nucleosynthetic osmium isotope anomalies in acid leachates of the murchison meteorite abstract we present osmium isotopic results obtained by sequential leaching of the murchison meteorite which reveal the existence of very large internal anomalies of nucleosynthetic origin e 184 os from 108 to 460 e 186 os from 14 1 to 12 6 e 188 os from 2 6 to 1 6 e 190 os from 1 7 to 1 1 despite these large variations the isotopic composition of the total leachable osmium weighted average of the leachates is close to that of bulk chondrites this is consistent with efficient large scale mixing of os isotopic anomalies in the protosolar nebula the os isotopic anomalies are correlated and can be explained by the variable contributions of components derived from the s r and p processes of nucleosynthesis surprisingly much of the s process rich osmium is released by relatively mild leaching suggesting the existence of an easily leachable s process rich presolar phase or alternatively of a chemically resistant r process rich phase taken together with previous evidence for a highly insoluble s process rich carrier such as sic these results argue for the presence of several presolar phases with anomalous nucleosynthetic compositions in the murchison meteorite the s process composition of os released by mild leaching diverges slightly from that released by aggressive digestion techniques perhaps suggesting that the presolar phases attacked by these differing procedures condensed in different stellar environments the correlation between e 190 os and e 188 os can be used to constrain the s process 190 os 188 os ratio to be 1 275 0 043 such a ratio can be reproduced in a nuclear reaction network for a macs value for 190 os of 200 22 mbarn at 30 kev more generally these results can help refine predictions of the s process in the os mass region which can be used in turn to constrain the amount of cosmoradiogenic 187 os in the solar system and hence the age of the galaxy we also present evidence for extensive internal variation of 184 os abundances in the murchison meteorite a steep anti correlation is observed between e 184 os and e 188 os since 184 os is formed uniquely by the p process this anti correlation cannot be explained by variable addition or subtraction of s process os to average solar system material instead this suggests that p process rich presolar grains e g supernova condensates may be present in meteorites in sufficient quantities to influence the os isotopic compositions of the leachates nevertheless 184 os is a low abundance isotope and we cannot exclude the possibility that the measured anomalies for this isotope reflect unappreciated analytical artifacts

bright prospects for radar detection of europa s ocean abstract the surface of europa has been hypothesized to include an ice regolith layer from hundreds of meters to kilometers in thickness however contrary to previous claims it does not present a significant obstacle to searching for europa s ocean with radar sounding this note corrects prior volume scattering loss analyses and expands them to includes observational and thermo mechanical constraints on pore size and regolith depth this provides a more physically realistic range of potential ice regolith volume scattering losses for radar sounding observations of europa s ice shell in the hf and vhf frequency bands we conclude that for the range of physical processes and material properties observed or hypothesized for europa volume scattering losses are not likely to pose a major obstacle to radar penetration

dim prospects for radar detection of europa s ocean abstract the thickness of a porous regolith on europa is estimated to be 1 km provided that this regolith contains as little as 1 by volume of cavities with sizes comparable to the radar wavelength its presence poses an insurmountable obstacle in the search for europa s ocean by means of a sounding radar

zirconium isotope evidence for incomplete admixing of r process components in the solar nebula abstract isotopic anomalies in mo and zr have recently been reported for bulk chondrites and iron meteorites and have been interpreted in terms of a primordial nucleosynthetic heterogeneity in the solar nebula we report precise zr isotopic measurements of carbonaceous ordinary and enstatite chondrites eucrites mesosiderites and lunar rocks all bulk rock samples yield isotopic compositions that are identical to the terrestrial standard within the analytical uncertainty no anomalies in 92zr are found in any samples including high nb zr eucrites and high and low nb zr calcium aluminum rich inclusions cais these data are consistent with the most recent estimates of

intrinsic w nucleosynthetic isotope variations in carbonaceous chondrites implications for w nucleosynthesis and nebular vs parent body processing of presolar materials abstract the progressive dissolution of the carbonaceous chondrites orgueil ci1 murchison cm2 and allende cv3 with acids of increasing strength reveals correlated w isotope variations ranging from 3 5 e182w and 6 5 e183w in the initial leachate acetic acid to 60 e182w and 40 e183w in the leachate residue the observed variations are readily explained by variable mixing of s process depleted and s process enriched components one w s process carrier is sic however the observed anomaly patterns and mass balance considerations require at least on additional s process carrier possibly a silicate or sulfide the data reveal well defined correlations which provide a test for s process nucleosynthesis models the correlations demonstrate that current models need to be revised and highlight the need for more precise w isotope data of sic grains furthermore the correlations provide a mean to disentangle nucleosynthetic and radiogenic contributions to 182w e182wcorrected e182wmeasured 1 41 0 05 e183wmeasured e182wcorrected e182wmeasured 0 12 0 06 e184wmeasured a prerequisite for the successful application of the hf w chronometer to samples with nucleosynthetic anomalies the overall magnitude of the w isotope variations decreases in the order ci1 cm2 cv3 this can be interpreted as the progressive thermal destruction of an initially homogeneous mixture of presolar grains by parent body processing however not only the magnitude but also the w anomaly patterns of the three chondrites are different in particular leach step 2 that employs nitric acid reveals a s deficit signature for murchison but a s excess for orgueil and allende this could be the result of redistribution of anomalous w into a new phase by parent body alteration or the fingerprint of dust processing in the solar nebula given that the thermal and aqueous alteration of murchison is between the ci and cv3 chondrites parent body processing is probably not the sole cause for creating the different pattern small scale nebular redistribution of anomalous w may have played a role as well similar nebular processes possibly acted differently on specific carrier phases and elements resulting in the diverse nucleosynthetic signatures observed in planetary materials today

origin of isotopic heterogeneity in the solar nebula by thermal processing and mixing of nebular dust we have investigated mo and w isotope compositions in acid leachates and an insoluble residue from the murchison carbonaceous chondrite the new data reveal variable enrichments of s and r process isotopes and demonstrate that several isotopically diverse presolar components are present in murchison the insoluble residue is enriched in s process mo and w evidently due to the enrichment of presolar sic grains in contrast mo and w released by leaching with weak acids are depleted in s process isotopes most likely reflecting the isotope composition of the homogenized portion of the protosolar nebula the mo and w isotope compositions of the different leach steps are broadly correlated as expected from s process nucleosynthesis theory indicating that mo and w are presumably hosted in the same carriers however at the bulk meteorite scale no nucleosynthetic w isotope anomalies have been identified except for ivb iron meteorites in spite of large mo isotope heterogeneities among the same samples this decoupling of mo and w isotopes in bulk meteorites may reflect physical mixing of varying proportions of isotopically diverse presolar components with a normal solar nebula component due to the high w mo ratio and near terrestrial w isotope composition of the latter such mixing has no measurable effect on w isotopes but results in large mo isotope variations alternatively thermal processes within the solar nebula imparted mo isotope heterogeneity on an initially homogeneous mixture of presolar dust while w was not affected removal of volatile mo oxides during the thermal destruction of fragile presolar components would have created isotopically heterogeneous reservoirs of nebular dust accretion of meteorite parent bodies from such variably processed dust would thus result in mo isotope heterogeneities at the bulk meteorite scale other elements such as os and w were not or only slightly affected because they were more refractory during thermal processing and therefore remained isotopically homogeneous thermal processing of presolar dust within the solar nebula can thus account for both isotope heterogeneities observed for some elements and the lack of such isotopic heterogeneity for other elements

radar detectability of a subsurface ocean on europa abstract a spacecraft in orbit around jupiter s moon europa can use ice penetrating radar to probe for a possible liquid water ocean beneath europa s surface ice and to characterize other important subsurface structure consideration of available constraints on the properties of europa s ice possible subsurface temperature gradients and possible impurities in the ice places an upper limit of about 10 km on the depth to which an ocean might be detectable with an orbiting radar

molybdenum isotope anomalies in meteorites constraints on solar nebula evolution and origin of the earth the early evolution of the solar nebula involved substantial transport of mass resulting in mixing and homogenization of isotopically diverse materials that were contributed to the solar system from multiple stellar nucleosynthetic sources the efficiency of this mixing as well as its timescale can be quantified by determining nucleosynthetic isotope variations among meteorites and terrestrial planets here we present mo isotopic data for a wide range of samples including ca al rich inclusions chondrites and differentiated meteorites as well as martian and terrestrial samples most meteorites are depleted in s process mo relative to the earth and only the iab iiicd irons angrites and martian meteorites have terrestrial mo isotopic compositions in contrast most ca al rich inclusions are enriched in r process mo but one inclusion is characterized by a large s process deficit molybdenum isotopic anomalies in the bulk meteorites correlate with those in ru exactly as predicted from nucleosynthetic theory but no obvious correlation is apparent between mo and ni anomalies therefore s process mo and ru seem to be hosted in the same carrier which must be distinct from the carrier responsible for isotopic anomalies in the fe group elements ni cr ti furthermore the isotopic heterogeneity in mo and other elements contrasts with the isotopic homogeneity for hf and os indicating that different s process carriers once existed in the early solar nebula and that only some of these were heterogeneously distributed the mo isotopic anomalies of meteorites and their components decrease over time and with increasing size of the parent bodies providing evidence for a progressive homogenization of the solar nebula however the carbonaceous chondrites exhibit larger mo anomalies than expected for their age indicating that they received a greater portion of material from the outer solar system where homogenization was slow than other meteorite parent bodies and terrestrial planets compared to the meteorites earth is enriched in s process mo and must have accreted from material distinct from the meteorites combined mo and o isotopic data show that the composition of the earth cannot be reconstructed by any known combination of meteorites implying that meteorites may be inappropriate proxies for the isotopic composition of the bulk earth this is exemplified by the covariation of 92mo and 142nd anomalies in chondrites showing that the 142nd deficit of chondrites compared to the accessible earth may not unequivocally be interpreted as a signature of an early differentiation of the earth however further high precision isotopic data are needed to evaluate the role of chondrites in defining the isotopic composition of the earth

expected seismicity and the seismic noise environment of europa seismic data will be a vital geophysical constraint on internal structure of europa if we land instruments on the surface quantifying expected seismic activity on europa both in terms of large recognizable signals and ambient background noise is important for understanding dynamics of the moon as well as interpretation of potential future data seismic energy sources will likely include cracking in the ice shell and turbulent motion in the oceans we define a range of models of seismic activity in europa s ice shell by assuming each model follows a gutenberg richter relationship with varying parameters a range of cumulative seismic moment release between 10 16 and 10 18 nm yr is defined by scaling tidal dissipation energy to tectonic events on the earth s moon random catalogs are generated and used to create synthetic continuous noise records through numerical wave propagation in thermodynamically self consistent models of the interior structure of europa spectral characteristics of the noise are calculated by determining probabilistic power spectral densities of the synthetic records while the range of seismicity models predicts noise levels that vary by 80 db we show that most noise estimates are below the self noise floor of high frequency geophones but may be recorded by more sensitive instruments the largest expected signals exceed background noise by 50 db noise records may allow for constraints on interior structure through autocorrelation models of seismic noise generated by pressure variations at the base of the ice shell due to turbulent motions in the subsurface ocean may also generate observable seismic noise

models of radar absorption in europan ice abstract the detection of a sub surface present day ocean on europa is of considerable interest one possible method of detecting an ocean is by an orbiting radar sounder the effects of a range of possible europan ice chemistries on radar attenuation are investigated using plausible europa ice temperature profiles ice chemistries are derived from geochemical models of europa predicting a sulfate dominated ocean a chloride dominated ocean scaled from the earth and on experimental data on marine ice formed beneath ice shelves on earth on low salinity sea ice and models of rock and ice mixtures chloride ions are expected to dominate the radar absorption because they are incorporated into the ice lattice though if freezing rates are rapid or similar to sea ice then brine pockets will dominate losses in the case of an ocean being present underneath the ice the range of attenuation found in the models is from about 5 db km for rock ice mixtures up to 80 db km for sea ice models however perhaps the best model at present is for ice formed from a plausible sulfate dominated ocean with the fraction of chloride incorporated into the ice set to the same as for low accretion rate ronne ice shelf marine ice this has a radar absorption of 9 16 db km for surface temperatures of 50 100 k in the case of a convecting isothermal ice layer beneath a conducting ice lid absorption in the conducting lid is lower for all the models than it is over an ocean as the convecting ice is modeled to be 250 260 k absorption in the isothermal layers is very high but the interface between conducting and convecting ice may be marked by a reflection coefficient that enables it to be imaged it is concluded that realistic ice penetrating radars are likely to be able to penetrate some kilometers into the ice though problems of interpretation caused by scattering are not considered here

the lithophile trace elements in enstatite chondrites we report on the abundances of a selected set of lithophile trace elements namely rees y rb ba sr zr hf nb th u in a comprehensive suite of enstatite chondrites ec 13 eh and 11 el eh3 and el3 display only minor deviations from chondritic distributions for these elements in most metamorphosed ec a wide range of compositions is observed and suggests a mobility of many of the elements studied during the history of these rocks for example el6 chondrites exhibit light ree and nb depletions negative eu anomalies and positive y anomalies more important trace element fractionations are observed in metamorphosed eh like st marks rb depletion lap 02225 rb nb zr eu light ree depletions and galim b which displays large ba sr eu nb and light ree depletions leaching experiments were undertaken to investigate the contributions of sulfides in the whole rock budgets these phases control not only the ree budget but also important fractions of the other elements we studied these fractions strongly depend on the type of the rock eh or el and metamorphic grade for many elements the sulfide contributions increase with the metamorphic grades the trace element abundances of silicate residues are extremely variable negative sm and yb anomalies are observed in el3 and eh3 residues and are certainly the results of early nebular processes such anomalies are lacking in residues obtained with most metamorphosed ec underlining the importance of trace element redistributions during metamorphism in addition el6 residues display distinctive positive y anomalies that could be potentially ascribed to a less chalcophile behavior than ho in the conditions that prevailed during el metamorphism

the origin of oldhamite in unequilibrated enstatite chondrites abstract we report the results of an ion probe study of rare earth elements rees in six unequilibrated enstatite chondrites oldhamite is confirmed as the major but not the only ree carrier in these meteorites data are also provided for other minerals enstatite niningerite and alabandite that carry detectable amounts of rees although the variety of ree patterns in oldhamite is not as extreme as in hibonite there are seven distinct ree patterns four of which form a continuum that characterize most oldhamite grains from e chondrites two of these patterns f and g were each found in only one weathered grain there is no correlation between ree pattern and oldhamite petrologic setting our trace element data are used to evaluate earlier work and a number of elements zr y sc rees sr se and probably sb and cs including both refractory and volatile species under oxidizing conditions are found enriched in oldhamite a comparison of ree patterns with the results of equilibrium condensation calculations indicates that nebular processes were important in determining the composition of the oldhamite precursors whereas metamorphic processes also affected oldhamite compositions enrichments of chalcophiles are not necessarily due to interaction of oldhamite with nebular gas at low temperatures as previously suggested oldhamite like hibonite was formed from melts whose trace element compositions were determined by high temperature transient events in the solar nebula

samarium neodymium chronology and rubidium strontium systematics of an allende calcium aluminum rich inclusion with implications for 146sm half life abstract calcium aluminum rich inclusions cais are primitive objects that formed within the protoplanetary disk surrounding the young sun recent pb pb chronologic studies have demonstrated that cais are the oldest solar system solids crystallizing 4567 ma ago amelin et al 2002 connelly et al 2012 the isotope systematics of cais therefore provide critical insight into the earliest history of the solar system although sm nd and rb sr geochronometers are highly effective tools for investigating cosmochemical evolution in the early solar system previous studies of cais have revealed evidence for isotopically disturbed systems here we report new age data for allende cai al3s4 derived from both the long lived 147sm 143nd and short lived 146sm 142nd isotopic systems the 147sm 143nd chronometer yields an age of 4560 34 ma that is concordant with 207pb 206pb ages for cais and indicates that the sm nd system was not significantly disturbed by secondary alteration or nucleosynthetic processes the slope of the 146sm 142nd isochron defines the solar system initial 146sm 144sm of 0 00828 0 00044 this value is significantly different from the value of 0 0094 determined by kinoshita et al 2012 ages recalculated from all published 146sm 142nd isochron data using the traditional 103 ma half life and the initial 146sm 144sm value determined here closely match pb pb and 147sm 143nd ages determined on the same samples in contrast ages recalculated using the 68 ma half life determined by kinoshita et al 2012 and either of the initial 146sm 144sm values are often anomalously old this is particularly true for the youngest samples with 146sm 142nd isochron ages that are most sensitive to the choice of 146sm half life used in the age calculation in contrast to the sm nd isotope system the rb sr system is affected by alteration but yields an apparent isochron with a slope corresponding to a much younger age of 4247 110 ma although the rb sr system in cais appears to be disturbed the initial 87sr 86sr value determined from the isochron is 0 698942 0 000008 and closely approximates estimates of the initial solar system value although this isochron may be a mixing line it might also record alteration on the allende parent body in which rb was added to the al3s4 cai that was initially largely devoid of rb

geologic mapping of europa galileo data enable the major geological units structures and surface features to be identified on europa these include five primary units plains chaos band ridge and crater materials and their subunits along with various tectonic structures such as faults plains units are the most widespread ridged plains material spans a wide range of geological ages including the oldest recognizable features on europa and appears to represent a style of tectonic resurfacing rather than cryovolcanism smooth plains material typically embays other terrains and units possibly as a type of fluid emplacement and is among the youngest material units observed at global scales plains are typically mapped as undifferentiated plains material although in some areas differences can be discerned in the near infrared which might be related to differences in ice grain size chaos material is composed of plains and other preexisting materials that have been severely disrupted by inferred internal activity chaos is characterized by blocks of icy material set in a hummocky matrix band material is arrayed in linear curvilinear wedge shaped or cuspate zones with contrasting albedo and surface textures with respect to the surrounding terrain bilateral symmetry observed in some bands and the relationships with the surrounding units suggest that band material forms by the lithosphere fracturing spreading apart and infilling with material derived from the subsurface ridge material is mapped as a unit on local and some regional maps but shown with symbols at global scales ridge material includes single ridges doublet ridges and ridge complexes ridge materials are considered to represent tectonic processes possibly accompanied by the extrusion or intrusion of subsurface materials such as diapirs the tectonic processes might be related to tidal flexing of the icy lithosphere on diurnal or longer timescales crater materials include various interior smooth central rough inner and annular massif and exterior continuous ejecta subunits structural features and landforms are shown with conventional symbols type localities for the units are identified along with suggestions for portraying the features on geological maps including colors and letter abbreviations for material units implementing these suggestions by the planetary mapping community would facilitate comparisons of maps for different parts of europa and contribute to an eventual global synthesis of its complex geology on the basis of initial mapping results a stratigraphic sequence is suggested in which ridged plains form the oldest unit on europa followed by development of band material and individual ridges band materials tend to be somewhat older than ridges but in many areas the two units formed simultaneously similarly the formation of most chaos follows the development of ridged plains although chaos is among the youngest materials on europa some chaos units might have formed contemporaneously with ridged plains smooth plains generally embay all other units and are late stage in the evolution of the surface c 1 craters are superposed on ridged plains but are crosscut by other materials including bands and ridges most c2 craters postdate all other units but a few c2 craters are cut by ridge material c3 craters constitute the youngest recognizable material on europa

nucleosynthetic nd isotope anomalies in primitive enstatite chondrites abstract we carried out stepwise dissolutions of four primitive enstatite chondrites ec belonging to the eh subgroup large nd isotope anomalies are found in the most refractory phases dissolved using strong acids residues are characterized by excesses in 142nd and deficits in 145nd 148nd and 150nd isotopes the nd anomalies measured in the alha77295 residue are even greater than those measured in the murchison carbonaceous chondrite cc using a similar analytical technique qin et al 2011 once corrected for a common sm nd evolution the 142nd excess in the alha77295 residue is equal to 700 ppm relative to the terrestrial standard value the nd isotope patterns measured in ec and cc residues can be adjusted to coincide by adding a small amount of an s process rich carrier phase such as sic and 0 075 is required to fit the alha7795 residue small isotope differences still persist between these residues even if they can be considered similar within error in enstatite chondrites residues have a deficit in 150nd similar to or smaller than that measured in 148nd whereas in sic extracted from carbonaceous chondrites or in whole rock the deficit in 150nd is always greater than that in 148nd moreover in a binary 142nd 148nd diagram the best fit lines obtained for leachates and residues from carbonaceous chondrites and enstatite chondrites have slightly different slopes for the same 148nd 144nd ratio the anomalous component in an enstatite chondrite has a higher 142nd 144nd ratio compared to carbonaceous chondrites a feature already observed at the whole rock scale our results suggest that different chondrite groups sample different reservoirs of presolar grains formed in different environments assuming that the carrier of this anomalous component measured in residues of enstatite chondrites are sic our results may suggest that different meteorite parent bodies sample reservoirs of presolar sic formed in different stellar environments this could explain why alha77295 the sample which is the most enriched in presolar grains has a bulk 142nd isotope composition similar to the terrestrial value further investigation of enstatite chondrites is needed to test whether the isotope composition of the most refractory phases is similar to that measured in carbonaceous chondrites and in particular the 144sm that is a p process isotope only finally this study highlights the difficulty of interpreting the 142nd excess in terrestrial samples relative to chondrites since incomplete mixing of nucleosynthetic material in the solar nebula creates significant 142nd variation as shown by alha77295

old sm nd ages for cumulate eucrites and redetermination of the solar system initial 146sm 144sm ratio article i nfo sm 142 nd systematics short lived 146 sm 142 nd and long lived 147 sm 143 nd chronometers have been measured in three cumulate eucrites binda moore county and moama the two major mineral phases plagioclase and pyroxene present in these achondrites are characterized by a wide range of sm nd ratios that allows well resolved sm nd isochrons this group of meteorites thus is suitable to better constrain the initial 146 sm 144 sm ratio of the solar system binda and moore county give concordant ages of 4544 88 and 4542 85 ma respectively with initial 143 nd 144 nd ratios slightly higher to within error of chondritic these ages are in agreement with most of the radiometric ages determined on basaltic eucrites a best estimate for the solar system initial 146 sm 144 sm ratio is obtained using the five point regression line determined for binda the 146 sm 144

revised correlation of the frasnian famennian boundary and kellwasser events upper devonian in shallow marine paleoenvironments of new york state abstract the frasnian famennian boundary upper devonian is exposed in a 200 km long outcrop belt in new york state with deeper paleoenvironments to the west and shallower ones to the east geochronology in the eastern end of the outcrop belt has been based primarily on lithostratigraphic correlation with western sections which were dated using conodonts we collected conodonts and brachiopods from several measured sections and numerous other localities and these collections suggest that these east west lithostratigraphic correlations require revision we correlate the wiscoy formation with the upper angola formation and the canaseraga with the upper hanover thus the canaseraga formation contains the frasnian famennian boundary and upper kellwasser event and the dark shale above the wiscoy is equivalent to the pipe creek formation and lower kellwasser event these new correlations imply that the lower kellwasser event had greater impact on the shelly benthos of new york than the upper kellwasser at least for the subset of taxa examined here all strophomenid brachiopods and rugose corals were extirpated at the lower kellwasser along with numerous other brachiopods the final species of atrypid brachiopod persisted to the upper kellwasser

a passive probe for subsurface oceans and liquid water in jupiter s icy moons abstract we describe an interferometric reflectometer method for passive detection of subsurface oceans and liquid water in jovian icy moons using jupiter s decametric radio emission dam the dam flux density exceeds 3000 times the galactic background in the neighborhood of the jovian icy moons providing a signal that could be used for passive radio sounding an instrument located between the icy moon and jupiter could sample the dam emission along with its echoes reflected in the ice layer of the target moon cross correlating the direct emission with the echoes would provide a measurement of the ice shell thickness along with its dielectric properties the interferometric reflectometer provides a simple solution to sub jovian radio sounding of ice shells that is complementary to ice penetrating radar measurements better suited to measurements in the anti jovian hemisphere that shadows jupiter s strong decametric emission the passive nature of this technique also serves as risk reduction in case of radar transmitter failure the interferometric reflectometer could operate with electrically short antennas thus extending ice depth measurements to lower frequencies and potentially providing a deeper view into the ice shells of jovian moons

a shorter 146sm half life measured and implications for 146sm 142nd chronology in the solar system radiometric dating relies on measuring the abundance of long lived radionuclides relative to the abundance of their radiogenic decay products a process determined by the original radionuclide s half life for primordial radionuclides that decay slowly such as 146sm decaying to 142nd this method provides the timing of some of the earliest processes in solar system history using accelerator mass spectrometry kinoshita et al p 1614 1 provide a revised estimate for the 146sm half life of 68 7 million years which is 30 shorter than the previously accepted value this shorter half life suggests that reductions need to be made in the estimated ages for differentiation of earth s mantle and the solidification of the moon s magma ocean and for other more recent processes 1 lookup doi 10 1126 science 1215510

nucleosynthetic components of the early solar system inferred from ba isotopic compositions in carbonaceous chondrites abstract the ba isotopic composition of primitive meteorites is one of the more useful tracers to study nucleosynthetic processes in the early solar system because the seven stable ba isotopes consist of p r and s process nucleosynthetic components and possible decay products from presently extinct 135 cs ba isotopic analyses were performed on acid leachates from five carbonaceous chondrites murchison cm2 sayama cm2 allende cv3 isuna co3 and maralinga ck4 and one basaltic achondrite juvinas eucrite the ba isotopic data of acid treatment fractions in carbonaceous chondrites suggest the presence of independent nucleosynthetic components for s and r processes in the solar system the isotopic patterns from the acid residual fractions of two cm2 meteorites murchison and sayama show an enrichment of s process isotopes which is similar to that of presolar sic grains on the other hand their acid leachates have an excess of r process components among the ba isotopes in many cases of carbonaceous chondrites other than cm meteorites the excess of r process isotopes is too small for a detailed discussion about the nucleosynthetic contribution this may be interpreted as metamorphic destruction of presolar grains in meteorite matrices associated with petrographic type meteorites juvinas shows no isotopic anomalies of ba because the isotopic record in the early solar system was reset possibly by magmatic processes in the parent body

assessing the detectability of europa s eutectic zone using radar sounding abstract radar sounding is a geophysical method capable of directly imaging subsurface interfaces within the ice shell of the icy moons including jupiter s moon europa for this reason both the european space agency s jupiter icy moons explorer and the national aeronautics and space administration s europa clipper missions have ice penetrating radar sounders in their payloads in addition to the ice ocean interface and shallow water lenses liquid water in the eutectic zone of europa s ice shell could also be a target for radar sounding investigations however the wide range of possible configurations for eutectic zone water bodies and the overlying ice make their absolute echo strength difficult to predict to address this challenge we employ a suite of simple water configurations and scattering models to bound the eutectic detectability in terms of its effective reflectivity we find that for each configuration a range of physically plausible eutectic parameters exist that could produce detectable echoes with effective reflectivity values greater than 50 db at hf or vhf frequencies

mechanics of tidally driven fractures in europa s ice shell abstract a fracture mechanics model is developed for the initiation and propagation of a crack through a porous ice layer of finite thickness under gravitational overburden it is found that surface cracks generated in response to a tidally induced stress field may penetrate through the entire outer brittle layer if a subsurface ocean is present on europa such penetration is found to be very unlikely in the absence of an ocean a cycloidal crack would then form as a sequence of near instantaneous discrete failures each extending roughly the brittle layer thickness in range linked with a much lower apparent propagation speed set by the moving tidal stress field the implications of this porous ice fracture model for ice penetrating radar scattering loss and seismic activity are quantified

silicon isotope evidence against an enstatite chondrite earth the compositions of earth materials are strikingly similar to those of enstatite chondrite meteorites in many isotope systems although this suggests that earth largely accreted from enstatite chondrites definitive proof of this model has been lacking by comparing the silicon si isotope signatures of several extraterrestrial materials with terrestrial samples we show that they cannot be explained by core formation scenarios involving a bulk earth of enstatite chondrite composition si isotope similarities between the bulk silicate earth and the moon preclude the existence of a hidden reservoir in the lower mantle a necessary condition of the enstatite chondrite model and require an equilibrium process after the moon forming impact a three end member chondritic mixing model for earth reconciles the si isotope similarities between enstatite chondrites and earth

convection driven compaction as a possible origin of enceladus s long wavelength topography 1 the long wavelength surface topography of enceladus shows depressions about 1 km in depth and 102 km wide one possible cause of this topography is spatially variable amounts of compaction of an initially porous ice shell driven by spatial variations in heat flux here we show that the heat flux variations associated with convection in the shell can quantitatively match the observed features we develop a simple model of viscous compaction that includes the effect of porosity on thermal conductivity and find that an initial shell porosity of at least 20 25 is required to develop the observed topography over 1 ga this mechanism produces topographic depressions not rises above convective upwellings and does not generate detectable gravity anomalies unlike transient dynamic topography it can potentially leave a permanent record of ancient convective processes in the shallow lithospheres of icy satellites

lu hf and sm nd isotopic systematics in chondrites and their constraints on the lu hf properties of the earth sm nd and lu hf isotopic data are presented for 19 chondritic meteorites six carbonaceous chondrites five l chondrites seven h chondrites and a single enstatite chondrite the primary goal of the study is to better define the bulk silicate earth bse reference values for hf isotopes except for one sample with lower sm nd the sm nd data define a cluster around the accepted reference values for chondrites and terrestrial planets giving a mean 147sm 144nd of 0 1960 0 0005 and a mean 143nd 144nd of 0 512631 0 000010 uncertainties are two standard errors it seems appropriate to retain the presently accepted sm nd reference parameters 147sm 144nd 0 1966 and 143nd 144nd 0 512638 when fractionation corrected to 146nd 144nd 0 7219 lu hf isotopic data are not clustered but spread along an approximate 4 5 ga isochron trend with a range of 176lu 177hf from 0 0301 to 0 0354 the data are similar to many of the samples of chondrites presented by bizzarro et al nature 421 2003 931 but lack the range to lower lu hf shown by those authors our chondrite data define a regression line of 4 44 0 34 ga when 1 867 10 11 year 1 is used for the decay constant of 176lu science 293 2001 683 earth planet sci lett 219 2004 311 324 combining our data with the main population of analyses from bizzarro et al nature 421 2003 931 yields 4 51 0 24 ga unless samples of eucrite meteorites and deviating replicates of chondrites with 176lu 177hf less than 0 030 are employed no combination of the main population of chondrite lu hf data yields a regression with sufficiently low error to constrain the decay constant of 176lu sample heterogeneity seems to hinder the acquisition of reproducible lu hf analyses from small manually ground pieces of chondrites and we suggest that analysis of powders prepared from large volumes of meteorite will be needed to adequately characterize the lu hf isotope systematics of chondritic reservoirs and of bse our results for carbonaceous chondrites show higher average 176lu 177hf and 176hf 177hf than ordinary chondrites and the mean of carbonaceous chondrites also coincides with replicate analyses of a powder representing a large volume of meteorite the allende powder from the smithsonian institution use of the carbonaceous chondrite mean for bse lu hf characteristics results in a bse hf nd point that lies well within the array of terrestrial compositions and leads to plausible initial ehf values for precambrian rocks an improved objective resolution of meteorite data and of meteoritic models for the earth needs to occur before bse can be established for lu hf

ree and actinide microdistribution in sahara 97072 and alha77295 eh3 chondrites a combined cosmochemical and petrologic investigation abstract we report the results of rare earth elements rees and u th inventory of individual minerals oldhamite enstatite and niningerite in two of the most unequilibrated and primitive eh3 known so far alha77295 and sahara 97072 under the highly reducing condition that prevailed during the formation of enstatite chondrites rees are mainly chalcophile and concentrated in oldhamite the study is guided by detailed petrographic investigations of the individual minerals in chondrules complex sulfide metal clasts and enstatite dominated matrices we developed two textural parameters in order to resolve the evolution of oldhamite condensates and their residence in the solar gas prior to their accretion in the individual objects or in matrices and relate these textural features to the measured ree patterns of the individual oldhamite crystals these textural parameters are the crystal habit of oldhamite grains idiomorphic or anhedral and their host assemblages ree concentrations were measured by sims and la icpms oldhamite grains display ree enrichments 10 100 ci four types of ree patterns are encountered in oldhamite in alha77295 in general the ree distributions cannot be assigned to a specific oldhamite bearing assemblage the most represented ree pattern is characterized by both slight to large positive eu and yb anomalies and is enriched in light rees relative to heavy rees this pattern is present in 97 of oldhamite in sahara 97072 suggesting a different source region in the reduced part of the nebula or different parental eh asteroids for the two eh3 chondrites different parental asteroids are also supported by mgs fes zoning profiles in niningerite grains adjacent to troilite revealing both normal and reverse zoning trends and different mns contents the observed homogeneity of ree distribution in oldhamite grains in sahara 97072 is not related to the mild metamorphic event identified in this meteorite that caused breakdown of the major k and rb bearing sulfide djerfisherite ree concentrations in enstatite range between 0 2 and 8 ci hence enstatite is an important ree host next to oldhamite most patterns are characterized by negative eu and yb anomalies niningerites are negligible contributors to bulk eh3 ree inventory average positive eu and yb anomalies observed in most oldhamite are complimentary to the negative ones in enstatite thus explaining the flat patterns of the bulk meteorites the condensation calculations based on cosmic abundances predict that the first oldhamite condensates should have flat ree patterns with eu and yb depletions since eu and yb condense at lower temperature than other ree however this pattern is seen in enstatite our findings are at odds with the predicted negative eu and yb anomalies in oldhamite earliest condensates from a closed system in a reduced solar source our petrographic mineral chemistry and ree abundances of oldhamite enstatite and niningerite discards an origin of oldhamite by impact melting rubin et al 2009 our results do not support in first order the scenario of the incorporation of ree in the earth s core to explain 142nd excess in terrestrial samples relative to chondrites because oldhamite is the major ree carrier phase and has super chondritic sm nd ratios

lead isotopes behavior in the fumarolic environment of the piton de la fournaise volcano reunion island abstract the recent activity of the piton de la fournaise volcano offers a rare opportunity to address the issue of pb isotope behavior in volcanic fumaroles as the composition of the degassing source is accurately and precisely known gas sublimates formed between 2007 and 2011 at temperature ranging from 400 to ca 100 c include na k sulfate aphthitalite ca cu sulfate e g gypsum na sulfate thenardite ca mg al fe fluoride e g ralstonite and native sulfur the high temperature deposits show trace element patterns typical of volcanic gas with pb concentration up to 836 ppm while the low temperature deposits are depleted in most volatile elements pb only for low temperature fluoride samples do pb isotope compositions plot significantly outside the field of lavas the isotopic shift is ascribed to leaching ubiquitous unradiogenic phases e g sulfides by acidic gas condensates the similarity in pb isotope signature between lavas and sublimate samples more representative of the gas phase sulfates indicates that the net fractionation of pb isotopes resulting from volatilization and condensation processes is smaller than the precision of pb isotope measurements better than 60 ppm a m u the absence of net fractionation could result from negligible isotope fractionation during pb volatilization followed by extensive condensation of gaseous pb with possibly significant isotopic fractionation at this stage although this scenario has to be refined by more direct measurement of the gas phase and its general applicability tested it suggests that a small fraction resolving very small isotopic differences between magmas and their gaseous products remains an analytical challenge high precision pb isotope measurements rest not only on instrumental performance but also on high yield chemistry as pb isotopes drastically fractionate 800 ppm a m u upon elution on anionic resin for 50 pb recovery the estimated isotopic bias is plus or minus 60 80 ppm a m u depending on which of the early isotopically light or late isotopically heavy pb fraction is lost

temperatures on europa from galileo photopolarimeter radiometer nighttime thermal anomalies galileo observations of europa s thermal emission show low latitude diurnal brightness temperatures in the range of 86 to 132 kelvin nighttime temperatures form an unexpected pattern with high temperatures on the bright ejecta blanket of the crater pwyll and an equatorial minimum in temperatures after sunset uncorrelated with surface albedo or geology the nighttime anomalies may be due to regional thermal inertia variations of an unknown origin which are equivalent to a two to threefold variation in thermal conductivity or to endogenic heat fluxes locally reaching 1 watt per square meter endogenic heat flow at this high level although consistent with some geological evidence is theoretically unlikely