mineralogical characterization of some basaltic asteroids in the neighborhood of 4 vesta first results abstract we present reflectance spectra of 19 v type asteroids obtained at the 3 6 m telescopio nazionale galileo covering 0 8 to 2 5 m for 8 of these asteroids we obtained also visible spectra in the same observational run the range from 0 8 to 2 5 m encompassing the 1 and 2 m pyroxene features allows a precise mineralogical characterization of these asteroids the obtained data suggests the possible coexistence of distinct mineralogical groups among the v type asteroids either probing different layers of 4 vesta or coming from different bodies no clear correlation was found between mineralogies and the objects being or not member of the vesta dynamical family

seismic moulin tremor through glacial moulins meltwater is routed from the glacier surface to its base moulins are a main feature feeding subglacial drainage systems and thus influencing basal motion and ice dynamics but their geometry remains poorly known here we show that analysis of the seismic wavefield generated by water falling into a moulin can help constrain its geometry we present modeling results of hour long seimic tremors emitted from a vertical moulin shaft observed with a seismometer array installed at the surface of the greenland ice sheet the tremor was triggered when the moulin water level exceeded a certain height which we associate with the threshold for the waterfall to hit directly the surface of the moulin water column the amplitude of the tremor signal changed over each tremor episode in close relation to the amount of inflowing water the tremor spectrum features multiple prominent peaks whose characteristic frequencies are distributed like the resonant modes of a semiopen organ pipe and were found to depend on the moulin water level consistent with a source composed of resonant tube waves water pressure waves coupled to elastic deformation of the moulin walls along the water filled moulin pipe analysis of surface particle motions lends further support to this interpretation the seismic wavefield was modeled as a superposition of sustained wave radiation by pressure sources on the side walls and at the bottom of the moulin the former was found to dominate the wave field at close distance and the latter at large distance to the moulin

the mineralogy of ordinary chondrites and implications for asteroid spectrophotometry abstract the normative mineralogies of 94 ordinary chondrites have been calculated from high quality bulk chemical analyses relative proportions of olivine orthopyroxene and metal are more variable within the h l and ll classes than has been recognized previously mineralogy within each chondrite class varies systematically with oxidation state these data have important implications for the design of reflectance spectroscopy studies that match asteroid and meteorite spectral features and for quantitative spectral interpretations of asteroids they also provide a tool with which to predict mineral abundances in unsampled asteroids that formed under different redox conditions

vibrational modes of hydraulic fractures inference of fracture geometry from resonant frequencies and attenuation oscillatory seismic signals arising from resonant vibrations of hydraulic fractures are observed in many geologic systems including volcanoes glaciers and ice sheets and hydrocarbon and geothermal reservoirs to better quantify the physical dimensions of fluid filled cracks and properties of the fluids within them we study wave motion along a thin hydraulic fracture waveguide we present a linearized analysis valid at wavelengths greater than the fracture aperture that accounts for quasi static elastic deformation of the fracture walls as well as fluid viscosity inertia and compressibility in the long wavelength limit anomalously dispersed guided waves known as crack or krauklis waves propagate with restoring force from fracture wall elasticity at shorter wavelengths the waves become sound waves within the fluid channel wave attenuation in our model is due to fluid viscosity rather than seismic radiation from crack tips or fracture wall roughness we characterize viscous damping at both low frequencies where the flow is always fully developed and at high frequencies where the flow has a nearly constant velocity profile away from viscous boundary layers near the fracture walls most observable seismic signals from resonating fractures likely arise in the boundary layer crack wave limit where fluid solid coupling is pronounced and attenuation is minimal we present a method to estimate the aperture and length of a resonating hydraulic fracture using both the seismically observed quality factor and characteristic frequency finally we develop scaling relations between seismic moment and characteristic frequency that might be useful when interpreting the statistics of hydraulic fracture events

tide modulated ice flow variations drive seismicity near the calving front of bowdoin glacier greenland glacier microseismicity is a promising tool to study glacier dynamics however physical processes connecting seismic signals and ice dynamics are not clearly understood at present particularly the relationship between tide modulated seismicity and dynamics of calving glaciers remains elusive here we analyze records from an on ice seismometer placed 250 m from the calving front of bowdoin glacier greenland using high frequency glacier flow speed measurements we show that the microseismic activity is related to strain rate variations the seismic activity correlates with longitudinal stretching measured at the glacier surface both higher melt rates and falling tides accelerate glacier motion and increase longitudinal stretching long term microseismic monitoring could therefore provide insights on how a calving glacier s force balance and flow regime react to changes at the ice ocean interface

basal dynamics of kronebreen a fast flowing tidewater glacier in svalbard non local spatio temporal response to water input we evaluate the variability in basal friction for kronebreen svalbard a fast flowing tidewater glacier we invert 3 years 2013 15 of surface velocities at high temporal resolution generally 11 days to estimate the changing basal properties of the glacier our results suggest that sliding behaviour of kronebreen within a year is primarily influenced by changes in water input patterns during the meltwater season and basal friction is highly variable from a year to another at present models usually employ parameterisations to encompass the complex physics of glacier sliding by mathematically simulate their net effect for such ice masses with strong seasonal variations of surface melt the spatio temporal patterns of basal friction imply that it is neither possible nor appropriate to use a parameterisation for bed friction that is fixed in space and or time at least in a timescale of a few years basal sliding may not only be governed by local processes such as basal topography or summer melt but also be mediated by factors that vary over a larger distance and over a longer time period such as subglacial hydrology organisation ice thickness changes or calving front geometry

nucleation and seismic tremor associated with the glacial earthquakes of whillans ice stream antarctica 1 the ability to monitor transient motion along faults is critical to improving our ability to understand many natural phenomena such as landslides and earthquakes here we usedata from a gps and seismometer network that were deployed to monitor the regularly repeating glacial earthquakes of whillans ice stream west antarctica to show that a unique pattern of precursory slip precedes complete rupture along the bed of the ice stream additionally we show that rupture can be independently tracked by increased levels of microseismic activity including harmonic tremor that are coincident with the onset of slip at any location thus providing a remote means of monitoring stress and rupture propagation during the glacial earthquakes

s type asteroids ordinary chondrites and space weathering the evidence from galileo s fly bys of gaspra and ida new observations of the s type asteroids gaspra and ida especially by the galileo spacecraft demonstrate that a space weathering process operates which modifies the reflectance spectra of fresh material to be redder straighter and have shallower absorption bands the weathering process appears similar to but less potent than that observed on the moon it operates in the sense that it would tend to convert spectra of ordinary chondrites oc to having the spectral traits of s type asteroids these results appear to resolve the major obstacles of the long standing s type conundrum about the provenance of ordinary chondrite meteorites a wide body of recent research which is reviewed here builds on previous meteoritical evidence to support a new developing consensus that the larger s type asteroids are a diverse assortment of silicaceous assemblages which includes the ordinary chrondite parent bodies recent fairly realistic laboratory simulations of space weathering processes have changed oc spectra to resemble s type spectra j f bell s highly regarded earlier paradigm that oc parent bodies would be found only among sub 10 km main belt asteroids has been tested by an extensive observational survey by r binzel and his proteges the result is that no small main belt analog for the ocs has been found not even the somewhat oc like object boznemcova this article reviews the history of the s type conundrum which set the stage for galileo s historic flybys i review the findings about gaspra and ida including results about their geology their geophysical structure and probable origins and about ida s small moonlet dactyl density constraints on ida set by dactyl s orbit rule out for ida at least the classic view of s types as metallic stripped cores of differentiated precursor asteroids new analysis of the galileo spectral images of ida is presented that provides strong evidence that space weathering occurs on ida and that ida and the koronis family asteroids in general are plausibly oc like in composition after reviewing 1990s developments on the s type conundrum i advocate a new perspective that the ordinary chondrite parent bodies are among the s type asteroids a diverse grouping that also contains other silicaceous and silicate metal assemblages presumably including various stony irons and primitive achondrites represented in meteorite collections gaspra may be such a metal rich assemblage

metal silicate mixtures spectral properties and applications to asteroid taxonomy the reflectance spectra of combinations of olivine orthopyroxene and iron meteorite metal show systematic variations in spectral properties which can be used to constrain many of the physical and chemical properties of the assemblages the presence of metal most noticeably affects band area ratios peak peak and peak minimum reflectance ratios and band widths these parameters are also affected to varying degrees by the abundance and grain size of the metal and silicates and the composition of the silicates band width and band areas are useful for determining metal abundance in olivine metal and orthopyroxene metal assemblages respectively mafic silicate grain size variations are best determined using band depth criteria band centers are most useful for determining mafic silicate composition analysis of the reflectance spectrum of the s class asteroid 8 flora on the basis of these spectral parameters indicates a surface composed of approximately 50 wt metal 40 wt olivine fa 35 10 10 wt orthopyroxene fs 30 25 35 and perhaps a few weight percent of clinopyroxene a substantial amount of the surface seems to consist of a fine grained 45 m size component analysis of the reflectance spectrum of the a class asteroid 446 aeternitas suggests a surface assemblage of approximately 35 wt metal 55 wt olivine fa 20 10 7 wt clinopyroxene fs 17 and 3 wt orthopyroxene fs 45 a substantial fine grained 45 m size surface component is also indicated for this asteroid

truly undrained response of granular soils with no membrane penetration effects conventional and truly undrained behaviour of granular soils is compared by direct experimental measurements the truly undrained behaviour was determined by compensation for membrane penetration induced volume changes using a feedback controlled water injection system a more reliable nondestructive specimen specific method is presented to measure the magnitude of membrane penetration for use in the injection routine this new method unlike the existing methods does not make any assumptions regarding either the constitutive behaviour or isotropy of sands it is shown that the truly undrained pore pressures predicted by correcting those observed in conventional undrained tests are too large implying incorrect linkage between membrane penetration induced volume change and volumetric constitutive behaviour of the granular material the sand which responds in a strain hardening manner in conventional undrained loading may in fact be strain softening liquefiable when truly undrained a matter of serious practical concern resume les comportements conventionnel et vraiment non draine des sols pulverulents sont compares au moyen de mesures experimentales directes le comportement vraiment non draine a ete determine par compensation des changements de volume dus a la penetration de la membrane au moyen d un systeme de retroaction d injection d eau controlee l on presente une methode non destructive plus fiable adaptee au specimen cette methode contrairement aux methodes existantes ne comporte aucune hypothese quant aux lois de comportement ou a l isotropie des sables l on montre que les pressions interstitielles non drainees predites en corrigeant les valeurs observees dans les essais conventionnels non draines sont trop grandes ce qui implique un lien incorrect entre le changement de volume induit par la penetration de la membrane et la loi de comportement volumetrique du materiau pulverulent le sable qui reagit en ecrouissage dans un chargement non draine peut en fait etre en antiecrouissage liquefiable lorsqu il est vraiment non draine un point ayant une implication pratique importante

a previously unreported type of seismic source in the firn layer of the east antarctic ice sheet we identify a unique type of seismic source in the uppermost part of the east antarctic ice sheet recorded by temporary broadband seismic arrays in east antarctica these sources termed firnquakes are characterized by dispersed surface wave trains with frequencies of 1 10 hz detectable at distances up to 1000 km events show strong dispersed rayleigh wave trains and an absence of observable body wave arrivals most events also show weaker love waves initial events were discovered by standard detection schemes additional events were then detected with a correlation scanner using the initial arrivals as templates we locate sources by determining the l2 misfit for a grid of potential source locations using rayleigh wave arrival times and polarization directions we then perform a multiple filter analysis to calculate the rayleigh wave group velocity dispersion and invert the group velocity for shear velocity structure the resulting velocity structure is used as an input model to calculate synthetic seismograms inverting the dispersion curves yields ice velocity structures consistent with a low velocity firn layer 100 m thick and show that velocity structure is laterally variable the absence of observable body wave phases and the relative amplitudes of rayleigh waves and noise constrain the source depth to be less than 20 m the presence of love waves for most events suggests the source is not isotropic we propose the events are linked to the formation of small crevasses in the firn and several events correlate with shallow crevasse fields mapped in satellite imagery

distributed acoustic sensing of seismic properties in a borehole drilled on a fast flowing greenlandic outlet glacier distributed acoustic sensing das is a new technology in which seismic energy is recorded at high spatial and temporal resolution along a fibre optic cable we show analyses from the first glaciol

modelling the long term mass balance and firn evolution of glaciers around kongsfjorden svalbard we analyse the long term 1961 2012 distributed surface mass balance and firn evolution of the kongsvegen and holtedahlfonna glacier systems in northwestern svalbard we couple a surface energy balance model to a firn model with forcing provided from regional climate model output in situ observational data are used to calibrate model parameters and validate the output the simulated area averaged surface mass balance for 1961 2012 is slightly positive 0 08 m w e a 1 which only fractionally compensates for mass loss by calving refreezing of percolating water in spring summer 0 13 m w e a 1 and stored water in fall winter 0 18 m w e a 1 provides a buffer for runoff internal accumulation i e refreezing below the previous year s summer surface in the accumulation zone peaks up to 0 22 m w e a 1 and is unaccounted for by stake observations superimposed ice formation in the lower accumulation zone ranges as high as 0 25 m w e a 1 a comparison of the periods 1961 99 and 2000 12 reveals 21 higher annual melt rates since 2000 and a 31 increase in runoff which can only in part be ascribed to recent warmer and drier conditions in response to firn line retreat both albedo lowering snow ice albedo feedback and lower refreezing rates refreezing feedback further amplified runoff

characterization of seasonal glacial seismicity from a single station on ice record at holtedahlfonna svalbard glacial seismicity provides important insights into glacier dynamic processes we study the temporal distribution of cryogenic seismic signals icequakes at holtedahlfonna svalbard between april

spectral slope variations for osiris rex target asteroid 101955 bennu possible evidence for a fine grained regolith equatorial ridge ongoing spectroscopic reconnaissance of the osiris rex target asteroid 101955 bennu was performed in july 2011 and may 2012 near infrared spectra taken during these apparitions display slightly more positive redder spectral slopes than most previously reported measurements while observational systematic effects can produce such slope changes and these effects cannot be ruled out we entertain the hypothesis that the measurements are correct under this assumption we present laboratory measurements investigating a plausible explanation that positive spectral slopes indicate a finer grain size for the most directly observed sub earth region on the asteroid in all cases the positive spectral slopes correspond to sub earth latitudes nearest to the equatorial ridge of bennu if confirmed by osiris rex in situ observations one possible physical implication is that if the equatorial ridge is created by regolith migration during episodes of rapid rotation that migration is most strongly dominated by finer grain material alternatively after formation of the ridge by regolith of any size distribution larger sized equatorial material may be more subject to loss due to centrifugal acceleration relative to finer grain material where cohesive forces can preferentially retain the finest fraction rozitis b maclennan e emery j p 2014 nature 512 174 176

spatially resolved spectral observations of asteroid 951 gaspra on october 29 1991 the galileo spacecraft encountered asteroid 951 gaspra with a telescopic ccd camera and a near infrared mapping spectrometer that provided the first optically resolved views of any asteroid data from these two sensors were combined to detect the spectral signature of iron bearing minerals on this s type asteroid a minimum of two spectral units were identified on 951 gaspra both containing a higher relative abundance of olivine than those found in ordinary chondrites these data indicate that this s asteroid is an object that has undergone igneous differentiation processes a 2 7 m spectral feature was also detected on the surface of 951 gaspra and may be due to the presence of structural oh

estimating the long term calving flux of kronebreen svalbard from geodetic elevation changes and mass balance modelling this study independently quantifies geodetic elevation change and models surface mass balance to solve the continuity equation the approach is tested on two dynamically different glaciers kongsvegen and kronebreen in northwest svalbard through two time epochs 1966 1990 95 i and 1990 95 2007 ii on kongsvegen a dynamically inactive glacier the residual term represents an error associated with determining elevation changes and surface mass balance it is apparent that centerline mass balance estimates are not representative of the entire glacier which we relate to center line accumulation being larger than the elevation bin average on kronebreen a fast flowing and actively calving glacier a significant part of the residual is identified with the long term calving flux for both glaciers the cumulative surface mass balance remained close to zero during the first epoch but became increasingly negative in the second epoch the long term calving flux of kronebreen is estimated to be 0 14 0 03 km3 w e a 1 during epoch i and 0 20 0 05 km3 w e a 1 in epoch ii

subglacial discharge at tidewater glaciers revealed by seismic tremor subglacial discharge influences glacier basal motion and erodes and redeposits sediment at tidewater glacier termini discharge drives submarine terminus melting affects fjord circulation and is a central component of proglacial marine ecosystems however our present inability to track subglacial discharge and its variability significantly hinders our understanding of these processes here we report observations of hourly to seasonal variations in 1 5 10 hz seismic tremor that strongly correlate with subglacial discharge but not with basal motion weather or discrete icequakes our data demonstrate that vigorous discharge occurs from tidewater glaciers during summer in spite of fast basal motion that could limit the formation of subglacial conduits and then abates during winter furthermore tremor observations and a melt model demonstrate that drainage efficiency of tidewater glaciers evolves seasonally glaciohydraulic tremor provides a means by which to quantify subglacial discharge variations and offers a promising window into otherwise obscured glacierized environments

a 15 year record of frontal glacier ablation rates estimated from seismic data we present a unique time series of continuous glacier frontal ablation rates with weekly resolution over 15 years estimated from seismic calving observations at kronebreen svalbard using linear statistical models we calibrate the seismic record with seven years of satellite derived frontal ablation measurements the two basic input parameters required for our models are the cumulative duration of individual seismic calving events and the incompleteness of the seismic record to correct for the effect of seismic background noise frontal ablation follows the seasonal glacier speed up peaking 1 2 months after the melt season maximum short lived peaks are associated with melt and rain events cumulative frontal ablation of kronebreen between 2001 and 2015 is about 4 0 km3 3 7 gt with the greatest annual loss 0 45 km3 between 2013 and 2014 at the onset of the recent accelerated retreat of the glacier our approach provides a potential method for monitoring tidewater glaciers worldwide that have sufficiently close seismic instrumentation

chelyabinsk meteorite explains unusual spectral properties of baptistina asteroid family we investigated the spectral and compositional properties of chelyabinsk meteorite to identify its possible parent body in the main asteroid belt our analysis shows that the meteorite contains two spectrally distinct but compositionally indistinguishable components of ll5 chondrite and shock blackened impact melt material our x ray diffraction analysis confirms that the two lithologies of the chelyabinsk meteorite are extremely similar in modal mineralogy the meteorite is compositionally similar to ll chondrite and its most probable parent asteroid in the main belt is a member of the flora family our work confirms previous studies e g vernazza et al 2008 nature 454 858 860 de leon j licandro j serra ricart m pinilla alonso n campins h 2010 astron astrophys 517 a23 dunn t l burbine t h bottke w f clark j p 2013 icarus 222 273 282 linking ll chondrites to the flora family intimate mixture of ll5 chondrite and shock blackened impact melt material from chelyabinsk provides a spectral match with 8 flora the largest asteroid in the flora family the baptistina family and flora family overlap each other in dynamical space mineralogical analysis of 298 baptistina and 11 small family members shows that their surface compositions are similar to ll chondrites although their absorption bands are subdued and albedos lower when compared to typical s type asteroids a range of intimate mixtures of ll5 chondrite and shock blackened impact melt material from chelyabinsk provides spectral matches for all these baf members we suggest that the presence of a significant shock impact melt component in the surface regolith of baf members could be the cause of lower albedo and subdued absorption bands the conceptual problem with part of this scenario is that impact melts are very rare within ordinary chondrites of the 42 000 ordinary chondrites less than 0 5 203 of them contain impact melts a major reason that impact melts are rare in meteorites is that high impact velocities v 10 km s are needed to generate the necessary shock pressures and temperatures e g pierazzo e melosh h j 1998 hydrocode modeling of oblique impacts the fate of the projectile in origin of the earth and moon proceedings of the conference lpi contribution no 957 unless the target material is highly porous nearly all asteroid impacts within the main belt are at 5 km s bottke w f nolan m c greenberg r kolvoord r a 1994 collisional lifetimes and impact statistics of near earth asteroids in tucson gehrels t ed hazards due to comets and asteroids the university of arizona press arizona pp 337 357 which prevents them from producing much impact melt unless they are highly porous however shock darkening is an equally efficient process that takes place at much lower impact velocities 2 km s and can cause the observed spectral effects spectral effects of shock darkening and impact melt are identical the parent asteroid of baf was either a member of the flora family or had the same basic composition as the floras ll chondrite the shock pressures produced during the impact event generated enough impact melt or shock blackening to alter the spectral properties of baf but keep the baf composition largely unchanged collisional mixing of shock blackened impact melt and ll5 chondritic material could have created the baptistina asteroid family with composition identical to those of the floras but with subdued absorption

spectral properties and rotational spectral heterogeneity of 433 eros composite spectra of different rotational aspects of the s asteroid 433 eros were assembled from previous studies covering the wavelength range 0 33 2 5 m these data allow us to measure significant attributes of eros s spectrum its mafic mineral absorptions and the degree and nature of compositional heterogeneity of its surface we also evaluated previous s asteroid taxonomies using independent methods and from this test determined that the taxonomy of gaffey et al 1993 provides a sound basis for relating eros to other s asteroids on average eros resembles the s iv asteroids which bear the closest resemblance to ordinary chondrites in mafic mineralogy however eros also exhibits distinct rotational spectral variations comparable to the greatest yet recognized on an s asteroid one side of the asteroid has a shorter wavelength 1 m absorption and a stronger 2 m absorption than the global average and is interpreted to be richer in pyroxene the opposite face has a longer wavelength 1 m absorption and a weaker 2 m absorption and is interpreted to be richer in olivine the pyroxene rich side coincides with a facet like face identified in radar studies and the olivine rich side coincides with a convex shaped face each side of the asteroid exhibits spectral affinities with a different spectral class of s asteroids demonstrating that such subdivisions of s asteroids represent different parts of a compositional continuum high spatial resolution measurement of the mineralogic and elemental compositions and especially the geologic settings of these different materials by the near earth asteroid rendezvous mission will provide a great advance in the understanding of the origin and evolution of a candidate ordinary chondrite parent body

the near radio science investigations the science objectives for the near earth asteroid rendezvous near radio science team include determining the masses of asteroids 253 mathilde to within 10 and 433 eros 0 1 while the near spacecraft is in orbit about eros the radiometric spacecraft tracking data the optical landmark tracking data and the lidar altimetry measurements will be used to determine the gravity field of eros comparisons of this gravity field with one determined from eros shape models assuming constant density will provide constraints upon the internal structure of this asteroid in addition the spin state principal axes and moments of inertia will be determined as part of the radio science activities a campaign to meet the radio science objectives will require the close cooperation of the near navigation imaging and lidar teams

basal icequakes recorded beneath an alpine glacier glacier d argentiere mont blanc france evidence for stick slip motion while basal icequakes associated with glacier motion have been detected under antarctica for several decades there remains very little evidence of stick slip motion for alpine glaciers here we analyzed 2357 basal icequakes that were recorded at glacier d argenti ere mont blanc massif between february and november of 2012 and that are likely to be associated with basal sliding these events have been classified into 18 multiplets based on their waveforms the strong similarity of the waveforms within each multiplet suggests an isolated repeating source despite this similarity the peak amplitude within each multiplet varies gradually in time by up to a factor of 18 the distribution of these events in time is relatively complex for long time scales we observe progressive variations in the amplitudes of events within each multiplet for intermediate time scales hours the events occur regularly in time with typical return times of several minutes up to several hours for short time scales from 0 01 to 100 s the largest multiplet shows clus tering in time with a power law distribution of the interevent times the location of these events and their focal mechanisms are not well constrained because most of these events were detected by a single seismometer nevertheless the locations can be estimated with an accuracy of a few tens of meters using a polarization analysis the estimated average depth of the basal events is 179 m which is in good agreement with the estimated glacier thickness the relative changes in distance between the source and the sensor can be measured accurately by correlating separately the p wave and s wave parts of the seismograms of each event with the template waveforms which are obtained by averaging the signals within each multiplet we observed small variations in the times between the p wave and the s wave of up to 0 6 ms over 50 days these variations cannot be explained by displacement of the sensor with respect to the glacier but might be due to small changes in the seismic wave velocities with time finally we found using numerical simulations that the observed signals are better explained by a horizontal shear fault with slip parallel to the glacier flow than by a tensile fault these results suggest that the basal events are associated with stick slip motion of the glacier over rough bedrock the rupture length and the slip are difficult to estimate nonetheless the rupture length is likely to be of the order of meters and the total seismic slip accumulated over one day might be as large as the glacier motion during the most active bursts

a bounding surface plasticity model for sands exhibiting particle crushing a new bounding surface constitutive model for sands is presented and is suited to a wide range of stresses including those sufficient to cause particle crushing the basic concepts of critical sta

effect of friction fatigue on pile capacity in dense sand the paper presents the results of a series of field tests performed to study the causes of friction fatigue experienced by displacement piles four instrumented model piles were installed at a dense sand test bed site the test series was designed to impose different levels of cyclic loading during pile installation static and cyclic load tests were subsequently performed to study the differences in the axial capacities developed for ostensibly monotonic and cyclic installations the test results indicated that the mobilized horizontal effective stress regime that controls pile side friction primarily depends on the in situ sand state as reflected by the cone penetration test cpt qc resistance a zone of highly stressed sand that produced a concentration of high shear resistance was mobilized in the vicinity of the pile base the horizontal effective stress that acted on the pile shaft reduced in response to cyclic loading with the largest reductions occurring for high intensity cyclic loading or when the pile had experienced only a few load cycles during installation although cyclic loading caused a reduction in the horizontal effective stress that acted on the pile shaft the elevated stress built up in the vicinity of the pile base during installation remained higher than that remote from the base the elevated stress in the vicinity of the pile base only dissipated after cyclic tension loading had been applied

a critical evaluation of oxidation versus reduction during metamorphism of l and ll group chondrites and implications for asteroid spectroscopy modal mineralogies of individual equilibrated petrologic type 4 6 l and ll chondrites have been measured using an electron microprobe mapping technique and the chemical compositions of coexisting silicate minerals have been analyzed progressive changes in the relative abundances and in the molar fe mn and fe mg ratios of olivine low ca pyroxene and diopside occur with increasing metamorphic grade variations in olivine low ca pyroxene ratios ol px and in metal abundances and compositions with petrologic type support the hypothesis that oxidation of metallic iron accompanied thermal metamorphism in ordinary chondrites modal ol px ratios are systematically lower than normative ol px ratios for the same meteorites suggesting that the commonly used c i p w norm calculation procedure may not adequately estimate silicate mineral abundances in reduced chondrites ol px ratios calculated from visnir reflectance spectra of the same meteorites are not in agreement with other ol px determinations possibly because of spectral complexities arising from other minerals in chondrites characteristic features in visnir spectra are sensitive to the proportions and compositions of olivine and pyroxenes the minerals most affected by oxidative metamorphism this work may allow spectral calibration for the determination of mineralogy and petrologic type and thus may be useful for spectroscopic studies of asteroids

a spectral analysis of ordinary chondrites s type asteroids and their component minerals genetic implications three salient features of visible and infrared reflectance spectra of ordinary chondrites ocs and s type asteroids are 1 albedo at 0 56 m 2 continuum slope and 3 depth of the electronic absorption band due to octahedrally coordinated fe2 in olivine and pyroxene these quantities were numerically extracted from the spectra of 23 ocs representing all metamorphic grades and 39 s type asteroids to be plotted in a three dimensional coordinate system the spectral characteristics of three ocs which were comminuted melted recrystallized and recomminuted are also presented in the same format the results show that although laboratory simulation of melt alteration in an asteroidal regolith does alter oc spectra the spectral parameters of these altered meteorites do not change enough to leave the parametric region defined by unaltered oc spectra when the region containing the 39 s asteroid spectra is compared with that of the altered and unaltered ocs it is found that not one of the ocs falls within the s asteroid region the differences may be largely attributed to spectral differences between the respective metallic components the range of s asteroid parameters is then compared with potential pure end member components most likely to result from magmatic differentiation of a chondritic protoasteroid olivine orthopyroxene clinopyroxene and fe ni meteorite metal alternatively represented by the m asteroids it is found that the s asteroid array is consistent with random mixtures of the differentiated components except for a notable dominance of the spectral characteristics of the opaque metallic component these results suggest that the m asteroids may form a composition continuum with the s asteroids we discuss a scenario consistent with this analysis and with the bell et al theory of the geological structure of the asteroid belt ordinary chondritic protoasteroids of all sizes were probably the dominant primary condensates in the inner portion of the main asteroid belt these were later heated by electromagnetic induction or by 26al nuclide decay as a result the smaller ones were subjected to various degrees of metamorphism while the larger ones were subjected to large scale magmatic differentiation petrological domains of the s asteroids beneath a mixed regolith may be large and supply achondrites irons and stony irons to earth rather than well mixed breccias of these components the smaller oc protoasteroids may still be abundant in the asteroid belt but if small enough to escape differentiation may also be small enough to escape earth based identification

core formation in asteroids chemical arguments based on the s concentrations in the metallic magmas that formed magmatic iron meteorites and on the lack of pyroxene in pallasites suggest that core formation in asteroids was accompanied by 40 melting of the associated silicates the existence of plagioclase free residues from partial melting such as lodranite meteorites indicates that metal did not segregate from silicates when the amount of partial melting was only 15 thus core formation in asteroids requires substantial melting of an asteroid high interfacial energies between metallic melts and silicates require that metallic spherules sink through partially molten silicates to form cores in asteroids and planetesimals the globule sinking mechanism is not very efficient because silicate crystal liquid mixtures have high yield strengths making it difficult for the globules to sink calculations suggest that the melt fraction must reach 50 before globules can sink alternatively porous flow of molten metal is possible when the amount of metal is high enough to form an interconnected network about 50 this can be achieved by high initial abundances of metal or by gradual removal of silicate melt thereby enriching the residue in the metal sulfide assemblage this also requires removal of 50 silicate partial melt though not necessarily all at once such high amounts of melting were not always attained in asteroids so many asteroids probably consist of partially differentiated silicates and metallic masses that did not segregate to a core s asteroids might represent such partially differentiated bodies

mineralogical petrological characterization of near earth asteroids studies of near earth asteroids are aimed at determining their dynamical and structural history the mineralogy and petrology of 17 near earth asteroids are characterized using reflectance spectroscopy with ground based telescopes as one method to address their major issues implications for the origin and evolution are discussed in a separate paper assuming the surfaces are composed of cosmically abundant materials the presence of certain mineralogical species can be determined from diagnostic absorption features and spectral characteristics which have been studied under known laboratory conditions and understood in terms of crystal field theory with one possible exception the surface composition of near earth asteroids consists of common rock forming minerals such as olivine pyroxene and phyllosilicates opaque components are present but cannot be mineralogically identified with existing experimental data the spectrum of 2201 oljato cannot be interpreted in terms of common rock forming minerals this spectrum was examined for cometary features because its high orbital eccentricity suggests a possible relation to comets no common cometary features are identified in its spectrum the predominance of mafic silicate absorption features in spectra of near earth asteroids compared to the majority of main belt asteroids may be a primary compositional feature or may be the signature of relatively fresher asteroid material

motion of an antarctic glacier by repeated tidally modulated earthquakes subglacial seismicity reveals information about glacier behaviour analysis of repeated seismic events beneath an antarctic outlet glacier is consistent with sliding of debris laden ice over a bedrock asperity with an event frequency that is modulated by the ocean tides

composition and size of apollo asteroid 1984 kb abstract reflection spectra and thermal emission radiometry were obtained for the earth crossing asteroid 1984 kb the spectrum exhibits the spectral signatures of olivine pyroxene and nife metal it is typical of class s objects and suggests a surface material similar to the rare lodranite meteorites a standard asteroid thermal model implies a radius of 0 7 km and an albedo of 0 16 similar to class s objects an analysis of the same thermal data with a bare rock thermal model gives an albedo inconsistent with the ir spectrum suggesting that this object has a significant regolith despite its small size

interpretation of moduli from self boring pressuremeter tests in sand the pressuremeter is a unique method for assessing directly the in situ shear stiffness of soils however the correct interpretation and application of the measured modulus must account for the relevant stress and strain level acting around the pressuremeter during the test a method to correct the measured unload reload shear modulus from self bored pressuremeter tests in sands is proposed the method has been evaluated using extensive data obtained from 47 tests performed in a large calibration chamber using pluvially deposited silica sand and from 25 tests performed in situ in a natural deposit of relatively clean silica sand at the river po italy a consistent relationship was obtained between the corrected unload reload shear modulus and the small strain shear modulus determined from resonant column tests and field cross hole tests suggestions are given to link the measured moduli with moduli values required for geotechnical design problems the importance of strain level stress strain model yie

iceberg calving as a primary source of regional scale glacier generated seismicity in the st elias mountains alaska 1 since the installation of the alaska regional seismic network in the 1970s data analysts have noted nontectonic seismic events thought to be related to glacier dynamics while loose associations with the glaciers of the st elias mountains have been made no detailed study of the source locations has been undertaken we performed a two step investigation surrounding these events beginning with manual locations that guided an automated detection and event sifting routine results from the manual investigation highlight characteristics of the seismic waveforms including single peaked narrowband spectra emergent onsets lack of distinct phase arrivals and a predominant cluster of locations near the calving termini of several neighboring tidewater glaciers through these locations comparison with previous work analyses of waveform characteristics frequency magnitude statistics and temporal patterns in seismicity we suggest calving as a source for the seismicity statistical properties and time series analysis of the event catalog suggest a scale invariant process that has no single or simple forcing these results support the idea that calving is often a response to short lived or localized stress perturbations our results demonstrate the utility of passive seismic instrumentation to monitor relative changes in the rate and magnitude of iceberg calving at tidewater glaciers that may be volatile or susceptible to ensuing rapid retreat especially when existing seismic infrastructure can be used

origin of rapidly solidified metal troilite grains in chondrites and iron meteorites inclusions of troilite and metallic fe ni 0 2 4 mm in size with a dendritic or cellular texture were observed in 12 ordinary chondrites cooling rates in the interval 1400 950 c calculated from the spacing of secondary dendrite arms or cell widths and published experimental data range from 10 7 to 104 c sec in 8 of these chondrites which are breccias containing some normal slow cooled metal grains the inclusions solidified before they were incorporated into the breccias their cooling rates of 1 300 c sec indicate cooling by radiation or by conduction in contact with cold silicate or hot silicate volumes only 6 40 mm in size this is quantitative evidence that these inclusions and their associated clasts were melted on the surface of a parent body by impact and were not formed at depth from an internally derived melt in ramsdorf rose city and shaw which show extensive reheating to 1000 c fe fes textures in melted areas are coarser and indicate cooling rates of 10 1 to 10 4 c sec during solidification this metal may have solidified inside hot silicate volumes that were 10 300 cm in size as shaw and rose city are breccias of unmelted and melted material their melted metal did not necessarily cool through 1000 c within a few m of the surface shock melted fine grained irregular intergrowths of metal and troilite formed in situ in many irons and some chondrites by rapid solidification at cooling rates of 105 c sec their kamacite and taenite compositions may result from annealing at 250 c of metallic glass or exceedingly fine grained quench products

quantified mineralogical evidence for a common origin of 1929 kollaa with 4 vesta and the hed meteorites abstract in this paper we present the first correlation of derived mineral abundances of v class asteroid 1929 kollaa 4 vesta and the hed meteorites we demonstrate that 1929 kollaa has a basaltic composition consistent with an origin within the crustal layer of 4 vesta and show a plausible genetic connection between kollaa and the cumulate eucrite meteorites these data support the proposed delivery mechanism of hed meteorites to the earth from vesta and provide the first mineralogical constraint derived from the observation of a small v class vesta family asteroid on the crustal thickness of 4 vesta

the distribution of basaltic asteroids in the main belt abstract we present the observational results of a survey designed to target and detect asteroids whose photometric colors are similar to those of vesta family members and thus may be considered as candidates for having a basaltic composition fifty basaltic candidates were selected with orbital elements that lie outside of the vesta dynamical family optical and near infrared spectra were used to assign a taxonomic type to 11 of the 50 candidates ten of these were spectroscopically confirmed as v type asteroids suggesting that most of the candidates are basaltic and can be used to constrain the distribution of basaltic material in the main belt using our catalog of v type candidates and the success rate of the survey we calculate unbiased size frequency and semi major axis distributions of v type asteroids these distributions in addition to an estimate for the total mass of basaltic material suggest that vesta was the predominant contributor to the basaltic asteroid inventory of the main belt however scattered planetesimals from the inner solar system a 2 0 au and other partially fully differentiated bodies likely contributed to this inventory in particular we infer the presence of basaltic fragments in the vicinity of asteroid 15 eunomia which may be derived from a differentiated parent body in the middle main belt 2 5 a 2 8 we find no asteroidal evidence for a large number of previously undiscovered basaltic asteroids which agrees with previous theories suggesting that basaltic fragments from the 100 differentiated parent bodies represented in meteorite collections have been battered to bits burbine t h meibom a binzel r p 1996 meteorit planet sci 31 607 620

ccd reflectance spectra of selected asteroids i presentation and data analysis considerations abstract narrowband reflectance spectra of 35 asteroids have been obtained with a ccd spectrograph from 1984 to 1987 as part of a search for weak features in the reflectance spectra of asteroids that would expand our knowledge of their surface mineralogical composition spectra obtained of primitive asteroids were examined for evidence of aqueous alteration products the spectrum of 1 ceres shows weak absorption features at 0 60 and 0 67 m not yet explained by laboratory reflectance spectra spectra of some main belt and outer belt c and p class asteroids show weak absorption features that have analogues among spectra of cm carbonaceous chondrites and terrestial phyllosilicates weak absorption features are seen in the spectra of some asteroids located in the hilda and cybele groups beyond the outer edge of the main asteroid belt that do not have analogues among laboratory spectra the trojan d class asteroids observed show no sign of absorption features suggesting that aqueous alteration did not operate at that heliocentric distance features present in the spectra of ordinary chondrites were sought in spectra of asteroids located in possible source regions for the ordinary chondrites spectra of asteroids located near the 3 1 kirkwood gap both in and outside of the proposed chaotic zone show no resemblance to laboratory spectra of ordinary chondrites

moon near infrared spectral reflectance a first good look a positive identification of the minerals olivine plagioclase and several types of pyroxenes were made at several locations on the lunar surface by using remote measurements for example the crater aristarchus is found to have an average pyroxene composition of augite and plagioclase is obviously present a dark mantle deposit in the crater j herschel is at least partly composed of a mixture of 70o7o olivine and 30o7o pyroxene these determinations were possible because the reflectance spectra for 10 20 km diameter lunar areas have been measured for the first time in the ir spectral region 0 65 2 5 m with sufficient spectral resolution and photometric precision to define mineral electronic absorption bands the reflectance for all lunar regions observed over 100 to present continues to increase toward longer wavelengths to at least 2 5 m and several mineral absorption bands appear the telescopic spectra are of similar quality and contain features similar to laboratory spectra of lunar samples the absorption features in several spectra have been quantitatively analyzed using newly developed computer processing techniques including thermal flux removal and absorption band fitting to produce these mineral identifications detection and quantitative analysis of these absorptions provide a much improved basis for remotely determining and mapping surface mineralogy quantitatively from the ground or using airborne or spacecraft platforms

metal and associated phases in bishunpur a highly unequilibrated ordinary chondrite it appears that the highly unequilibrated bishunpur ordinary chondrite preserves phase relations acquired during solar nebular processes to a relatively high degree metamorphic temperatures may not have exceeded 300 350 c the major categories of metal are 3 kinds of metal in the metal matrix three kinds in chondrule interiors and 2 kinds in chondrule rims the fine grained matrix metal is highly variable in composition the kamacite co content 7 8 2 0 mg g is within the l group range 6 7 8 2 mg g but extends well above and below its ni content 38 5 mg g is considerably lower than in more equilibrated chondrites and taenite is ni rich 450 mg g and unzoned these compositions imply equilibration at very low temperatures of about 300 350 c it seems unlikely that volume diffusion could account for the observed relatively unzoned phases a better model involves mass transport by grain boundary diffusion and grain growth at the indicated temperatures we find no evidence that the matrix was ever at higher temperatures large 50 650 m polycrystalline metal aggregates consisting of individually zoned crystals are also found in the matrix they probably represent clusters formed in the solar nebula a few large 50 250 m round monocrystalline grains are also present in the matrix metal bearing chondrules tend to be highly reduced they contain low ni metal that occasionally contains si and or cr silicates in these chondrules tend to have low feo feo mgo ratios the si rich metal grains are never in contact with silicates and are always surrounded by troilite with a poorly characterized ca cr sulfide at the metal troilite interface they appear to be high temperature nebular condensates that avoided oxidation even during the chondrule forming process silicon contents drop below our detection limit when the sulfide coating is absent much more common in chondrule interiors are si free spheroidal metal grains not associated with sulfides these have ni and co contents very similar to the si bearing grains and appear to be oxidized variants of the same material the third class of chondrule metal is fine 1 m dusty grains inside individual olivine grains these seem to reflect high temperature in situ reduction of feo from the olivine the composition of kamacite is different in sulfide rich and sulfide poor chondrule rims and in both cases it is dissimilar to the compositions in the chondrule interiors and matrix this indicates that chondrule rims could not have resulted from reactions with the matrix but are primary features acquired prior to accretton

dynamic perennial firn aquifer on an arctic glacier ice penetrating radar and gps observations reveal a perennial firn aquifer pfa on a svalbard ice field similar to those recently discovered in southeastern greenland a bright widespread radar reflector separates relatively dry and water saturated firn this surface the phreatic firn water table is deeper beneath local surface elevation maxima shallower in surface lows and steeper where the surface is steep the reflector crosscuts snow stratigraphy we use the apparent deflection of accumulation layers due to the higher dielectric permittivity below the water table to infer that the firn pore space becomes progressively more saturated as depth increases our observations indicate that pfas respond rapidly subannually to surface forcing and are capable of providing significant input to the englacial hydrology system

mineralogical interpretation of reflectance spectra of eros from near near infrared spectrometer low phase flyby high signal to noise near infrared spectrometer nis spectra acquired during the low phase flyby of the near earth asteroid rendezvous near mission to 433 eros are analyzed to determine mineral chemistry and proportions of mafic silicates across the asteroid s surface at 2 68 5 50 km spatial resolution spectral band parameters are derived and compared with those of laboratory samples of known mineral composition grain size distribution and terrestrial meteoritic and lunar pyroxene spectral properties the nis derived band parameters are consistent with ordinary chondrite meteorites we invoke the presence of a clinopyroxene component in the spectra which is consistent with ordinary chondrite mineralogy and or some degree of partial melting of ordinary chondritic material spectra measured across the surface of eros can reveal small but real spectral variations most relative spectra are uniform to within 1 2 some areas suggest compositional variations of a few percent spectral slope variations of a few percent are seen indicating a non uniform distribution of materials affecting the slope parameter but with no resolved absorption bands we find no correlation of slope with viewing geometry or compositional variation the band parameter values do not consistently indicate a specific ordinary chondrite class but eros is definitely undifferentiated with possible compositional variations of no more than 1 2

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 dark side of iapetus abstract this paper presents new photometric and spectrophotometric observations of the dark leading hemisphere of saturn s satellite iapetus spectrophotometry from 0 3 1 0 um may 1979 shows the dark hemisphere to be very red similar to a few asteroids and the moon but with no spectral features attributable to olivine or pyroxene near infrared spectrophometry in the regions 1 4 2 5 um may 1981 and 3 0 3 8 um february 1981 reveals water ice absorption bands probably resulting from the polar caps intruding onto the dark hemisphere the reflectance of iapetus is unlike that of carbonaceous chondrites or c type asteroids and most closely resembles the reflectance and low albedo of carbonaceous organic residue from the murchison c2 carbonaceous chondrite the murchison material has the same red slope and a probable spectral feature near 0 6 um seen in iapetus data three hypotheses for the formation of the dark hemisphere are discussed in light of the observational data the favored hypothesis is that debris from phoebe or other unknown outer satellites of saturn impacts the dark hemisphere of iapetus as poynting robertson drag causes the debris to spiral toward saturn the high velocity impacts preferentially remove ice from the satellite s surface causing enrichment of included carbonaceous material intrinsic to iapetus the reflectance of phoebe itself is significantly different from that of iapetus suggesting that relatively little phoebe debris lies on the dark hemisphere there remains the possibility that the impacting debris originates from another body of composition similar to the murchison residue and that this material is exposed on the surface of iapetus

metallic minerals thermal histories and parent bodies of some xenolithic ordinary chondrite meteorites we have studied metal grains in the hosts and lithic fragments of widely differing petrologic types in four xenolithic chondrftes using reflected light microscopy and electron probe analysis in weston and fayetteville which both contain solar flare tracks and solar wind gases kamacite taenite and tetrataenite ordered feni and troilite show a variety of textures on a wood plot of central ni content vs dimension taenite analyses scatter as if metal grains cooled at rates of 10 1000 and 1 100 k myr respectively through 700 k although metal in an h6 clast in fayetteville plots coherently with a cooling rate of 50 k myr we propose that metal grains cooled at these rates in chondritic clasts at different locations before host and clasts were compacted and were not subsequently heated above 650 k we predict a similar history for all gas rich ordinary chondrites by contrast metallic minerals throughout bhola and mezo madaras show more uniform textures and plot coherently giving cooling rates in the range 750 to 600 k of 0 1 and 1 k myr respectively we conclude that host and xenoliths in both chondrites were slowly cooled after compaction thus clasts in these chondrites experienced peak metamorphic temperatures and slow cooling through 700 k in different environments according to the conventional onion shell model for h l or ll chondrite parent bodies material of petrologic types 3 5 was arranged in successive shells around a type 6 core prior to catastrophic collisions which mixed all types intimately but if peak metamorphic temperatures were reached during not after accretion as seems plausible maximum metamorphism may have occurred in planetesimals 10 km in radius cooling through 700 k may then have occurred in larger bodies that accreted from these planetesimals iron meteorites mesosiderites and some achondrites may also have experienced melting in planetesimals and slow cooling in larger bodies

antarctic icequakes triggered by the 2010 maule earthquake in chile large earthquakes can trigger seismicity in remote regions analysis of seismic data from antarctica reveals ice quakes coincident with passing seismic waves from the 2010 chile earthquake suggesting that the ice sheet is sensitive to such triggers

the barringer award address presented 1996 july 25 berlin germany impact experiments related to the evolution of planetary regoliths impact induced comminution of planetary surfaces is pervasive throughout the solar system and occurs on submillimeter to global scales resulting in comminution products that range from fine grained surface soils to massive polymict ejecta deposits to collisionally fragmented objects within this wide range of comminution products we define regoliths in a narrow sense as materials that were processed by repetitive impacts to dimensional scales comparable to or smaller than that of component minerals of the progenitor rock s in this paper we summarize a wide variety of impact experiments and other observations that were primarily intended to understand the evolution of regoliths on lunar basalt flows and we discuss some of their implications for asteroidal surfaces cratering experiments in both rock and noncohesive materials combined with photogeologic observations of the lunar surface demonstrate that craters 500 m in diameter contribute most to the excavation of local bedrock for subsequent processing by micrometeorites the overall excavation rate and thus growth rate of the debris layer decreases with time because the increasingly thicker fragmental layer will prevent progressively larger projectiles from reaching bedrock typical growth rates for a 5 m thick lunar soil layer are initially 3 ga ago a few mm ma and slowed to 1 mm ma at present the coarse grained crater ejecta are efficiently comminuted by collisional fragmentation processes and the mean residence time of a 1 kg rock is typically 10 ma the actual comminution of either lithic or monomineralic detritus is highly mineral specific with feldspar and mesostasis comminuting preferentially over pyroxene and olivine thus resulting in mechanically fractionated fines especially at grain sizes 20 m such fractionated fines also participate preferentially in the shock melting of lunar soils thus giving rise to agglutinate melts as a consequence agglutinate melts are systematically enriched in feldspar components relative to the bulk composition of their respective host soil s compositionally homogeneous impact derived glass beads in lunar soils seem to result from micrometeorite impacts on rock surfaces reflecting lithic regolith components and associated mineral mixtures cumulatively experimental and observational evidence from lunar mare soils suggests that regoliths derive substantially from the comminution of local bedrock the addition of foreign exotic components is not necessary to explain the modal and chemical compositions of diverse grain size fractions from typical lunar soils regoliths on asteroids are qualitatively different from those of the moon the modest impact velocities in the asteroid belt some 5 km s 1 are barely sufficient to produce impact melts also substantially more crater mass is being displaced on low gravity asteroids compared to the moon collisional processing of surface boulders should therefore be more prominent in producing comminuted asteroid surfaces these processes combine into asteroidal surface deposits that have suffered modest levels of shock metamorphism compared to the moon impact melting does not seem to be a significant process under these conditions however the role of cometary particles encountering asteroid surfaces at presumably higher velocities has not been addressed in the past unfortunately the asteroidal surface processes that seemingly modify the spectral properties of ordinary chondrites to match telescopically obtained spectra of s type asteroids remain poorly understood at present despite the extensive experimental and theoretical insights summarized in this report and our fairly mature understanding of lunar surface processes and regolith evolution

the thermal regime of sub polar glaciers mapped by multi frequency radio echo sounding radio echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale radar signals of 320 370 mhz penetrate ice at sub freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water radar signals of 5 20 mhz on the other hand see through both the cold and the temperate ice down to the glacier bed radio echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in svalbard kongsvegen uversbreen midre lovenbreen and austre broggerbreen in the ablation area of kongsvegen a cold surface layer 50 160m thick was underlain by a warm basal layer which is advected from the temperate accumulation area the surface ablation of this cold layer may be compensated by freezing at its lower cold temperate interface this requires that the free water content in the ice at the freezing interface is about 1 of the volume the cold surface layer is thicker beneath medial moraines and where cold based hanging glaciers enter the main ice stream on uversbreen the thermal regime was similar to that of kongsvegen a temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between kongsvegen and uversbreen where meltwater accumulates during the summer near the subglacial lake setevatnet 250 m a s l lovenbreen was frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer up to 50m thick was fed by temperate ice from two cirques on austre broggerbreen a temperate basal layer was not detected by radio echo soundings but the basal ice was observed to be at the melting point in two boreholes

observed spectral properties of near earth objects results for population distribution source regions and space weathering processes abstract we present new visible and near infrared spectroscopic measurements for 252 near earth neo and mars crossing mc objects observed from 1994 through 2002 as a complement to the small main belt asteroid spectroscopic survey smass http smass mit edu combined with previously published smass results we have an internally consistent data set of more than 400 of these objects for investigating trends related to size orbits and dynamical history these data also provide the basis for producing a bias corrected estimate for the total neo population stuart and binzel 2004 icarus 170 295 311 we find 25 of the 26 bus 1999 phd thesis taxonomic types are represented with nearly 90 of the objects falling within the broad s q x and c complexes rare a and e types are more common in the mc than neo population about 5 compared to 3 orbits in terms of possible space weathering effects we see a size dependent transition from ordinary chondrite like q type objects to s type asteroids over the size range of 0 1 to 5 km where the transition is effectively complete at 5 km a match between the average surface age of 5 km asteroids and the rate of space weathering could constrain models for both processes however space weathering may proceed at a very rapid rate compared with collisional timescales in this case the presence or absence of a regolith may be the determining factor for whether or not an object appears space weathered thus 0 1 to 5 km appears to be a critical size range for understanding the processes timescales and conditions under which a regolith conducive to space weathering is generated retained and refreshed

evidence for deep icequakes in an alpine glacier to obtain more reliable information about the focal depth distribution of icequakes in april 1997 we operated an array of seven portable digital seismographs on unteraargletscher central swiss alps over 5000 events were detected by at least two instruments during the 9 day recording period p wave velocities 3770 m f were determined from several calibration shots detonated at the glacier surface as well as in a 49 m deep borehole whereas s wave velocities 1860 ms 1 were derived from a simultaneous inversion for vp vs6 applied to 169 icequakes so far hypocentral locations have been calculated for over 300 icequakes besides confirming the occurrence of shallow events associated with the opening of crevasses our results show that a small but significant fraction of the hypocenters are located at or near the glacier bed one event was found at an intermediate depth of about 120 m three dimensional particle motion diagrams of both explosions and icequakes clearly demonstrate that all vertical component seismograms from shallow sources are dominated by the rayleigh wave on the other hand for events occurring at depths greater than about 40 m the rayleigh wave disappears almost entirely therefore a qualitative analysis of the signal character provides direct information on the focal depth of an event and was used as an independent check of the locations obtained from traditional arrival time inversions thus our results demonstrate that deep icequakes do occur and that simple rheological models according to which brittle deformation is restricted to the uppermost part of a glacier may need revision

regoliths on small bodies in the solar system a regolith is defined as a layer or mantle of loose incoherent rocky material of whatever origin that nearly everywhere forms the surface of the land and rests on coherent bedrock the regoliths on many planetary bodies are the result of continual impacts which transform coherent surfaces into fragmental debris the present investigation is concerned with the special case of regolith formation and evolution on small objects such as asteroids and meteorite parent bodies first order models of regolith evolution on asteroidal surfaces are constructed on the basis of data provided by studies of lunar samples and meteorites it appears that regolith formation proceeds by deposition of discrete layers of the widely spread ejecta primarily from the larger impacts moderate size 100 300 km diameter asteroids are covered by modest regoliths of the order of one km in depth small rocky asteroids develop negligible regoliths

mainbelt asteroids dual polarization radar observations observations of 20 asteroids in the main belt between mars and jupiter provide information about the nature of these objects surfaces at centimeter to kilometer scales at least one asteroid pallas is extremely smooth at centimeter to meter scales each asteroid appears much rougher than the moon at some scale between several meters and many kilometers the range of asteroid radar albedos is very broad and implies substantial variations in porosity or metal concentration or both the highest albedo estimate for the asteroid psyche is consistent with a surface having porosities typical of lunar soil and a composition nearly entirely metallic

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

spectral properties of near earth asteroids evidence for sources of ordinary chondrite meteorites although ordinary chondrite oc meteorites dominate observed falls the identification of near earth and main belt asteroid sources has remained elusive telescopic measurements of 35 near earth asteroids 3 kilometers in diameter revealed six that have visible wavelength spectra similar to laboratory spectra of oc meteorites near earth asteroids were found to have spectral properties that span the range between the previously separated domains of oc meteorites and the most common s class asteroids suggesting a link this range of spectral properties could arise through a diversity of mineralogies and regolith particle sizes as well as through a time dependent surface weathering process

deep icequakes what happens at the base of alpine glaciers 1 basal seismicity cannot be attributed exclusively to glacier stick slip motion as shown by previous studies on temperate alpine glaciers there also exist basal seismic sources which are not due to pure shear mechanisms their moment tensors have substantial if not dominant isotropic components based on first motion data of high quality seismic records from gornergletscher and triftgletscher switzerland we argue that the observed isotropic components can be explained by tensile faulting the implied coseismic volumetric change can be both positive fracture opening and negative fracture collapse we attribute these observations to hydraulic processes near water filled cavities whose connectivity to the subglacial drainage system changes over time thus our proposed icequake source mechanisms cannot be reconciled with pure shear sources at the glacier bed which would be expected for basal stick slip motion this sliding mode has recently been proposed as a realitively common mechanism which can substantially enhance subglacial erosion the existence of several seismic source mechanisms tensile shear or some combination of the two of basal icequakes implies that a solid understanding about the nature of these events is indispensible if conclusions about glacier sliding subglacial erosion and other basal processes are to be drawn from observed seismicity

galileo encounter with 951 gaspra first pictures of an asteroid galileo images of gaspra reveal it to be an irregularly shaped object 19 by 12 by 11 kilometers that appears to have been created by a catastrophic collisional disruption of a precursor parent body the cratering age of the surface is about 200 million years subtle albedo and color variations appear to correlate with morphological features brighter materials are associated with craters especially along the crests of ridges have a stronger 1 micrometer absorption and may represent freshly excavated mafic materials darker materials exhibiting a significantly weaker 1 micrometer absorption appear concentrated in interridge areas one explanation of these patterns is that gaspra is covered with a thin regolith and that some of this material has migrated downslope in some areas

intermediate depth icequakes and harmonic tremor in an alpine glacier glacier d argentiere france evidence for hydraulic fracturing we detected several thousand deep englacial icequakes on glacier d argentiere mont blanc massif between 30 march and 3 may 2012 these events have been classified in eight clusters inside each cluster the waveforms are similar for p waves and s waves although the time delay between the p waves and s waves vary by up to 0 03 s indicating an extended source area although these events were recorded by a single accelerometer they were roughly located using a polarization analysis the deepest events were located at a depth of 130 m 60 m above the ice bed interface the clusters are separated in space the largest cluster extends over about 100 m for this cluster the strike of the rupture plane is nearly parallel to the direction of the open crevasses and the dip angle is 56 deep icequakes occur in bursts of activity that last for a few hours and are separated by quiet periods many events occurred on 28 29 april 2012 during the warmest days when snow melting was likely important the distribution of events in time and space obeys a power law as also observed for earthquakes but with larger exponents the polarity of the p waves for all of the events is consistent with tensile faulting finally between 25 april and 3 may we observed a gliding harmonic tremor with a fun damental resonance frequency that varied between 30 hz and 38 hz with additional higher frequency harmonics during this time we also observed shallow hybrid events with high frequency onsets and a monochromatic coda these events might be produced by the propagation of fractures and the subsequent flow of water into the fracture the strongest resonance was observed just after a strong burst of deep icequakes and during an un usually warm period when the snow height decreased by 60 cm in one week the res onance frequency shows a succession of several sharp decreases and phases of progressive increases one of the strongest negative steps of the resonance frequency on 28 april coincides with a burst of deep icequakes these events appear to be associated with the propagation of fractures which can explain the decrease in the resonance frequency finally we observed an acceleration of glacier flow on 29 april and suggested that melt water had reached the ice bed interface these observations suggest that deep icequakes are due to hydraulic fracturing and that they can be used to track fluid flow inside glaciers

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

petrography mineral chemistry and origin of type i enstatite chondrites abstract optical and cathodoluminescence petrography were coupled with electron microprobe analysis to relate the textures and chemical compositions of minerals in the chondrules and matrix of the indarch kota kota adhi kot and abee type i enstatite chondrites clinoenstatites fall into two distinct chemical groups with characteristic red or blue luminescence red crystals are higher in ti al cr mn and ca and lower in na than blue ones rare forsterites in indarch and kota kota show distinct compositions associated with orange or blue luminescence the chemical ranges are indistinguishable for each color type in chondrules of all textural types and the presence of both color types in a single chondrule or a metal fragment requires mechanical aggregation of both crystals and liquids of both color types porphyritic chondrules are ascribed mainly to aggregation of existing crystals because both types of pyroxene and olivine occur in the same chondrule large crystals of one color type are surrounded by fine grained crystals of another type in some barred and radiating chondrules all types of chondrules are surrounded by fine grained rims rich in sulfide the matrix contains many broken chondrules and individual silicate grains but is rich in sulfide and metal analyses are given of albite minor elements and luminescence color vary between chondrites kamacite schreibersite oldhamite and niningerite although the mineral assemblages do not fit theoretical condensation sequences in detail the red pyroxene and orange olivine might result ultimately from near equilibrium crystallization in which early reduced condensates reacted with a gas while the blue crystals might result from fractional condensation in which early condensates were removed mechanically from a gas subsequent episodes involving mixing melting crystallization condensation fracturing and mechanical aggregation would be needed to produce the complex textures

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

excitation of a buried magmatic pipe a seismic source model for volcanic tremor recent observations of seismic events at various volcanoes suggest that harmonic tremor results from the sustained occurrence of so called long period or low frequency events accordingly we can view the long period volcanic event as the elementary process of tremor and interpret it as the impulse response of the tremor generating system we present a seismic model in which the source of tremor is the acoustic resonance of a fluid filled volcanic pipe triggered by excess gas pressure the model consists of three elements namely a triggering mechanism a resonator and a radiator for simplicity we assume a hemispherical trigger cylindrial resonator and circular radiator set in a vertical configuration with the trigger capping the top of the pipe and the disk shaped radiator shutting off its bottom considering the simple case of a source buried in a homogeneous half space we then apply the discrete wave number method to obtain a complete representation of the ground motion response at near and intermediate distances the results demonstrate that the displacement attributed to the pipe dominates the near field motion while that due to the disk is representative of the intermediate and far fields the trigger itself has a smaller contribution mainly limited to the field in the proximity of the source the characteristics displayed by the free surface response evolve from a strong impulsive signature in the immediate vicinity of the epicenter to a well developed harmonic wave train dominated by rayleigh waves at larger distances no clear shear arrival can be detected in the synthetic seismograms the displacement spectrum reflects the organ pipe modes of the conduit and the bandwidth associated with the dominant spectral peak of motion is controlled by the combined losses due to viscous attenuation in the fluid and elastic radiation into the solid in the case of the cylindrical magma column considered the radiation loss is proportional to the square of the pipe radius while the loss related to viscous damping is inversely proportional to the same factor indicating that the relative importance of the two loss mechanisms is critically dependent on the geometry of the magma reservoir the relative importance of the pipe and disk elements likewise is a function of the conduit cross section this suggests the possibility of determining the geometry of the source as well as the radiation loss and in situ magma viscosity from a comparison of near and far field observations

a visible spectroscopic survey of the flora clan abstract we observed 47 flora clan members at the eso european southern observatory in the wavelength range 4900 9200 a we found 42 objects with common characteristics a maximum around 7500 a and a reflectivity gradient spanning a continuous but limited range only five objects show different spectral behavior one is probably v type looking for meteorite analogs we only find four ordinary chondrites that present features similar to those of the lower part of the flora spectral distribution this behavior is consistent as the consequence of some space weathering process

the meteorite asteroid connection two olivine rich asteroids two asteroids have clear indications of olivine rich surface petrology without any indication of pyroxene or plagioclase suggesting that the olivine may be quite pure they provide probable examples of mantles of differentiated parent asteroids exposed by fragmentation and are good candidates for the parent bodies of the unusual olivine meteorite brachina or the olivine iron alloy meteorites called pallasites

impact history of eros craters and boulders abstract preliminary measurements of craters and boulders have been made in various locations on eros from images acquired during the first nine months of near shoemaker s orbital mission including the october 2000 low altitude flyover we offer some very preliminary qualitative analysis of later laf images and very high resolution images obtained during near s landing on 12 february 2001 craters on eros 100 m diameter closely resemble the saturated crater population of ida eros is more heavily cratered than gaspra but lacks the saturated giant craters of mathilde these craters and the other large scale geological features were formed over a duration of very roughly 2 gyr while eros was in the main asteroid belt between the time when its parent body was disrupted and eros was injected into an earth approaching orbit probably tens of myr ago saturation equilibrium had been expected to shape eros crater population down to very small sizes as on the lunar maria however craters

sustained seismic tremors and icequakes detected in the ablation zone of the greenland ice sheet during summer 2011 seismic activity in the ablation zone of the western greenland ice sheet gris was monitored using a network of three component seismometers the seismic record includes a large variety of icequakes and seismic tremors that demonstrate a clear correlation with subglacial water flow we verified the existence of well known shallow icequakes related to surface crevasse formation deep icequakes located at 100 160 m depth and narrow banded short term seismic tremors tens of seconds in duration in addition we present previously unreported long term tremors lasting several hours using attenuation of the measured tremor amplitude we locate the epicentre of this long term tremor to a large moulin within our study area between 3 and 11 hz our continuous seismic record is dominated by this moulin tremor and shows strong correlation with the water level of the generating moulin we argue that monitoring of icequake and glacial tremor sources bears high potential for investigating glacier hydraulics and dynamics and is thus an ideal supplement to traditional glaciological measurements

reflectance spectra of featureless materials and the surface mineralogies of m and e class asteroids this study was supported by grants in aid of research from the central research fund of the university of alberta to d g w s from sigma xi the scientific research society and the geological society of america 3741 87 to e a c and nasa planetary geology and geophysics grant nagw 642 to m j g

effects of temperature on remotely sensed mineral absorption features laboratory spectral reflectance of mafic silicates has been measured over a temperature range characteristic of solar system objects to study the variation of diagnostic mineral absorption bands this information has become increasingly important with recent improvements in the quality of remotely sensed planetary data and the concurrent increase in sophistication of quantitative and qualitative spectrum analysis techniques in this study visible and near ir reflectance spectra 0 4 2 5 m of pyroxenes and olivine were obtained over a sample temperature range of 80 448 k these are the first published reflectance data for these minerals at temperatures significantly below ambient 300 k additionally thermal radiation emitted from the samples at elevated temperatures was effectively removed disclosing for the first time the high temperature reflectance behavior of pyroxenes in the diagnostic 2 m spectral region as expected from basic physical considerations fe2 crystal field absorptions in all samples become narrower with decreasing temperature the three components of the composite olivine band centered near 1 m become better resolved with decreased temperature and show changes in relative absorption strength there is not however any significant wavelength shift of the olivine reflectance minimum both orthopyroxene and clinopyroxene spectra show dramatic changes in band symmetry with temperature with the greatest change in the longer wavelength edge despite these significant changes in shape little if any change is observed in the wavelength position of reflectance minima of pyroxene absorptions near 1 m the 2 m pyroxene absorptions in contrast demonstrate major shifts of reflectance minima but in different directions in orthopyroxene spectra the band shifts to longer wavelengths with increased temperature while for the clinopyroxene spectra the band shifts to shorter wavelengths this behavior results in greatly improved spectral differentiation of orthopyroxene and clinopyroxene components in a mixture such as a basalt at reduced temperatures application of the results presented here to remote sensing mineral characterization techniques currently in use for determination of pyroxene composition can provide a moderate improvement to quantitative interpretations from 5 to 20 wt feo for orthopyroxenes and 5 wt cao for clinopyroxenes depending on planetary surface temperature

asteroid 6 hebe the probable parent body of the h type ordinary chondrites and the iie iron meteorites the s iv type asteroid 6 hebe is identified as the probable parent body of the h type ordinary chondrites and of the iie iron meteorites the ordinary chondrites are the most common type of meteorites falling to earth but prior to the present study no large mainbelt source bodies have been confirmed hebe is located adjacent to both the v6 and 3 1 resonances and has been previously suggested as a major potential source of the terrestrial meteorite flux hebe exhibits subtle rotational spectral variations indicating the presence of some compositional variations across its surface the silicate portion of the surface assemblage of hebe is consistent both in overall average and in its range of variation with the silicate components in the suite of h type chondrites the high albedo of hebe rules out a lunar style space weathering process to produce the weakened absorption features and reddish spectral slope in the s type spectrum of hebe linear unmixing models show that a typical ni fe metal spectrum is consistent with the component that modifies an h chondrite spectrum to produce the s type spectrum of hebe on the basis of the association between the h chondrites and the he iron meteorites our model suggests that large impacts onto the relatively metal rich h chondrite target produced melt bodies sheets or pods that differentiated to form thin laterally extensive near surface layers of ni fe metal fragments of the upper silicate portions of these melt bodies are apparently represented by some of the igneous inclusions in h chondrite breccias alternately masses of metal could have been deposited on the surface of hebe by the impact of a core or core fragment from a differentiated parent body of h chondrite composition subsequent impacts preferentially eroded and depleted the overlying silicate and regolith components exposing and maintaining large masses of metal at the optical surface of hebe in this interpretation the nonmagmatic iie iron meteorites are samples of the ni fe metal masses on the surface of hebe whereas the h chondrites are samples from between and or beneath the metal masses

seismic multiplet response triggered by melt at blood falls taylor glacier antarctica 1 meltwater input often triggers a seismic response from glaciers and ice sheets it is difficult however to measure melt production on glaciers directly while subglacial water storage is not directly observable therefore we document temporal changes in seismicity from a dry based polar glacier taylor glacier antarctica during a melt season using a synthesis of seismic observation and melt modeling we record icequakes using a dense six receiver network of three component geophones and compare this with melt input generated from a calibrated surface energy balance model in the absence of modeled surface melt we find that seismicity is well described by a diurnal signal composed of microseismic events in lake and glacial ice during melt events the diurnal signal is suppressed and seismicity is instead characterized by large glacial icequakes we perform network based correlation and clustering analyses of seismic record sections and determine that 18 of melt season icequakes are repetitive multiplets the epicentral locations for these multiplets suggest that they are triggered by meltwater produced near a brine seep known as blood falls our observations of the correspondingp wave first motions are consistent with volumetric source mechanisms we suggest that surface melt enables a persistent pathway through this cold ice to an englacial fracture system that is responsible for brine release episodes from the blood falls seep the scalar moments for these events suggest that the volumetric increase at the source region can be explained by melt input

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