including k feldspar k rich glass and phosphates the samples analysed in this study include five apollo 11 high ti basalts one apollo 14 high al basalt seven apollo 15 low ti basalts and five apollo 17 high ti basalts together with the samples analysed in two previous similar studies pb pb isochron ages have been determined for all of the major basaltic suites sampled during the apollo missions the accuracy of these ages has been assessed as part of a thorough review of existing age determinations for apollo basalts which reveals a good agreement with previous studies of the same samples as well as with average ages that have been calculated for the emplacement of the different basaltic suites at the apollo landing sites furthermore the precision of the new age determinations helps to resolve distinctions between the ages of different basaltic suites in more detail than was previously possible the proposed ages for the basaltic surface flows at the apollo landing sites have been reviewed in light of these new sample ages finally the data presented here have also been used to constrain the initial pb isotopic compositions of the mare basalts which indicate a significant degree of heterogeneity in the lunar mantle source regions even among the basalts collected at individual landing sites

pristine lunar glasses criteria data and implications major element analyses of several thousand glasses from all of the apollo landing sites have resulted in the identification of 25 groups of pristine i e volcanic glass the nickel in these pristine glasses is shown to be indigenous not meteoritic contamination and to be correlated with mg the chemical data indicate that these glasses are consistently better candidates for primary magmas than the majority of crystalline mare basalts the pristine glasses support the view that assimilative processes ringwood and kesson 1976 involving two cumulate systems in the differentiated mantle operated during mare petrogenesis the reality of those assimilative interactions is evident by the occurrence of two linear arrays among the chemistries of the glasses data suggest that these cumulate components in the differentiated mantle persist for lateral distances of at least 1000 km and therefore appear to be products of a vast magma ocean that existed early in lunar history alternative hypotheses claiming that the highlands crust and mare source regions were produced by serial magmatism without a magma ocean have not yet considered all of the constraints derived from the pristine glasses

mineral chemistry and in situ upb geochronology of the mare basalt northwest africa 10597 implications for low ti mare volcanism around 3 0 ga abstract unbrecciated mare basalts are rare in the lunar meteorite collection found in 2015 northwest africa nwa 10597 is a medium grained low ti mare basalt with a subophitic texture the meteorite consists mostly of mm sized pyroxene and plagioclase with minor olivine spinel ilmenite phosphates silica and trace zr rich minerals such as baddeleyite zirconolite and tranquillityite a portion of plagioclase and silica has been transformed to their high pressure polymorphs due to shock metamorphism nwa 10597 has a low tio2 content 2 9 wt but is relatively enriched in rare earth elements ree laaverage 65 ci with an overall unfractionated pattern except for a negative eu anomaly calculated ree concentrations of parent melts in equilibrium with mg rich pyroxene and ca rich plagioclase suggest no significant assimilation of ree rich melts after the onset of pyroxene crystallization in situ u pb analyses of baddeleyite and apatite reveal a mutually consistent age of 3 0 ga which is also in excellent agreement with that of low ti mare basalts nwa 4734 and lapaz icefield lap 02205 dated with other independent techniques the concordance suggests no significant thermal disturbance in the u pb isotopic system of nwa 10597 although it was heavily shocked nwa 10597 closely resembles nwa 4734 in terms of petrographic texture mineral chemistry and geochronology indicating a pairing relationship

application of proton microprobe data to trace element partitioning in volcanic rocks abstract in situ proton microprobe analyses are used to calculate partition coefficients d for mn fe cu zr ga rb sr y zr ba and pb and more restricted data for ni ge nb and as in pyroxenes olivines biotites hornblendes feldspars and fe ti oxides from 32 volcanic rocks all with glassy matrices these range from leucitite and picritic basalt to high silica and peralkaline rhyolites data for pigeonite aenigmatite allanite and leucite are included where these occur as additional phases coefficients have also been rayleigh fractionation corrected this correction being significant for those elements with high coefficients in specific mineral phases and where pronounced crystallisation has occurred partition coefficients are presented as plots vs nbo t ratios of coexisting glasses melts negative correlations are observed based on log transformed data for mn zn fe and y pyroxenes mn zn and fe olivines mn and zn fe ti oxides nb y sr and zr hornblendes sr plagioclase and ba cu zn and fe feldspars these element partition coefficients are not correlated with bulk mineral compositions zr and ga are not correlated with either glass or mineral compositions except zr in hornblende the correlations support the role of melt polymerisation in controlling element partitioning at least for those elements listed although possible effects of temperature cannot be uniquely isolated in the present data set the coefficients presented here are generally consistent with published values for equivalent rock compositions one difference being that some of the higher published coefficients e g sr in plagioclase are not matched in the present data set from a practical viewpoint the relative regularity of the coefficient data presented does facilitate choice of relevant coefficient values that are required for petrogenetic modelling procedures

the origin of geochemical diversity of lunar mantle sources inferred from the combined u pb rb sr and sm nd isotope systematics of mare basalt 10017 the results of our combined u pb rb sr and sm nd isotope study of mare basalt 10017 contribute to the understanding of the petrogenetic processes involved in the origin of geochemical diversity in lunar mare basalt sources as well as the u pb isotope systematics of the moon the rb sr sm nd and 238 u 206 pb isotope systems yield concordant crystallization ages of 3 633 0 057 ga 3 678 0 069 ga and 3 616 0 098 ga respectively the 235 u 207 pb isochron yields an older though still concordant age of 3 80 0 12 ga neither the 206 pb 207 pb system nor u pb concordia system yields an age for 10017 that is concordant with the age determined from the sm nd rb sr and 238 u 206 pb systems the initial 87 sr 86 sr of 10017 is 0 69941 7 and the initial end is 3 2 0 4 initial pb isotopic compositions determined from the u pb isochrons are 206 pb 204 pbi 31 11 and 207 pb 204 pbi 34 15 together these initial pb compositions constrain the l value of the 10017 source to be 70 30 assuming a single stage pb growth model this is considerably lower than l values typically estimated for mare basalt sources 100 600 regardless the l values calculated for the sources of mare basalts as well as other lunar samples show a range that is larger than can be explained by fractionation of u from pb solely by crystallization of silicate phases and ilmenite during magma ocean solidification and formation of lunar mantle sources the u pb isotope systematics may reflect late stage formation of a sulfide phase which strongly fractionates pb from u but has minimal effect on rb sr or sm nd compositions during crystallization of the lunar magma ocean 2007 elsevier ltd all rights reserved

near earth asteroid surface roughness depends on compositional class radar observations of 214 near earth asteroids neas reveal a very strong correlation of circular polarization ratio with visible infrared taxonomic class establishing distinct differences in the centimeter to several decimeter structural complexity of objects in different spectral classes the correlation may be due to the intrinsic mechanical properties of different mineralogical assemblages but also may reflect very different formation ages and collisional histories the highest ratios are measured for groups associated with achondritic igneous rocky meteorites the e class whose parent body may be 3103 eger and the v class derived from the mainbelt asteroid and dawn mission target 4 vesta

apollo 15 yellow brown volcanic glass chemistry and petrogenetic relations to green volcanic glass and olivine normative mare basalts abstract apollo 15 yellow brown glass is one of twenty five high mg primary magmas emplaced on the lunar surface in pyroclastic eruptions forty spherules of this glass were individually analyzed by electron microprobe and inaa for major and trace elements e g sc v cr co la ce nd sm eu ho tm yb lu hf ta and u the abundances demonstrate that this primary magma was produced by partial melting of differentiated cumulates in the lunar mantle models are developed to explain the possible source regions of several apollo 15 and apollo 12 low ti mare magmas as being products of hybridization involving three ancient differentiated components of a primordial lunar magma ocean a early olivine orthopyroxene cumulates b late stage clinopyroxene pigeonite ilmenite plagioclase cumulates and c late stage inter cumulus liquid isotopic constraints on sm nd fractionation and least squares tests of potential mixing models require models of apollo 15 yellow brown glass and apollo 12 and 15 olivine mare basalts involving low f 3 cumulate remelting of sources in which olivine and orthopyroxene are residual phases models of the apollo 15 green glass composition indicate higher 4 7 degrees of melting but with only a slight preference for orthopyroxene rich relative to orthopyroxene free sources the modeled dependence on residual orthopyroxene in mare source regions places source depths at 400 km or greater in order to maintain olivine and orthopyroxene on the liquidus hybridization at such depths would likely result from convective overturn of the primordial magma ocean and suggests that separate fractionating masses were positioned at various depths our models for developing hybridized source regions of primary low ti mare magmas do not require selective contamination of primary liquids the preferred model for apollo 15 yellow brown glass is presented as the commingling of 95 early cumulate olivine orthopyroxene 1 9 clinopyroxene 0 27 pigeonite 1 7 plagioclase 0 02 ilmenite and 0 56 trapped liquid respective proportions for the apollo 15 olivine mare basalt source model are 98 5 0 37 0 0 79 0 16 and 0 13 and the proportions used for the preferred apollo 12 olivine mare basalt model are 97 6 0 73 0 24 0 77 0 42 and 0 21 our preferred model for the green glass source composition f 0 07 requires the commingling of 97 4 early olivine orthopyroxene 0 18 clinopyroxene 1 32 pigeonite 0 85 plagioclase and 0 28 trapped liquid

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

pb isotopes in the impact melt breccia 66095 association with the imbrium basin and the isotopic composition of lithologies at the apollo 16 landing site recent in situ secondary ion mass spectrometry sims pb isotope analyses of lunar basalts have provided precise crystallisation ages and initial pb isotopic compositions for these samples in this

radar observations and physical model of asteroid 6489 golevka abstract we report 8510 mhz 3 5 cm radar observations of the earth crossing asteroid eca 6489 golevka 1991 jx obtained between june 3 and june 15 1995 at goldstone the very large array and the evpatoria ukraine and kashima japan radio antennas one dimensional doppler spectra are used to estimate the object s convex hull refine the ephemeris and yield four possible pole directions three dimensional modeling using two dimensional delay doppler images and published lightcurves unambiguously defines the pole and reveals an extraordinarily angular shape with flat sides sharp edges and corners and peculiar concavities the equivalent diameter of the object is 530 30 m with moments of inertia about the long intermediate short axes proportional to 1 00 1 38 1 39 0 1 the asteroid s pole direction is 202 5 45 5 and its sidereal period is p 6 0289 0 0001 h the asteroid s circular polarization ratio sc oc 0 23 0 02 is lower than the average for radar detected near earth asteroids and reveals only a modest degree of near surface roughness at scales near the 3 5 cm wavelength however the approximately lambertian radar scattering law implies considerable surface roughness at larger scales the asteroid s radar scattering law is modeled as cosn with 0 25 0 12 and n 1 7 0 7 giving an equivalent spherical albedo of 0 18 0 09 this value is in the middle of the distribution of albedos of s class asteroid s previously imaged by radar the hapke parameters describing the object s optical scattering properties are w 0 173 0 006 h 0 024 0 012 b0 1 03 0 45 g 0 34 0 02 and 20 5 both the optical and the radar scattering properties are consistent with those of a typical s class asteroid goldstone vla plane of sky images do not resolve the asteroid but do provide astrometry with uncertainties less than 0 1 arcsec integration of an orbit based on all available radar and optical astrometry shows that golevka has an insignificant probability of collision with any planet during at least the next nine centuries we investigate golevka s dynamical environment assuming uniform density some areas of the surface are characterized by large enough slopes that we expect that they are exposed solid monolithic rock

ion microprobe studies of trace elements in apollo 14 volcanic glass beads comparisons to apollo 14 mare basalts and petrogenesis of picritic magmas abstract the major element geochemistry of picritic lunar glass beads indicates that they represent primary basaltic liquid compositions and as such provide unique information concerning the origin of mare basalts and characteristics of the lunar interior this study used ion microprobe techniques for trace element analysis of individual glass beads representing seven compositionally distinct types of picritic glass beads from the apollo 14 site high ti glasses 17 11 tio2 red black orange intermediate ti glasses 5 4 tio2 yellow low ti glasses 2 8 tio2 lap low alkali picritic papike et al 1989 very low ti glasses ba sr 1 of these glasses are different from low ti mare basalts at other sites but are similar to crystalline basalts at the apollo 14 site the intermediate to high ti picritic glasses exhibit a flat to slightly positive lree slope and a negative hree slope the orange glass has a higher total ree abundance and a slightly larger negative eu anomaly than the red black and yellow glasses relative to the apollo 17 high ti glasses apollo 14 high ti glasses are enriched in ree lree hree y v zr sr ba and ba sr and are similar in alkali elements li rb co and sc trace element modeling within the context of liquid lines of descent and major element characteristics indicates that the picritic glass beads at the a 14 site are not related by low pressure fractional crystallization to each other or to crystalline basalts at the apollo 14 or other landing sites a possible exception is the relationship between lap and basalts of the high al basalt suite the wide range of primary magma compositions and the lack of petrogenetic linkage via crystal fractionation to crystalline basalts indicates that either a wide compositional range of evolved mare basalts has not yet been sampled or a unique mechanism is selectively tapping these picritic magmas directly from their mantle source region the wide range of major and trace element characteristics of the volcanic glass beads is consistent with derivation from mineralogically distinct sources which consist of varying proportions of olivine orthopyroxene clinopyroxene ilmenite plagioclase kreep component the evolved kreep component may have been incorporated into these primary picritic magmas by either assimilation fractional crystallization type processes afc or by hybridization of the mantle source the former appears less likely due to the general systematic increase in incompatible elements relative to ti concentration and the apparent lack of crystallization that is required in afc type models the hybridization processes may be the result of sinker mechanisms as proposed by ringwood and kesson 1976 a manifestation of original mantle inhomogeneities or a magma ocean stirred by large impacts

an extension of the bus asteroid taxonomy into the near infrared the availability of asteroid spectral measurements extending to the near infrared resulting from the development of new telescopic instruments such as spex rayner 2003 provides a new basis for classifying asteroid reflectance spectra we present an asteroid taxonomy classification system based on reflectance spectrum characteristics for 371 asteroids measured over the wavelength range 0 45 to 2 45 microns this system of 24 classes is constructed using principal component analysis following most closely the visible wavelength taxonomy of bus 1999 which itself builds upon the system of tholen 1984 nearly all of the bus taxonomy classes are preserved with one new class sv defined for each class we present boundary definitions spectral descriptions and prototype examples a flow chart method is presented for classifying newly acquired data spanning this wavelength range when data are available only in the near infrared range 0 85 to 2 45 microns classification is also possible in many cases through an alternate flow chart process within our sample several classes remain relatively rare only 6 objects fall into the a class 349 dembowska and 3628 boznemcova reside as the only objects in their respective r and o classes eight q class objects are all near earth asteroids we note 1904 massevitch as an outer main belt v type while 15 other v type objects have inner main belt orbits consistent with an association with vesta

basaltic magmatism on the moon a perspective from volcanic picritic glass beads abstract it is widely accepted that basaltic magmas are products of partial fusion of periodotite within planetary mantles as such they provide valuable insights into the composition structure and processes of planetary interiors those compositions which approach primary melt compositions provide the most direct information about planetary interiors and serve as a starting point to understand basaltic evolution within the collection of lunar samples returned by the apollo and luna missions are homogeneous picritic glass beads of volcanic origin these picritic glasses are our closest approximations to primary magmas as such these glass beads provide a unique perspective concerning the origin of mare basalts the characteristics of the lunar interior and processes in the early differentiation of the moon we have obtained trace element data for these picritic glasses using sims techniques these data and literature isotopic and experimental data on the picritic glasses are placed within the framework of mare basaltic magmatism the volcanic glasses are very diverse in their trace element characteristics for example they have a wide range of ree pattern shapes and concentrations like the crystalline mare basalts all picritic glasses have a negative eu anomaly unlike the crystalline mare basalts there is little correlation between the size of the eu anomaly and overall ree concentrations trace element differences among the various glasses suggests that a kreep component was incorporated into their mantle source this implies large scale mixing of the lunar magma ocean derived cumulate pile subtle differences among glasses suggest that local mixing of sources may also have been an important process preservation of subtle chemical differences in the picritic glasses and crystalline basalts may be interpreted as indicating that they were produced by small to moderate degrees of partial melting and that the lunar mantle did not experience extensive melting during episodes of mare volcanism several lines of evidence are consistent with the view that the picritic glasses were derived from mantle sources that were compositionally distinct from the sources for crystalline mare basalts these are parallel but no common liquid lines of descent chemical differences between picritic glasses and the more primitive crystalline mare basalts experimental studies indicating that the picritic glasses are multiply saturated at depths greater than that of the mare basalts differences in lead isotopic data and the mode of eruption i e fire fountaining for glass beads these data also provide circumstantial evidence that suggests that the picritic glasses were derived from a source somewhat more volatile rich than that of the mare basalts several petrogenetic models are suggested by the trace element characteristics of the picritic glasses 1 1 partial melting of heterogeneous lunar mantle at depths greater than 300 km to produce the parental magmas picritic for both the mare basalts and picritic glasses picritic magmas represented by glass beads were erupted to the surface with small degrees of fractional crystallization while mare basalts were produced by larger degrees of fractional crystallization 15 30 of similar but not identical picritic magmas 2 2 picritic magmas represented by the glass beads were generated at depths greater than 400 km in a volatile enriched relative to the mare basalt source heterogeneous mantle while mare basalts are fractional crystallization products of picritic magmas generated at depths of less than 400 km 3 3 the picritic magmas represented by the glass beads represent polybaric melting that initiated at depths of at least 1000 km a primitive mantle component or less processed cumulate mantle components may have been involved in the generation of the picritic glasses in any of these models

uranium lead systematics of low ti basaltic meteorite dhofar 287a affinity to apollo 15 green glasses article i nfo dhofar 287 is a lunar meteorite found in oman in 2001 which consists of a major portion 95 of low ti mare basalt dho 287a and a minor attached part 5 of regolith breccia dho 287b here we report the u pb systematics of dho 287a using data collected with a sensitive high resolution ion microprobe shrimp in situ analyses of five merrillite and three apatite grains which are resistant to secondary petrologic events resulted in a total pb u isochron age of 3 34 0 20 ga in 238 u 206 pb 207 pb 206 pb 204 pb 206 pb 3 d space 95 confidence level the observed pb pb isochron of these eight phosphates coupled with four plagioclase grains alsoyieldeda 207 pb 206 pbageof3 35 0 13ga thisformationage whenconsideredasthecrystallizationageof

an extremely low source in the moon uthpb smnd rbsr and isotopic systematics and age of lunar meteorite asuka 881757 abstract we have undertaken u th pb sm nd rb sr and 40 ar 39 ar isotopic studies on asuka 881757 a coarse grained basaltic lunar meteorite whose chemical composition is close to low ti and very low ti vlt mare basalts the pb pb internal isochron obtained for acid leached residues of separated mineral fractions yields an age of 3940 28 ma which is similar to the u pb 3850 150 ma and th pb 3820 290 ma internal isochron ages the sm nd data for the mineral separates yield an internal isochron age of 3871 57 ma and an initial 143 nd 144 nd value of 0 50797 10 the rb sr data yield an internal isochron age of 3840 32 ma 87 rb 1 42 10 11 yr 1 and a low initial 87 sr 86 sr ratio of 0 69910 2 the 40 ar 39 ar age spectra for a glass fragment and a maskelynitized plagioclase are relatively flat and give a weighted mean plateau age of 3798 12 ma we interpret these ages to indicate that the basalt crystallized from a melt 3 87 ga ago the sm nd age and an impact event disturbed the rb sr system and completely reset the k ar system at 3 80 ga the slightly higher pb pb age compared to the sm nd age could be due to the secondary pb from terrestrial and or lunar surface pb contamination that remained in the residues after acid leaching alternatively the following interpretation is also possible the meteorite crystallized at 3 94 ga the pb pb age and the sm nd rb sr and k ar systems were disturbed by an impact event at 3 80 ga the crystallization age obtained here is older than those reported for low ti basalts 3 2 3 5 ga and for vlt basalts 3 4 ga but similar to ages of some mare basalts indicating that the basalt may have formed from a magma related to a basin forming event imbrium the age span for vlt basalts from different sampling sites suggest that they were erupted over a wide area during an interval of at least 500 million years the impact event that thermally reset the k ar system of asuka 881757 must have been post imbrium perhaps orientale in age the lead isotopic composition of asuka 881757 is nonradiogenic compared with typical apollo mare basalts and the estimated 238 u 204 pb value for the basalt source is 10 3 this source value is the lowest so far measured for lunar rocks a large positive nd value 7 4 0 5 and the time averaged 147 sm 144 nd ratio for the basalt source are similar to those for some apollo 12 15 and 17 basalts suggesting a lree depleted mantle which is consistent with the global magma ocean hypothesis the u th pb sm nd and rb sr data on asuka 881757 suggest that the basalt was derived from a low u pb low rb sr and high sm nd source region mainly composed of olivine and orthopyroxene with minor amounts of plagioclase or clinopyroxene and with sulfides enriched in volatile chalcophile elements the basalt source may be deep in origin and different in chemistry from those previously estimated from studies of apollo and luna mare basalts indicating heterogeneous sources for mare basalts

gravitational differentiation due to initial chemical stratification origin of lunar asymmetry by the creep of dense kreep abstract models for the evolution of the moon must explain a number of important characteristics of its magmatic history primary among them is the emplacement of mare basalts primarily on one side of the moon and in a region of the surface roughly correlating with that containing high subsurface concentrations of kreep it is thus important to explore mechanisms which will regionally concentrate a kreep layer early in lunar evolution and which 400 500 myr later give rise to mare basalt generation beneath the same region gravitational instability of a chemically dense ilmenite rich cumulate created during the fractionation of an anorthositic crust is one candidate model if so gravitational instability must occur at long wavelength to explain the hemispheric asymmetry we examine the rayleigh taylor instability of a dense layer near the surface of a sphere representing the lunar mantle in which the viscosity varies with depth our results show that spherical harmonic degree 1 is the fastest growing wavelength of instability if the viscosity of the dense layer is sufficiently low relative to that of the deeper mantle or if the viscosity of the mantle increases with depth however the viscosity increase cannot be distributed over a depth that is too large we explore whether a residual kreep like layer near the base of anorthositic crust might give rise to these needed conditions

u pb ages of angrites abstract precise u pb ages determined with double spike 202 pb 205 pb thermal ionization m1ass spectrometry are reported for angrites angra dos reis ador lewis cliff 86010 lew and d orbigny nineteen of 23 acid washed pyroxene fractions from these meteorites and whole rock fractions from d orbigny contain between 0 5 and 1 3 pg of total common pb indistinguishable from analytical blank measured 206 pb 204 pb ratios in these fractions are between 6300 and 14 100 for ador 1160 4500 for lew and 608 8500 for d orbigny blank corrected 206 pb 204 pb ratios for all three meteorites vary from 2160 to over 100 000 these fractions yielded precise and reproducible 207 pb 206 pb dates with the average values of 4557 65 0 13 ma for ador 4558 55 0 15 ma for lew and 4564 42 0 12 ma for d orbigny pb pb isochrons including data with slightly elevated common pb and u pb upper concordia intercepts yield similar dates the implications of these new pb isotopic ages of angrites are threefold first they demonstrate that ador and lew are not coeval and the group of slowly cooled angrites is therefore genetically diverse second the new age of lew suggests an upward revision of 53 mn 53 cr absolute ages by 0 7 ma third a precise age of d orbigny allows consistent linking of the 53 mn 53 cr and 26 al 26 mg extinct nuclide chronometers to the absolute lime scale

trace element partitioning between high an plagioclase and basaltic to basaltic andesite melt at 1 atmosphere pressure we determined plagioclase melt partition coefficients for 18 elements by performing controlled cooling rate 1 atmosphere experiments using both natural and synthetic basaltic 51 wt sio2 and basaltic andesite 56 wt sio2 powders in a vertical quench furnace the experiments produced an69 to an87 composition plagioclase three starting powders were gorda ridge basalt synthetic diopside 40 albite 28 anorthite 32 mixture and arenal volcano costa rica basaltic andesite the gorda and synthetic powders were doped at both low concentrations 20 200 ppm and high concentration 200 5000 ppm whereas the arenal powder was doped only at high concentrations resulting in two doped gorda powders low np and high sdp two doped diopside albite anorthite powders low dad high sdd and one doped arenal powder high ar99 2 trace elements concentrations in both glass and plagioclase were measured by secondary ion mass spectrometry sims and or by laser ablation inductively coupled plasma mass spectrometry la icp ms results for the partitioning of trace elements between plagioclase and melt at different doping levels demonstrate both adherence to henry s law and good agreement between the different analytical techniques in general plagioclase melt partition coefficients determined in the an69 73 range are similar to other published values however some of those occurring for plagioclase compositions an75 are distinctly lower than those predicted by current regression formulations we applied a two lattice melt model to these data to account for differences in melt composition and temperature and found that there were no aberrations associated with partition coefficients a new set of regression formulations is determined involving the newly determined dataset for plagioclase with an contents between 75 and 87