plate boundary observatory and related networks gps data analysis methods and geodetic products the geodesy advancing geosciences and earthscope gage facility global positioning system gps data analysis centers produce position times series velocities and other parameters for approximately two thousand continuously operating gps receivers spanning a quadrant of earth s surface encompassing the high arctic north america and caribbean the purpose of this review is to document the methodology for generating station positions and their evolution over time and to describe the requisite tradeoffs involved with combination of results gage gps analysis involves formal merging within a kalman filter of two independent loosely constrained solutions one is based on precise point positioning produced with the gps inferred positioning system orbit analysis simulation gipsy oasis software at central washington university cwu and the other is a network solution based on phase and range double differencing produced with the gps at mit gamit software at new mexico institute of mining and technology nmt the primary products generated are the position time series that show motions relative to a north america reference frame and secular motions of the stations represented in the velocity field the position time series themselves contain a multitude of signals in addition to the secular motions co seismic and post seismic signals seasonal signals from hydrology and transient events some understood and other not yet fully explained are all evident in the time series and ready for further analysis and interpretation we explore the impact of analysis assumptions on the reference frame realization and on the final solutions and we compare within the gage solutions and with others

evidence for excavation of deep crustal material of a vesta like body from ca compositional gradients in pyroxene abstract recent discovery of basaltic achondrite asteroids in the main belt has provided a link between basaltic achondrites howardite eucrite and diogenite and asteroid 4 vesta a spectral study suggests that these asteroids are fragments ejected from vesta and that vesta s eucritic crust is of substantial thickness we computed the cooling rate and burial depth of the moore county cumulate eucrite on the basis of ca compositional gradients and the width of augite lamella in pyroxene to obtain information on the early evolution of the parent body our calculations show that 1 moore county cooled initially at a rate of 0 00016 c yr which corresponds to a burial depth of about 8 km 2 after this cooling a sudden temperature rise occurred probably due to an impact and finally 3 moore county cooled down again at a rate of 0 35 c yr the latter events may correspond to the excavation of crustal material the burial depth of moore county is consistent with the result of a recent spectral study in which the largest observed eucritic fragment 10 km sets a lower limit on the thickness of the eucritic crust reheating and excavation of a deep crustal material imply impact events which are supported by spectral observations

petroleum geochemistry of the zala basin hungary the zala basin is a subbasin within the pannonian basin of hungary oil and smaller amounts of gas are produced from upper triassic through miocene reservoirs our geochemical study of oils and rocks in the basin indicate that two and possibly three genetic oil types are present in the basin miocene source rocks previously believed by explorationists to be the predominant source rock have expelled minor amounts of hydrocarbons the main source rock is the upper triassic rhaetian kossen marl formation or its stratigraphic equivalent oils derived from the triassic source rock are recognizable by their isotopic and biological marker composition and high content of metals in other areas of europe upper triassic source rocks have been correlated with large oil accum lations e g molassa and villafortuna fields po basin and other fields in italy or are postulated to be good potential source rocks e g bristol channel trough knowledge of the geochemical characteristics of oils derived from these upper triassic source rocks and understanding of the source rock distribution and maturation history are important for recognizing triassic oil source bed relationships and for further exploration in other basins in hungary and other parts of europe where triassic source rocks are present

discovery of a basaltic asteroid in the outer main belt visible and near infrared spectroscopic observations of the asteroid 1459 magnya indicate that it has a basaltic surface magnya is at 3 15 astronomical units au from the sun and has no known dynamical link to any family to any nearby large asteroid or to asteroid 4 vesta at 2 36 au which is the only other known large basaltic asteroid we show that the region of the belt around magnya is densely filled by mean motion resonances generating slow orbital diffusion processes and providing a potential mechanism for removing other basaltic fragments that may have been created on the same parent body as magnya magnya may represent a rare surviving fragment from a larger differentiated planetesimal that was disrupted long ago

surface lithologic heterogeneity of asteroid 4 vesta abstract high precision spectrophotometry of 4 vesta the third largest asteroid was used to establish the surface composition of this body and to investigate mineralogical variations across its surface the average surface of vesta is analogous to howardite and or polymict eucrite assemblages regolith derived members of the hed meteorite suite which consist of a eucrite matrix containing differing amounts of a diogenite component color and or spectral changes which exhibit a consistent relationship to rotational phasing are evident in 16 of 18 studies of vesta dating back to 1929 including the present work after elimination of possible sources of spurious spectral or color changes it is concluded that these variations arise from hemispheric variations in surface materials and hence provide a means of spatially resolving subhemispheric compositional units on the surface of vesta the background surface of vesta is a relatively dark howardite or polymict eucrite pyroxene plagioclase assemblage with several compositionally distinct bright regions clustered in one hemisphere viewed around the maximum in vesta s lightcurve these include what appears to be an olivine bearing unit suggested name leslie formation located near vesta s equator which probably represents an impact basin and or its associated ejecta that penetrated through the basaltic crust other high albedo compositional units including an apparently low calcium eucrite region and several diogenite pyroxenite regions at least one located near the southern pole may be smaller shallower impact basins by analogy to the eucrite meteorites which represent surface flows or shallow intrusions and which constitute the major component of the regolith derived howardites and polymict eucrites we conclude that the howardite polymict eucrite units represent a regolith gardened original surface of vesta it is probable that the low albedo of the background surface on vesta is due to an age related darkening effect similar to that inferred from the galileo images of gaspra and ida this mechanism is consistent with the correlation of absorption feature intensity with the lightcurve vesta appears to have an old eucritic surface darkened with age and represented among the meteorites by the regolith derived howardites and polymict eucrites on which several impacts on one hemisphere have exposed fresher brighter diogenite and olivine bearing material based on qualitative analysis of the mineralogical variations as a function of rotation a generalized lithologic map of vesta was produced there is reasonable control on the longitude of lithologic features but little control on their latitudes except where specifically noted in producing this map discrete circular features were used on the plausible assumption that impacts have been the most important geologic process on this surface for most of the age of the solar system the shape of the features has thus been assumed rather than derived and is subject to future revision as data improve

implications of temperature dependent near ir spectral properties of common minerals and meteorites for remote sensing of asteroids remote sensing analysis of common mafic silicates on bodies like asteroid 433 eros may be in error unless temperature effects are considered in this paper spectral sensitivity to temperature as a function of wavelength from 0 4 to 2 5 microns is quantified using new measurements of reflectance spectra of olivine and two ordinary chondrites the new data were obtained at higher temperature resolution and with greater accuracy than previous measurements we use a simple thermal model to show that the temperature difference between terrestrial ambient conditions and those prevailing on main belt asteroids as well as the temperature variations expected on the surfaces of individual asteroids during observations by spacecraft are large enough to cause easily detectable spectral differences therefore interpretations of asteroid spectra using spectra of minerals and meteorites obtained at terrestrial ambient conditions are suspect

siderophile and other geochemical constraints on mixing relationships among hed meteoritic breccias we have used neutron activation and electron probe fused bead techniques to analyze the bulk major and trace element compositions of 104 named hed meteorites about 100 102 distinct meteorites depending upon pairings including 32 polymict eucrites 30 howardites and six diogenites most were not previously analyzed for siderophile trace elements many not even for major elements our typical sample was 350 mg and in some cases two separate chips were analyzed as a test of meteorite heterogeneity meteorites with extraordinary compositions include bluewing 001 an unequilibrated eucrite that is rich in ti sm and other incompatible elements y 791192 a cumulate dominated polymict eucrite and lew 87002 an oddly sm rich howardite dominated by a ferroan variety of diogenite the eucrite diogenite mixing ratio is the single most important factor determining the compositions of polymict heds but wide ranges in eucrite incompatible element contents in diogenite cr and v contents and in sc contents of both eucrites and diogenites make for diversity among the polymict heds as our new siderophile data help to show the common practice of describing the entire class of howardites as regolith breccias is erroneous most howardites are fragmental breccias showing no sign of origin from true in the lunar sense i e soil like near surface regolith howardites are highly diverse in ni content often remarkably ni poor compared to lunar regolith breccias however the few 8 howardites with between 300 and 1200 lg g ni consistently show some combination of other traits suggestive of regolith origin most importantly all four cases or five if we include malvern which appears to have been altered by annealing of howardites known to have enrichments in solar wind noble gases belong to the 300 lg g ni group in many cases an abundance of glasses particularly in spheroidal or turbid brown form provides additional evidence for regolith origin we propose that the important subset of howardites that are regolith breccias be formally distinguished by the designation regolithic howardite apart from high siderophile levels the regolithic howardites are compositionally distinctive in having al2o3 consistently near 8 9 wt corresponding to a eucrite diogenite mixing ratio of precisely 2 1 assuming the heds are reasonably representative of the ancient i e pre vestoid launch surface of vesta this clustering of regolith composition is difficult to explain unless most of the ancient diogenite component was brought to the surface in a single early episode i e probably a single great impact after which smaller scale cratering with no further major excavations of diogenite until the vestoid forming event efficiently homogenized the surface such a single excavation model may also help to explain why diogenites in marked contrast with eucrites are seldom polymict and why al2o3 poor diogenite dominated howardites consistently lack major siderophile enrichments the low siderophile contents of polymict eucrites are most enigmatic possibly in the hedasteroidal context low collision velocities etc only materials blended by multiple impacts consistently acquire major enrichments in siderophile elements 2009 elsevier ltd all rights reserved

space weathering on airless bodies resolving a mystery with lunar samples using new techniques to examine the products of space weathering of lunar soils we demonstrate that nanophase reduced iron npfe0 is produced on the surface of grains by a combination of vapor deposition and irradiation effects the optical properties of soils both measured and modeled are shown to be highly dependent on the cumulative amount of npfe0 which varies with different starting materials and the energetics of different parts of the solar system the measured properties of intermediate albedo asteroids the abundant s type asteroids in particular are shown to directly mimic the effects predicted for small amounts of npfe0 on grains of an ordinary chondrite regolith this measurement and characterization of space weathering products seems to remove a final obstacle hindering a link between the abundant ordinary chondrite meteorites and common asteroids

impact excavation on asteroid 4 vesta hubble space telescope results hubble space telescope images of asteroid 4 vesta obtained during the favorable 1996 apparition show an impact crater 460 kilometers in diameter near the south pole color measurements within the 13 kilometer deep crater are consistent with excavation deep into a high calcium pyroxene rich crust or olivine upper mantle about 1 percent of vesta was excavated by the crater formation event a volume sufficient to account for the family of small vesta like asteroids that extends to dynamical source regions for meteorites this crater may be the site of origin for the howardite eucrite and diogenite classes of basaltic achondrite meteorites

oxygen and asteroids hundreds of thousands of asteroids have been discovered in the asteroid belt and in near earth space oxygen is an abundant element in meteorites and presumably in most asteroids spectral reflectance measurements of asteroids in the visible and near infrared can identify oxygen bearing minerals such as those found in the olivine pyroxene and serpentine groups due to their distinctive absorption features interpretation of the mineralogy of asteroids is complicated by the effects of space weathering which tends to redden and darken the surfaces of asteroids asteroids are primarily classified into a number of taxonomic classes and subclasses according to their spectral properties in the visible wavelength region however asteroids with similar spectral properties in the visible may have different spectral properties in the near infrared and therefore different interpreted mineralogies definite trends in the abundances of different taxonomic classes versus heliocentric distance are apparent these trends appear to be a function of both composition differences and degree of heating however dynamical processes have significantly affected these trends close observation of asteroids by spacecraft such as near shoemaker to 433 eros and hayabusa to 25143 itokawa are currently the best way to discern the mineralogies of individual asteroids

vesta and the vestoids a new rock group abstract moderate spectral resolution observations of the 505 nm fe2 pyroxene absorption feature were obtained for 13 asteroids dynamically linked to 4 vesta or located between vesta and the 3 1 resonance gap eleven showed spectra with deep 0 9 m mafic silicate absorptions suggesting a pyroxene composition binzel and xu 1993 spectra of only six of these asteroids show the absorption feature centered at 506 5 nm suggestive of an augite high calcium component to the surface pyroxenes consistent with previous spectral observations across the surface of vesta cochran and vilas 1998 five of the six asteroids include all objects observed at heliocentric distances between vesta and the 3 1 resonance gap the spectrum of only one asteroid interior to vesta s orbit showed this feature no correlation between the presence or absence of this feature and the strength of the 1 m mafic silicate feature was found

discovery of coesite and stishovite in eucrite howardite eucrite diogenite meteorites heds probably originated from the asteroid 4 vesta we investigated one eucrite bereba to clarify a dynamic event that occurred on 4 vesta using a shock induced high pressure polymorph we discovered high pressure polymorphs of silica coesite and stishovite originating from quartz and or cristobalite in and around the shock melt veins of bereba lamellar stishovite formed in silica grains through a solid state phase transition a network like rupture was formed and melting took place along the rupture in the silica grains nanosized granular coesite grains crystallized from the silica melt based on shock induced high pressure polymorphs the estimated shock pressure condition ranged from 8 to 13 gpa considering radiometric ages and shock features the dynamic event that led to the formation of coesite and stishovite occurred ca 4 1 ga ago which corresponds to the late heavy bombardment period ca 3 8 4 1 ga deduced from the lunar cataclysm there are two giant impact basins around the south pole of 4 vesta although the origin of heds is thought to be related to dynamic events that formed the basins ca 1 0 ga ago our findings are at variance with that idea

composition of the northern regions of vesta analyzed by the dawn mission abstract the surface composition of the northern regions of vesta observed by the dawn spacecraft offers the possibility to test several hypotheses related to impact related processes we used mostly imaging spectrometry in the visible and near infrared to assess the distribution of mafic lithologies hydrated components and albedo properties and use the link with howardite eucrite and diogenite meteorites heds to investigate the origin of those materials we established that rheasilvia ejecta reached part of the northern regions and have a diogenitic rich composition characteristic of the lower crust investigations of the antipodes of the two major impact basins rheasilvia and veneneia did not reveal any correlation between geographic location geological features and the surface composition the northern wall of mamilia crater which is one of the freshest craters above 22 n contains relatively pure eucritic rich diogenitic rich and dark hydrated materials which are representative of the rest of the northern regions and most of vesta with the exception of an olivine like component found in bellicia crater by ammannito et al ammannito e et al 2013a nature 504 7478 122 125 we determined that similar types of materials are found in various proportions over a large region including bellicia arruntia and pomponia craters and their origin does not seem to be related to rheasilvia ejecta these materials are hydrated which could indicate an exogenous origin and not as dark as expected for carbonaceous chondrites which likely compose the majority of dark hydrated materials on vesta spectral mixture analysis reveals that mixtures of pyroxenes hypersthene pigeonite and diopside could offer an alternative interpretation to olivine in this area

the geologic history of vesta inferred from combined 207pb 206pb and 40ar 39ar chronology of basaltic eucrites abstract eucrites represent samples of mafic crust of the parent body likely vesta and record a complex geologic history involving magmatism metamorphism impact processing and metasomatism for better understanding of the geologic history we present combined 207pb 206pb and 40ar 39ar chronology of four basaltic eucrites showing distinct petrologic features agoult an equilibrated eucrite with granulitic textures camel donga a brecciated equilibrated eucrite enriched in metallic iron dag 380 a partially equilibrated monomict eucrite and nwa 049 a metasomatized polymict eucrite comprising mostly unequilibrated clasts the 207pb 206pb dating in combination with the acid washing technique was applied to pyroxene rich and plagioclase rich fractions while the 40ar 39ar dating was performed mainly on plagioclase grains using the laser incremental heating method the pb isotopic data for acid leaching residues are more radiogenic than those for acid washes reflecting efficient removal of non radiogenic pb components by the acid washing among the residues however only those of the agoult and camel donga plagioclase rich fractions yielded isochrons rather than errorchrons with 207pb 206pb ages of 4532 39 0 87 ma and 4515 43 0 42 ma respectively the trace element systematics further suggest that these residues essentially represent contaminant oxide minerals such as ilmenite and chromite rather than plagioclase on the other hand the ar isotopic data for agoult and camel donga yielded plateau ages with weighted means of 4494 9 ma and 3749 25 ma in contrast to those for dag 380 and nwa 049 that did not return any plateau the 207pb 206pb and 40ar 39ar ages of agoult are interpreted to reflect the time of the u pb and k ar system closure during a prolonged thermal metamorphism by combining the ages reported here and in the literature with the calculated closure temperatures the cooling rate of agoult is determined to be 11 2 c ma this cooling rate corresponds to a burial depth of 10 20 km indicating that granulitic eucrites were originally crystallized near the surface and were subsequently buried and metamorphosed the 20 ma younger 207pb 206pb ages of camel donga than agoult are considered to reflect delayed burial metamorphism in the source region whereas the plateau 40ar 39ar age would record the time of an impact causing brecciation and efficient ar degassing of the buried crust furthermore the model 207pb 206pb dates calculated for acid washed pyroxenes imply that the burial metamorphism of agoult and dag 380 were broadly contemporaneous and also that nwa 049 was metasomatized by fluids within the uppermost crust later than 4 4 ga

zinc isotopes in heds clues to the formation of 4 vesta and the unique composition of pecora escarpment 82502 the 66zn permil deviation of the 66zn 64zn ratio from a terrestrial standard values for a suite of 20 non antarctic hed howardite eucrite diogenite meteorites and one mesosiderite and for 8 antarctic eucrites and diogenites were measured in order to determine the role of volatization in the formation of their presumed parent body the asteroid 4 vesta the 20 non antarctic heds had 66zn values that ranged from 2 0 to 1 67 with a mean value of 0 01 0 39 2se this range likely represents a small scale heterogeneity due to brecciation induced by multiple impacts the non antarctic eucrites 66zn 0 00 0 58 2se n 12 were isotopically the same as the diogenites 66zn 0 31 0 80 2se n 4 and the howardites 66zn 0 26 0 37 2se n 4 on average non antarctic eucrite falls were isotopically heavier 0 50 than non antarctic finds 1 00 the antarctic finds studied were all unbrecciated samples and they were significantly heavier than the non antarctic samples with a 66zn range of 1 63 to 6 22 for 4 eucrites mean 4 32 and 0 94 to 1 60 for 3 diogenites mean 1 23 excluding one anomalous sample while their zn concentration is significantly lower than the brecciated samples these data suggest that the unbrecciated eucrites probably represent the eucritic crust shortly after differentiation and cooling of the parent asteroid at which time volatization of lighter zinc isotopes led to an isotopically heavy crust early impact events caused the ejection of these unbrecciated meteorites which were subsequently spared from brecciation caused by multiple additional impacts on the much larger vesta the range of 66zn values and zn concentration for the brecciated heds in this study supports a major contribution to the vestan surface by chondritic impactors 1 30 66zn 0 76 for ordinary and carbonaceous chondrites the anomalous eucrite pca 82502 66zn 7 75 is significantly isotopically lighter than the other heds and is the natural sample with the lightest zn isotopic composition reported in the solar system to date this meteorite most likely originated from a distinct parent body

a petrologic and isotopic study of lodranites evidence for early formation as partial melt residues from heterogeneous precursors abstract we have conducted petrologic chemical and isotopic studies of lodranites in an attempt to constrain their genesis lodran gibson y 791491 y 791493 y 74357 y 8002 y 75274 mac 88177 lew 88280 eet 84302 fro 90011 and que 93148 are classified as lodranites lodranites and acapulcoites are indistinguishable on the basis of oxygen isotopic compositions but are distinct in average grain sizes of their mafic silicates with lodranites being significantly coarser grained lodranites exhibit a diverse range of petrologic and mineralogic features they range widely in mafic silicate compositions fa3 13 plagioclase 0 11 4 vol fe ni metal 0 5 20 vol and troilite 0 2 5 3 vol contents and shock levels s1 s4 they appear to have experienced high peak temperatures and rapid cooling in the temperature range recorded by metallographic cooling rates i e 700 350 c the only dated lodranite gibson cooled to ar closure temperatures at 4 49 0 01 ga lodranites formed from chemically and isotopically heterogeneous precursors in which the mineral and oxygen isotopic compositions were correlated heating of their parent body to temperatures between 1050 1200 c resulted in formation of fe ni fes and basaltic partial melts depletions of troilite and or plagioclase in most lodranites testify to the removal of some of these partial melts although melt migration was complex lodranites appear to have experienced a complex cooling history of slow cooling at high temperatures followed by rapid cooling at intermediate temperatures possibly related to breakup of the parent body lodranites were liberated from their parent body during 1 3 impact events with most having cosmic ray exposure ages of 5 5 7 ma the acapulcoites are samples from the same parent body but were heated to lower temperatures and thus experienced lower degrees of partial melting

mineralogical analysis of the oppia quadrangle of asteroid 4 vesta evidence for occurrence of moderate reflectance hydrated minerals abstract quadrangle av 10 oppia is one of five quadrangles that cover the equatorial region of asteroid 4 vesta this quadrangle is notable for the broad spectrally distinct ejecta that extend south of the oppia crater these ejecta exhibit the steepest reddest visible spectral slope observed across the asteroid and have distinct color properties as seen in multispectral composite images compared to previous works that focused on the composition and nature of unusual orange ejecta found on vesta here we take into account a broader area that includes several features of interest with an emphasis on mineralogy as inferred from data obtained by dawn s visible infrared mapping spectrometer vir our analysis shows that the older northern and northeastern part of av 10 is dominated by howardite like material while the younger southwestern part including oppia and its ejecta blanket has a markedly eucritic mineralogy the association of the mineralogical information with the geologic and topographic contexts allows for the establishment of relationships between the age of the main formations observed in this quadrangle and their composition a major point of interest in the oppia quadrangle is the spectral signature of hydrous material seen at the local scale this material can be mapped by using high resolution vir data combined with multispectral image products from the dawn framing camera fc so as to enable a clear correlation with specific geologic features hydrated mineral phases studied previously on vesta generally correlate with low albedo material delivered by carbonaceous asteroids however our analysis shows that the strongest oh signature in av 10 is found in a unit west of oppia previously mapped as light mantle material and showing moderate reflectance and a red visible slope with the available data we cannot yet assess the presence of water in this material however we offer a possible explanation for its origin

glass veins in the unequilibrated eucrite yamato 82202 the unequilibrated eucrite yamato 82202 y82202 contains a network of relatively thick up to 1 mm in width glass veins the host of the meteorite represents a monomict breccia composed of volcanic rock that crystallized 4 3 ga ago as a lava flow on the surface of 4 vesta the veins formed 3 90 0 04 ga ago probably as a result of frictional melting associated with impact under conditions of low effective oxygen fugacity and higher sulfur fugacity the glass contains disordered structural elements characteristic of pyroxene and feldspar reminiscent of the eucritic target lithology the unequilibrated pyroxenes of the volcanic host and the pristine character of the glass indicate that this meteoritic material did not experience significant thermal metamorphism after initial crystallization of the lava hence it was not affected by regional metamorphism caused by burial to a significant depth or by long term contact metamorphism associated with a thick lava flow large intrusion or hot layer of impact ejecta the meteorite resided at a shallow depth though not at the surface on 4 vesta or on one of the vestoids until it was ejected and traveled to earth probably with other hed materials that have 36ar exposure ages of 13 ma these data suggest that the surface of the asteroid 4 vesta has significant though probably small proportions of glass as well as unequilibrated volcanic rock

vesta as the howardite eucrite and diogenite parent body implications for the size of a core and for large scale differentiation if vesta is the parent body of the howardite eucrite and diogenite hed meteorites then geo chemical and petrologic constraints for the meteorites may be used in conjunction with astronomical constraints for the size and mass of vesta to 1 determine the size of a possible metal core in vesta and 2 model the igneous differentiation and internal structure of vesta the density of vesta and petrologic models for hed meteorites together suggest that the amount of metal in the parent body is 25 mass with a best estimate of 5 assuming no porosity for a porosity of up to 5 in the silicate fraction of the asteroid the permissible metal content is 30 these results suggest that any metal core in the hed parent body and vesta is not unusually large a variety of geochemical and other data for hed meteorites are consistent with the idea that they originated in a magma ocean it appears that diogenites formed by crystal accumulation in a magma ocean cumulate pile and that most noncumulate eucrites excepting such eucrites as bouvante and statinem formed by subsequent crystallization of the residual melts modelling results suggest that the hed parent body is enriched in rare earth elements by a factor of 2 5 3 5 relative to ci chondrites and that it has approximately chondritic mg si and al sc ratios stokes settling calculations for a vesta wide nonturbulent magma ocean suggest that early crystallizing magnesian olivine orthopyroxene and pigeonite would have settled relatively quickly permitting fractional crystallization to occur but that later crystallizing phases would have settled or floated an order of magnitude more slowly allowing instead a closer approach to equilibrium crystallization for the more evolved eucritic melts this would have inhibited the formation of a plagioclase flotation crust on vesta plausible models for the interior of vesta which are consistent with the data for hed meteorites and vesta include a metal core 130 km radius an olivine rich mantle 65 220 km thick a lower crustal unit 12 43 km thick composed of pyroxenite from which diogenites were derived and an upper crustal unit 23 42 km thick from which eucrites originated the present shape of vesta with 60 km difference in the maximum and minimum radius suggests that all of the crustal materials and possibly some of the underlying olivine from the mantle could have been locally excavated or exposed by impact cratering

vesta vestoids and the howardite eucrite diogenite group relationships and the origin of spectral differences spectra of asteroid 4 vesta and 21 small estimated diameters less than 10 km asteroids with vesta like spectral properties vestoids were measured at visible and near infrared wavelengths similar to0 44 to similar to1 65 mum all of the measured small asteroids except for 2579 spartacus have reflectance spectra consistent with surface compositions similar to eucrites and howardites and consistent with all being derived from vesta none of the observed asteroids have spectra similar to diogenites we find no spectral distinction between the 15 objects tabulated as members of the vesta dynamical family and 6 of the 7 sampled non family members that reside just outside the semi major axis a eccentricity e and inclination i region of the family the spectral consistency and close orbital a e i match of these non family objects to vesta and the vesta family imply that the true bounds of the family extend beyond the subjective cut off for membership asteroid 2579 spartacus has a spectrum consistent with a mixture of eucritic material and olivine spartacus could contain olivine rich material from vesta s mantle or may be unrelated to vesta altogether laboratory measurements of the spectra of eucrites show that samples having nearly identical compositions can display a wide range of spectral slopes finer particle sizes lead to an increase in the slope which is usually referred to as reddening this range of spectral variation for the best known meteoritic analogs to the vestoids regardless of whether they are actually related to each other suggests that the extremely red spectral slopes for some vestoids can be explained by very fine grained eucritic material on their surfaces

the south african polymict eucrite macibini the polymict eucrite macibini is a fragmental breccia predominantly composed of eucritic materials with minor proportions maximum 2 vol of diogenitic material hence it is intermediate between the yamato 74159 type polymict eucrites which contain negligible amounts of magnesian orthopyroxene and the howardites the present study provides mineralogical and bulk compositional data for the meteorite breccia and for six clasts these clasts include both volcanic and igneous rocks and a variety of impact generated rocks a broad range of degrees of postcrystallization metamorphism affected these materials before the final aggregation of the breccia clast a is a fragment of unequilibrated eucrite with subophitic texture the edges of the zoned pyroxenes in this clast are composed of a host of fe rich augite containing vermicules blebs and lamellae composed of a mixture of fe rich olivine and silica similar features occur as fragments in lunar breccias and are attributed by some workers to the breakdown of pyroxferroite an fe rich pyroxenoid however textures and compositions of these augite olivine silica intergrowths in clast a suggest that in this case they are the result of decomposition in a series of steps of fe rich subcalcic augite among the fragments of impact generated material in macibini is clast 2 an earlier formed clastic breccia that was lithified before being broken apart and included in the meteorite breccia clast 3 is an impact melt breccia that is composed of rock and mineral fragments in a devitrified groundmass clast c is also an impact melt breccia that has a coarser grained hornfelsic groundmass that resulted from extensive metamorphism after formation

the effects of space weathering on apollo 17 mare soils petrographie and chemical characterization the lunar soil characterization consortium a group of lunar sample and remote sensing scientists has undertaken the extensive task of characterization of the finest fractions of lunar soils with respect to their mineralogical and chemical makeup these compositional data form the basis for integration and modeling with the reflectance spectra of these same soil fractions this endeavor is aimed at deciphering the effects of space weathering of soils on airless bodies with quantification of the links between remotely sensed reflectance spectra and composition a beneficial byproduct is an understanding of the complexities involved in the formation of lunar soil several significant findings have been documented in the study of the 2x whereas the abundance of agglutinitic glass increases by only 10 15 this is evidence for a large contribution from surface correlated nanophase fe0 to the is feo values particularly in the 10 m size fraction the surface nanophase fe0 is present largely as vapor deposited patinas on the surfaces of almost every particle of the mature soils and to a lesser degree for the immature soils keller et al 1999a it is reasoned that the vapor deposited patinas may have far greater effects upon reflectance spectra of mare soils than the agglutinitic fe0

anatomy of a partially differentiated asteroid a near sighted view of acapulcoites and lodranites with the insertion of the near spacecraft into orbit around the asteroid 433 eros a new stage of asteroid exploration has begun with the return of spatially resolved mineralogical geological and chemical information from specific asteroids in this paper we outline the features of a partially differentiated asteroid using the acapulcoite and lodranite meteorites as a guide such a body would likely contain a variety of lithologies including chondritic rocks largely unaltered by melting residues of partial melts and basaltic and fe ni fes rocks crystallized from the partial melts the presence or nature of the regolith remains largely unconstrained mineralogical and isotopic heterogeneities preserved in these rocks suggest spatial separation of these rock types by distances in excess of 200 m spacecraft based remote sensing instrumentation should detect substantial spectral heterogeneity most prominently manifested in the band area ratio and chemical heterogeneity observation of these various lithologies in situ would provide important new constraints on the processes involved during the earliest differentiation of asteroids

survey and evaluation of eucrite bulk compositions the purpose of this survey is to establish reference bulk elemental abundances for the eucrites and thereby provide the basis to test core formation models as well as partial melting fractional crystallization and magma ocean theories for the eucrite parent body in order to evaluate bulk elemental abundances for the eucrites 296 peer reviewed articles monographs theses or books and 143 abstracts dating from 1938 to 1997 were surveyed of the 101 eucrites having at least one set of elemental abundance analyses reported in the literature 20 were selected for in depth examination the selection criteria of our sample were based on the total number of analyses available for a given eucrite and the total number of elements for which data exist the mean bulk elemental abundance 1 standard deviation and the percent deviation were calculated for each element in a given eucrite in order to evaluate the quality of the mean abundances the elements were then grouped according to availability of data and percent deviations possible reasons for the different deviations in the different groups are briefly discussed from the major element abundances the normative cipw composition the molar compositions of pyroxene olivine and plagioclase and the bulk densities were calculated and compared to petrographic observations the calculated norms for the noncumulates agree well with the observations while the norms for the cumulates do not possible reasons for this are discussed unfortunately analyses of many elements are poorly represented in the literature and many bulk analyses suffer from unacceptable levels of uncertainty therefore future work requires bulk elemental analyses for some of the more poorly characterized elements in eucrites especially those of key elements used for planetary modeling

impact origin of the vesta family the compelling petrographic link consolmagno and drake 1977 gaffey 1983 between basaltic achondrite meteorites and the 530 km diameter asteroid 4 vesta has been tempered by a perceived difficulty in launching rocks from this asteroid s surface at speeds sufficient to bring them to earth wasson and wetherill 1979 without obliterating vesta s signature crust i address this impasse in response to recent imaging zellner et al 1996 dumas and hainaut 1996 of a 450 km impact basin across vesta s southern hemisphere thomas et al 1997 and model the basin forming collision using a detailed two dimensional hydrocode with brittle fracture including self gravitational compression cf asphaug and melosh 1993 a 42 km diameter asteroid striking vesta s basaltic crust atop a denser mantle and iron core at 5 4 km s launches multikilometer fragments up to 600 m s without inverting distal stratigraphy according to the code this modeling together with collisional dynamical rheological and exposure age timescales marzari et al 1996 welten et al 1996 and observations of v type asteroids binzel and xu 1993 suggests a recent 1 ga impact origin for the vesta family and a possible vesta origin for earth approaching v type asteroids cruik shank et al 1991

complexities in pyroxene compositions derived from absorption band centers examples from apollo samples hed meteorites synthetic pure pyroxenes and remote sensing data we reexamine the relationship between pyroxene composition and near infrared absorption bands integrating measurements of diverse natural and synthetic samples we test an algorithm plc involving a two part linear continuum removal and parabolic fits to the 1 and 2 m bands a computationally simple approach which can easily be automated and applied to remote sensing data employing a suite of synthetic pure pyroxenes the plc technique is shown to derive similar band centers to the modified gaussian model plc analyses are extended to natural pyroxene bearing materials including 1 bulk lunar basalts and pyroxene separates 2 diverse lunar soils and 3 hed meteorites for natural pyroxenes the relationship between composition and absorption band center differs from that of synthetic pyroxenes these differences arise from complexities inherent in natural materials such as exsolution zoning mixing and space weathering for these reasons band center measurements of natural pyroxene bearing materials are compositionally nonunique and could represent three distinct scenarios 1 pyroxene with a narrow compositional range 2 complexly zoned pyroxene grains or 3 a mixture of multiple pyroxene or nonpyroxene components therefore a universal quantitative relationship between band centers and pyroxene composition cannot be uniquely derived for natural pyroxene bearing materials without additional geologic context nevertheless useful relative relationships between composition and band center persist in most cases these relationships are used to interpret m3 data from the humboldtianum basin four distinct compositional units are identified 1 mare humboldtianum basalts 2 distinct outer basalts 3 low ca pyroxene bearing materials and 4 feldspathic materials

optical effects of space weathering the role of the finest fraction the optical properties of lunar softs are different than those of rocks from which they are derived as a consequence of lunar space weathering soils are darker and exhibit a distinctive red sloped continuum and weaker mineral absorption bands the accumulation of dark glass welded aggregates agglutinates has been thought to account for these optical effects of space weathering on lunar soils spectroscopic analyses of agglutinate separates and size fractions for a suite of lunar softs presented here indicate that the agglutinate paradigm is insufficient to fully account for lunar optical alteration it is the finest fraction of lunar soils 25 gm which constitute 25 wt that dominates the optical properties of the bulk soil unlike size fractions of most silicates for which the finest fraction is the brightest the lunar soil size fractions all have comparable albedos in the short wavelength visible in the near infrared however it is the finest fraction that exhibits the steep red continuum and weak absorption bands the properties of the finest fraction cannot be duplicated by preparing a fine fraction by grinding larger agglutinate rich soil particles these results suggest space weathering on airless bodies is dominated by surface correlated processes perhaps associated with the development of fine grained fe o on or near the surface of grains and the accumulation of the larger agglutinates is not necessarily required to account for lunar optical alteration

revisiting spectral parameters of silicate bearing meteorites visible and near infrared reflectance spectra of a sample of silicate bearing meteorites have been used to evaluate the spectral parameters space defined in the pioneering work of gaffey et al 1993 the studied sample consisted of 91 ordinary chondrites 47 basaltic achondrites and 21 different laboratory mixtures obtained from the relab database our results indicate that the spectral parameter space in particular the bar versus band i center is not suitable enough to identify the mineralogy of meteorites and asteroids the grain size of the sample also appears as a very sensitive parameter and can play an important role in locating an object in the spectral parameter space finally the application of our study to the question of a genetic link between v type asteroids and hed meteorites shows that these bodies plot in distinct regions in the bar versus band i center space this result further confirms that those spectral parameters cannot uniquely define the mineralogy of a sample

high calcium pyroxene as an indicator of igneous differentiation in asteroids and meteorites our analyses of high quality spectra of several s type asteroids 17 thetis 847 agnia 808 merxia and members of the agnia and merxia families reveal that they include both low and highcalcium pyroxene with minor amounts of olivine 0 4 high calcium pyroxene is a spectrally detectable and petrologically important indicator of igneous history and may prove critical in future studies aimed at understanding the history of asteroidal bodies the silicate mineralogy inferred for thetis and the merxia and agnia family members requires that these asteroids experienced igneous differentiation producing broadly basaltic surface lithologies together with 4 vesta and its smaller vestoid family members and the main belt asteroid 1489 magnya these new asteroids provide strong evidence for igneous differentiation of at least five asteroid parent bodies based on this analysis of a small subset of the near infrared asteroid spectra taken to date with spex at the nasa irtf we expect that the number of known differentiated asteroids will increase consistent with the large number of parent bodies inferred from studies of iron meteorites

almahata sitta asteroid 2008 tc3 and the search for the ureilite parent body abstract this article explores what the recovery of 2008 tc3 in the form of the almahata sitta meteorites may tell us about the source region of ureilites in the main asteroid belt an investigation is made into what is known about asteroids with roughly the same spectroscopic signature as 2008 tc3 a population of low inclination near earth asteroids is identified with spectra similar to 2008 tc3 five asteroid families in the main belt as well as a population of ungrouped asteroids scattered in the inner and central belts are identified as possible source regions for this near earth population and 2008 tc3 three of the families are ruled out on dynamical and spectroscopic grounds new near infrared spectra of 142 polana and 1726 hoffmeister lead objects in the two other families also show a poor match to almahata sitta thus there are no main belt spectral analogs to almahata sitta currently known space weathering effects on ureilitic materials have not been investigated so that it is unclear how the spectrum of the main belt progenitor may look different from the spectra of 2008 tc3 and the almahata sitta meteorites dynamical arguments are discussed as well as ureilite petrogenesis and parent body evolution models but these considerations do not conclusively point to a source region either other than that 2008 tc3 probably originated in the inner asteroid belt

presidential address presented 2000 august 28 chicago illinois usa the eucrite vesta story many lines of evidence indicate that meteorites are derived from the asteroid belt but in general identifying any meteorite class with a particular asteroid has been problematical one exception is asteroid 4 vesta where a strong case can be made that it is the ultimate source of the howardite eucrite diogenite hed family of basaltic achondrites visible and near infrared reflectance spectra first suggested a connection between vesta and the basaltic achondrites experimental petrology demonstrated that the eucrites the relatively unaltered and unmixed basaltic achondrites were the product of approximately a 10 melt studies of siderophile element partitioning suggested that this melt was the residue of an asteroidal scale magma ocean mass balance considerations point to a parent body that had its surface excavated but remains intact modern telescopic spectroscopy has identified kilometer scale vestoids between vesta and the 3 1 orbit orbit resonance with jupiter dynamical simulations of impact into vesta demonstrate the plausibility of ejecting relatively unshocked material at velocities consistent with these astronomical observations hubble space telescope images show a 460 km diameter impact basin at the south pole of vesta it seems that nature has provided multiple free sample return missions to a unique asteroid major challenges are to establish the geologic context of the hed meteorites on the surface of vesta and to connect the remaining meteorites to specific asteroids

mantle material in the main belt battered to bits the complete or near complete differentiation of a chondritic parent body is believed to result in an object with an fe ni core a thick olivine dominated mantle and a thin plagioclase pyroxene crust compositional groupings of iron meteorites give direct evidence that at least 60 chondritic parent bodies have been differentiated and subsequently destroyed a long standing problem has been that our meteorite collections and apparently our asteroid observations as well show a great absence of olivine dominated metal free mantle material while the basaltic achondrites hed meteorites represent metal free pyroxene dominated crustal samples the isotopic and geochemical evidence implies that this class is derived from only one parent body perhaps vesta thus the meteoritic and perhaps astronomical evidence also suggests a great absence of crustal material resulting from the collisional disruption of numerous parent bodies

rotational spectral variations of asteroid 8 flora implications for the nature of the s type asteroids and for the parent bodies of the ordinary chondrites abstract the new interpretive calibrations olivine pyroxene abundance spectral signature of chondritic metal grains have been applied to visible and near infrared spectral reflectance data for the typical s type asteroid 8 flora chondritic metal grains do not exhibit the steeply reddened spectral signature previously associated with a nickel iron nife metal phase the conditions required to produce a s type spectral curve from a chondritic material are much more restrictive and improbable than previously supposed five mineralogic and patrologic parameters have been derived for the surface material of flora from the analysis of the spectral reflectance and rotational spectral variations of this object these include bulk mineralogy nife metal olivine pyroxene mafic mineral abundance ol py 2 8 metal nature abundant 50 and coarse grained in the substrate pyroxene composition orthopyroxene f s 50 and or abundant clinopyroxene and spatial mineralogic variations olivine pyroxene ratio and pyroxene composition do not covary in a chondritic manner all of the diagnostic mineralogic properties of the flora surface material indicate that this is a differentiated body none of the derived surface properties unambiguously support a chondritic type material and several contradict any type of undifferentiated assemblage flora is most probably the residual core of an intensely heated thermally evolved and magmatically differentiated planetesimal which was subsequently disrupted the present surface samples layers formed at and near the core mantle boundary in the parent body several lines of evidence suggest that the s type asteroids as a class are predominantly the core fragments of disrupted differentiated planetesimals a main belt source of the ordinary chondrites remains elusive