three dimensional imaging of ordinary chondrite microporosity at 2 6 μm resolution abstract we show that high resolution 2 6 m voxel synchrotron x ray microtomography ct scans are able to observe the majority of microporosity in ordinary chondrites this porosity is present in the form of microcracks and voids among and between mineral grains we examined in total seven small 6 12 mm 3 chips of the ordinary chondrites baszkowka l5 s1 alh a77258 h5 s2 moorleah l6 s3 and kyushu l6 s5 these four samples were chosen because of their variable impact histories using ct and various digital isolation and visualization techniques we found that the structure of microporosity varies with the degree of compaction and shock loading experienced by the materials the microporosity in the compacted and more strongly shock samples moorleah and kyushu is visible as sheet like fractures within brittle silicates as well as in discontinuous distributed voids sometimes associated with chondrule rims and grain boundaries in samples that have experienced less shock and only mild compaction we found few if any microcracks in the silicate grains of the materials microporosity in the baszkowka and alh a77258 samples is largely represented by intergranular voids with occasional intragranular voids being present regardless of degree of shock loading ductile fe ni or fes grains give no evidence of shock related internal fractures contributing to porosity

the wood lake ontario h4 ordinary chondrite a new canadian meteorite1 the wood lake meteorite was found in the muskoka region of ontario in july 2003 we examine the mineralogy physical properties shock and weathering state of this recently reported canadian meteo

petrophysical and paleomagnetic data of drill cores from the bosumtwi impact structure ghana physical properties from rocks of the bosumtwi impact structure ghana central africa are essential to understand the formation of the relatively young 1 07 ma and small 10 5 km impact crater and to improve its geophysical modeling results of our petrophysical studies of deep drill cores lb 07a and lb 08a reveal distinct lithological patterns but no depth dependence the most conspicuous difference between impactites and target lithologies are the lower bulk densities and significantly higher porosities of the suevite and lithic breccia units compared to meta graywacke and metapelites of target lithologies magnetic susceptibility shows mostly paramagnetic values 200 500 10 6 si throughout the core with an exception of a few metasediment samples and correlates positively with natural remanent magnetization nrm and q values these data indicate that magnetic parameters are related to inhomogeneously distributed ferrimagnetic pyrrhotite the paleomagnetic data reveals that the characteristic direction of nrm has shallow normal in a few cases shallow reversed polarity which is in agreement with the lower jaramillo n polarity chron direction and is carried by ferrimagnetic pyrrhotite however our study has not revealed the expected high magnetization body required from previous magnetic modeling furthermore the lb 07a and lb08 a drill cores did not show the predicted high content of melt in the rocks requiring a new interpretation model for magnetic data

incompletely compacted equilibrated ordinary chondrites we document the size distributions and locations of voids present within five highly porous equilibrated ordinary chondrites using high resolution synchrotron x ray microtomography ct and helium pycnometry we found total porosities ranging from 10 to 20 within these chondrites and with ct we show that up to 64 of the void space is located within intergranular voids within the rock given the low s1 s2 shock stages of the samples and the large voids between mineral grains we conclude that these samples experienced unusually low amounts of compaction and shock loading throughout their entire post accretionary history with fe metal and fes metal abundances and grain size distributions we show that these chondrites formed naturally with greater than average porosities prior to parent body metamorphism these materials were not fluffed on their parent body by impact related regolith gardening or events caused by seismic vibrations samples of all three chemical types of ordinary chondrites ll l h are represented in this study and we conclude that incomplete compaction is common within the asteroid belt

density porosity and magnetic susceptibility of carbonaceous chondrites abstract we report physical properties bulk and grain density magnetic susceptibility and porosity measured using nondestructive and noncontaminating methods for 195 stones from 63 carbonaceous chondrites grain densities over the whole population average 3 44 g cm 3 ranging from 2 42 g cm 3 ci1 orgueil to 5 66 g cm 3 cb bencubbin magnetic susceptibilities in log units of 10 9 m3 kg 1 averaged log 4 22 ranging from 3 23 cv3 axtell to 5 79 cb bencubbin porosities averaged 17 ranging from 0 for a number of meteorites to 41 for one stone of the co ornans notably we found significant differences in porosity between the oxidized and reduced cv subgroups with the porosities of cvo averaging approximately 20 and cvr porosities approximately 4 overall porosities of carbonaceous chondrite falls trend with petrographic type from type 1 ci near 35 type 2 cm cr averaging 23 type 3 cv co 21 to type 4 ck and some co averaging 15 there is also a significant decrease in porosity between meteorites of shock stage s1 and those of s2 indicative of shock compression

fulgurite morphology a classification scheme and clues to formation fulgurites are natural glasses formed by cloud to ground lightning several different morphologies of fulgurites have been reported in previous studies including sand fulgurites rock fulgurites and clay fulgurites herein we examine sand clay and caliche fulgurites and demonstrate that these differ systematically in their morphology we further use morphological features to constrain properties of fulgurite forming lightning strikes we classify fulgurites into four types of morphologies with an additional minor type type i fulgurites are sand fulgurites consisting of thin glass walls type ii fulgurites are clay fulgurites consisting of thick melt rich walls type iii fulgurites are caliche fulgurites consisting of thick glass poor walls and type iv fulgurites are rock fulgurites consisting of glasses with walls consisting of surrounding unmelted rock fulgurite morphology shows that the energy of fulgurite forming strikes is between 1 and 30 mj m of fulgurite formed suggests heating rates in the order of 1 000 k s and lightning channel thicknesses of about 1 mm diameter lightning generates mixtures of at least two components in most fulgurites an sio2 glass identified as lechatelierite and a groundmass of more varied composition in addition to these four primary types a fifth type droplet fulgurites is morphologically dissimilar from the other types but is compositionally related to the type ii or iv fulgurites additionally two fulgurites both from york county pennsylvania usa showed the reduction of iron to iron metal with an assortment of fe ti and si p compounds with stoichiometry that ranges from nearly pure fe metal to fesi these metal silicides include stoichiometric fe3si fe2si and fe5si3 and possibly fe8si3 and fe7si3 and provide a terrestrial source for these phases which are typically associated with extraterrestrial material

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

mineralogical and spectroscopic investigation of the tagish lake carbonaceous chondrite by x ray diffraction and infrared reflectance spectroscopy abstract we have carried out a sample correlated spectroscopic and mineralogical investigation of samples from seven different collection sites of the tagish lake c2 chondrite rietveld refinement of high resolution powder x ray diffraction xrd data was used to determine quantitative major mineral abundances thermal infrared 400 4500 cm 1 2 2 25 0 m spectra of the same samples were obtained using diffuse biconical reflectance infrared fourier transform spectroscopy drifts our results are in good agreement with previous studies of the mineralogy of the tagish lake meteorite we find however that tagish lake is more varied in major mineralogy than has previously been reported in particular we observed two new distinct lithologies an inclusion poor magnetite and sulfide rich lithology and a carbonate rich siderite dominated lithology in addition to the previously documented carbonate rich and carbonate poor lithologies grain density for each tagish lake sample was calculated from the measured mineral modal abundances and known mineral densities for powders from three originally intact inclusion rich samples the calculated grain density is 2 77 0 05 g cm 3 in excellent agreement with those reported in the literature for other intact inclusion rich tagish lake samples tagish lake disaggregated samples have a significantly higher calculated grain density due to their lower saponite serpentine content likely a result of mineral separation in the meltwater holes from which they were collected the disaggregated samples may not therefore adequately represent bulk samples of the tagish lake meteorite the predominance of very fine grained material in the tagish lake samples investigated in this study is expected to produce infrared spectra representative of asteroidal regolith gypsum and talc have been found by xrd in powders from the inclusion rich intact tagish lake samples in this study and may have been present in the parent body if present these hydrous sulfates would complicate the interpretation of possible hydrated mineral features in asteroid infrared spectra

the porosities of ordinary chondrites models and interpretation densities and porosities for 285 ordinary chondrites have been assembled and analyzed measured chondrite porosities are bimodal finds have an average porosity of 30 we conclude that mild degrees of weathering fill pore spaces lowering grain densities and porosities without significantly changing the bulk size or mass of the sample by assuming an original pristine grain density as a function of the meteorite s mineralogy determined by its class we can derive model pristine porosities these model porosities cluster around an average value of 10 for all classes of ordinary chondrites ordinary chondrites do not show any correlation of porosity model or measured with petrographic grade or sample size over a range from 0 2 g to 2 kg however we do see a correlation between shock state and porosity shock blackened meteorites are less porous than other meteorites furthermore less severely shocked meteorites show a much broader range of porosities with the maximum porosity seen among meteorites of a given shock class falling linearly as a function of that shock class this is consistent with the idea that shock compresses and closes pore space analysis of meteorite porosity provides a lower bound to the fine scale porosity of asteroids our densities even with 10 primordial porosity are significantly higher than inferred densities of possible asteroid parent bodies these asteroids are probably loose piles of rubble

the role of regolith redistribution in influencing the evolution of the shapes of asteroids major surface fissures and relatively large scale angular surface irregularities are expected to have been present on many asteroids at early stages in their histories as a byproduct of at least two processes impact disruption and reassembly into rubble piles for all classes of asteroid and for carbonaceous chondrite parent bodies aqueous alteration which led to the low bulk densities currently being observed for asteroids however in all cases where high enough resolution images exist such abrupt deep irregularities are not observed we model the spatial redistribution of impact generated regolith on an asteroid with an idealized irregular shape to show how the complex gravitational field of such a body will lead to the systematic infilling of deep valleys in the surface our analysis emphasizes the high efficiency with which regolith redistribution can act to disguise the internal structures of asteroids with sizes in the 20 100 km range

extensive impact melting on the h chondrite parent asteroid during the cataclysmic bombardment of the early solar system evidence from the achondritic meteorite dar al gani 896 dag 896 is an olivine rich microporphyritic rock of komatiitic composition both the olivine composition fa 17 5 2 1 mn mg 0 0061 and the bulk oxygen isotopic composition delta 17 o 2 55 delta 18 o 3 50 indicate that dag 896 is a sample of the h chondrite parent body the bulk chemistry shows an h chondritic distribution of lithophile elements whereas chalcophile and siderophile elements are strongly depleted indicating formation through whole rock melting or nearly so of h chondrite material nearly complete loss of the metal plus sulfide component and crystallization without significant igneous fractionation superheated severely shocked chondritic relics similar to10 vol typically in the form of corroded lithic fragments 100 mum in size intimately distributed within the igneous lithology indicate that melting was triggered by a highly energetic impact which possibly induced shock pressures of similar to80 100 gpa the relatively young 3 704 0 035 ga ar 40 ar 39 crystallization age is consistent with the impact melting origin as magmatism in the asteroid belt was active only in the first hundred million years of solar system history 1ased on textural data and thermodynamic crystallization modelling we infer that dag 896 crystallized from a liquidus temperature of similar to1630degreesc under relatively slow cooling rates similar to10degreesc h 1 to 1300degreesc before quenching the two stage cooling history indicates that a reasonable formation environment might be a dike intruding cooler basement below a crater floor metal silicate fractionation may have been accomplished at least at the centimeter scale of the studied meteorite sample through differential acceleration of immiscible liquids of different density during the intense flow regimes associated with the excavation and modification stages of the cratering mechanism alternatively dag 896 may represent a surface sample of a differentiated melt body at the floor of an impact crater as gravitational settling appears to be an effective process at the surface of a chondritic parent asteroid for metal particles 1 to 10 mm in size typically observed in partially differentiated impact melt rocks stokes law indicates a settling velocity 1 in h 1 during the first few hours of crystallization on asteroidal bodies of 25 kin radius the similar to3 7 ga age of dag 896 nearly overlaps with the slightly older resetting ages of h chondrites all impact melts available from the literature indicating that the h chondrite parent asteroid underwent extensive impact melting at the enduring of the cataclysmic bombardment of the early solar system such an age overlap may also indicate early disruption of the initial h chondrite parent asteroid the close similarity between the bulk composition and degassing age of dag 896 and silicate inclusions in he iron meteorites is further evidence in support of a common origin by impact melting and metal silicate segregation on the h chondrite parent asteroid our new high precision oxygen isotopic measurements of h chondrites delta 17 o 0 77 0 04 should be extended to iies to verify this possible petrogenetic link

modal mineralogy of cv3 chondrites by x ray diffraction psd xrd abstract using position sensitive detector x ray diffraction psd xrd we determine a complete modal mineralogy for all phases present in abundances greater than 1 wt in vigarano efremovka mokoia grosnaja kaba and allende reduced cv3 samples are comprised of vol olivine 83 85 enstatite 6 5 8 1 anorthite 1 1 1 2 magnetite 1 4 1 8 sulphide 2 4 5 1 fe ni metal 2 2 2 the oxidized samples are comprised of olivine 76 3 83 9 enstatite 4 8 7 8 anorthite 1 1 1 7 magnetite 0 3 6 1 sulphide 2 9 8 1 fe ni metal 0 2 1 1 fe oxide 0 2 7 and phyllosilicate 1 9 4 2 when our modal data is used to calculate a bulk chemistry that is compared to literature data a near 1 1 correlation is observed psd xrd data indicates that olivine compositions may span almost the entire fe mg solid solution series in all cv samples and that these contain a component 4 13 of fine grained olivine that is more fe rich fa 60 than is typically reported modal mineralogy shows that there are mineralogic differences between cv3 samples classified as oxidized and reduced but that these sub classes are most clearly distinguished by the relative abundance of metal and ni content of sulphide rather than abundance of magnetite the most significant difference in modal mineralogy observed is the relative absence of phyllosilicate in reduced cv that essentially escaped aqueous alteration fayalite ferrous olivine and magnetite are typically considered secondary alteration products the abundances of these minerals overlap in oxidized and reduced samples and correlate positively supporting common conditions of formation in a relatively oxidizing environment the abundances of fayalite ferrous olivine and magnetite show no relationship to petrographic type and if these abundances were used as a proxy for alteration allende would be the least altered cv contrary to all previous data the implication is that thermal metamorphism on the parent body was de coupled from formation of fe rich secondary minerals low temperature fluid assisted metamorphism can also not easily explain the origin of fayalite ferrous olivine and magnetite since the reduced cvs appear to be largely unaffected by this process parent body models require an anhydrous low temperature mechanism of secondary alteration the alternative is that these phases formed prior to accretion of the final cv parent body

physical properties of the drill core from the el gygytgyn impact structure ne russia the el gygytgyn impact structure in northeast russia was drilled in 2008 2009 the 3 5 ma old structure has a rim to rim diameter of 18 km and is the only known impact structure that has been formed on a siliceous volcanic target the petrophysical rock and paleomagnetic properties including attempted reorientation of samples along the el gygytgyn drill core were analyzed physical properties such as bulk density porosity seismic velocity and electrical conductivity clearly showed the propagation of shock and the associated fracturing the grain density however was probably influenced by the postimpact hydrothermal activity and or the distribution of impact melt the highest values of electrical conductivity coincided with higher concentrations of particular metals as indicated by raschke et al 2012a the rock and paleomagnetic investigations showed iron titanium oxides with varying oxidation reduction states as the main magnetic fraction in the core samples and indicated them as carriers for remanent magnetization with few exceptions most samples showed normal polarity of characteristic remanent magnetization and confirmed that the impact occurred after the gauss gilbert approximately 3 596 ma reversal shallower inclinations than that expected for a 3 5 ma dipole field were probably due to impact related block movements and or compaction

mineralogy of tagish lake an ungrouped type 2 carbonaceous chondrite in this paper we describe the recovery handling and preliminary mineralogical investigation of the tagish lake meteorite tagish lake is a type 2 carbonaceous chondrite which bears similarities to ci1 and cm chondrite groups but is distinct from both abundant phyllosilicates as well as chondrules however sparse and common olivine grains in the matrix preclude any other classification the bulk density of tagish lake 1 67 g cc which is far lower than ci or cm chondrites 2 2 2 3 and 2 6 2 9 g cc respectively or any other meteorite for that matter we have identified two lithologies a dominant carbonate poor lithology and a less abundant carbonate rich lithology the meteorite is a breccia at all scales we have noted similarities between tagish lake and some clasts within the enigmatic meteorite kaidun possibly there are genetic relationships here worth exploring in the paper we describe a clast of cm1 material within tagish lake which is very similar to a major lithology in kaidun

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

radar constraints on asteroid regolith properties using 433 eros as ground truth abstract radar data enable us to estimate an asteroid s near surface bulk density thus providing a joint constraint on near surface porosity and solid density we investigate two different approaches to simplifying this joint constraint estimating solid densities by assuming uniform porosities for all asteroids and estimating porosities by assuming uniform mineralogy within each taxonomic class methods used to estimate asteroids near surface solid densities from radar data have not previously been calibrated via independent estimates recent spacecraft results on the chondritic nature of 433 eros now permit such a check and also support porosity estimation for s class objects we use radar albedos and polarization ratios estimated for 36 main belt asteroids and nine near earth asteroids to estimate near surface solid densities using two methods one of which is similar to the uncalibrated algorithms used in previous studies the other of which treats eros as a calibrator we also derive porosities for the same sample by assigning solid densities for each taxonomic class in advance density estimation results obtained for eros itself are consistent with the uncalibrated method being valid in the mean those derived for the full sample imply that uncalibrated solid densities are at most a few tens of percent too large on average however some derived densities are extremely low whereas most porosity estimates are physically plausible we discuss the relative merits of these two approaches

exposure history of the mocs l6 chondrite a study of strewn field samples we measured cosmogenic radionuclides 10be 26al and 36cl and noble gases he ne and ar in 10 specimens of the mocs l6 chondrite to determine the exposure history and preatmospheric relationship among fragments from known locations in the strewn field cosmogenic noble gas contents alone are consistent with a simple irradiation exposure of 15 2 ma however mocs has very low 22ne 21ne ratios indicative of deep burial in a large meteoroid but radionuclide levels at saturation values typical for much smaller meteoroids this paradox suggests a possible complex exposure for the latter case we propose a two stage exposure history in which mocs initially was deeply buried in a large object for 110 ma followed by exposure in a 65 cm object for 10 5 ma relative shielding was inferred from the measured 22ne 21ne ratios assuming constant 22ne 21ne production for all samples during the first stage these shielding levels which are supported by estimates based on 36cl production by neutron capture indicate a possible relationship between depth of samples in the mocs meteoroid and fall location in the strewn field

experimental impacts into chondritic targets part i disruption of an l6 chondrite by multiple impacts mr after each shot was impacted by a 3 18 mm ceramic sphere at a nominal speed of 2 km s 1 this continued until the mass of the largest remaining piece was less than half the mass of the target presented to that shot ms two chunks of bushveldt gabbro with similar initial masses were also impacted under the same conditions until mr was less than half m0 the two gabbro targets required a total of 1 51 10 7 and 1 75 10 7 erg g 1 to attain 0 27 and 0 33 mr m0 respectively the chondrite however was considerably tougher reaching 0 40 and 0 21 mr m0 only after receiving 2 37 10 7 and 3 10 10 7 erg g 1 respectively the combined ejecta and spallation products from the gabbro impacts were coarser than those from the chondrite and in sufficient quantities that the new surface areas exceeded those from the meteorite until the fifth shot in the chondrite series which was the number of impacts required to disrupt each gabbro target i e mr m0 0 5 unlike the behavior shown in previous regolith evolution series neither gabbro target produced an enhancement in the size fraction reflecting the mean size of the crystals composing the rock about 3 mm an effect possibly related to the width of the shock pulse the original chondrite was so fine grained and fractured and the variance in its grain size distribution so large that effects related to grain size were relegated to the 63 m fraction impacts into alh 85017 produced abundant fine grained debris but otherwise the slopes of its size distributions were comparable to those from other experiments involving natural and fabricated terrestrial targets the characteristic slopes of the chondrite s size distributions however were notably more constant over the entire nine impact series than those from any of the terrestrial targets a testament to the control over comminution apparently exerted by pre existing fractures and other microscopic damage in the meteorite the enhancement in the finer fraction of debris from alh 85017 indicates that ordinary chondrites in solar orbit would be very efficient contributors to the cosmic dust complex at the same time the greater resistance to disruption displayed by ordinary chondrites relative to that exhibited by igneous rocks indicates that a selection effect could be operative between the annealed ordinary chondritic breccias and relatively weaker differentiated meteorites preferential survival from their time in the regoliths of their parent bodies through their transit to earth and passage through the atmosphere suggests that meteorite collections could be biased in favor of the ordinary chondrites

petrological constraints on the density of the martian crust new insights into the chemistry of the martian crust have been made available since the derivation of crustal thickness maps from mars global surveyor gravity and topography data that used a conservative range of density values 2700 3100 kg m3 a new range of crustal density values is calculated from the major element chemistry of martian meteorites 3100 3700 kg m3 igneous rocks at gusev crater 3100 3600 kg m3 and from the surface concentration of fe al ca si and k measured by the gamma ray spectrometer on board mars odyssey 3250 3450 kg m3 in addition the density of mineral assemblages resulting from low pressure crystallization of primary melts of the primitive mantle are estimated for plausible conditions of partial melting corresponding to the noachian to amazonian periods 3100 3300 kg m3 despite the differences between these approaches the results are all consistent with an average density above 3100 kg m3 for those materials that are close to the surface the density may be compatible with the measured mass of mars and the moment of inertia factor but only if the average crustal thickness is thicker than previously thought approaching 100 km a thicker crust implies that crustal delamination and recycling could be possible and may even control its thickness globally or locally alternatively and considering that geoid to topography ratios argue against such a thick crust for the highlands our results suggest the existence of a buried felsic or anorthositic component in the southern hemisphere of mars

annama h chondrite mineralogy physical properties cosmic ray exposure and parent body history the fall of the annama meteorite occurred early morning local time on april 19 2014 on the kola peninsula russia based on mineralogy and physical properties annama is a typical h chondrite it has a high ar ar age of 4 4 ga its cosmic ray exposure history is atypical as it is not part of the large group of h chondrites with a prominent 7 8 ma peak in the exposure age histograms instead its exposure age is within uncertainty of a smaller peak at 30 4 ma the results from short lived radionuclides are compatible with an atmospheric pre entry radius of 30 40 cm however based on noble gas and cosmogenic radionuclide data annama must have been part of a larger body radius 65 cm for a large part of its cosmic ray exposure history the 10be concentration indicates a recent 3 5 ma breakup which may be responsible for the annama parent body size reduction to 30 35 cm pre entry radius

the fall and recovery of the tagish lake meteorite the tagish lake c2 ungrouped carbonaceous chondrite fall of january 18 2000 delivered 10 kg of one of the most primitive and physically weak meteorites yet studied in this paper we report the detailed circumstances of the fall and the recovery of all documented tagish lake fragments from a strewnfield at least 16 km long and 3 to 4 km wide nearly 1 kg of pristine meteorites were collected one week after the fall before new snow covered the strewnfield the majority of the recovered mass was collected during the spring melt ground eyewitnesses and a variety of instrument recorded observations of the tagish lake fireball provide a refined estimate of the fireball trajectory from its calculated orbit and its similarity to the remotely sensed properties of the d and p class asteroids the tagish lake carbonaceous chondrite apparently represents these outer belt asteroids the cosmogenic nuclide results and modeled production indicate a prefall radius of 2 1 2 4 m corresponding to 60 90 tons consistent with the observed fireball energy release the bulk oxygen isotope compositions plot just below the terrestrial fractionation line tfl following a trend similar to the cm meteorite mixing line the bulk density of the tagish lake material 1 64 0 02 g cm 3 is the same within uncertainty as the total bulk densities of several c class and especially d and p class asteroids the high microporosity of tagish lake samples 40 provides an obvious candidate material for the composition of low bulk density primitive asteroids

portales valley a meteoritic sample of the brecciated and metal veined floor of an impact crater on an h chondrite asteroid a shower of meteorite fragments fell at 0730 h local time on 1998 june 13 near the town of portales new mexico thus far 51 pieces of the portales valley h6 meteorite have been recovered this meteorite has an unusually large number of metallic veins some of these veins are also unusually thick having widths on the order of centimeters these wide veins have fine widmanstatten structure which is the first time it has been seen in an ordinary chondrite this structure indicates the metallic veins and the host chondrite cooled slowly these veins appear to have been produced by shock metamorphic processes which we infer produced a 20 km diameter impact crater on an h chondrite planetesimal

physical properties of martian meteorites porosity and density measurements martian meteorites are fragments of the martian crust these samples represent igneous rocks much like basalt as such many laboratory techniques designed for the study of earth materials have been applied to these meteorites despite numerous studies of martian meteorites little data exists on their basic structural characteristics such as porosity or density information that is important in interpreting their origin shock modification and cosmic ray exposure history analysis of these meteorites provides both insight into the various lithologies present as well as the impact history of the planets surface we present new data relating to the physical characteristics of twelve martian meteorites porosity was determined via a combination of scanning electron microscope sem imagery image analysis and helium pycnometry coupled with a modified archimedean method for bulk density measurements our results show a range in porosity and density values and that porosity tends to increase toward the edge of the sample preliminary interpretation of the data demonstrates good agreement between porosity measured at 100 and 300 magnification for the shergottite group while others exhibit more variability in comparison with the limited existing data for martian meteorites we find fairly good agreement although our porosity values typically lie at the low end of published values surprisingly despite the increased data set there is little by way of correlation between either porosity or density with parameters such as shock effect or terrestrial residency further data collection on additional meteorite samples is required before more definitive statements can be made concerning the validity of these observations

effective radium 226 concentration in meteorites the analysis of noble gases in meteorites provides constraints on the early solar system and the pre solar nebula this requires a better characterization and understanding of the capture production and release of noble gases in meteorites the knowledge of transfer properties of noble gases for each individual meteorite could benefit from using radon 222 radioactive daughter of radium 226 the radon 222 emanating power is commonly quantified by the effective radium 226 concentration ecra the product of the bulk radium 226 concentration and of the emanation coefficient e which represents the probability of one decaying radium 226 to inject one radon 222 into the free porous network owing to a non destructive high sensitivity accumulation method based on long photomultiplier counting sessions we are now able to measure ecra of meteorite samples which usually have mass smaller than 15 g and ecra 0 5 bq kg 1 we report here the results obtained from 41 different meteorites based on 129 measurements on 70 samples using two variants of our method showing satisfactory repeatability and a detection limit below 10 2 bq kg 1 for a sample mass of 1 g while two meteorites remain below detection level we obtain for 39 meteorites heterogeneous ecra values with mean min max range of ca 0 1 0 018 1 30 bq kg 1 carbonaceous chondrites exhibit the largest ecra values and eucrites the smallest such values are smaller than typical values from most terrestrial rocks but comparable with those from archean rocks mean of ca 0 18 bq kg 1 an end member of terrestrial rocks using uranium concentration from the literature e is inferred from ecra for all the meteorite samples values of e for meteorites mean 40 4 are higher than e values for archean rocks and reported values for lunar and martian soils exceptionally large e values likely suggest that the 238u 226ra pair would not be at equilibrium in most meteorites and that uranium and or radium are most likely not uniformly distributed ecra of meteorites is correlated with e and seems to mainly reflect the gas permeability of the meteorite which could be one important property preserved in the meteorite of its parent body characterizing its history in space possibly modified by alteration shock metamorphism and eventually weathering on earth larger radon emanation values are associated with larger concentrations of the heaviest noble gases argon krypton xenon and larger 20ne 22ne and 36ar 38ar ratios suggesting earth s atmosphere contamination or solar wind implantation and probably a similar carrier phase such as q phase an unclear correlation is observed with 40ar which may rule out a purely radiogenic effect on radon emanation thus larger radon emanation suggests a larger capacity of collecting solar and terrestrial gases which should imply higher loss of gases generated in the meteorite and larger dispersion of pb u ratios for age determination this study provides the first quantification of natural radon 222 loss from meteorites and opens promising perspectives to quantify the relationship between pore space connectivity and the transfer properties for noble gases in meteorites and other extraterrestrial bodies

modeling the structure of high porosity asteroids abstract a number of asteroids have been observed to have extremely low bulk densities in the 1 3 g cm 3 range given reasonable compositions based on meteorite analogues this bulk density implies bulk porosities of 40 60 suggesting that many asteroids are rubble piles held together by self gravity and containing significant empty space perhaps more empty space than solid material simple energy balance calculations and accretional models of disrupted asteroids suggest that materials in porous asteroids may be sorted by particle size the large irregular pieces and larger voids fractures are probably located deeper inside the asteroid and the fine particle size fractions that are observed on their surfaces are restricted to the surface regolith zone the large interior voids fractures are preserved from infilling by the effects of friction on the smaller size fractions friction tends to dominate the downward pull of gravity and prevents the fine fractions from filtering into the interior of the asteroid and infilling the large fractures and voids friction may also play a role in allowing shattered asteroids to maintain their relief features and shape by resisting the movements of pieces within the object in effect providing strength to non coherent objects

3 56ga tonalite in the central part of the bastar craton india oldest indian date abstract the lack of information regarding early achaean rocks from the indian peninsula is mainly due to the absence of high quality u pb zircon ages a tonalite sample from the ttg gneiss supracrustal association from the central part of the bastar craton in central india is dated at 3 56 ga this is the oldest protolith age so far recorded from india these ttg gneisses have enclaves of metasedimentary and metavolcanic rocks that may provide important information on the first billion year history of the indian craton this new date for tonalite from the bastar craton is the first precise u pb zircon age from india s first u pb geochronology laboratory located at the geological survey of india which hopefully will remedy the paucity of good geochronological data for older rocks of the indian peninsula

the porosity and permeability of chondritic meteorites and interplanetary dust particles abstract we have investigated the porosity of a large number of chondritic interplanetary dust particles idps and meteorites by three techniques standard liquid gas flow techniques a new noninvasive ultrasonic technique and image processing of backscattered images the latter technique is obviously best suited to sub kilogram sized samples we have also measured the gas and liquid permeabilities of some chondrites by two techniques standard liquid gas flow techniques and a new nondestructive pressure release technique we find that chondritic idps have a somewhat bimodal porosity distribution peaks are present at 0 and 4 porosity a tail then extends to 53 type 1 3 chondrite matrix porosities range up to 30 with a peak at 2 the bulk porosities for type 1 3 chondrites have the same approximate range as exhibited by the matrix which indicates that other components of the bulk meteorites including chondrules and aggregates have the same average porosity as the matrix these results reveal that the porosities of primitive materials at scales ranging from nanogram to kilogram are similar which implies that similar accretion dynamics operated through 12 orders of size magnitude permeabilities of the investigated chondrites vary by several orders of magnitude and there appears to be no simple dependence of permeability with degree of aqueous alteration chondrite type or porosity

thermal evolution of kuiper belt objects with implications for cryovolcanism abstract we investigate the internal thermal evolution of kuiper belt objects kbos small radii 2500 kg m 3 bodies orbiting beyond neptune focusing on pluto s moon charon in particular our calculations are time dependent and account for differentiation we review evidence for ammonia hydrates in the ices of kbos and include their effects on the thermal evolution a key finding is that the production of the first melt at the melting point of ammonia dihydrate 176 k triggers differentiation of rock and ice the resulting structure comprises a rocky core surrounded by liquids and ice enclosed within a 100 km thick undifferentiated crust of rock and ice this structure is especially conducive to the retention of subsurface liquid and bodies the size of charon or larger radii 600 km are predicted to retain some subsurface liquid to the present day we discuss the possibility that this liquid can be brought to the surface rapidly via self propagating cracks we conclude that cryovolcanism is a viable process expected to affect the surfaces of large kbos including charon

porosity and density of ordinary chondrites clues to the formation of friable and porous ordinary chondrites densities and porosities of meteorites are physical properties that can be used to infer characteristics of asteroid interiors we report density and porosity measurements of 42 pieces of 30 ordinary chondrites and provide a quantification of the errors of the gas pycnometer method used in this study based on our measurements we find that no significant correlation exists between porosity and petrologic grade chemical group sample mass bulk and grain density or shock level to investigate variations in porosity and density between pieces of a meteorite we examined stones from two showers holbrook and pultusk examination of nine samples of holbrook suggests relative homogeneity in porosity and density between pieces of this shower measurements of three samples of pultusk show homogeneity in bulk density in contrast to wilkison and robinson 2000 a study that reported significant variations in bulk density between 11 samples of pultusk finally examination of two friable ordinary chondrites bjurbole and allegan reveal variability in friability and porosity among pieces of the same fall we suggest that friable ordinary chondrites may have formed in a regolith or fault zone of an asteroid

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

near s flyby of 253 mathilde images of a c asteroid on 27 june 1997 the near earth asteroid rendezvous near spacecraft flew within 1212 kilometers of asteroid 253 mathilde mathilde is an irregular heavily cratered body measuring 66 kilometers by 48 kilometers by 46 kilometers the asteroid s surface is dark estimated albedo between 0 035 and 0 050 and similar in color to some cm carbonaceous chondrites no albedo or color variations were detected the volume derived from the images and the mass from doppler tracking of the spacecraft yield a mean density of 1 3 0 2 grams per cubic centimeter about half that of cm chondrites indicating a porous interior structure

one meteorite less from vietnam among the four declared meteorites from vietnam the two most recent ones phuoc binh 1941 and fuc bin 1971 appear to be the same following a visit to the hanoi museum and an analysis of the literature phuoc binh l5 with a fall date of 1941 july 18 should be the correct entry

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

petrology of the yamato nakhlites the yamato nakhlites y 000593 y 000749 and y 000802 were recovered in 2000 from the bare icefield around the yamato mountains in antarctica consisting of three independent specimens with black fusion crusts they are paired cumulate clinopyroxenites we obtained the intercumulus melt composition of the yamato nakhlites and here call it the yamato intercumulus melt yim the yim crystallized to form the augite rims the olivine rims and the mesostasis phases in the cumulates the augite rims consist of two layers inner and outer the crystallization of the inner rim drove the interstitial melt into the plagioclase liquidus field subsequently the residual melt crystallized pigeonites and plagioclase to form the outer rims and the mesostasis three types of inclusions were identified in olivine phenocrysts rounded vitrophyric angular vitrophyric and monomineralic augite inclusions the monomineralic augite inclusions are common and may have been captured by growing olivine phenocrysts the rounded vitrophyric inclusions are rare and may represent the composition of middle stage melts whereas the angular vitrophyric inclusions seem to have been derived from fractionated late stage melts glass inclusions occur in close association with titanomagnetite and ferroan augite halo in phenocryst core augites and the assemblages may be magmatic inclusions in augites we compared the yim with compositions of magmatic inclusions in olivine and augite the composition of magmatic inclusions in augite is similar to the yim phenocrystic olivines contain exsolution lamellae augite magnetite aggregates and symplectites in the cores the symplectites often occur at the boundaries between olivine and augite grains the aggregates symplectite and lamellae formed by exsolution from the host olivine at magmatic temperatures we present a formational scenario for nakhlites as follows 1 accumulation of augite olivine and titanomagnetite phenocrysts took place on the floor of a magma chamber 2 olivine exsolved augite and magnetite as augite magnetite aggregates symplectites and lamellae 3 the overgrowth on olivine phenocrysts formed their rims and the inner rims crystallized on augite phenocryst cores and finally 4 the outer rim formed surrounding the inner rims of augite phenocrysts and plagioclase and minor minerals crystallized to form mesostasis under a rapid cooling condition probably in a lava flow or a sill

deuterium enrichments in chondritic macromolecular material implications for the origin and evolution of organics water and asteroids here we report the elemental and isotopic compositions of the insoluble organic material iom isolated from several previously unanalyzed meteorites as well as the reanalyses of h isotopic compositions of some previously measured samples alexander et al 2007 the iom in ordinary chondrites ocs has very large d enrichments that increase with increasing metamorphism and decreasing h c the most extreme d value measured being almost 12 000 we propose that such large isotopic fractionations could be produced in the oc parent bodies through the loss of isotopically very light h2 generated when fe was oxidized by water at low temperatures 200 c we suggest that similar isotopic fractionations were not generated in the iom of cv and co chondrites with similar metamorphic grades and iom h c ratios because proportionately less water was consumed during metamorphism and the remaining water buffered the h isotopic composition of the iom even a h was being lost from it hydrogen would also have been generated during the alteration of ci cm and cr carbonaceous chondrites the iom in these meteorites exhibit a considerable range in isotopic compositions but all are enriched in d as well as 15n relative to terrestrial values we explore whether these enrichments could also have been produced by the loss of h2 but conclude that the most isotopically anomalous iom compositions in meteorites from these groups are probably closest to their primordial values the less isotopically anomalous iom has probably been modified by parent body processes the response of iom to these processes was complex and varied presumably reflecting differences in conditions within and between parent bodies the d enrichments associated with h2 generation along with exchange between d rich iom and water in the parent bodies means that it is unlikely that any chondrites retain the primordial h isotopic composition of the water ice that they accreted the h isotopic compositions of the most water rich chondrites the cms and cis are probably the least modified and their compositions d 25 suggest that their water did not form at large radial distances from the sun where ice is predicted to be very d rich yet models to explain the o isotopic composition of inner solar system bodies require that large amounts of ice were transported from the outer to the inner solar system

why aqueous alteration in asteroids was isochemical high porosity high permeability carbonaceous chondrite meteorites are the most compositionally primitive rocks in the solar system but the most chemically pristine ci1 and cm2 chondrites have experienced pervasive aqueous alteration apparently within asteroid parent bodies unfractionated soluble elements suggest very limited flow of liquid water indicting a closed system at scales large than 100 s m consistent with data from oxygen isotopes and meteorite petrography however numerical studies persistently predict large scale 10 s km water transport in model asteroids either in convecting cells or via exhalation flow an open system at scales up to 10 s km these models have tended to use permeabilites in the range 10 13 to 10 11 m2 we show that the permeability of plausible chondritic starting materials lies in the range 10 19 to 10 17 m2 0 1 10 d around six orders of magnitude lower than previously assumed this low permeability is largely a result of the extreme fine grain size of primitive chondritic materials applying these permeability estimates in numerical models we predict very limited liquid water flow distances of 100 s m at most even in a high porosity water saturated asteroid with a high thermal gradient over millions of years isochemical alteration with flow over minimal lengthscales is not a special circumstance it is inevitable once we consider the fundamental material properties of these rocks to achieve large scale flow it would require average matrix grain sizes in primitive materials of 10 s 100 s m orders of magnitude larger than observed finally in addition to reconciling numerical modelling with meteorite data our work explains several other features of these enigmatic rocks most particularly why the most chemically primitive meteorites are also the most altered

trace element mobility during spheroidal weathering of basalts and andesites in hawaii and guatemala abstract trace element mobility has been studied in spheroidally weathered corestone shell complexes developed on late tertiary and quaternary volcanic rocks the parent materials are basalts and andesites related to 1 a subduction zone tecuamburro and moyuta volcanoes guatemala and 2 a hot spot hawaiian islands of oahu maui and hawai i the initial major element compositions are largely preserved in the corestones each corestone sample shows major element abundances characteristic of the different magmatic processes through which the lavas were generated however the changes in trace element compositions due to weathering show similar patterns in the corestone shell complexes independent of the tectonic setting and age element mobility within the different corestone shell complex was determined using an isovolumetric reference frame in this method bulk density is chosen as an independent measure of the extent of weathering based on volumetric concentrations the notion of element immobility cannot be applied to all the corestone shell complexes elements commonly assumed to be immobile e g zr ti and al vary in volumetric concentration for some corestone shell complex despite petrographic evidence of only minor weathering two corestones oahu and tecuamburro have become enriched in ree 3 relative to other lava flows from the same volcanoes and display negative ce anomalies the exfoliated shells from these complexes tend to have lower concentrations of ree 3 and have positive ce anomalies the fractionation of ce from the other rare earth elements ree is inferred to be a manifestation of changes in the valence state of ce from trivalent to tetravalent under oxidizing conditions in settings where the development of corestone shell complex is advanced an acidic solution can mobilize trivalent ree leach them out of more extensively weathered materials and transport them to less acidic portions of the regolith undergoing incipient weathering the precipitation of the ree 3 in the rinds and centers of the corestones are likely due to increases of the ph of the weathering solution systematic weathering induced ree behavior enrichment of most ree with lesser ce enrichment resulting in a negative ce anomaly can be discerned even in corestone samples that exhibit major element abundances and petrographic features otherwise similar to unweathered basalts and andesites

the orbit atmospheric dynamics and initial mass of the park forest meteorite the fireball accompanying the park forest meteorite fall l5 was recorded by ground based videographers satellite systems infrasound seismic and acoustic instruments this meteorite shower produced at least 18 kg of recovered fragments on the ground simon et al 2004 by combining the satellite trajectory solution with precise ground based video recording from a single site we have measured the original entry velocity for the meteoroid to be 19 5 0 3 km s the earliest video recording of the fireball was made near the altitude of 82 km the slope of the trajectory was 29 from the vertical with a radiant azimuth astronomical of 21 and a terminal height measured by infrared satellite systems of 18 km the meteoroid s orbit has a relatively large semi major axis of 2 53 0 19 au large aphelion of 4 26 0 38 au and low inclination the fireball reached a peak absolute visual magnitude of 22 with three major framentation episodes at the altitudes of 37 29 and 22 km acoustic recordings of the fireball airwave suggest that fragmentation was a dominant process in production of sound and that some major fragments from the fireball remained supersonic to heights as low as 10 km seismic and acoustic recordings show evidence of fragmentation at 42 36 29 and 17 km examination of implied energies initial masses from all techniques satellite optical infrasound seismic modeling leads us to conclude that the most probable initial mass was 11 3 10 3 kg corresponding to an original energy of 0 5 kt tnt 2 1 x 10 12 j and a diameter of 1 8 m these values correspond to an integral bolometric efficiency of 7 2 early fragmentation ram pressures of 30 seconds

mechanisms of weathering of meteorites recovered from hot and cold deserts and the formation of phyllosilicates abstract petrographic mineralogical and chemical analysis of naturally weathered equilibrated ordinary chondrites collected from hot deserts and antarctica has revealed striking similarities and also pronounced differences in weathering between the two environments terrestrial weathering in all meteorites studied is dominated by oxidation and hydration of fe ni metal producing fe oxides and oxyhydroxides that have partially replaced the metal grains and have also occluded primary intergranular pores to form veins troilite weathers readily in hot desert environments but undergoes very little alteration under antarctic conditions most of the primary porosity of ordinary chondrites has been occluded by the time that 15 to 25 of the initial fe 0 and fe 2 has been oxidised to fe 3 in both environments results from modelling the volume changes upon alteration of primary minerals to a range of weathering products demonstrates that the primary porosity of most meteorites is sufficient to accommodate weathering products dilation of primary pores and brecciation which has been observed in parts of some meteorites will only occur if the meteorite is especially metal rich or has a low primary porosity these weathering products are absent from recent falls but have formed in a fall after 100 yr of museum storage cl bearing akaganeite and hibbingite are common weathering products in antarctic finds but occur in abundance in only one hot desert meteorite daraj 014 the majority of fe rich weathering products in meteorites from both environments contain low but variable concentrations of si mg and ca in most meteorites a proportion of these elements are inferred to be present as a very finely crystalline mineral with a 1 0 nm lattice fringe spacing where seen within intragranular fractures this mineral has a topotactic relationship with olivine and orthopyroxene in the heavily weathered antarctic finds alha 78045 and 77002 si is concentrated in cronstedtite a fe rich phyllosilicate an unidentified hydrous si fe ni mg mineral or gel has also partially replaced taenite in alha 78045 in addition to fe rich weathering products hot desert meteorites contain sulphates ca carbonate and silica whereas such minerals are largely absent from antarctic finds the abundance of silicate weathering products in antarctic meteorites is unexpected and indicates that olivine and pyroxene undergo significant chemical weathering in these environments as preterrestrial cronstedtite is abundant in cm2 carbonaceous chondrites the antarctic environment may be a powerful analog for aqueous alteration in the asteroidal parent bodies of primitive meteorites

a comprehensive study of distribution laws for the fragments of kosice meteorite in this study we conduct a detailed analysis of the kosice meteorite fall february 28 2010 to derive a reliable law describing the mass distribution among the recovered fragments in total 218 fragments of the kosice meteorite with a total mass of 11 285 kg were analyzed bimodal weibull bimodal grady and bimodal lognormal distributions are found to be the most appropriate for describing the kosice fragmentation process based on the assumption of bimodal lognormal bimodal grady bimodal sequential and bimodal weibull fragmentation distributions we suggest that prior to further extensive fragmentation in the lower atmosphere the kosice meteoroid was initially represented by two independent pieces with cumulative residual masses of approximately 2 and 9 kg respectively the smaller piece produced about 2 kg of multiple lightweight meteorite fragments with the mean around 12 g the larger one resulted in 9 kg of meteorite fragments recovered on the ground including the two heaviest pieces of 2 374 kg and 2 167 kg with the mean around 140 g based on our investigations we conclude that two to three larger fragments of 500 1000 g each should exist but were either not recovered or not reported by illegal meteorite hunters

physical properties of ordinary chondrites physical properties intrinsic and bulk densities porosity compressional and shear wave velocities thermal diffusivity and conductivity are measured on 11 ordinary chondrites one carbonaceous chondrite and two achondritic clasts of a mesosiderite with the previously reported results from antarctic ordinary chondrites the data are useful in clarifying the difference between h and l chondrites for example the intrinsic density of h chondrites 3800 kg m3 is generally higher than that of l chondrites 3600 kg m3 the sample porosity less than 20 strongly controls its elastic wave velocities thermal diffusivity and conductivity the variations of elastic wave velocities and thermal properties with porosity show that as with lunar rocks chondrites contain many cracks these cracks are thought to be created on their parent bodies by the cumulative effects of many mutual collisions and impacts thermal properties are linear functions of elastic wave velocities for both h and l chondrites the difference between h and l chondrites can be attributed to the content of metallic fe ni correlations between petrologic types which roughly represent metamorphic temperature and porosity are less obvious for l chondrites than for h chondrites since porosity is not changed significantly by impact events it appears that the sintering process for l chondrites is independent of the metamorphic events represented by petrologic type

bulk density of asteroid 243 ida from the orbit of its satellite dactyl during its reconnaissance of the asteroid 243 ida the galileo spacecraft returned images of a second object 1993 243 1 dactyl1 the first confirmed satellite of an asteroid sufficient data were obtained on the motion of dactyl to determine its orbit as a function of ida s mass here we apply statistical and dynamical arguments to constrain the range of possible orbits and hence the mass of ida combined with the volume of ida2 this yields a bulk density of 2 6 0 5 g cm 3 allowing for the uncertainty in the porosity of ida this density range is consistent with a bulk chon dritic composition and argues against some but not all classes of meteoritic igneous rock types that have been suggested as compositionally representative of s type asteroids like ida

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

density magnetic susceptibility and the characterization of ordinary chondrite falls and showers bulk and grain densities of 132 ordinary chondrites from the vatican observatory collection were measured and compared with their magnetic susceptibility for the most part using previously measured values ten new susceptibility measures were taken for this study grain density and magnetic susceptibility combined provide a reliable method of classifying un weathered ordinary chondrites unlike traditional chemical tests this method is fast nondestructive and characterizes the whole rock making it especially appropriate for surveying large collections the system is less viable for finds extensive weathering of metallic iron in an h chondrite can cause it to plot among l chondrites while heavily weathered l chondrites plot among the ll group this system has revealed outlier stones that may be misclassified meteorites or mislabeled samples in every case where the magnetic susceptibility of a meteorite does not fit its putative classification the grain density is also found to be in disagreement in a manner consistent with either severe weathering or misidentification an analysis of stones from five showers shows that excluding outliers these samples tend to cluster tightly within their appropriate groups in a plot of grain versus magnetic susceptibility

an estimate of eros s porosity and implications for internal structure abstract earth based spectral measurements and near shoemaker magnetometer x ray and near infrared spectrometer data are all consistent with eros having a bulk composition and mineralogy similar to ordinary chondrite meteorites oc by comparing the bulk density of 433 eros 2 67 0 03 g cm 3 with that of ocs 3 40 g cm 3 we estimate the total porosity of the asteroid to be 21 33 macro or structural porosity best estimated to be 20 is constrained to be between 6 and 33 we conclude that eros is a heavily fractured body but we find no evidence that it was ever catastrophically disrupted and reaccumulated into a rubble pile

the taxonomic distribution of asteroids from multi filter all sky photometric surveys abstract the distribution of asteroids across the main belt has been studied for decades to understand the current compositional distribution and what that tells us about the formation and evolution of our solar system all sky surveys now provide orders of magnitude more data than targeted surveys we present a method to bias correct the asteroid population observed in the sloan digital sky survey sdss according to size distance and albedo we taxonomically classify this dataset consistent with the bus and binzel bus s j binzel r p 2002 icarus 158 146 177 and bus demeo et al demeo f e binzel r p slivan s m bus s j 2009 icarus 202 july 160 180 systems and present the resulting taxonomic distribution the dataset includes asteroids as small as 5 km a factor of three in diameter smaller than in previous work such as by mothe diniz et al mothe diniz t carvano j m a lazzaro d 2003 icarus 162 march 10 21 because of the wide range of sizes in our sample we present the distribution by number surface area volume and mass whereas previous work was exclusively by number while the distribution by number is a useful quantity and has been used for decades these additional quantities provide new insights into the distribution of total material we find evidence for d types in the inner main belt where they are unexpected according to dynamical models of implantation of bodies from the outer solar system into the inner solar system during planetary migration levison h f bottke w f gounelle m morbidelli a nesvorn d tsiganis k 2009 nature 460 july 364 366 we find no evidence of s types or other unexpected classes among trojans and hildas albeit a bias favoring such a detection finally we estimate for the first time the total amount of material of each class in the inner solar system the main belt s most massive classes are c b p v and s in decreasing order excluding the four most massive asteroids 1 ceres 2 pallas 4 vesta and 10 hygiea that heavily skew the values primitive material c p types account for more than half main belt and trojan asteroids by mass most of the remaining mass being in the s types all the other classes are minor contributors to the material between mars and jupiter

magnetic classification of stony meteorites 2 non ordinary chondrites a database of magnetic susceptibility measurements on different non ordinary chondrites c e r and ungrouped populations is presented and compared to our previous similar work on ordinary chondrites it provides an exhaustive study of the amount of iron nickel magnetic phases essentially metal and magnetite in these meteorites in contrast with all the other classes cm and cv show a wide range of magnetic mineral content with a two orders of magnitude variation of whether this is due to primary parent body differences metamorphism or alteration remains unclear c34 and c2 yield similar values to the ones shown by ck and cm respectively by order of increasing the classes with well grouped are r co ck ci kak cr e ch cb based on magnetism eh and el classes have indistinguishable metal content outliers that we suggest may need to have their classifications reconsidered are acfer 202 co elephant moraine eet 96026 c45 meteorite hills met 01149 and northwest africa nwa 521 ck asuka a 88198 lapaz icefield lap 031156 and sahara 98248 r values can also be used to define affinities of ungrouped chondrites and propose pairing particularly in the case of cm and cv meteorites

preliminary interpretation of magnetic anomalies over japan and its surrounding area the anomalies of geomagnetic total force over japan and its surrounding area 20 50 n and 120 160 e were interpreted by a magnetization of the earth s surface layer in a direction parallel to the main magnetic field a negative magnetization anomaly in the japan sea may be attributable to the thinness of the magnetized part of the crust in comparison with the japan island this is in accordance with the underground high temperature gradient suggested from the observed high heat flow values in the japan sea area

simulation experiments for shocked primitive materials in the solar system abstract shock recovery experiments were conducted on porous mixtures initial porosity 35 5 in silicate metal and silicate metal sulfide systems in an attempt to simulate impact phenomena of unconsolidated porous materials similar to ordinary chondrites in a wide range of shock pressures from 20 to 70 gpa the textures and chemical compositions of shocked samples were investigated in detail features such as grain deformation fracture density decrease and heterogeneous meltings are found at

a terrestrial origin for sulfate veins in ci1 chondrites white sulfate veins are a very well known petrological feature of the chemically primitive ci1 carbonaceous chondrites sulfate veins were first described in the orgueil meteorite in 1961 almost one century after its fall however we have observed such veins to form easily during typical sample storage we suggest that all ci1 sulfate veins formed during the terrestrial residence of these heavily brecciated porous stones reacting with atmospheric water sulfates originally present in the meteorites dissolved and remobilized and or sulfides oxidised filling the many open spaces offered to them by the very porous rock sulfate veins in ci1 chondrites can no longer be used as evidence of a late stage oxidation event in the ci1 parent body or of centimeter scale fluid transport on the parent asteroid

spectra of extremely reduced assemblages implications for mercury we investigate the possibility that mercury s crust is very reduced with feo concentrations of less than 0 1 wt we believe that such a surface could have a composition of enstatite plagioclase diopside and sulfide similar to the mineral assemblages found in aubritic meteorites to test this hypothesis we investigated the spectra of aubrites and their constituent minerals as analogs for the surface of mercury we found that some sulfides have distinctive absorption features in their spectra shortwards of 0 6 m that may be apparent in the spectrum of such an object determination of the surface composition of mercury using orbital x ray spectroscopy should easily distinguish between a lunar highlands and enstatite basalt composition since these materials have significant differences in concentrations of al mg s and fe the strongest argument against mercury having an enstatite basalt composition is its extreme spectral redness significant reddening of the surface of an object such as mercury is believed to require reduction of feo to nanophase iron thus requiring a few percent feo in the material prior to alteration

the formation of ca fe rich silicates in reduced and oxidized cv chondrites the roles of impact modified porosity and permeability and heterogeneous distribution of water ices cv vigarano type carbonaceous chondrites comprising allende like cvoxa and bali like cvoxb oxidized and reduced cvred subgroups experienced differing degrees of fluid assisted thermal and shock metamorphism the abundance and speciation of secondary minerals produced during asteroidal alteration differ among the subgroups 1 ferroan olivine and diopside hedenbergite solid solution pyroxenes are common in all cvs 2 nepheline and sodalite are abundant in cvoxa rare in cvred and absent in cvoxb 3 phyllosilicates and nearly pure fayalite are common in cvoxb rare in cvred and virtually absent in cvoxa 4 andradite magnetite and fe ni sulfides are common in oxidized cvs but rare in reduced cvs the latter contain kirschsteinite instead thus a previously unrecognized correlation exists between meteorite bulk permeabilities and porosities with the speciation of the ca fe rich silicates pyroxenes andradite kirschsteinite among the cvox and cvred meteorites the extent of secondary mineralization was controlled by the distribution of water ices permeability and porosity which in turn were controlled by impacts on the asteroidal parent body more intense shock metamorphism in the region where the reduced cvs originated decreased their porosity and permeability while simultaneously expelling intergranular ices and fluids the mineralogy petrography and bulk chemical compositions of both the reduced and oxidized cv chondrites indicate that mobile elements were redistributed between ca al rich inclusions dark inclusions chondrules and matrices only locally there is no evidence for large scale several cm fluid transport published 53mn 53cr ages of secondary fayalite in cv co and unequilibrated ordinary chondrites and carbonates in ci cm and cr chondrites are consistent with aqueous alteration initiated by heating of water ice bearing asteroids by decay of 26al not shock metamorphism

modal mineralogy of carbonaceous chondrites by x ray diffraction and mossbauer spectroscopy carbonaceous chondrites are among the most analyzed geological materials on earth however despite this attention and unlike most terrestrial rocks little is known on the abundance of individual phases within them here we show how a combination of several novel x ray diffraction xrd techniques including a high brightness x ray microsource and mssbauer spectroscopy allows a complete modal mineralogy to be ascertained from even the most highly unequilibrated fine grained chondrites for all minerals of abundance 1 wt knowledge of the modal mineralogy of a sample also allows us to calculate grain density we analyzed allende murchison tagish lake and orgueil based on our modal data the grain density estimates for allende murchison and orgueil are close to literature values in the case of tagish lake there is no published grain density although a bulk density measurement does exist taking our estimate of grain density and the measured bulk density we calculate an exceptionally high porosity of 41 for this meteorite similar to some chondritic idps and in line with a porosity calculated from an entry model for the tagish lake fireball although it is an oxidized cv magnetite is present in allende at a level of 0 5 wt or 0 3 vol a result that is substantiated by several other instrumental studies this may be an oxidized meteorite but that oxidation is not manifested in abundant magnetite in addition we note appreciable fayalitic olivine in orgueil detected by both xrd and mossbauer we employed microsource xrd to look at heterogeneity in mineral abundance in orgueil and found substantial variation with phyllosilicates varying inversely with olivine the data suggest that orgueil was initially composed primarily of anhydrous materials which have been partially but not completely altered although the data are preliminary comparison between our xrd modal assessment bulk chemistry grain density and mossbauer data suggests that our estimates of mineral abundance are robust the advent of microsource xrd allows similar modal data to be acquired from samples as small as a few hundred micrograms

exposure history of the st robert h5 fall the compositionally typical h5 chondrite st robert has an exposure age 7 8 ma indistinguishable from that of the main cluster of h chondrites small values of the cosmogenic 22ne 21ne ratio in interior samples imply a pre atmospheric radius on the order of 40 cm sample depths based on tracks and the production rates of bhattacharya et al 1973 range from 6 to 40 cm and are generally larger than depths estimated from published 60co activities perhaps because the track production rates adopted are too high depth profiles of the production rates of 14c 36cl 26al 10be and 21ne in stony material show increases with depth and reach levels 5 to 15 higher than expected from modeling calculations the maximum concentrations in st robert are however generally comparable to those measured for the l5 chondrite knyahinya whose pre atmospheric radius of 45 cm is thought to lead to the maximum possible production rates in chondrites we infer that the pre atmospheric radius of st robert was within 5 cm of the value that supports maximum production rates i e 45 5 cm this radius corresponds to a pre atmospheric mass of 1 3 0 4 103 kg the agreement of exposure ages for st robert obtained in several different ways and the similarity of the depth profiles for 14c 26al 10be and 21ne argue against a lengthy pre exposure of st robert on the parent body and against a two stage exposure after launch from the parent body following morbidelli and gladman 1998 we suggest that st robert was chipped from deep in its parent body spent the next 7 8 ma without undergoing a major collision was nudged gradually into an orbital resonance with jupiter and then traveled quickly to earth

density porosity and magnetic susceptibility of achondritic meteorites as part of a large scale survey of meteorite bulk and grain densities porosities and magnetic susceptibilities we measured these properties for 174 stones from 106 achondritic meteorites these include four lunar meteorites 15 stones from 10 shergottites nakhlites and chassignites sncs 96 stones from 56 howardites eucrites and diogenites heds 17 stones from nine aubrites two angrites and 16 stones from 10 ureilites four stones of three acapulcoites as well as four stones of three lodranites and 15 stones from eight primitive achondrites those meteorites derived from basalts and crustal material of differentiated parent bodies have lower densities and magnetic susceptibilities on an average than the more primitive achondrites which have a higher percentage metal a notable exception is the one chassignite in the study chassigny which has a high grain density of 3 73 0 04 g cm 3 ureilites have magnetic susceptibilities consistent with primitive achondrites but lower grain densities porosities do not vary considerably between most of the groups with most stones 5 14 porous although on an average ureilites and brachinites have lower porosities with most stones less than 7 porous for primitive achondrites the higher metal content causes finds to exhibit weathering effects similar to what is observed in ordinary chondrites with a reduction in grain density magnetic susceptibility and porosity as compared with unweathered falls for lunites sncs and heds no such effect is observed we also observe that grain density and magnetic susceptibility used in conjunction distinguish shergottites nakhlites and chassignites from each other shergottites and nakhlites have low grain densities averaging 3 31 and 3 41 g cm 3 respectively whereas chassigny is 3 7 g cm 3 in magnetic susceptibility shergottities and chassignites are similar averaging 2 85 and 2 98 in log units of 10 9 m3 kg 1 respectively with nakhlites averaging higher at 3 42