very preliminary reference moon model abstract the deep structure of the moon is a missing piece to understand the formation and evolution of the earth moon system despite the great amount of information brought by the apollo passive seismic experiment alsep the lunar structure below deep moonquakes which occur around 900 km depth remains largely unknown we construct a reference moon model which incorporates physical constraints and fits both geodesic lunar mass and polar moment of inertia and love numbers and seismological body wave arrivals measured by apollo network data in this model the core radius is constrained by the detection of s waves reflected from the core in a first step for each core radius a radial model of the lunar interior including p and s wave velocities and density is inverted from seismic and geodesic data in a second step the core radius is determined from the detection of shear waves reflected on the lunar core by waveform stacking of deep moonquake apollo records this detection has been made possible by careful data selection and processing including a correction of the gain of horizontal sensors based on the principle of energy equipartition inside the coda of lunar seismic records and a precise alignment of sh waveforms by a non linear inversion method the very preliminary reference moon model vpremoon obtained here has a core radius of 380 40 km and an average core mass density of 5200 1000 kg m 3 the large error bars on these estimates are due to the poorly constrained s wave velocity profile at the base of the mantle and to mislocation errors of deep moonquakes the detection of horizontally polarized s waves reflected from the core and the absence of detection of vertically polarized s waves favour a liquid state in the outermost part of the core all these results are consistent within their error bars with previous estimates based on lunar rotation dissipation williams et al 2001 and on lunar induced magnetic moment hood et al 1999

seismic detection of the lunar core despite recent insight regarding the history and current state of the moon from satellite sensing and analyses of limited apollo era seismic data deficiencies remain in our understanding of the deep lunar interior we reanalyzed apollo lunar seismograms using array processing methods to search for the presence of reflected and converted seismic energy from the core our results suggest the presence of a solid inner and fluid outer core overlain by a partially molten boundary layer the relative sizes of the inner and outer core suggest that the core is 60 liquid by volume based on phase diagrams of iron alloys and the presence of partial melt the core probably contains less than 6 weight of lighter alloying components which is consistent with a volatile depleted interior

indicators of aqueous alteration in cm carbonaceous chondrites microtextures of a layered mineral containing fe s o and ni a petrographic and transmission electron microscopy study of the mighei murchison and murray cm carbonaceous chondrites shows that much of the cm matrix material was probably produced by aqueous alteration of olivine pyroxene sulfide and metal the amount of cm matrix appears to be proportional to the degree of alteration as suggested by mcsween 1979 and microtextures of pcp poorly characterized phase provide evidence of the progressive alteration pcp is divided into two major types one occurs in chondrules and aggregates and consists largely of an fe ni s o phase type i and the other occurs in matrix and consists of the fe ni s o phase and cronstedtite in various proportions type ii microtextures of pcp suggest that it resulted from a three stage alteration process 1 1 type i was produced by alteration of kamacite in chondrules and aggregates presumably early in the parent body regolith 2 2 as the alteration advanced olivine and pyroxene were converted to serpentine type i pcp separated from chondrules and aggregates into the matrix during regolith gardening simultaneously the fe ni s o phase reacted with si released by alteration of olivine and pyroxene producing well formed platy cronstedtite and coherent intergrowths of the fe ni s o phase and cronstedtite the fe ni s o phase also recrystallized into platy and pod like crystals fe s ni cr and p were leached out of type i pcp and were deposited as small grains of fe ni sulfides magnetite chromite and a mineral unidentified containing fe ni cr and p as a result pcp came to consist primarily of the fe ni s o phase and cronstedtite i e type ii pcp 3 3 during continued alteration the well formed crystals of the fe ni s o phase cronstedtite and their intergrowths in type ii pcp were replaced by poorly formed fibers in comparison to other cm chondrites mighei murchison and murray are relatively unaltered their matrices retain abundant amounts of the fe ni s o phase and cronstedtite commonly as distinctive pcp grains which account for a large proportion of the fe in these meteorite matrices in more altered cm chondrites much of the fe ni s o phase was probably consumed to produce cronstedtite magnetite and sulfides with further alteration cronstedtite itself reacted with the serpentine to form ferroan serpentine thus the cm matrix was increasingly enriched in mg with alteration and pcp was increasingly degraded and intimately mixed with the magnesian phyllosilicates

aragonite breunnerite calcite and dolomite in the cm carbonaceous chondrites high fidelity recorders of progressive parent body aqueous alteration abstract carbonate minerals in cm carbonaceous chondrite meteorites along with the silicates and sulphides with which they are intergrown provide a detailed record of the nature and evolution of parent body porosity and permeability and the chemical composition temperature and longevity of aqueous solutions fourteen meteorites were studied that range in petrologic subtype from mildly aqueously altered cm2 5 to completely hydrated cm2 0 all of them contain calcite whereas aragonite occurs only in the cm2 5 cm2 2 meteorites and dolomite in the cm2 2 cm2 0 all of the aragonite crystals and most of the calcite and dolomite grains formed during early stages of parent body aqueous alteration by cementation of pores produced by the melting of tens of micrometre size particles of h2o rich ice aragonite was the first carbonate to precipitate in the cm2 5 to cm2 2 meteorites and grew from magnesium rich solutions in the least altered of these meteorites the aragonite crystals formed in clusters owing to physical restriction of aqueous fluids within the low permeability matrix the strong correlation between the petrologic subtype of a meteorite the abundance of its aragonite crystals and the proportion of them that have preserved crystal faces is because aragonite was dissolved in the more altered meteorites on account of their higher permeability and or greater longevity of the aqueous solutions dolomite and breunnerite formed instead of aragonite in some of the cm2 1 and cm2 2 meteorites owing to higher parent body temperatures the pore spaces that remained after precipitation of aragonite dolomite and breunnerite cements were occluded by calcite following completion of cementation the carbonates were partially replaced by phyllosilicates and sulphides calcite in the cm2 5 cm2 2 meteorites was replaced by fe rich serpentine and tochilinite followed by mg rich serpentine in the cm2 1 and cm2 0 meteorites dolomite breunnerite and calcite were replaced by fe rich serpentine and fe ni sulphide again followed by mg rich serpentine the difference between meteorites in the mineralogy of their replacive sulphides may again reflect greater temperatures in the parent body regions from where the more highly altered cms were derived this transition from fe rich to mg rich carbonate replacement products mirrors the chemical evolution of parent body solutions in response to consumption of fe rich primary minerals followed by the more resistant mg rich anhydrous silicates almost all of the cms examined contain a second generation of calcite that formed after the sulphides and phyllosilicates and by replacement of remaining anhydrous silicates and dolomite dedolomitization the ca and co2 required for this replacive calcite is likely to have been sourced by dissolution of earlier formed carbonates and ions may have been transported over metre plus distances through high permeability conduits that were created by impact fracturing

carbonates in cm2 chondrites constraints on alteration conditions from oxygen isotopic compositions and petrographic observations high precision measurements of the oxygen isotopic compositions of carbonates calcite and dolomite from five cm2 chondrites are presented and put into context of the previously determined mineralogic alteration index mai which places these meteorites into an alteration sequence the carbonate oxygen isotopic compositions range from 20 0 to 35 7 for 18o 8 0 to 17 7 for 17o and 0 7 to 2 7 for 17o carbonate 17o values are inversely correlated with mai and track the evolution of fluid composition from higher to lower 17o values with increasing alteration on the cm parent body similar 17o values for calcite and dolomite fractions from the same splits of the same meteorites indicate that calcite and dolomite in each split precipitated from a single fluid reservoir however reversed calcite dolomite fractionations 18odol 18occ indicate that the fluid was subject to processes such as freeze thaw or evaporation that fractionated isotopes in a mass dependent way consideration of the carbonate isotopic data in the context of previously proposed models for aqueous alteration of carbonaceous chondrites has provided important insights into both the evolving alteration conditions and the utility of the models themselves the data as a whole indicate that the isotopic evolution of the fluid was similar to that predicted by the closed system two reservoir models but that a slightly larger matrix water fractionation factor may apply in the context of this model more altered samples largely reflect greater reaction progress and thus probably indicate more extended times of fluid exposure petrographic observations of carbonates reveal a trend of variable carbonate morphology correlated with alteration that is also consistent with changes in the duration of fluid rock interaction the data can also be reconciled with fluid flow models in a restricted region of the parent body which is consistent with assertions that the different types of carbonaceous chondrites derive from different regions of their parent bodies in this case the model results for a 9 km radius body and our data place the location of the cm chondrite formation in a 100 m thick zone 1 km from the surface the size of this zone could be increased if the model parameters were adjusted

fluid evolution in cm carbonaceous chondrites tracked through the oxygen isotopic compositions of carbonates the oxygen isotopic compositions of calcite grains in four cm carbonaceous chondrites have been determined by nanosims and results reveal that aqueous solutions evolved in a similar manner between parent body regions with different intensities of aqueous alteration two types of calcite were identified in murchison mighei cold bokkeveld and lapaz icefield 031166 by differences in their petrographic properties and oxygen isotope values type 1 calcite occurs as small equant grains that formed by filling of pore spaces in meteorite matrices during the earliest stages of alteration on average the type 1 grains have a 18o of 32 36 vsmow and 17o of between 2 and 1 most grains of type 2 calcite precipitated after type 1 they contain micropores and inclusions and have replaced ferromagnesian silicate minerals type 2 calcite has an average 18o of 21 24 vsmow and a 17o of between 1 and 3 such consistent isotopic differences between the two calcite types show that they formed in discrete episodes and from solutions whose 18o and 17o values had changed by reaction with parent body silicates as predicted by the closed system model for aqueous alteration temperatures are likely to have increased over the timespan of calcite precipitation possibly owing to exothermic serpentinisation the most highly altered cm chondrites commonly contain dolomite in addition to calcite dolomite grains in two previously studied cm chondrites have a narrow range in 18o 25 29 vsmow with 17o 1 to 3 these grains are likely to have precipitated between types 1 and 2 calcite and in response to a transient heating event and or a brief increase in fluid magnesium calcium ratios in spite of this evidence for localised excursions in temperature and or solution chemistry the carbonate oxygen isotope record shows that fluid evolution was comparable between many parent body regions the cm carbonaceous chondrites studied here therefore sample either several parent bodies with a very similar initial composition and evolution or more probably a single c type asteroid

improved gravity field of the moon from lunar prospector an improved gravity model from doppler tracking of the lunar prospector lp spacecraft reveals three new large mass concentrations mascons on the nearside of the moon beneath the impact basins mare humboltianum mendel ryberg and schiller zucchius where the latter basin has no visible mare fill although there is no direct measurement of the lunar farside gravity lp partially resolves four mascons in the large farside basins of hertzsprung coulomb sarton freundlich sharonov and mare moscoviense the center of each of these basins contains a gravity maximum relative to the surrounding basin the improved normalized polar moment of inertia 0 3932 0 0002 is consistent with an iron core with a radius of 220 to 450 kilometers

oxygen isotope studies of carbonaceous chondrites abstract the carbonaceous chondrites display the widest range of oxygen isotopic composition of any meteorite group as a consequence of the interaction of primordial isotopic reservoirs in the solar nebula these isotopic variations can be used to identify the reservoirs and to determine conditions and loci of their interactions we present a comprehensive set of whole rock analyses of cv co ck cm cr ch and ci chondrites as well as selected components of some of these meteorites a simple model is developed which describes the isotopic behavior during parent body aqueous alteration processes the process of thermal dehydration also produces a recognizable effect in the oxygen isotopic composition

the oxygen isotope record in murchison and other carbonaceous chondrites the ranges of 18o and 17o in components of the murchison c2 chondrite exceed those in all other meteorites analyzed previous authors have proposed that c2 chondrites are the products of aqueous alteration of anhydrous silicates a model is presented to determine whether the isotopic variations can be understood in terms of such alteration processes the minimum number two of initial isotopic reservoirs is assumed two major stages of reservoir interaction are required one at high temperature to produce the16o mixing line observed for the anhydrous minerals and another at low temperature to produce the matrix minerals the isotopic compositions severely constrain the conditions of the low temperature process requiring temperatures 44 extension of the model to the data on c1 chondrites requires aqueous alteration in a warmer wetter environment

temperatures of aqueous alteration and evidence for methane generation on the parent bodies of the cm chondrites aqueous alteration of primitive meteorites was among the earliest geological processes during the evolution of our solar system clumped isotope thermometry of carbonates in the cm chondrites cold bokkeveld murray and murchison demonstrates that they underwent aqueous alteration at 20 71 c from a fluid with 18 o vsmow of 2 0 to 8 1 and 17 o vsmow of 0 1 to 3 0 the 13 c vpdb values of these carbonates exhibit a negative correlation with the 18 o vsmow of their formation waters consistent with formation and escape of 13 c depleted ch 4 during aqueous alteration methane generation under these conditions implies that the alteration fluid was characterized by an eh 0 67 and ph 12 5 or lower at the highest alteration temperatures our findings suggest that methane generation may have been a widespread consequence of planetesimal and planetary aqueous alteration perhaps explaining the occurrence of methane on titan triton pluto and other kuiper belt objects

episodic carbonate precipitation in the cm chondrite alh 84049 an ion microprobe analysis of o and c isotopes we have determined the o and c isotope compositions of dolomite grains and the c isotope compositions of calcite grains in the highly altered cm1 chondrite alh 84049 using secondary ion mass spectrometry sims chemically zoned dolomite constitutes 0 8 volume percent vol of the sample and calcite 0 9 vol thirteen separate dolomite grains have 13c values that range from 37 to 60 2 18 o values from 25 to 32 3 and 17 o values from 10 to 16 3 vsmow intragrain 13 c values in dolomite vary up to 10 the 13 c values of three calcite grains are distinct from those of dolomite and range from 10 to 13 2 pdb calcite and dolomite appear to record different precipitation episodes carbon isotope values of both dolomite and calcite in this single sample encompass much of the reported range for cm chondrites our results imply that bulk carbonate c and o isotope analyses may oversimplify the history of carbonate precipitation multiple generations of carbonates with variable isotope compositions exist in alh 84049 and perhaps in many cm chondrites this work shows that one should exercise caution when using a clumped isotope approach to determine the original temperature and the isotopic compositions of water for cm chondrite carbonates less altered cm meteorites with more homogeneous c isotope compositions however may be suitable for bulk carbonate analyses but detailed carbonate petrologic and isotopic characterization of individual samples is advised

a seismic model of the lunar mantle and constraints on temperature and mineralogy abstract we determine seismic profiles of the moon s interior using travel times obtained from a re analysis of the apollo data due to the limited number of quakes and stations travel times errors were determined and used in the inversions our model has a mean crustal thickness of about 30 km in the region of the apollo network with a 10 km zone of brecciation below the crust mean values of seismic velocities in the upper mantle are rather well constrained and are in the range 7 6 7 8 and 4 35 4 45 km s 1 for p and s waves respectively velocity variations in the middle mantle are less well defined in the zone of deep moonquakes below 740 km depth velocities increase slightly to 8 15 0 23 and 4 5 0 10 km s 1 for p and s waves respectively we analyse the seismic profile in term of mineralogy and temperature constraints our preferred models are a pyroxenite model for the upper mantle and a magnesian rich model for the lower mantle with increasing mg with depth we find temperatures of about 1100 k elastic lithosphere limit and 1500 k thermal lithosphere limit for radii of about 1400 and 1000 km respectively and show that the lunar mantle is probably depleted in th and u by at least 70 compared to an earth reference value of 25 7 ppb u for a crustal thickness of 40 km with a mean 1010 ppb th concentration we then find bulk th and u abundances comparable to and possibly lower than currently accepted terrestrial values

the hydrology of carbonaceous chondrite parent bodies and the evolution of planet progenitors oxygen isotope ratio data from carbonaceous chondrites are explained if aqueous fluids flowed from high to low temperatures within the parent objects of these primitive meteorites recognition of ancient hydrological activity on primitive asteroid precursors affords a new class of constraints on the heat sources ages and sizes of planet precursors in the early solar system based on the geological evolution of planetesimals

an early lunar core dynamo driven by thermochemical mantle convection although the moon currently has no internally generated magnetic field palaeomagnetic data combined with radiometric ages of apollo samples provide evidence for such a magnetic field from 3 9 to 3 6 billion years gyr ago1 possibly owing to an ancient lunar dynamo1 2 but the presence of a lunar dynamo during this time period is difficult to explain1 2 3 4 because thermal evolution models for the moon5 yield insufficient core heat flux to power a dynamo after 4 2 gyr ago here we show that a transient increase in core heat flux after an overturn of an initially stratified lunar mantle might explain the existence and timing of an early lunar dynamo using a three dimensional spherical convection model6 we show that a dense layer enriched in radioactive elements a thermal blanket at the base of the lunar mantle can initially prevent core cooling thereby inhibiting core convection and magnetic field generation subsequent radioactive heating progressively increases the buoyancy of the thermal blanket ultimately causing it to rise back into the mantle the removal of the thermal blanket proposed to explain the eruption of thorium and titanium rich lunar mare basalts7 plausibly results in a core heat flux sufficient to power a short lived lunar dynamo

modal mineralogy of cm2 chondrites by x ray diffraction psd xrd part 1 total phyllosilicate abundance and the degree of aqueous alteration abstract cm carbonaceous chondrites are samples of incompletely serpentinized primitive asteroids using position sensitive detector x ray diffraction psd xrd and a pattern stripping technique we quantify the modal mineralogy of cm2 chondrites mighei murray murchison nogoya and cold bokkeveld there is a narrow range in the combined modal volume vol of the most abundant phases mg serpentine 25 33 and fe cronstedtite 43 50 cold bokkeveld is anomalous in containing more mg serpentine 49 59 than fe cronstedtite 19 27 even including cold bokkeveld the range in modal total phyllosilicate is 73 79 average 75 total phyllosilicate abundance provides a non ambiguous measure of the degree of aqueous alteration and indicates that these meteorites have all experienced essentially the same degree of aqueous alteration this reflects pervasive hydration of matrix across cm2 samples apparent differences in the alteration of chondrules observed in petrographic studies represent various stages in the progression towards complete hydration of all components but are not manifest in significant differences in modal mineralogy for all samples there is a limited range in olivine 6 9 and pyroxene 5 abundances modal abundances of the remaining identified phases also show a limited range calcite 0 1 3 gypsum 0 1 6 magnetite 1 1 2 4 pentlandite 0 2 1 and pyrrhotite 1 3 8 as expected we observe a strong negative correlation in the modal abundance of anhydrous fe mg silicates olivine pyroxene and total phyllosilicate mg serpentine fe cronstedtite consistent with the idea that phyllosilicate is forming by aqueous alteration of the anhydrous components the negative correlation in the modal abundance between mg serpentine and fe cronstedtite indicates a mineralogic transformation of fe cronstedtite to mg serpentine by fluid driven recrystallisation or b that these meteorites had different initial abundances of olivine and pyroxene the observed positive correlation in the relative proportion of mg serpentine with increasing total phyllosilicate abundance reflects the evolution of increasingly mg rich phyllosilicate during aqueous alteration fe cronstedtite is the dominant phyllosilicate while cm chondrule olivines are forsteritic and will form mg serpentine during aqueous alteration this implies that matrix olivine was more fe rich than chondrule olivine prior to aqueous alteration

thermal state and solidification regime of the martian core insights from the melting behavior of feni s at 20 gpa abstract a series of multi anvil experiments have been conducted to define the iron rich liquidus of the iron nickel sulfur feni s system at 20 gpa the estimated pressure of the martian core mantle boundary cmb the liquidus curve of feni s containing about 9 wt ni has a concave up shape and is as much as 400 k lower than the liquidi previously applied to the martian core with sparse experimental constraints unlike existing liquidi of fe s and feni s at 23 gpa which predict a fully molten core for a narrow range of sulfur content between 14 and 15 wt s our results are consistent with a molten state for all proposed core compositions and establishes a new minimum cmb temperature of 1500 k for 10 wt s and 1250 k for 16 wt s extrapolating our feni s liquidus to high pressures and comparing it to calculated areotherms we find that three core crystallization regimes are possible for a martian core with moderate sulfur content 10 to 13 wt or lower crystallization takes the form of iron snow near the cmb while for cores with higher sulfur content 15 16 wt solidification occurs near the center of the planet in the form of solid fe3s at an intermediate sulfur content of 14 wt fe3s would precipitate over a broad depth range and may appear fully molten to surface observations

minor and trace element concentrations in carbonates of carbonaceous chondrites and implications for the compositions of coexisting fluids abstract abundances of fe mg mn sr na b and ba in meteoritic calcites and dolomites have been determined using the ion microprobe the compositions of these carbonates are consistent with their precipitation from or recrystallization in equilibrium with aqueous solutions at low temperatures coexisting calcites and dolomites in cm chondrites are not in equilibrium and presumably formed in distinct events calculated molar element ca ratios for fluids in equilibrium with these carbonates suggest that dolomites in cm and cl chondrites formed from compositionally similar brines calcite solutions were also saline but lower in mg fe and mn calculations suggest that these solutions became more like dolomite solutions with increasing alteration of the host cm meteorite reflecting progressive evolution of solution compositions asteroid brines may have formed by membrane nitration after the formation of compacted phyllosilicates lowered permeability by addition of components to fluids during phyllosilicate forming reactions or through low pressure boiling occurrences of vein filling calcite followed by dolomite and later by sulfates in carbonaceous chondrites represent the final stages of a protracted aqueous alteration sequence

the formation and alteration of the renazzo like carbonaceous chondrites i implications of bulk oxygen isotopic composition abstract to better understand the role of aqueous alteration on the cr chondrite parent asteroid a whole rock oxygen isotopic study of 20 meteorites classified as renazzo like carbonaceous chondrites cr was conducted the cr chondrites analyzed for their oxygen isotopes were dhofar 1432 elephant moraine eet 87770 eet 92042 eet 96259 gao guenie b graves nunataks gra 95229 gra 06100 grosvenor mountains gro 95577 gro 03116 lapaz ice field lap 02342 lap 04720 meteorite hills met 00426 north west africa nwa 801 pecora escarpment pca 91082 queen alexandra range que 94603 que 99177 and yamato 793495 y 793495 three of the meteorites asuka 881595 a 881595 gra 98025 and met 01017 were found not to be cr chondrites the remaining samples concur petrographically and with the well established oxygen isotope mixing line for the cr chondrites their position along this mixing line is controlled both by the primary oxygen isotopic composition of their individual components and their relative degree of aqueous alteration combined with literature data and that of this study we recommend the slope for the cr mixing line to be 0 70 0 04 2 with a 17 o intercept of 2 23 0 14 2 thin sections of al rais shisr 033 renazzo and all but 3 samples analyzed for oxygen isotopes were studied petrographically the abundance of individual components is heterogeneous among the cr chondrites but feo poor chondrules and matrix are the most abundant constituents and therefore dominate the whole rock isotopic composition the potential accreted ice abundance physico chemical conditions of aqueous alteration e g temperature and composition of the fluid and its duration control the degree of alteration of individual cr chondrites combined with literature data we suggest that lap 02342 was exposed to lower temperature fluid during alteration than gra 95229 with only two falls terrestrial alteration of the cr chondrites complicates the interpretation of their whole rock isotopic composition particularly in the most aqueously altered samples and those with relatively higher matrix abundances we report that que 99177 is the isotopically lightest whole rock cr chondrite known 18 o 2 29 17 o 4 08 possibly due to isotopically light unaltered matrix which shows that the anhydrous component of the cr chondrites is isotopically lighter than previously thought although it experienced aqueous alteration que 99177 provides the best approximation of the pristine cr chondrite parent body s oxygen isotopic composition before aqueous alteration took place using this value as a new upper limit on the anhydrous component of the cr chondrites water rock ratios were recalculated and found to be higher than previously thought ratios now range from 0 281 to 1 157 we also find that according to their oxygen isotopes a large number of cr chondrites appear to be minimally aqueously altered although sample heterogeneity complicates this interpretation

abundances of presolar silicon carbide grains in primitive meteorites determined by nanosims abstract it has been suggested that the matrices of all chondrites are dominated by a common material with ivuna like ci abundances of volatiles presolar grains and insoluble organic matter iom e g alexander 2005 however matrix normalized abundances of presolar silicon carbide sic grains estimated from their noble gas components show significant variations in even the most primitive chondrites huss and lewis 1995 huss et al 2003 in contradiction to there being a common chondrite matrix material here we report presolar sic abundances determined by nanosims raster ion imaging of iom extracted from primitive members of different meteorite groups we show that presolar sic abundance determinations are comparable between nanosims instruments located at three different institutes between residues prepared by different demineralization techniques and between microtomed and non microtomed samples our derived sic abundances in cr chondrites are comparable to those found in the ci chondrites 30 ppm and are much higher than previously determined by noble gas analyses the revised higher cr sic abundances are consistent with the crs being amongst the most primitive chondrites in terms of the isotopic compositions and disordered nature of their organic matter similar abundances between cr1 cr2 and cr3 chondrites indicate aqueous alteration on the cr chondrite parent body has not progressively destroyed sic grains in them a low sic abundance for the reduced cv3 rbt 04133 can be explained by parent body thermal metamorphism at an estimated temperature of 440 c minor differences between primitive members of other meteorite classes which did not experience such high temperatures may be explained by prolonged oxidation at lower temperatures under which sic grains formed outer layers of sio2 that were not thermodynamically stable leading to progressive degassing destruction of sic

presumption of large scale heterogeneity at the top of the outer core basal layer abstract a layer of reduced p velocity gradient with thickness of about 100 200 km has been identified at the base of the liquid core from seismological methods it has been interpreted as a dense layer resulting from partial re melting of the inner core which is depleted in light elements with respect to the liquid core during freezing in an attempt to specify where freezing and re melting occur the structure of this basal layer is investigated with the seismological core phase pkpbc which has its turning point in the lower third of the outer core the large pkpbc data set of the ehb catalog distributed by the international seismological centre is analyzed in order to compensate for the uneven distribution of the data and to minimize the influence of mantle heterogeneities the travel time anomalies are binned inside equal area and equal azimuth sectors sampling the base of the liquid core at different depths most of the observed variations in the binned travel time residuals are not significant according to their confidence level the only features which could be significant are a large patch with a velocity increase of about 0 5 located at the top of the basal layer beneath the eastern hemisphere and the complementary velocity decrease beneath the western hemisphere and the south pole this observation suggests that some freezing or re melting processes occur at the top of the basal layer with a hemispherical dissymmetry if confirmed it may give strong constraints on the fate of the light elements during the freezing and re melting process and on their interaction with the basal layer and the overlying liquid core

magnetic field generation in the lunar core the role of inner core growth abstract the source of the magnetic field recorded in the lunar crust remains an unresolved problem the field was most likely produced by a self sustaining dynamo in the moon s electrically conducting metal core but heat flux across the core mantle boundary was probably insufficient to power a dynamo for the field s currently known duration from 4 2 to 3 56 ga since seismic measurements indicate the existence of a solid iron inner core in addition to a still liquid iron alloy outer core inner core solidification and its associated thermochemically driven convection in the outer core could have been responsible for extending the dynamo s lifetime even in the absence of superadiabatic heat flux here we present a coupled mantle core thermal evolution model of the moon and show that core solidification could explain the onset and shutoff of the lunar dynamo consistent with the global magnetic field inferred from the paleomagnetic record

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

the lunar dynamo background it is unknown whether the moon has a fully differentiated and melted structure with a metallic core or retains a partially primordial unmelted interior the differentiation history of the moon is manifested by its record of past magnetism paleomagnetism although the moon today does not have a global magnetic field the discovery of remanent magnetization in lunar rocks and in the lunar crust demonstrated that there was a substantial lunar surface field billions of years ago however the origin intensity and lifetime of this field have been uncertain as a result it has been unclear whether this magnetization was produced by a dynamo in the moon s advecting metallic core or by fields generated externally to the moon establishing whether the moon formed a core dynamo would have major implications for understanding its interior structure thermal history and mechanism of formation as well for our understanding of the physics of planetary magnetic field generation the interior structure of the moon and the lunar dynamo new magnetic measurements of lunar rocks have demonstrated that the ancient moon generated a dynamo magnetic field in its advecting liquid metallic core innermost red shell this dynamo may have been driven by convection possibly powered by crystallization of the core innermost red sphere and or stirring from the solid mantle thick green shell the magnetic field was recorded as magnetization by rocks on the lunar surface image created by hernan canellas the interior structure of the moon and the lunar dynamo new magnetic measurements of lunar rocks have demonstrated that the ancient moon generated a dynamo magnetic field in its advecting liquid metallic core innermost red shell this dynamo may have been driven by convection possibly powered by crystallization of the core innermost red sphere and or stirring from the solid mantle thick green shell the magnetic field was recorded as magnetization by rocks on the lunar surface image created by hernan canellas advances a new generation of laboratory magnetic studies of lunar rocks and spacecraft measurements of lunar crustal magnetic fields have produced major advances in our understanding of the evolution of ancient magnetic fields on the moon it has now been established that a dynamo magnetic field likely existed on the moon from at least 4 5 billion to 3 56 billion years ago with an intensity similar to that at the surface of earth today the field then declined by at least an order of magnitude by 3 3 billion years ago the early epoch of high field intensities may require an exceptionally energetic power source such as mechanical stirring from mantle precession the extended history of the lunar dynamo appears to demand long lived power sources such as mantle precession and core crystallization outlook measurements of the intensity of the ancient lunar dynamo have shown that it was surprisingly intense and long lived the next phase of lunar magnetic exploration will be to obtain more accurate measurements of field paleointensities and to determine when the dynamo initiated and finally disappeared this will be coupled with the continued development of magnetohydrodynamic models for characterizing mechanical and other unusual dynamo mechanisms and further investigations into the thermal structural and geodynamical history of the lunar core and mantle the eventual availability of absolutely oriented samples and in situ spacecraft measurements of bedrock should enable the first measurements of the paleo orientation of lunar magnetic fields such directional data could determine the lunar field s geometry and reversal frequency as well as constrain ancient local and global scale tectonic events

radar enabled recovery of the sutter s mill meteorite a carbonaceous chondrite regolith breccia doppler weather radar imaging enabled the rapid recovery of the sutter s mill meteorite after a rare 4 kiloton of tnt equivalent asteroid impact over the foothills of the sierra nevada in northern california the recovered meteorites survived a record high speed entry of 28 6 kilometers per second from an orbit close to that of jupiter family comets tisserand s parameter 2 8 0 3 sutter s mill is a regolith breccia composed of cm mighei type carbonaceous chondrite and highly reduced xenolithic materials it exhibits considerable diversity of mineralogy petrography and isotope and organic chemistry resulting from a complex formation history of the parent body surface that diversity is quickly masked by alteration once in the terrestrial environment but will need to be considered when samples returned by missions to c class asteroids are interpreted

sulfur contents of the parental metallic cores of magmatic iron meteorites abstract magmatic iron meteorites are thought to be samples of the central metallic cores of asteroid sized parent bodies sulfur is believed to have been an important constituent of these parental cores but due to the low solubility of s in solid metal initial s contents for the magmatic groups cannot be determined through direct measurements of the iron meteorites however experimental solid metal liquid metal partition coefficients show a strong dependence on the s content of the metallic liquid thus by using the experimental partition coefficients to model the fractional crystallization trends within magmatic iron meteorite groups the s contents of the parental cores can be indirectly estimated modeling the au ga ge and ir fractionations in four of the largest magmatic iron meteorite groups leads to best estimates for the s contents of the parental cores of 12 1 5 wt for the iiiab group 17 1 5 wt for the iiab group and 1 1 wt for the ivb group the iva elemental fractionations are not adequately fit by a simple fractional crystallization model with a unique initial s content these s content estimates are much higher than those recently inferred from crystallization models involving trapped melt the discrepancy is due largely to the different partition coefficients that are used by the two models when only partition coefficients that are consistent with the experimental data are used the trapped melt model and the low s contents it advocates cannot match the ge and ir fractionations that are observed in iiiab iron meteorites

paleointensity determination using anhysteretic remanence and saturation isothermal remanence 1 determining the strength of ancient planetary magnetic field is pivotal to understanding the evolution of planets and asteroids in the solar system while the thellier type double heating technique provides the most faithful field strength information for rocks carrying a thermoremanent magnetization trm many extraterrestrial rock samples respond unfavorably to heat treatment the present study systematically examined the two well known normalization techniques that avoid any heating by comparing the ratios of trm anhysteretic remanent magnetization arm and trm saturation isothermal remanent magnetization sirm both the ratios of trm arm and trm sirm are dependent on the grain size as well as the volume concentration of magnetite the remanence ratios also were found to increase as the alternating field increased during demagnetization for fine grained magnetite a new calibration relation of 2 60 1 32 for the trm arm and of 3 62 1 28 10 2 for the trm sirm was defined for an external field of 50 t the trm sirm is superior to trm arm because the former showed less dispersion in the grain size dependence the volume concentration dependence and the stability against af demagnetization in addition the standard error of the mean for the trm sirm ratio was smaller than that for the trm arm ratio thus whenever heating is inapplicable the sirm method seems to be a better choice than the arm method however it should be emphasized that the uncertainty of trm arm and trm sirm is still nearly an order of magnitude larger than that of the high fidelity thellier estimation and thus must be limited in use only when samples are irreversibly altered during heating in practice the best approach is to carry out both arm and sirm methods and check whether the two estimations agree within the uncertainties

sound velocity of fe s liquids at high pressure implications for the moon s molten outer core article history sound velocities of fe and fe s liquids were determined by combining the ultrasonic measurements and synchrotron x ray techniques under high pressure temperature conditions from 1 to 8 gpa and 1573 k to 1973 k four different liquid compositions were studied including fe fe 10 wt s fe 20 wt s and fe 27 wt s our data show that the velocity of fe rich liquids increases upon compression and decreases with increasing sulfur content whereas temperature has negligible effect on the velocity of fe s liquids the sound velocity data were combined with ambient pressure densities to fit the murnaghan equation of state eos compared to the lunar seismic model our velocity data constrain the sulfur content at 4 3 wt indicating a significantly denser 6 5 0 5g cm3 and hotter 1870 100 70 k outer core than previously estimated a new lunar structure model incorporating available geophysical observations points to a smaller core radius our model suggests a top down solidification scenario for the evolution of the lunar core such iron snow process may have been an important mechanism for the growth of

carbonate compositions in cm and ci chondrites and implications for aqueous alteration abstract carbonate minerals in fourteen cm chondrites and two ci chondrites have been analyzed by electron microprobe to provide a better understanding of the aqueous processes that affected carbonaceous chondrite parent bodies calcites in cm chondrites and dolomites and magnesites in ci chondrites display the compositions expected of stable phases formed at low temperatures dolomites in cm chondrites identified here for the first time in five members of the group have small amounts of excess ca which may reflect metastable growth the distribution of fe between dolomite and coexisting serpentine differs in the two chondrite groups if the distributions reflect an approach to chemical equilibrium then the difference implies higher alteration temperatures for the ci group than the cm group in agreement with the results of previously published oxygen isotope thermometry and mineral solubility modeling of the alteration process dolomite fe contents are relatively uniform in the two chondrite groups dolomite mn contents by contrast vary widely the variations may reflect transport controlled coprecipitation of mn resulting from a heterogeneous distribution of the element in the anhydrous precursor material if this interpretation is correct then the altering fluids were essentially immobile while hydration reactions proceeded on the meteorite parent bodies the near closed system character of the alteration process long known from bulk chemical analyses of the meteorites is a direct consequence of the limited mobility of dissolved species

progressive aqueous alteration of cm carbonaceous chondrites abstract cm chondrites are aqueously altered rocks that contain 9 wt h 2 o i e indigenous water bound in phyllosilicates also present are clumps of serpentine tochilinite intergrowths previously called poorly characterized phases or pcp pentlandite and ni bearing pyrrhotite we studied 11 cm chondrites that span the known range from least altered to most altered we used various petrologic properties many previously identified that provide information regarding the degree of aqueous alteration there are no known unaltered or slightly altered cm chondrites e g rocks containing numerous chondrules with primary igneous glass some cm properties result from processes associated with early and intermediate stages of the alteration sequence i e hydration of matrix alteration of chondrule glass and production of large pcp clumps other petrologic properties reflect processes active throughout the alteration sequence these include oxidation of metallic fe ni alteration of chondrule phenocrysts changes in pcp composition reflecting an increase in the phyllosilicate sulfide ratio and changes in carbonate mineralogy reflecting the development of dolomite and complex carbonates at the expense of ca carbonate on the basis of these parameters we propose a numerical alteration sequence for cm chondrites because there are no known cm samples that display only incipient alteration the least altered sample was arbitrarily assigned to subtype 2 6 the most altered cm chondrites currently classified cm1 are assigned to subtype 2 0 these highly altered rocks have essentially no mafic silicates they contain chondrule pseudomorphs composed mainly of phyllosilicate however their bulk compositions are cm like and they are closer in texture to other c2 chondrites than to ci1 chondrites which lack chondrule pseudomorphs using several diagnostic criteria we assigned petrologic subtypes 0 1 to every cm chondrite in our study que 97990 cm2 6 murchison cm2 5 kivesvaara cm2 5 murray cm2 4 2 5 y 791198 cm2 4 que 99355 cm2 3 nogoya cm2 2 cold bokkeveld cm2 2 que 93005 cm2 1 lap 02277 cm2 0 met 01070 cm2 0 the proposed cm numerical alteration sequence improves upon the existing scheme of browning et al 1996 in that it does not require a complicated algorithm applied to electron microprobe data to determine the average matrix phyllosilicate composition the new sequence is more comprehensive and employs petrologic subtypes that are easier to use and remember than mineralogic alteration index values new neutron activation analyses of que 97990 que 93005 met 01070 murchison and crescent together with literature data confirm the compositional uniformity of the cm group different degrees of alteration among cm chondrites do not lead to resolvable bulk compositional differences this suggests that the textural differences among individual cm chondrites reflect progressive alteration of similar hypothetical cm3 0 starting materials in different regions of the same parent body with minimal aqueous transport of materials over appreciable e g meters distances

isotopic composition of carbonate in eeta 79001 and its relation to parent body volatiles calcite a probable extraterrestrial weathering product in the shergottite eeta 79001 has 13c 9 7 and 18o 21 0 in order to account for the large excess of 18o relative to the silicate substrate 18o 4 2 a parent body surface reservoir containing both water and carbon dioxide is required the inferred h2oco2 ratio is consistent with estimates for the degassed reservoir on mars

phase equilibria of a low s and c lunar core implications for an early lunar dynamo and physical state of the current core abstract multiple lines of geochemical and geophysical evidence suggest the moon has a small metallic core yet the composition of the core is poorly constrained the physical state of the core now or in the past depends on detailed knowledge of its composition and unfortunately there is little available data on relevant multicomponent systems i e fe ni s c at lunar interior conditions in particular there is a dearth of phase equilibrium data to elucidate whether a specific core composition could help to explain an early lunar geodynamo and magnetic field intensities or current solid inner core liquid outer core states we utilize geochemical information to estimate the ni s and c contents of the lunar core and then carry out phase equilibria experiments on several possible core compositions at the pressure and temperature conditions relevant to the lunar interior the first composition is 0 5 wt s and 0 375 wt c based on s and c contents of apollo glasses a second composition contains 1 wt each of s and c and assumes that the lunar mantle experienced degassing of up to 50 of its s and c finally a third composition contains c as the dominant light element phase equilibrium experiments were completed at 1 3 and 5 gpa using piston cylinder and multi anvil techniques the first composition has a liquidus near 1550 c and solidus near 1250 c the second composition has a narrower liquidus and solidus temperatures of 1400 and 1270 c respectively while the third composition is molten down to 1150 c as the composition crystallizes the residual liquid becomes enriched in s and c but s enrichment is greater due to the incorporation of c but not s into solid metallic feni comparison of these results to thermal models for the moon allow an evaluation of which composition is consistent with the geophysical data of an early dynamo and a currently solid inner and liquid outer core composition 1 has a high enough liquidus to start crystallizing early in lunar history 4 3 ga consistent with the possible core dynamo initiated by crystallization of a solid inner core composition 1 also stays partially molten throughout lunar history and could easily explain the seismic data composition 2 on the other hand can satisfy one or the other set of geophysical data but not both and thus seems like a poor candidate for a lunar core composition composition 3 remains molten to temperatures that are lower than current estimates for the lunar core thus ruling out the possibility of a c rich and s poor lunar core the s and c poor core composition studied here composition 1 is consistent with all available geochemical and geophysical data and provides a simple heat source and mechanism for a lunar core dynamo core crystallization that would obviate the need for other primary mechanisms such as impacts core mantle coupling or unusual thermal histories

the carbon and oxygen isotopic composition of meteoritic carbonates the 13c12c and 18o16o isotopic ratios of carbonates from carbonaceous and ordinary chondrites have been measured on co2 released by the action of h3po4 on whole rock samples carbonates from ci cm and cr carbonaceous chondrites exhibit a range in 18o of ca 15 20 5 to 35 1 relative to smow limited data from co2 water equilibration experiments suggest that meteoritic carbonates do not possess grossly anomalous 17o isotopic compositions therefore they are truly enriched in 13c with 13c between 23 7 and 80 7 relative to pdb large internal variations in 13c and 18o were found in individual meteorites and suggest that two or more isotopically distinct carbonates of different origin may be present the abundance 13c and 18o of carbonate in cm2 chondrites may be related to the extent of aqueous alteration of the meteorites carbonates in ci and cr chondrites have a median 13c ca 50 to 60 whereas 13c of cm meteorites lie in the range 40 to 50 although exceptions exist in both sets of samples cv3 and co3 carbonaceous chondrites and unequilibrated ordinary chondrites release small amounts of co2 on acid treatment which might be from carbonate dissolution but which is not enriched in 13c exhibiting 13c values ca 0 10 the exception to this is bishunpur with 13c ca 23 5 the difference in 13c of the ci cm and cr vs cv co and ordinary chondrite carbonates may be a result of the progressive enrichment in 13c of percolating fluids brought about by increasing solubilization of exotic 13c enriched grains

chondritic lithic clasts in the cb ch like meteorite isheyevo fragments of previously unsampled parent bodies the cb ch like chondrite isheyevo is characterized by the absence of fine grained interchondrule matrix material the only present fine grained material is found as chondritic lithic clasts in contrast to the pristine high temperature components of isheyevo these clasts experienced extensive aqueous alteration in an asteroidal setting hence the clasts are foreign objects that either accreted together with the high temperature components or were added later to the final isheyevo parent body during regolith gardening in order to constrain the origin and secondary alteration of the clasts in isheyevo we studied their mineralogy petrography structural order of the polyaromatic carbonaceous matter and oxygen isotopic compositions of carbonates three main groups of clasts were defined based on mineralogy and petrology group i clasts consist of phyllosilicates carbonates magnetite and lath shaped fe ni sulfides group ii clasts contain different abundances of anhydrous silicates embedded in a hydrated matrix sulfides magnetite and carbonates are rare with only a few exceptions groups i and ii clasts did not experienced significant thermal metamorphism group iii clasts are characterized by the absence of magnetite and the presence of fe ni metal in addition to aqueous alteration they experienced thermal metamorphism as reflected by the structure of their polyaromatic carbonaceous matter while there are some similarities between the isheyevo clasts ci chondrites and the matrices of cm and cr chondrites on the whole the characteristics of the clasts do not match those of any of these aqueously altered meteorite classes nor do they match those of similar material in various types of chondritic clasts present in other meteorite groups we conclude that the isheyevo clasts represent fragments of previously unsampled parent bodies

carbonates in cm chondrites complex formational histories and comparison to carbonates in ci chondrites cm chondrites are primitive solar system materials that have undergone high degrees of aqueous alteration resulting in the formation of secondary minerals including carbonates two different carbonate minerals calcite aragonite and dolomite together constitute 1 4 2 8 vol of cm chondrites in contrast ci chondrites contain four different carbonate minerals calcite aragonite dolomite breunnerite and siderite ci chondrites have abundant dolomite a mineral that seems to be absent in the most aqueously altered cm chondrites in this study carbonates in seven cm chondrites y 791198 lapaz icefield 04796 cold bokkeveld nogoya queen alexandra range 93005 allan hills 83100 and meteorite hills 01070 were studied petrographically and by electron microprobe the results indicate that carbonate formation in cm chondrites differs from that in ci chondrites and is more complex than previously recognized our studies of cm chondrites indicate that 1 carbonates formed on the parent asteroid in an aqueous environment that gradually changed in composition 2 at some stage ca and mg activities in the environment were high enough to form metastable dolomite and 3 dolomites disappeared in the most aqueously altered cm chondrites

topography of the moon from the clementine lidar range measurements from the lidar instrument carried aboard the clementine spacecraft have been used to produce an accurate global topographic model of the moon this paper discusses the function of the lidar the acquisition processing and filtering of observations to produce a global topographic model and the determination of parameters that define the fundamental shape of the moon our topographic model a 72nd degree and order spherical harmonic expansion of lunar radii is designated goddard lunar topography model 2 gltm 2 this topographic field has an absolute vertical accuracy of approximately 100 m and a spatial resolution of 2 5 the field shows that the moon can be described as a sphere with maximum positive and negative deviations of 8 km both occurring on the farside in the areas of the korolev and south pole aitken s p aitken basins the amplitude spectrum of the topography shows more power at longer wavelengths as compared to previous models owing to more complete sampling of the surface particularly the farside a comparison of elevations derived from the clementine lidar to control point elevations from the apollo laser altimeters indicates that measured relative topographic heights generally agree to within 200 m over the maria while the major axis of the lunar gravity field is aligned in the earth moon direction the major axis of topography is displaced from this line by approximately 10 to the east and intersects the farside 24 north of the equator the magnitude of impact basin topography is greater than the lunar flattening 2 km and equatorial ellipticity 800 m which imposes a significant challenge to interpreting the lunar figure the floors of mare basins are shown to lie close to an equipotential surface while the floors of unflooded large basins except for s p aitken lie above this equipotential the radii of basin floors are thus consistent with a hydrostatic mechanism for the absence of significant farside maria except for s p aitken whose depth and lack of mare require significant internal compositional and or thermal heterogeneity a macroscale surface roughness map shows that roughness at length scales of 10 1 10 2 km correlates with elevation and surface age

viscoelastic tides of mercury and the determination of its inner core size we computed interior structure models of mercury and analyzed their viscoelastic tidal response the models are consistent with mercury surface space environment geochemistry and ranging mission inferences of mean density mean moment of inertia moment of inertia of mantle and crust and tidal love number k2 based on these constraints we predict the tidal love number h2 to be in the range from 0 77 to 0 93 using an andrade rheology for the mantle the tidal phase lag is predicted to be 4 at maximum the corresponding tidal dissipation in mercury s silicate mantle induces a surface heat flux smaller than 0 16 mw m2 we show that independent of the adopted mantle rheological model the ratio of the tidal love numbers h2 and k2 provides a better constraint on the maximum inner core size with respect to other geodetic parameters e g libration amplitude or a single love number provided it responds elastically to the solar tide for inner cores larger than 700 km and with the expected determination of h2 from the upcoming bepicolombo mission it may be possible to constrain the size of the inner core the measurement of the tidal phase lag with an accuracy better than 0 5 would further allow constraining the temperature at the core mantle boundary for a given grain size and therefore improve our understanding of the physical structure of mercury s core

the oxygen isotope evolution of parent body aqueous solutions as recorded by multiple carbonate generations in the lonewolf nunataks 94101 cm2 carbonaceous chondrite abstract the cm2 carbonaceous chondrite lon 94101 contains aragonite and two generations of calcite that provide snapshots of the chemical and isotopic evolution of aqueous solutions during parent body alteration aragonite was the first carbonate to crystallize it is rare heterogeneously distributed within the meteorite matrix and its mean oxygen isotope values are 18o 39 9 0 6 17o 0 3 1 0 1 calcite precipitated soon afterwards and following a fall in solution mg ca ratios to produce small equant grains with a mean oxygen isotope value of 18o 37 5 0 7 17o 1 4 1 1 1 these grains were partially or completely replaced by serpentine and tochilinite prior to precipitation of the second generation of calcite which occluded an open fracture to form a millimetre sized vein and replaced anhydrous silicates within chondrules and the matrix the vein calcite has a mean composition of 18o 18 4 0 3 17o 0 5 0 5 1 petrographic and isotopic results therefore reveal two discrete episodes of mineralisation that produced calcite generations with contrasting 18o and mean 17o values the aragonite and equant calcite crystallized over a relatively brief period early in the aqueous alteration history of the parent body and from static fluids that were evolving chemically in response to mineral dissolution and precipitation the second calcite generation crystallized from solutions of a lower 17o and a lower 18o and or higher temperature as two generations of calcite whose petrographic characteristics and oxygen isotopic compositions are similar to those in lon 94101 occur in at least one other cm2 multiphase carbonate mineralisation could be the typical outcome of the sequence of chemical reactions during parent body aqueous alteration it is equally possible however that the second generation of calcite formed in response to an event such as impact fracturing and concomitant fluid mobilisation that affected a large region of the common parent body of several cm2 meteorites these findings show that integrated petrographic chemical and isotopic studies can provide new insights into the mechanisms of parent body alteration including the spatial and temporal dynamics of the aqueous system

fluid flow and chemical alteration in carbonaceous chondrite parent bodies abstract carbonaceous chondrites are a class of primitive meteorites that likely represent early solar system materials thus providing critical insights about planetary evolution however evidence shows that they have undergone considerable processing elucidating the complex formation history of aqueously altered chondrite groups has been a principal objective of cosmochemistry fulfilling this objective requires understanding the nature of the water rock interactions involved many current alteration models are generally founded upon an assumption of uniform alteration in a closed system in these models different chondrite groups must originate on separate parent bodies contrary to this common view we show that chondrite data are consistent with non uniform alteration in a convecting system so that multiple chondrite groups can form within a single body

extended chronologies of aqueous alteration in the cm2 carbonaceous chondrites evidence from carbonates in queen alexandra range 93005 abstract the antarctic cm2 carbonaceous chondrite que 93005 contains four compositionally distinct carbonates namely breunnerite calcite dolomite and a ca poor dolomite these carbonates can form monomineralic grains or may be intergrown as bimineralic grains consisting of dolomite plus breunnerite and dolomite plus calcite or polymineralic grains containing an intergrowth of breunnerite ca poor dolomite and calcite carbonates in all grain types have inclusions of fe ni sulphides and or mg fe phyllosilicates in the bimineralic grains dolomite crystallised first to be overgrown by breunnerite or partially replaced by calcite polymineralic grains are concentrically layered with breunnerite crystallising first on pore margins to be later etched then overgrown and partially replaced by ca poor dolomite that was itself partly dissolved prior to being overgrown by calcite calcite and dolomite have also cemented fractures that cross cut the fine grained rims to aqueously altered chondrules and were formed by expansion of the chondrules during their hydration overall the sequence of mineralisation in que 93005 was 1 dolomite 2 breunnerite 3 ca poor dolomite then 4 calcite this secular change in carbonate composition and mineralogy reflects changing solution composition and probably also provenance mg fe phyllosilicates replaced dolomite breunnerite and ca poor dolomite prior to calcite crystallisation and most or all of the sulphides formed after both the phyllosilicates and calcite following sulphide crystallisation the edges of carbonate grains were abraded either by impact gardening or as a consequence of fluidisation of the matrix during rapid loss of gas or vapour determination of the crystallisation age of dolomite via the mn cr system indicates that aqueous alteration of que 93005 began on or before 3 93 0 23 ma after the formation of the oldest solar system solids overall the water rock ratio and fo2 during alteration of que 93005 was similar to that of the cm1s and cr1s but the lower degree of alteration of que 93005 overall suggests that alteration timescales were shorter possibly due to loss of intergranular liquid water during fluidisation

an oxygen isotope dichotomy in cm2 chondritic carbonates a sims approach abstract we present petrologic and secondary ion mass spectrometry sims oxygen isotope analyses of ca carbonate within a group of paired antarctic cm2 chondrites the carbonates can be grouped into two isotopically and morphologically distinct populations type 1 grains small matrix grains possess average 18 o of 33 7 2 3 1 and average 17 o of 0 81 0 90 1 type 2 grains calcite aggregates possess distinct oxygen isotopic compositions average 18 o of 19 4 1 5 1 and average 17 o of 1 98 0 9 1 these differences are interpreted to indicate that the two populations of calcite formed under different conditions at different times the carbonates have textural features that suggest an extraterrestrial origin the data presented here fall within error of a previously measured array for carbonates from cm falls benedix et al 2003 the presence of two generations of carbonate suggests carbonate formation in two discrete events on the parent body of these meteorites the oxygen isotopic data presented here deviate from prior bulk carbonate measurements undertaken for these meteorites most likely this deviation is because bulk carbonate analyses included vein carbonate which formed during terrestrial weathering

bottom up versus top down solidification of the cores of small solar system bodies constraints on paradoxical cores abstract the slopes of the adiabatic gradient of liquid iron and iron alloys are calculated at high pressure conditions and compared to liquidi slopes the controversial thermal expansion of liquid iron results in uncertainties in the pressure conditions and compositional range over which adiabats are steeper than the liquidi and hence over the conditions at which planetary cores would be expected to begin crystallization from the top down as opposed to the bottom up if the liquid iron thermal expansion is relatively high 13 2 10 5 k as indicated by a large number of studies the cores of almost all objects smaller than callisto pressures 8 gpa for 10 wt s compositions hence top down crystallization and compositional stratification may be an endemic feature in the cores of small to mid size solar system bodies and the evolution of crystallization induced compositional stratification may provide a natural explanation for possible early shut offs of dynamos of small bodies in the solar system

oxygen isotope constraints on the alteration temperatures of cm chondrites abstract we report a systematic oxygen isotopic survey of ca carbonates in nine different cm chondrites characterized by different degrees of alteration from the least altered known to date paris 2 7 2 8 to the most altered alh 88045 cm1 our data define a continuous trend that crosses the terrestrial fractionation line tfl with a general relationship that is indistinguishable within errors from the trend defined by both matrix phyllosilicates and bulk o isotopic compositions of cm chondrites this bulk matrix carbonate bmc trend does not correspond to a mass dependent fractionation i e slope 0 52 as it would be expected during fluid circulation along a temperature gradient it is instead a direct proxy of the degree of o isotopic equilibration between 17 18 o rich fluids and 16 o rich anhydrous minerals our o isotopic survey revealed that for a given cm no carbonate is in o isotopic equilibrium with its respective surrounding matrix this precludes direct calculation of the temperature of carbonate precipitation however the o isotopic compositions of alteration water in different cms inferred from isotopic mass balance calculation and direct measurements define another trend cmw for cm water parallel to bmc but with a different intercept the distance between the bmc and cmw trends is directly related to the temperature of cm alteration and corresponds to average carbonates and serpentine formation temperatures of 110 c and 75 c respectively however carbonate o isotopic variations around the bmc trend indicate that they formed at various temperatures ranging between 50 and 300 c with 50 of the carbonates studied here showing precipitation temperature higher than 100 c the average 17 o and the average carbonate precipitation temperature per chondrite are correlated revealing that all cms underwent similar maximum temperature peaks but that altered cms experienced protracted carbonate precipitation event s at lower temperatures than the least altered cms our data suggest that the 17 o value of ca carbonates could be a reliable proxy of the degree of alteration experienced by cm chondrites

the origin and evolution of chondrites recorded in the elemental and isotopic compositions of their macromolecular organic matter extraterrestrial organic matter in meteorites potentially retains a unique record of synthesis and chemical thermal modification by parent body nebular and even presolar processes in a survey of the elemental and isotopic compositions of insoluble organic matter iom from 75 carbonaceous ordinary and enstatite chondrites we find dramatic variations within and between chondrite classes there is no evidence that these variations correlate with the time and or location of chondrite formation or with any primary petrologic or bulk compositional features that are associated with nebular processes e g chondrule and volatile trace element abundances nor is there evidence for the formation of the iom by fischer tropsch type synthesis in the nebula or in the parent bodies the elemental variations are consistent with thermal maturation and or oxidation of a common precursor for reasons that are unclear there are large variations in isotopic composition within and between chondrite classes that do not correlate in a simple way with elemental composition or petrologic type nevertheless because of the pattern of elemental variations with petrologic type and the lack of any correlation with the primary features of the chondrite classes at present the most likely explanation is that all iom compositional variations are the result of parent body processing of a common precursor if correct the range of isotopic compositions within and between chondrite classes implies that the iom is composed of several isotopically distinct components whose relative stability varied with parent body conditions the most primitive iom is found in the cr chondrites and bells cm2 isotopically the iom from these meteorites resembles the iom in interplanetary dust particles chemically their iom resembles the chon particles of comet halley despite the large isotopic anomalies in the iom from these meteorites it is uncertain whether the iom formed in the interstellar medium or the outer solar system although the former is preferred here

sound velocity measurements in liquid fe s at high pressure implications for earth s and lunar cores abstract the p wave velocity v p of liquid fe 57 s 43 was measured up to 5 4 gpa using an ultrasonic method combined with the synchrotron x ray technique the v p of liquid fe 57 s 43 showed little change with temperature but increased almost linearly from 3105 11 m s to 3845 9 m s with increasing pressure from 2 4 to 5 4 gpa this can be approximated by v p m s 2664 205 4 p where p is the pressure in gpa the v p of liquid fe 57 s 43 at 2 4 5 4 gpa was significantly lower than that of pure liquid fe however the pressure dependence of v p of the liquid fe 57 s 43 was markedly higher than that of pure liquid fe the marked difference in the pressure dependences of v p between pure liquid fe and liquid fe 57 s 43 may cause v p crossover at around 7 gpa as a result the v p of liquid fe 57 s 43 would become higher than that of pure liquid fe at pressures higher than 7 gpa thus s decreases v p at low pressures such as those of the lunar outer core but would increase it at the high pressures of the earth s outer core assuming the lunar core consists of a liquid fe fes outer core and a solid fe inner core the expected v p in the lunar outer core ranges from 3756 to 4230 m s

propagating long waves on oceanic density fronts an analytic model abstract an analytic model of long propagating free wave perturbations to an established upper ocean density front is developed the primary purpose of the model is to illuminate basic frontal wave mechanisms for possible subsequent use in more sophisticated numerical models the models is of the barotropic class but has ageostrophic dynamics because of the basic state adopted essentially stommel s model of the gulf stream with uniform potential vorticity and order one rossby number the model assumes inviscid dynamics apart from a narrow dissipative zone adjacent to the surface front the latter exerts a bulk effect on the large inviscid zone especially in generating small bur finite cross stream flow in the basic state for zero cross flow the resulting waves are stable have downstream phase speeds that are slow compared to the current speed and that increase with frequency and have anomalous dispersion the phase speeds compare well with the analysis of observations of propagating gulf stream me

correlated alteration effects in cm carbonaceous chondrites three parameters are proposed to determine the relative extent of alteration in cm chondrites the mineralogic alteration index monitors the relative progress of coupled substitutions in the progressive alteration of cronstedtite to mg serpentine and increases with increasing alteration to calculate values of this index an algorithm has been developed to estimate the average matrix phyllosilicate composition in individual cm chondrites the second parameter is the volume percent of isolated matrix silicates which decreases with progressive alteration due to mineral hydration finally the volume percent of chondrule alteration monitors the extent of chondrule phyllosilicate production and increases as alteration proceeds these parameters define the first cm alteration scale that relies on multiple indicators of progressive alteration the following relative order of increasing alteration is established by this model murchison bells pollen murray mighei nogoya cold bokkeveld the relative degree of aqueous processing cochabamba and boriskino experienced is less precisely constrained although both fall near the middle of this sequence a comparison between the mineralogic alteration index and literature values for the whole rock chemistry of cm chondrites reveals several correlations a positive nearly linear correlation between bulk h content and progressive cm alteration suggests an approximately constant production rate of new phyllosilicates relative to the mineralogical transition from cronstedtite to mg serpentine the abundance of trapped planetary 36ar decreases systematically in progressively altered cm chondrites suggesting the wholesale destruction of primary noble gas carrier phase s by aqueous reactions because low temperature fluid rock reactions are generally associated with large isotopic mass fractionation factors we also compared our model predictions with 18o values for bulk cm samples although some of these data are poorly resolved the order of increasing 18o values approximates the order of increasing alteration predicted by our model parameters multiple correlations between diverse alteration parameters strongly suggest that a different cm chondrites experienced similar kinds of processes and conditions and b cm materials experienced in situ alteration on the cm parent body or bodies

oxygen isotope fractionation during synthesis of camg carbonate and implications for sedimentary dolomite formation hydrous camg carbonate was synthesized at temperatures of 40 degrees 60 degrees and 80 degrees c in the laboratory this material has very similar mineralogical characteristics to natural disordered dolomite from the coorong region in south australia besides the dolomite variable amounts of amorphous carbonate are present in all samples the oxygen isotope compositions of synthesized bulk carbonate samples e g amorphous carbonate plus dolomite plot significantly lower than the northrop and clayton 1966 dolomite water equilibrium fractionated degassing of the samples however revealed relatively low oxygen isotope values for fast reacting using 100 h3po4 amorphous carbonate in contrast slow reacting dolomite has more positive oxygen isotope values and calculated carbonate water oxygen isotope fractionation values are close to strongest known dolomite water oxygen isotope fractionation published earlier on variations of reaction stabilization temperatures during synthesis gave evidence for dolomite formation from hypersaline solutions by a dissolution reprecipitation process it is likely that amorphous carbonate has been a problem in defining the dolomite water fractionation in the past moreover dolomite associated amorphous carbonate contents probably led to incorrect speculations about lower oxygen isotope fractionation in a so called protodolomite water system copyright c 2005 elsevier ltd

microstructure of calcite in the cm2 carbonaceous chondrite lon 94101 implications for deformation history during and or after aqueous alteration the microstructure of calcite in the cm2 carbonaceous chondrite lon 94101 has been characterized using electron backscatter diffraction ebsd analysis to reconstruct the parent body deformation history during and or after aqueous alteration the results suggest that at least two events of calcite crystallization have taken place during aqueous alteration and at least three episodes of deformation are recorded by the calcite the first event of calcite crystallization produced calcite grains scattered throughout the matrix and the second event formed a calcite vein via localized fluid flow the first episode of deformation is recorded in the crystallographic preferred orientations of the calcite grains and occurred via a directed stress probably induced by compaction in shallow crustal levels of the parent body the second episode of deformation is recorded in an e twin microstructure and it suggests a deformation induced via directed stress by impact processing also in shallow crustal levels the third episode of deformation generated subgrains in the calcite vein and in some calcite grains and fragmented and disrupted the calcite vein this could have been a result of a relatively forceful deformation event perhaps when the meteorite was released from its parent body this study shows that carbonate microstructures in carbonaceous chondrites is a powerful and versatile tool for reconstructing the history of deformation during and or after aqueous alteration

cm chondrites exhibit the complete petrologic range from type 2 to 1 we have characterized the most phyllosilicate rich members of the cm chondrite group based upon petrographic and compositional factors we conclude that these particular meteorites have experienced pervasive aqueous alteration far beyond that witnessed by typical cms the lack of anhydrous silicates cai and except as relicts chondrules merits the classification of type cmi for three meteorites eet 83334 alh 88045 and one kaidun lithology still other cms notably alh 83100 eet 90047 and yamato 82042 are clearly intermediate between types 1 and 2 brecciated cm chondrites like cold bokkeveld contain all of these varied lithologies the cm chondrites thus exhibit the complete petrologic range from 2 through 1 our results show that progressive aqueous alteration on the parent cm asteroid s was locally accompanied by significant increases in temperature to a peak of 450 c for the kaidun lithology fo2 and locally degree of chemical leaching all well beyond the conditions recorded by typical cm2s the most altered cms also are commonly deformed displaying a distinct lineation probably due to static rather than dynamic forces

carbonate abundances and isotopic compositions in chondrites we report the bulk c abundances and c and o isotopic compositions of carbonates in 64 cm chondrites 14 cr chondrites 2 ci chondrites lew 85332 c2 kaba cv3 and semarkona ll3 0 for the unheated cms the total ranges of carbonate isotopic compositions are 13c 25 75 and 18o 15 35 and bulk carbonate c contents range from 0 03 to 0 60 wt there is no simple correlation between carbonate abundance and isotopic composition or between either of these parameters and the extent of alteration unless accretion was very heterogeneous the uncorrelated variations in extent of alteration and carbonate abundance suggests that there was a period of open system behavior in the cm parent body probably prior to or at the start of aqueous alteration most of the ranges in cm carbonate isotopic compositions can be explained by their formation at different temperatures 0 130 c from a single fluid in which the carbonate o isotopes were controlled by equilibrium with water 18o 5 and the c isotopes were controlled by equilibrium with co and or ch4 13c 33 or 20 for co or ch4 dominated systems respectively however carbonate formation would have to have been inefficient otherwise carbonate compositions would have resembled those of the starting fluid a quite similar fluid composition 18o 5 5 and 13c 31 or 17 for co or ch4 dominated systems respectively can explain the carbonate compositions of the cis although the formation temperatures would have been lower 10 40 c and the relative abundances of calcite and dolomite may play a more important role in determining bulk carbonate compositions than in the cms the cr carbonates exhibit a similar range of o isotopes but an almost bimodal distribution of c isotopes between more 13c 65 80 and less altered samples 13c 30 40 this bimodality can still be explained by precipitation from fluids with the same isotopic composition 18o 9 25 and 13c 21 or 8 for co or ch4 dominated systems respectively if the less altered crs had higher mole fractions of co2 in their fluids semarkona and kaba carbonates have some of the lightest c isotopic compositions of the meteorites studied here probably because they formed at higher temperatures and or from more co2 rich fluids the fluids responsible for the alteration of chondrites and from which the carbonates formed were almost certainly accreted as ices by analogy with cometary ices co2 and or co would have dominated the trapped volatile species in the ices the chondrites studied are too oxidized for co dominated fluids to have formed in their parent bodies if ch4 was the dominant c species in the fluids during carbonate formation it would have to have been generated in the parent bodies from co and or co2 when oxidation of metal by water created high partial pressures of h2 the fact that the chondrite carbonate c h2o mole ratios are of the order predicted for co co2 h2o ices that experienced temperatures of 50 100 k suggests that the chondrites formed at radial distances of 4 15 au

a long lived lunar core dynamo paleomagnetic measurements indicate that a core dynamo probably existed on the moon 4 2 billion years ago however the subsequent history of the lunar core dynamo is unknown here we report paleomagnetic petrologic and 40ar 39ar thermochronometry measurements on the 3 7 billion year old mare basalt sample 10020 this sample contains a high coercivity magnetization acquired in a stable field of at least 12 microteslas these data extend the known lifetime of the lunar dynamo by 500 million years such a long lived lunar dynamo probably required a power source other than thermochemical convection from secular cooling of the lunar interior the inferred strong intensity of the lunar paleofield presents a challenge to current dynamo theory

neutral buoyancy of titanium rich melts in the deep lunar interior the absence of very deep moonquakes implies that the lower mantle of the moon is partially molten an analysis of the density range of lunar melts at high pressures suggests that only titanium rich melt is neutrally buoyant deep within the moon

strength of the geomagnetic field in the cretaceous normal superchron new data from submarine basaltic glass of the troodos ophiolite 1 we present here new paleointensity data from 39 sampling sites collected from the quenched margins of pillow lavas and dikes exposed within the troodos ophiolite similar to 92 ma formed during the cretaceous normal superchron cns a period of approximately 40 million years when the geomagnetic field reversed extremely infrequently if at all monte carlo simulations suggest that a minimum of 25 estimates are necessary for a reasonably robust estimate for the average field strength our data suggest a dipole strength equivalent to the present field or nearly twice the post cns average the mean and standard deviation of the dipole moment 81 43 zam 2 z 10 21 from the 57 data points compiled here agree remarkably well with those predicted from the long paleointensity record derived from dsdp site 522 the new data set for the cns suggests a picture of a strong and stable field during the period of time when it stopped reversing moreover the similarity of the cns data with the present geomagnetic field suggests that it is presently in a state of unusual polarity stability

terrestrial alteration of carbonate in a suite of antarctic cm chondrites evidence from oxygen and carbon isotopes the oxygen 18o 17o and carbon 13c fmod14c the fraction of modern 14c isotopic compositions of carbonate were measured for a set of paired antarctic cm chondrites eet 96006 eet 96016 eet 96017 and eet 96019 while the oxygen isotopic compositions do not plot on the terrestrial fractionation line and indicate that a component of the carbonate minerals has an extraterrestrial origin they also do not fall on the array defined for carbonates by cm falls and are thus consistent with the presence of a terrestrial carbonate component the 13c and fmod14c measurements of carbonate suggest the presence of at least two carbon sources carbonate derived from atmospheric co2 that is inferred to have been produced as a result of silicate weathering reactions and carbonate derived from another carbon source that is either old or non atmospheric the relationships between oxygen and carbon isotope data provide additional constraints on the weathering process and allow the possibility that rock dominated weathering of the meteorite caused the oxygen isotopic composition of antarctic water added to the meteorite to evolve away from the terrestrial mass fractionation array leading to formation of low temperature terrestrial alteration products that do not lie on the terrestrial fractionation line

organic thermometry for chondritic parent bodies abstract a unique spectroscopic feature has been identified in a study of twenty five different samples of meteoritic insoluble organic matter iom spanning multiple chemical classes groups and petrologic types using carbon x ray absorption near edge structure xanes spectroscopy the intensity of this feature a 1s exciton appears to provide a precise measure of parent body metamorphism the intensity of this exciton is also shown to correlate well with a large negative paramagnetic shift observed through solid state 13c nmr experiments reveal that upon heating primitive iom is transformed into material that is indistinguishable from that in thermally processed chondrites including the development of the 1s exciton a thermo kinetic expression is derived from the experimental data that allows the intensity of the 1s exciton to be used to estimated the effective temperature integrated over time a good correlation is observed between the intensity of the 1s exciton and previously published microraman spectral data these data provide a self consistent organic derived temperature scale for the purpose of calibrating raman based thermometric expressions

aragonite in the murray cm2 carbonaceous chondrite implications for parent body compaction and aqueous alteration the matrix of the cm2 carbonaceous chondrite murray contains rare micrometer sized prismatic crystals of aragonite that formed during late stage parent body aqueous alteration the aragonite was identified by x ray microanalysis coupled with electron backscatter diffraction ebsd tem selected area electron diffraction and cathodoluminescence spectroscopy the sixteen crystals found all occur within loose and elongate submillimeter sized clusters and one cluster is present in each of the two thin sections studied orientation determinations using ebsd show that the c axes of aragonite crystals within each cluster lie roughly in a plane itself aligned approximately parallel to the long axis of the host cluster aragonite is inferred to have crystallized after calcite but before completion of static impact related compaction the clusters developed by growth of aragonite within films of aqueous fluids that had a relatively high mg ca ratio these fluids were focused within zones of high porosity and permeability along a weak compactional fabric in the matrix and this fabric is also likely to have influenced the orientations of aragonite crystals as they grew these results suggest that aragonite probably occurs in most of those carbonaceous chondrites that have undergone moderate degrees of parent body aqueous alteration and may provide further insights into the evolution of pore fluid compositions and volumes and the chronology of asteroidal evolution

streaks in the vicinity of an oscillating front the fate of particles continuously injected at a fixed location in the vicinity of an oscillating front is studied by numerical integration of the hydrodynamic equations the analysis is straightforward when the injection is at a location that is always on one side of the front in this case the curve traced by these particles i e a streak line may be complicated and generally does not resemble the path of the initial particle released but at least is continuous however when the front oscillates across the source location the streak line is broken into a series of discontinuous segments moreover some segments later may recirculate past the source this can produce a complicated streak line pattern in which old segments intertwine with recent segments

thermodynamic properties of fe s alloys from molecular dynamics modeling implications for the lunar fluid core abstract density and sound velocity of fe s liquids for the p t parameters of the lunar core have not been constrained well from the analysis of seismic wave travel time weber et al 2011 proposed that the lunar core is composed of iron alloyed with 6 wt of light elements such as s a controversial issue in models of planetary core composition concerns whether fe s liquids under high pressure temperature conditions provide sound velocity and density data which match the seismic model here we report the results of molecular dynamics md simulations of iron sulfur alloys based on embedded atom model eam the results of calculations include caloric thermal and elastic properties of fe s alloys at concentrations of sulfur 0 18 at temperatures up to 2500 k and pressures up to 14 gpa the effect of sulfur on the elastic properties of fe rich melts is most evident in the notably decreased density with added s content in the md simulation the density and bulk modulus k t of liquid fe s decrease with increasing sulfur content while the bulk modulus k s decreases as a whole but has some fluctuations with increasing sulfur content the sound velocity increases with increasing pressure but depends weakly on temperature and the concentration of sulfur for a fluid fe s core of the moon 5 gpa 2000 k with 6 16 at s 3 5 10 wt the sound velocity and density may be estimated at the level of 4000 m s 1 and 6 25 7 0 g cm 3 comparison of thermodynamic calculations with the results of interpretation of seismic observations shows good agreement of p wave velocities in the liquid outer core while the core density does not match the seismic models at such concentrations of sulfur and a density by 20 35 higher than the model seismic density a radius for the fluid outer core should be less than about 330 km found by weber et al because at the specified mass and moment of inertia values of the moon an increase of the core density leads to a decrease of the core radius these results are important for modeling the current state and composition of the lunar core and can be applied to models of large satellites core properties

investigating the variations in carbon and nitrogen isotopes in carbonaceous chondrites the carbonaceous chondrites contain significant amounts of carbon and nitrogen bearing components the most abundant of which is organic matter stepped combustion data of whole rock and hf hcl residues of carbonaceous chondrites reveal that the organic material can be subdivided operationally into three components 1 free organic matter fom which is readily extractable from whole rock meteorites and is enriched in 13c and 15n 2 labile organic matter lom which has a macromolecular structure but is liberated by hydrous pyrolysis lom is the parent structure for some fom and is also enriched in 13c and 15n and 3 refractory organic matter rom which is also macromolecular but is virtually unaffected by hydrous pyrolysis and is relatively depleted in 13c and 15n the macromolecular entities lom and rom are by far the most abundant organic components present and as such the relative abundances of the 13c and 15n enriched lom and the 13c and 15n depleted rom will have a major influence on the overall isotopic composition of the whole rock meteorite laboratory experiments designed to simulate the effects of parent body aqueous alteration indicate that this form of processing removes lom from the macromolecular material allowing rom to exert a stronger influence on the overall isotopic compositions hence aqueous alteration of macromolecular materials on the meteorite parent body may have a significant control on the stable isotopic compositions of whole rock carbonaceous chondrites the enstatite chondrites are also carbon rich but have been subjected to high levels of thermal metamorphism on their parent body stepped combustion data of hf hcl residues of enstatite chondrites indicate that if they and carbonaceous chondrites inherited a common organic progenitor metamorphism under reducing conditions appears to incorporate and preserve some of the 13c enrichments in lom during graphitisation however when metamorphism is at its most extreme the 15n enrichments in lom are lost

the origin of chondritic macromolecular organic matter a carbon and nitrogen isotope study the n and c abundances and isotopic compositions of acid insoluble carbonaceous material in thirteen primitive chondrites five unequilibrated ordinary chondrites three cm chondrites three enstatite chondrites a ci chondrite and a cr chondrite have been measured by stepped combustion while the range of c isotopic compositions observed is only delta 13c 30 the n isotopes range from delta 15n approximately 40 to 260 after correction for metamorphism presolar nanodiamonds appear to have made up a fairly constant 3 4 wt of the insoluble c in all the chondrites studied the apparently similar initial presolar nanodiamond to organic c ratios and the correlations of elemental and isotopic compositions with metamorphic indicators in the ordinary and enstatite chondrites suggest that the chondrites all accreted similar organic material this original material probably most closely resembles that now found in renazzo and semarkona these two meteorites have almost m shaped n isotope release profiles that can be explained most simply by the super position of two components one with a composition between delta 15n 20 and 40 and a narrow combustion interval the other having a broader release profile and a composition of delta 15n approximately 260 although isotopically more subdued the ci and the three cm chondrites all appear to show vestiges of this m shaped profile how and where the components in the acid insoluble organics formed remains poorly constrained the small variation in nanodiamond to organic c ratio between the chondrite groups limits the local synthesis of organic matter in the various chondrite formation regions to at most 30 the most 15n rich material probably formed in the interstellar medium and the fraction of organic n in renazzo in this material ranges from 40 to 70 the isotopically light component may have formed in the solar system but the limited range in nanodiamond to total organic c ratios in the chondrite groups is consistent with most of the organic material being presolar