differentiation of vesta implications for a shallow magma ocean abstract the dawn mission confirms earlier predictions that the asteroid 4 vesta is differentiated with an iron rich core a silicate mantle and a basaltic crust and supports the conjecture of vesta being the parent body of the hed meteorites to better understand its early evolution we perform numerical calculations of the thermo chemical evolution adopting new data obtained by the dawn mission such as mass bulk density and size of the asteroid we have expanded the thermo chemical evolution model of neumann et al 2012 that includes accretion compaction melting and the associated changes of the material properties and the partitioning of incompatible elements such as the radioactive heat sources advective heat transport and differentiation by porous flow to further consider convection and the associated effective cooling in a potential magma ocean depending on the melt fraction the heat transport by melt segregation is modelled either by assuming melt flow in a porous medium or by simulating vigorous convection and heat flux of a magma ocean with a high effective thermal conductivity our results show that partitioning of 26al and its transport with the silicate melt is crucial for the formation of a global and deep magma ocean due to the enrichment of 26al in the liquid phase and its accumulation in the sub surface for formation times t 0 1 5 ma a thin shallow magma ocean with a thickness of 1 to a few tens of km forms its thickness depends on the viscosity of silicate melt the lifetime of the shallow magma ocean is o 10 4 o 10 6 years and convection in this layer is accompanied by the extrusion of 26al at the surface resulting in the formation of a basaltic crust the interior differentiates from the outside inwards with a mantle that is depleted in 26al and core formation is completed within 0 3 ma the lower mantle experiences a maximal melt fraction of 45 suggesting a harzburgitic to dunitic composition our results support the formation of non cumulate eucrites by the extrusion of early partial melt while cumulate eucrites and diogenites may form from the crystallising shallow magma ocean silicate melt is present in the mantle for up to 150 ma and convection in a crystallising core proceeds for approximately 100 ma supporting the idea of an early magnetic field to explain the remnant magnetisation observed in some hed meteorites

the geological nature of dark material on vesta and implications for the subsurface structure abstract deposits of dark material appear on vesta s surface as features of relatively low albedo in the visible wavelength range of dawn s camera and spectrometer mixed with the regolith and partially excavated by younger impacts the material is exposed as individual layered outcrops in crater walls or ejecta patches having been uncovered and broken up by the impact dark fans on crater walls and dark deposits on crater floors are the result of gravity driven mass wasting triggered by steep slopes and impact seismicity the fact that dark material is mixed with impact ejecta indicates that it has been processed together with the ejected material some small craters display continuous dark ejecta similar to lunar dark halo impact craters indicating that the impact excavated the material from beneath a higher albedo surface the asymmetric distribution of dark material in impact craters and ejecta suggests non continuous distribution in the local subsurface some positive relief dark edifices appear to be impact sculpted hills with dark material distributed over the hill slopes dark features inside and outside of craters are in some places arranged as linear outcrops along scarps or as dark streaks perpendicular to the local topography the spectral characteristics of the dark material resemble that of vesta s regolith dark material is distributed unevenly across vesta s surface with clusters of all types of dark material exposures on a local scale some craters expose or are associated with dark material while others in the immediate vicinity do not show evidence for dark material while the variety of surface exposures of dark material and their different geological correlations with surface features as well as their uneven distribution indicate a globally inhomogeneous distribution in the subsurface the dark material seems to be correlated with the rim and ejecta of the older veneneia south polar basin structure the origin of the dark material is still being debated however the geological analysis suggests that it is exogenic from carbon rich low velocity impactors rather than endogenic from freshly exposed mafic material or melt exposed or created by impacts

vesta surface thermal properties map the first ever regional thermal properties map of vesta has been derived from the temperatures retrieved by infrared data by the mission dawn the low average value of thermal inertia 30 10 j m 2 s 0 5 k 1 indicates a surface covered by a fine regolith a range of thermal inertia values suggesting terrains with different physical properties has been determined the lower thermal inertia of the regions north of the equator suggests that they are covered by an older more processed surface a few specific areas have higher than average thermal inertia values indicative of a more compact material the highest thermal inertia value has been determined on the marcia crater known for its pitted terrain and the presence of hydroxyl in the ejecta our results suggest that this type of terrain can be the result of soil compaction following the degassing of a local subsurface reservoir of volatiles

in flight calibration of the dawn framing camera we present a method for calibrating images acquired by the dawn framing camera fc that is based on the results of an in flight calibration campaign performed during the cruise from earth to vesta we describe this campaign and the data analysis in full both the primary camera fc2 and the backup camera fc1 are radiometrically and geometrically calibrated through observations of standard stars star fields and solar system objects the calibration in each spectral filter is accurate to within a few percent for point sources geometric distortion small by design is characterized with high accuracy dark current monitored on a regular basis is very low at flight operational temperatures out of field stray light was characterized using the sun as a stray light source in field stray light is confirmed in narrow band filter images of vesta its magnitude and distribution are scene dependent and expected to contribute significantly to images of extended objects description of a method for in field stray light correction is deferred to a follow up paper as is a discussion of the closely related topic of flat fielding

vesta s shape and morphology vesta s surface is characterized by abundant impact craters some with preserved ejecta blankets large troughs extending around the equatorial region enigmatic dark material and widespread mass wasting but as yet an absence of volcanic features abundant steep slopes indicate that impact generated surface regolith is underlain by bedrock dawn observations confirm the large impact basin rheasilvia at vesta s south pole and reveal evidence for an earlier underlying large basin veneneia vesta s geology displays morphological features characteristic of the moon and terrestrial planets as well as those of other asteroids underscoring vesta s unique role as a transitional solar system body

paleoceanographic history around the tsugaru strait between the japan sea and the northwest pacific ocean since 30 cal kyr bp abstract the paleoceanographic history around the tsugaru strait since 30 0 cal kyr bp was reconstructed using ecological and biogeographical habitats of diatom species and q mode factor analysis of diatom flora in six piston cores at 30 0 17 5 cal kyr bp a fall in sea level and the intensification of the oyashio current caused erosion of submarine sediments near the shore in the eastern area of the strait and led to deposition of the third and second sequences of thinly laminated layers tl3 and tl2 in the japan sea at 17 5 11 5 cal kyr bp cooling intensified around the strait producing an inflow of oyashio water into the japan sea through the strait at 15 5 14 5 cal kyr bp a cold water mass around the strait developed from subarctic sea ice to arctic waters at 13 0 11 2 cal kyr bp the younger dryas cooling was clearly recorded by the increasing of oceanic cold water diatom species in the eastern area of the tsugaru strait but not in the japan sea at 15 5 13 0 cal kyr bp and 11 25 10 25 cal kyr bp the warming around the younger dryas resulted in the deposition of thinly laminated layers off shimokita in the eastern area of the strait at 9 5 cal kyr bp the oyashio current water intruded into deep depths in the mixed water region off sanriku at 9 5 7 0 cal kyr bp the fluctuation of 1 5 kyr intervals in the strength of the tsushima warm current system in the japan sea was initiated

eucritic crust remnants and the effect of in falling hydrous carbonaceous chondrites characterizing the composition of vesta s marcia region abstract the equatorial marcia quadrangle region is characterized by the large relatively young impact craters marcia and calpurnia and their surrounding dark ejecta field a hill with a dark rayed crater named aricia tholus and an unusual diffuse material surrounding the impact crater octavia the spectral analysis indicates that while this region is relatively uniform in the pyroxene band centers it instead shows large differences in pyroxene band depths and reflectance a large variation of reflectance is seen in the quadrangle bright and dark materials are present as diffuse material and as concentrated spots and outcrops moreover oh signature is pervasive in the quadrangle with a few exceptions the region especially the marcia ejecta field is characterized by spectra showing the 2 m band shifted at long wavelengths this is commonly associated with eucritic material believed to have crystallized as lava on vesta s surface or within relatively shallow level dikes and plutons thus suggesting that this region is a remnant of the old vestan basaltic crust however other characteristics of the spectra do not fully fit the eucritic composition indicating an alternative explanation for the band center distribution including the presence of carbonaceous chondritic material mixed with the native vestan pyroxene the detailed mineralogical analysis of the marcia quadrangle indicates that this quadrangle is the result of the mixture of the vestan endogenic minerals with the exogenic carbonaceous chondrites the stratigraphic units around marcia clearly show the bright uncontaminated material interlaced and mixed with the dark material that contains a strong oh signature only few small areas can be considered as representative of the old vestan original material

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

volcanic eruptions and intrusions on the asteroid 4 vesta we use basic principles of fluid mechanics to explore the intrusive and eruptive consequences of early large scale silicate melting within the asteroid 4 vesta and relate our findings to the properties of the howardite eucrite diogenite meteorites surface lava flows on vesta would commonly have had widths ranging from a few hundred meters to a few kilometers and lengths lying between a few kilometers and at least several tens of kilometers flow thicknesses would have occupied a much narrower range lying between about 5 and 20 m these thicknesses imply cooling rates and plagioclase crystal growth rates which are extremely similar to those measured in the eucrite meteorites intrusions may have formed at very shallow depths as cooling dikes failed to erupt their contents completely to the surface or at the base of the crust where rising magmas would have been neutrally buoyant as the density structure of vesta s crust evolved deep intrusions would have had lateral extents up to 30 km and thicknesses up to 3 m shallow intrusions would have had vertical extents less than 10 km and widths of 1 m none of these intrusions and surface flows would have been thick enough or have formed frequently enough at a given location to have caused extensive thermal alteration of earlier eruptives lending support to the idea that burial and subsequent long term exposure to the rising geothermal gradient was the main mechanism of thermal metamorphism

mineralogy of marcia the youngest large crater of vesta character and distribution of pyroxenes and hydrated material abstract the young marcia crater on vesta displays several interesting features including pitted and smooth terrains exposure of relatively bright and dark material and enrichments of hydrated material in the ejecta several questions arise about the origin of marcia and of the dark material exogenic material vs volcanic or impact melts and the smooth and pitted terrains here we describe the results of the spectral and thermal analysis of the marcia crater with a particular effort to assess the composition of the different units identifying the presence of oh and its correlation with dark material detailed studies of the marcia crater wall smooth and floor units reveal a compositional rich terrain with small areas enriched in diogenites with respect to the general eucritic regolith dominating the equatorial region of vesta the signature of oh is particularly clear in the pitted floor dark material smooth unit and ejecta the pitted terrains beside their appearance also show thermal anomalies being colder with respect to the surrounding terrains the presence of oh concentrated in darker layers and the pitted crater floor indicate that the area where the marcia impact event occurred was rich in volatiles the results show how the relatively young impact events have modified the surface of vesta disrupting a layer of dark material once present on vesta s equatorial terrain and exposing fresh bright material rich in pyroxene

dawn completes its mission at 4 vesta the dawn mission was designed to test our hypothesis about the origin and evolution of the early solar system by visiting the largest differentiated basaltic asteroid 4 vesta believed to be a survivor from the earliest times of rocky body formation observations from orbit show that vesta is the parent body of the howardite eucrite diogenite meteorites vesta has an iron core and a eucritic diogenitic crust its surface is characterized by abundant impact craters but with no evident volcanic features it has two ancient impact basins in the southern hemisphere that are associated with circum planetary troughs the northern hemisphere is the more heavily cratered and contains the oldest terrains the surface of vesta is diverse with north south and east west dichotomies in the eucrite to diogenite ratio its surface contains both very bright and very dark material and its color varies strongly from region to region both the mineralogical and the elemental compositions agree with that expected for the hed parent body significant oh or h may be present in the upper crust and the presence of pits in fresh craters is consistent with the devolatilization of the surface after a collision either brought to or tapped a source of water on vesta the presence of dark material on the surface of vesta suggests efficient transport pathways for organic material and the mixing of the dark material with the more pristine pyroxene explains the varying albedo across the surface vesta has proven to be a reliable witness to the formation of the solar system

submarine landslide identified in md179 cores off joetsu area eastern margin of the sea of japan abstract gas hydrate is exposed on the sea floor and is buried in shallow sediments in the off joetsu area at the eastern margin of the sea of japan sediment cores recovered from topographic highs of the joetsu knoll and umitaka spur show pockmarks and mounds formed by gas hydrate dissociation but those from the un named ridge have no such topographic features all topographic highs and pockmarks mainly comprise bioturbated layers interbedded with thinly laminated tl layers which are common sea of japan sediments recovered sediments are however mostly disturbed by submarine landslides showing tilted horizons faults slump folds and breccia except that from the un named ridge the timing of events is well constrained by identification of the number of tl layers in some sediment cores landslides occurred both during the cold glacial period of the late mis3 to the last glacial maximum lgm and during the warm interglacial period of the post lgm all were caused by the explosive rise of gas hydrate formed at very shallow depths of the sea bottom by the supply of gas from the depth of the gas hydrate stability zone through gas chimney passages developed under the pockmarks seismic activity demands consideration as a factor because the off joetsu area is tectonically active

the geology of the marcia quadrangle of asteroid vesta assessing the effects of large young craters abstract we used dawn spacecraft data to identify and delineate geological units and landforms in the marcia quadrangle of vesta as a means to assess the role of the large relatively young impact craters marcia 63 km diam and calpurnia 53 km diam and their surrounding ejecta field on the local geology we also investigated a local topographic high with a dark rayed crater named aricia tholus and the impact crater octavia that is surrounded by a distinctive diffuse mantle crater counts and stratigraphic relations suggest that marcia is the youngest large crater on vesta in which a putative impact melt on the crater floor ranges in age between 40 and 60 ma depending upon choice of chronology system and marcia s ejecta blanket ranges in age between 120 and 390 ma depending upon choice of chronology system we interpret the geologic units in and around marcia crater to mark a major vestan time stratigraphic event and that the marcia formation is one of the geologically youngest formations on vesta marcia crater reveals pristine bright and dark material in its walls and smooth and pitted terrains on its floor the smooth unit we interpret as evidence of flow of impact melts and for the pitted terrain release of volatiles during or after the impact process the distinctive dark ejecta surrounding craters marcia and calpurnia is enriched in oh or h bearing phases and has a variable morphology suggestive of a complex mixture of impact ejecta and impact melts including dark materials possibly derived from carbonaceous chondrite rich material aricia tholus which was originally interpreted as a putative vestan volcanic edifice based on lower resolution observations appears to be a fragment of an ancient impact basin rim topped by a dark rayed impact crater octavia crater has a cratering model formation age of 280 990 ma based on counts of its ejecta field depending upon choice of chronology system and its ejecta field is the second oldest unit in this quadrangle the relatively young craters and their related ejecta materials in this quadrangle are in stark contrast to the surrounding heavily cratered units that are related to the billion years old or older rheasilvia and veneneia impact basins and vesta s ancient crust preserved on vestalia terra

introduction the geologic mapping of vesta the purpose of this paper is to introduce the geologic mapping of vesta special issue section of icarus which includes several papers containing geologic maps of the surface of vesta made to support data analysis conducted by the dawn science team during the vesta encounter july 2011 september 2012 in this paper we briefly discuss pre dawn knowledge of vesta provide the goals of our geologic mapping campaign discuss the methodologies and materials used for geologic mapping review the global geologic context of vesta discuss the challenges of mapping the geology of vesta as a small airless body and describe the content of the papers in this special issue section we conclude with a discussion of lessons learned from our quadrangle based mapping effort and provide recommendations for conducting mapping campaigns as part of planetary spacecraft nominal missions

grosvenor mountains 95 howardite pairing group insights into the surface regolith of asteroid 4 vesta regolithic howardites are analogs for the surface materials of asteroid 4 vesta recently mapped by the dawn spacecraft rigorously evaluating pairing of howardites recovered in 1995 in the grosvenor mountains gro 95 antarctica enables an examination of a larger more representative regolith sample previous work on two of the howardites studied here concluded that gro 95602 and gro 95535 are solar wind rich surface regolith samples and that they are not paired with each other leading to uncertainty regarding pairing relationships between the other gro 95 howardites based on petrology cosmic ray exposure history and terrestrial age four gro 95 howardites are paired the paired howardites gro 95534 95535 95574 95581 were from a meteoroid with radius of 10 15 cm a preatmospheric size comparable to that of kapoeta the largest known regolithic howardite the paired gro 95 howardites contain clasts of at least 18 separate hed lithologies providing evidence they were assembled from diverse source materials the total eucrite diogenite mixing ratio ratio of all eucrite lithologies to all diogenite lithologies in the paired gro 95 howardites is 2 1 petrographically determined basaltic eucrite cumulate eucrite ratios in regolithic howardites studied here and previously vary more widely than total eucrite diogenite ratios relative to eucritic pyroxene plagioclase is depleted in these howardites which provides evidence that plagioclase is preferentially comminuted in the vestan regolith the extent of plagioclase depletion could be an indicator of regolith maturity

spectroscopic characterization of mineralogy and its diversity across vesta the mineralogy of vesta based on data obtained by the dawn spacecraft s visible and infrared spectrometer is consistent with howardite eucrite diogenite meteorites there are considerable regional and local variations across the asteroid spectrally distinct regions include the south polar rheasilvia basin which displays a higher diogenitic component and equatorial regions which show a higher eucritic component the lithologic distribution indicates a deeper diogenitic crust exposed after excavation by the impact that formed rheasilvia and an upper eucritic crust evidence for mineralogical stratigraphic layering is observed on crater walls and in ejecta this is broadly consistent with magma ocean models but spectral variability highlights local variations which suggests that the crust can be a complex assemblage of eucritic basalts and pyroxene cumulates overall vesta mineralogy indicates a complex magmatic evolution that led to a differentiated crust and mantle

hydraulic conditions in experimental rill confluences and scour in erodible soils 1 few studies have examined processes active within rill networks or the effect of confluence geometry on rill sediment flux and it is not clear if observations from river confluences also apply at rill scale laboratory experiments were carried out in artificial rectangular rill channels with fixed and erodible beds to identify the effects of confluence geometry on hydraulic conditions and scour patterns symmetrical and asymmetrical confluences with angles from 19 to 90 were used hydraulic changes in the confluence zone in fixed bed experiments included decreased flow velocity increased shear velocity transition from supercritical to subcritical and from transitional to turbulent flow bed scour in the confluence zone resulted generally increasing with confluence angle but a more important influence was junction symmetry or asymmetry symmetrical confluences produced a symmetrical scour pattern mirroring the original channels but in asymmetrical confluences scour was more complex evolving to a symmetrical pattern with confluence angles higher than the original system results are consistent with channel evolution to an optimally branched system controlled by minimum power criteria but validation requires testing with more precise velocity measurement

elemental mapping by dawn reveals exogenic h in vesta s regolith using dawn s gamma ray and neutron detector we tested models of vesta s evolution based on studies of howardite eucrite and diogenite hed meteorites global fe o and fe si ratios are consistent with hed compositions neutron measurements confirm that a thick diogenitic lower crust is exposed in the rheasilvia basin which is consistent with global magmatic differentiation vesta s regolith contains substantial amounts of hydrogen the highest hydrogen concentrations coincide with older low albedo regions near the equator where water ice is unstable the young rheasilvia basin contains the lowest concentrations these observations are consistent with gradual accumulation of hydrogen by infall of carbonaceous chondrites observed as clasts in some howardites and subsequent removal or burial of this material by large impacts

olivine on vesta as exogenous contaminants brought by impacts constraints from modeling vesta s collisional history and from impact simulations the survival of asteroid vesta during the violent early history of the solar system is a pivotal constraint on theories of planetary formation particularly important from this perspective is the amount of olivine excavated from the vestan mantle by impacts as this constrains both the interior structure of vesta and the number of major impacts the asteroid suffered during its life the nasa dawn mission revealed that olivine is present on vesta s surface in limited quantities concentrated in small patches at a handful of sites not associated with the two large impact basins rheasilvia and veneneia the first detections were interpreted as the result of the excavation of endogenous olivine even if the depth at which the detected olivine originated was a matter of debate later works raised instead the possibility that the olivine had an exogenous origin based on the geologic and spectral features of the deposits in this work we quantitatively explore the proposed scenario of a exogenous origin for the detected vestan olivine to investigate whether its presence on vesta can be explained as a natural outcome of the collisional history of the asteroid over the last one or more billion years to perform this study we took advantage of the impact contamination model previously developed to study the origin and amount of dark and hydrated materials observed by dawn on vesta a model we updated by performing dedicated hydrocode impact simulations we show that the exogenous delivery of olivine by the same impacts that shaped the vestan surface can offer a viable explanation for the currently identified olivine rich sites without violating the constraint posed by the lack of global olivine signatures on vesta our results indicate that no mantle excavation is in principle required to explain the observations of the dawn mission and support the idea that the vestan crust could be thicker than indicated by simple geochemical models based on the howardite eucrite diogenite family of meteorites

predictions for impactor contamination on ceres based on hypervelocity impact experiments new experiments predict that ceres should be extensively contaminated with meteoritic debris derived from the asteroid belt all types of impactors likely contribute to the contamination ceres may accrete debris more efficiently if it is ice rich because of enhanced projectile survival and retention in porous ice targets experiments indicate that if a silicate regolith lag protects subsurface ice then some of the projectile should be injected into the regolith during high angle impacts thereby hiding part of the projectile component from view if impacts excavate ice sublimation will gradually concentrate projectile relics into a surficial lag in contrast if the near surface lacks ice then accreted meteoritic debris should be distributed throughout a vertically mixed regolith high resolution images may reveal pristine projectile relics lining some crater floors moreover we predict that the surface of ceres is not exclusively endogenic and may be dominated by delivered exogenic debris

reflectance properties and hydrated material distribution on vesta global investigation of variations and their relationship using improved calibration of dawn vir mapping spectrometer abstract vesta s surface albedo variations and hydrated material content share similar spatial distribution this observation is consistent with carbonaceous chondrite meteorites as a likely source material for dark surface units observed by the dawn spacecraft as presented by numerous publications while these deposits have been studied extensively by analysis of data from the framing camera fc and the visible and infrared spectrometer vir we performed a new analysis based on an improved calibration of vir first we identified instrument and calibration artifacts and we therefore developed corrections of the vir flat field and response function then we developed a photometric correction for vesta based on the lunar model by shkuratov et al shkuratov yu g et al 1999 icarus 141 132 155 http dx doi org 10 1006 icar 1999 6154 and a semi analytical inversion of the photometric parameters this photometric model combines minimization of the scattering effects due to the topography a disk function and variations of multiple scattering with phase angle the phase function caused by microscopic physical properties of the regolith the improved calibration and photometric correction enable more accurate analysis of the spectral properties of vesta s surface material especially the reflectance at 1 4 m and the 2 8 m hydroxyl absorption band depth we produced global and quadrangle maps that are used as a common dataset for this icarus special issue on vesta s surface composition the joint interpretation of both the 1 4 m reflectance and the 2 8 m absorption band depth reveals unusual spectral properties for a number of impact craters and ejecta compared to the rest of vesta an area including the bellicia arruntia and pomponia craters where olivine might be present has relatively high reflectance and a strong hydroxyl absorption band another area in the vicinity of capparonia crater has a high content of hydrated materials although with moderate reflectance and typical pyroxene rich composition ejecta blankets west of oppia crater have a spectral behavior similar to capparonia except for the wider and more complex shape of the hydroxyl absorption band on the other hand some low hydrated areas associated to crater floors and ejecta have higher reflectance and steeper spectral slope than most low hydrated terrains vesta a broad lane that extends from rheasilvia rim at matronalia rupes to the northern regions hosts little to no hydrated materials and exhibits a moderate spectral slope similar to rheasilvia s basin floor these properties reinforce the hypothesis that the lane is composed of ejecta from rheasilvia as indicated by the distribution of pyroxene compositions by previous results from dawn a few small and fresh craters exhibit an association between low reflectance little to no hydrated materials and a strong positive spectral slope suggesting optical effects by opaque coatings as opposed to carbonaceous chondrite deposits and possible coarser grains

geomorphological evidence for transient water flow on vesta abstract vesta the second most massive asteroid has long been perceived as anhydrous recent studies suggesting the presence of hydrated minerals and past subsurface water have challenged this long standing perception yet direct geologic indications of water activity on vesta s surface were unexpected herein we show evidence that transient water flowed on the surface in a debris flow like process and left distinctive geomorphologic features based on detailed analysis of highest resolution 20 m pixel images obtained by the dawn spacecraft we identify a class of locally occurring interconnected and curvilinear gully networks on the walls of young

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

dawn the vesta hed connection and the geologic context for eucrites diogenites and howardites the dawn mission has provided new evidence strengthening the identification of asteroid vesta as the parent body of the howardite eucrite and diogenite hed meteorites the evidence includes vesta s petrologic complexity detailed spectroscopic characteristics unique space weathering diagnostic geochemical abundances and neutron absorption characteristics chronology of surface units and impact history occurrence of exogenous carbonaceous chondritic materials in the regolith and dimensions of the core all of which are consistent with hed observations and constraints global mapping of the distributions of hed lithologies by dawn cameras and spectrometers provides the missing geologic context for these meteorites thereby allowing tests of petrogenetic models and increasing their scientific value

late quaternary climates of east asia deduced from the total organic carbon contents of cored sediments md179 3304 3312 off joetsu city japan sea abstract total organic carbon toc and total nitrogen tn concentrations are analyzed with high temporal resolution ca 100 years for cores md179 3304 and md179 3312 taken from the japan sea off joetsu city the temporal changes in toc and tn concentrations vary quasi regularly in similar patterns the age models are formed on the basis of the dates of 14c dating marker tephra beds tl layers and marine isotope events with depth toc concentration is high in mis 1 and 5 low in mis 2 and 4 and slightly elevated in mis 3 with frequent short fluctuations this general trend is very similar to lr04 curve except for the reduced dominance of toc around the mis 5 5 substage as shown typically in mis 3 there are many peaks of toc in a short interval the details of these toc peaks can be correlated with the warm interstadials of the greenland ice core we can identify a sawtooth like decreasing trend of toc in mis 3 in contrast the decreasing trend of 18o in the ice core corresponds to an increasing trend of toc in mis 5 the most plausible explanation for the correlation of climate changes between east asia and the north atlantic is oscillation of the arctic polar front through time the detailed correspondence of toc concentrations of the japan sea sediments to other common paleoclimate proxies means that the toc concentrations of these sediments is an excellent paleoclimate record in far east asia although the genetic relationship between air temperature and biological productivity in the japan sea is as yet unknown

global photometric properties of asteroid 4 vesta observed with dawn framing camera abstract dawn spacecraft orbited vesta for more than one year and collected a huge volume of multispectral high resolution data in the visible wavelengths with the framing camera we present a detailed disk integrated and disk resolved photometric analysis using the framing camera images with the minnaert model and the hapke model and report our results about the global photometric properties of vesta the photometric properties of vesta show weak or no dependence on wavelengths except for the albedo at 554 nm the global average geometric albedo of vesta is 0 38 0 04 and the bond albedo range is 0 20 0 02 the bolometric bond albedo is 0 18 0 01 the phase function of vesta is similar to those of s type asteroids vesta s surface shows a single peaked albedo distribution with a full width half max 17 relative to the global average this width is much smaller than the full range of albedos from 0 55 to 2 global average in localized bright and dark areas of a few tens of km in sizes and is probably a consequence of significant regolith mixing on the global scale rheasilvia basin is 10 brighter than the global average the phase reddening of vesta measured from dawn framing camera images is comparable or slightly stronger than that of eros as measured by the near earth asteroid rendezvous mission but weaker than previous measurements based on ground based observations of vesta and laboratory measurements of hed meteorites the photometric behaviors of vesta are best described by the hapke model and the akimov disk function when compared with the minnaert model lommel seeliger model and lommel seeliger lambertian model the traditional approach for photometric correction is validated for vesta for 99 of its surface where reflectance is within 30 of global average

the fate of pyroclasts produced in explosive eruptions on the asteroid 4 vesta we evaluate the consequences of explosive activity having taken place during volcanic eruptions on the differentiated asteroid 4 vesta which is the likely parent body of the howardite eucrite diogenite hed meteorites for a wide range of magma volatile contents we calculate the eruption speeds and subsequent trajectories of the pyroclastic magma droplets produced by considering the size distribution and eruption speeds of the droplets and the mass fluxes at which they are ejected we show that under all realistic circumstances the droplets will have formed lava fountains that were extremely optically dense as a result virtually all of the droplets will have reached the surface having suffered a negligible amount of radiative cooling and will have coalesced into lava ponds feeding lava flows typically 1 of the pyroclasts will have undergone enough cooling to allow them to accumulate into a recognizable fall deposit consisting of unwelded or partly welded volcanic glass beads this result is consistent with the apparent absence of identifiable pyroclastic material in the hed and other types of differentiated meteorites

mineralogical and spectral analysis of vesta s gegania and lucaria quadrangles and comparative analysis of their key features abstract this work is aimed at developing and interpreting infrared albedo pyroxene and oh band depths and pyroxene band center maps of vesta s gegania and lucaria quadrangles obtained from data provided by the visible and infrared vir mapper spectrometer on board nasa s dawn spacecraft the gegania and lucaria quadrangles span latitudes from 22 s to 22 n and longitudes from 0 e to 144 e the mineralogical and spectral maps identify two large scale units on this area of vesta which extend eastwards and westward of about 60 e respectively the two regions are not associated to large scale geological units which have a latitudinal distribution rather than longitudinal but are defined by different contents of carbonaceous chondrites cc the eastern region poor in ccs is brighter and oh depleted whereas the western one rich in ccs is darker and oh enriched a detailed analysis of the small scale units in these quadrangles is also performed almost all the units show the typical correspondence between high albedo deep pyroxene bands short band centers and absence of oh and vice versa only a few exceptions occur such as the ejecta from the aelia crater where dark and bright materials are intimately mixed the most characteristic features of these quadrangles are the equatorial troughs and the lucaria tholus the equatorial troughs consist of graben i e a depression limited by two conjugate faults the graben do not present their own spectral signatures but spectral parameters similar to their surroundings in agreement to their structural origin this is observed also in graben outside the gegania and lucaria quadrangles however it is possible to observe other structural features such as tectonic grooves characterized by a changing composition and hence an albedo variation this result is confirmed not only by mineralogical maps of vesta but also by analyzing the virtis rosetta observations of lutetia the albedo change is instead a typical behavior of geomorphic grooves finally ridges are characterized by a bluer color and in some cases shorter band centers than their surroundings suggesting that they are composed of fresher materials we also performed a comparative analysis between the three tholi of vesta i e lucaria which gives the name to its quadrangle aricia in the marcia quadrangle and brumalia numisia quadrangle whereas brumalia tholus is a young magmatic intrusion the absence of diogenites the low albedo and the orientation of aricia and lucaria tholi suggest that they are older features which are covered by dark materials and therefore experienced a different geological history than brumalia

sediment fabrics oxygenation history and circulation modes of japan sea during the late quaternary abstract the quaternary hemipelagic sediments of the japan sea are characterized by centimeter to decimeter scale alternations of heavily bioturbated organic poor light layers and finely laminated organic rich dark layers these dark and light layers which can be correlated throughout the deeper part of the basin are considered to reflect changes in bottom water oxygenation however depositional mechanisms responsible for individual dark layers and causes of oxygen depletion are not fully understood two possible settings for deposition of organic rich dark layers are recognized one is a stratified ocean like the black sea where limited vertical advection results in euxinic conditions in the deeper parts of the basin the other is an upwelling region like the arabian sea where the oxygen minimum zone is intensified by enhanced nutrient upwelling and surface productivity in this study fabrics of hemipelagic sediments deposited in the japan sea during the last 160 ka were studied in three cores collected from different latitudes and water depths fabrics were classified into 4 classes based on corresponding bottom water oxygenation level five dark layer types were defined based on the distribution patterns of sediment fabric classes within each dark layer comparison of dark layer types at shallower and deeper sites in a chronologic framework provided evidence for five different modes of deep water circulation these circulation modes which reflect relative intensities of upwelling and density stratification appear to be related to global sea level changes as well as climate impact on the nature of water influx through the tsushima strait

the sextilia region on asteroid 4vesta stratigraphy and variegation abstract mapping vesta surface composition in the sextilia region offers the unique possibility to investigate stratigraphic relationship of the surface compounds throughout the transition from rheasilvia vesta s prominent impact basin to vesta s northern equatorial region the vir data point to an upper eucrite dominated layer overlaying extended deposits of diogenite in the subsurface which reaches the surface at matronalia rupes the uplifted rim of the rheasilvia impact structure the dominance of diogenite in matronalia rupes suggests the existence of an extended diogenite rich layer and supports the magma ocean model as the most plausible formation model for vesta s interior local enrichment of diogenite outside of the rheasilvia impact basin are interpreted as outcrops of diogenite dominated breccia excavated during the rheasilvia impact event and re excavated by more recent impacts on the contrary the asymmetry in the distribution of diogenite rich outcrops in the norther parts i e the depletion of these deposits in the veneneia region is at odds with the equally distributed plutonic intrusions of diogenite rich material as proposed in the serial magmatism model but could be explained by an uneven distribution of its ejecta on vesta s surface due to an oblique rheasilvia impact

paleoceanographic changes of surface and deep water based on oxygen and carbon isotope records during the last 130 kyr identified in md179 cores off joetsu japan sea abstract we reconstructed the paleoenvironmental history of surface and deep water over the last 130 kyr from oxygen and carbon isotope ratios of planktonic and benthic foraminifera in two cores md179 3312 and md179 3304 from the joetsu basin eastern margin of the japan sea our data showed that paleoceanographic changes such as influx of surface currents and vertical circulation were associated with global glacial interglacial sea level change surface water conditions were influenced by the influx of tsushima current east china sea coastal or off shore waters through the tsushima strait during interglacial or interstadial stages and strongly affected by freshwater input during the glacial maximum during interglacial maximums such as marine isotope stages 1 and 5e development of well oxygenated bottom water was indicated a density stratified ocean with weak ventilation was inferred from the isotopic records of benthic foraminifera during the last glacial maximum local negative excursions in carbon isotopes during deglacial or interglacial periods may suggest the dissolution of gas hydrates or methane seep activities

mineralogy of carbonaceous chondrite clasts in hed achondrites and the moon the majority of the carbonaceous chondrite clasts found in howardites eucrites and diogenites are cm2 material a lesser proportion is cr2 material and other rare types are present a single clast that was found on the moon and called the bench crater meteorite is apparently shocked cm1 material the cm2 clasts are matrix supported mixtures of olivine pyroxene phyllosilicate sulfide bearing aggregates loose olivines and pyroxenes sulfides carbonates and sinuous spinel phyllosilicate diopside calcium aluminum rich inclusions cais magnetite and metal are rare some aggregates have fine grained rims of material resembling matrix the opaque fine grained matrix consists predominantly of serpentine of extremely variable composition and sulfides tochilinite is occasionally present the trace element data for one jodzie clast from this study and the average of similar clasts from kapoeta support a cm classification volatiles are depleted relative to ci and enriched relative to cr material the cr2 clasts are found in small numbers in only four howardites bholghati jodzie kapoeta and y793497 petrographically they are matrix supported mixtures of olivine aggregates sometimes containing sulfides loose olivines pyrrhotite pentlandite low ca pyroxene minor hedenbergite rare kamacite rare and only found within olivine ca carbonates and abundant magnetite framboids and plaquets phyllosilicates are fine grained and largely confined to matrix they are mixtures of serpentine and saponite the matrix of cr2 clasts also contains pyrrhotite pentlandite chromite and a significant fraction of poorly crystalline material with the same bulk composition as matrix phyllosilicate there is evidence of heating in a substantial number of clasts both cm2 and cr2 including 1 corrugated serpentine flakes 2 pseudomorphs of anhydrous ferromagnesian material after flaky phyllosilicates and 3 hedenbergite rims on calcite while the timing of the hedenbergite rims is debatable the destruction of phyllosilicates clearly occurred at a late stage plausibly during impact onto the hed asteroid s and moon and required peak heating temperatures on the order of 400 c we note that in general cm2 material was the most common carbonaceous chondrite lithology impacting the hed asteroids with howardites and eucrites taken together as it is for the earth today a total of 61 out of 75 carbonaceous chondrite clasts from hed meteorites belong to the cm clan petrologic grade 2 this is also supported by published siderophile and volatile element data on howardites eucrites and diogenites that are taken to indicate that cm like materials were the most common impactors on the hed asteroid s the ratio of cr cm clasts in hed asteroids is essentially the same as for modern falls at earth this may indicate that the ratio of disaggregated cm2 to cr2 asteroidal material has been approximately constant through the history of the solar system finally our results are also compatible with type 2 carbonaceous chondrites being equivalent to or from the same source as the material that originally accreted to form the hed asteroid

composition and mineralogy of dark material units on vesta vesta is the asteroid with the largest albedo variation among the known rocky solar system objects and shows a widespread occurrence of dark material dm and bright material bm units in the first observation phases by the dawn spacecraft two main extensions of low albedo areas were identified on vesta and found to be closely correlated with carbonaceous oh rich material in this work we use the hyperspectral data provided by the vir dawn imaging spectrometer onboard dawn to detect and analyze individual well defined dark material units we define dm units assuming a relative criterion i e reflectance lower than the surroundings by coupling visible and infrared images of the same area we are able to select real dark material units discarding false detections created by shadowing effects a detailed final catalogue of 123 dark units is presented containing the geographical parameters and the main spectral characteristics for each unit independently of the geological context of the dark units all dms show similar spectral properties dominated by the pyroxene absorption features as is the average spectrum of vesta this finding suggests a similar composition with the presence of darkening agents that also weaken pyroxene band depths the majority 90 of the dm units shows a positive correlation between low albedo and an oh band centered at 2 8 lm confirming the hypothesis that the darkening agents are carbonaceous chondrites probably delivered by low velocity impacts of primitive asteroids a comparison with laboratory spectra allows us to better constrain the size and the composition of the darkening agents these dm areas seem to be made of eucritic material the regolith grain size seems to be nearly constant around an average value of 25 lm and is quite homogenous at least in the first hundreds of meters beneath the vesta surface suggesting similar processing mechanisms for both dm and bm

delivering a projectile component to the vestan regolith abstract dark material on vesta may consist of carbonaceous chondrite like material delivered by impact events this study uses hypervelocity impact experiments to assess the viability of the impact delivery hypothesis experiments reveal that impact events deliver significant fractions of the projectile to the target during impacts at average vestan speeds hence dark material can plausibly be delivered to vesta by impacts with the projectile component accumulating in the regolith with time projectile retention is sensitive to impact angle ranging from 7 for 30 impacts measured from horizontal to 72 for vertical impacts averaged over the probability distribution of impact angles 17 of the projectile s mass remains in or near the crater projectile contaminated breccias largely remain inside the crater for vertical impacts in oblique impacts projectile contaminated pieces concentrate downrange beyond the crater rim based on experiments projectile delivery is expected for typical vestan impact conditions not only for extraordinary events such as low probability and very low speed e g

vesta s mineralogical composition as revealed by the visible and infrared spectrometer on dawn the dawn spacecraft mission has provided extensive new and detailed data on vesta that confirm and strengthen the vesta howardite eucrite diogenite hed meteorite link and the concept that vesta is differentiated as derived from earlier telescopic observations here we present results derived by newly calibrated spectra of vesta the comparison between data from the dawn imaging spectrometer vir and the different class of hed meteorites shows that average spectrum of vesta resembles howardite spectra nevertheless the vesta spectra at high spatial resolution reveal variations in the distribution of hed like mineralogies on the asteroid the data have been used to derive hed distribution on vesta reported in ammannito et al 2013 and to compute the average vestan spectra of the different hed lithologies reported here the spectra indicate that not only are all the different hed lithologies present on vesta but also carbonaceous chondritic material which constitutes the most abundant inclusion type found in howardites is widespread however the hydration feature used to identify carbonaceous chondrite material varies significantly on vesta revealing different band shapes the characteristic of these hydration features cannot be explained solely by infalling of carbonaceous chondrite meteorites and other possible origins must be considered the relative proportion of heds on vesta s surface is computed and results show that most of the vestan surface is compatible with eucrite rich howardites and or cumulate or polymict eucrites a very small percentage of surface is covered by diogenite and basaltic eucrite terrains are relatively few compared with the abundance of basaltic eucrites in the hed suite the largest abundance of diogenitic material is found in the rheasilvia region a deep basin where it clearly occurs below a basaltic upper crust however diogenite is also found elsewhere although the depth to diogenite is consistent with one magma ocean model its lateral extent is not well constrained

geologic mapping of vesta from 1994 hubble space telescope images we utilize the 56 images of asteroid 4 vesta obtained through four mineralogically diagnostic filters by the hubble space telescope zellneret al 1997 icarus to construct a geologic map vesta s surface is found to be geologically diverse and to be dichotomous at a hemispheric scale the eastern hemisphere longitude definition from thomaset al 1997 icarus is dominated by units interpreted to be impact excavated plutonic material composed of magnesium rich and calcium poor pyroxene the mineralogy of this region is most analogous to diogenite meteorites several eastern hemisphere units which have the deepest and broadest 1 m absorption bands may contain a substantial olivine component the locations of these units are consistent with a previous map based on rotationally resolved groundbased spectroscopy gaffey 1997 icarus the western hemisphere is dominated by units interpreted to consist of a single component of iron rich and relatively calcium rich pyroxene analogous to surface basalts such as eucrite meteorites we investigate the spectral properties of 20 representative surface regions and find a correlation between the 1 m absorption band depth and albedo the units with lower albedos have shallower band depths such a relation could arise from differences in lithologies differences in surface particle sizes or from a weathering effect which decreases albedo and band depth over time because of vesta s geologic diversity and hemispheric dichotomy it is apparent that any major impact events such as those possibly related to the formation of the vesta family binzel and xu 1993 science260 186 191 did not globally resurface the planet the spectral evidence for remnants of a basaltic crust implies that the oldest units on the surface date back to the time of their emplacement most likely 4 5 byr ago if a weathering process exists which alters the albedo then the lowest albedo units such as the feature with the proposed name olbers most likely represent remnants of vesta s ancient basaltic crust

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

land ocean linkages over orbital and millennial timescales recorded in late quaternary sediments of the japan sea late quaternary sediments of the japan sea are characterized by centimeter to meter scale alternations of dark and light layers which are synchronous basinwide high resolution analyses of the sediments from ocean drilling program site 797 reveal that deposition of the meter scale alternations reflect variations in paleoceanographic conditions which were closely associated with glacio eustatic sea level changes through the modulation of the volume and character of the influx to the sea through the tsushima strait the centimeter to decimeter scale alternations reflect millennial scale variations which are possibly associated with dansgaard oeschger d o cycles with each dark layer appearing to correspond to an interstadial this variability is attributed to the development of a humid climate in central to eastern asia and the consequent increase in discharge from the huanghe and changjiang rivers during interstadials this caused expansion of the east china sea coastal water ecscw which penetrated more strongly into the japan sea the increased influence of the lower salinity nutrient enriched ecscw reduced deep water ventilation and enhanced the surface productivity leading to the development of anoxic bottom waters and deposition of the dark layers thus the centimeter to decimeter scale alternations of the dark and light layers record wet and dry cycles in central to eastern asia possibly associated with d o cycles

sea surface temperatures and the history of monsoon upwelling in the northwest arabian sea during the last 500 000 years abstract arabian sea sediments record changes in the upwelling system off arabia which is driven by the monsoon circulation system over the nw indian ocean in accordance with climate models and differing from other large upwelling areas of the tropical ocean a 500 000 yr record of productivity at odp site 723 shows consistently stronger upwelling during interglaciations than during glaciations sea surface temperatures ssts reconstructed from the alkenone unsaturation index uk 37 are high up to 27 c during interglaciations and low 22 24 c during glaciations indicating a glacial interglacial temperature change of 3 c in spite of the dampening effect of enhanced or weakened upwelling the increased productivity is attributed to stronger monsoon winds during interglacial times relative to glacial times whereas the difference in ssts must be unrelated to upwelling and to the summer monsoon intensity the winter ne monsoon was more effective in cooling the arabian sea during glaciations then it is now

the chronostratigraphy of protoplanet vesta in this paper we present a time stratigraphic scheme and geologic time scale for the protoplanet vesta based on global geologic mapping and other analyses of nasa dawn spacecraft data complemented by insights gained from laboratory studies of howardite eucrite diogenite hed meteorites and geophysical modeling on the basis of prominent impact structures and their associated deposits we propose a time scale for vesta that consists of four geologic time periods pre veneneian veneneian rheasilvian and marcian the pre veneneian period covers the time from the formation of vesta up to the veneneia impact event from 4 6 ga to 2 1 ga using the asteroid flux derived chronology system or from 4 6 ga to 3 7 ga under the lunar derived chronology system the veneneian period covers the time span between the veneneia and rheasilvia impact events from 2 1 to 1 ga asteroid flux derived chronology or from 3 7 to 3 5 ga lunar derived chronology respectively the rheasilvian period covers the time span between the rheasilvia and marcia impact events and the marcian period covers the time between the marcia impact event until the present the age of the marcia impact is still uncertain but our current best estimates from crater counts of the ejecta blanket suggest an age between 120 and 390 ma depending upon choice of chronology system used regardless the marcia impact represents the youngest major geologic event on vesta our proposed four period geologic time scale for vesta is to a first order comparable to those developed for other airless terrestrial bodies

detection of new olivine rich locations on vesta abstract the discovery of olivine on vesta s surface by the vir imaging spectrometer onboard the dawn space mission has forced us to reconsider our views of vestan petrogenetic models olivines were expected to be present in the interior of vesta in the mantle of a vertically layered body as invoked by the magma ocean models or at the base or within the mantle crust boundary as proposed by fractionation models olivines have been detected by vir dawn in two wide areas near arruntia and bellicia regions located in the northern hemisphere interestingly these olivine rich terrains are far from the rheasilvia and the more ancient veneneia basins which are expected to have excavated the crust down to reach the mantle in this work we present our attempts to identify other undetected olivine rich areas on vesta by using spectral parameters sensitive to olivine such as the band area ratio bar and other specific parameters created for the detection of olivines on mars forsterite fayalite and a generic olivine index as a preliminary step we calibrated these parameters by means of vis ir spectra of different hed meteorite samples behaviors versus sample grain size and albedo were analyzed and discussed we selected the bar and the forsterite index as the best parameters that can be used on vesta a cross correlation analysis has been applied in order to detect olivine signature on the vir hyperspectral cubes these detections have then been confirmed by an anti correlation analysis between the bar and one of the olivine parameters independent of the first method applied in agreement with the recent discovery arruntia and bellicia were found to be as the most olivine rich areas i e where the parameter values are strongest in addition we detected 6 new regions all but one located in the vesta north hemisphere this result confirms again that the old petrogenetic models cannot be straightforwardly applied to vesta and should be reshaped in the view of these new detections an alternative and very recent option can be represented by the model according to which surface eruption of material from the mantle including olivine can reach the surface of vesta

a global database and statistical analyses of 4 vesta craters abstract in this paper we present a global database of craters larger than 0 7 km in diameter on the surface of 4 vesta which we created based on a global mosaic of the dawn spacecraft s high altitude mapping orbit hamo images at a resolution of 60 m pixel and cross checked using the images from the low altitude mapping orbit lamo mission phase the method to produce the crater database consists of visual crater identification and mathematical shape determination to give precise measurements topographic corrections have also been considered by combining the digital elevation model dem data in this global survey we calculated the morphometric parameters of the craters which consist of diameter depth depth to diameter ratio ellipticity and azimuth of the major axis our results show that the craters on 4 vesta are very shallow with a mean depth to diameter ratio of 0 065 which is similar to that of the craters on 1 ceres and 25143 itokawa but lower than for craters on other solid bodies the results also show that the fractions of craters with an ellipticity greater than 1 1 or 1 2 are smaller than those of craters on the martian surface which is probably because few secondaries exist on the surface of 4 vesta in addition the azimuths of the major axis are almost uniformly distributed in different directions our globally consistent crater database has many potential applications for future studies such as geologic mapping and surface age dating

small fresh impact craters on asteroid 4 vesta a compositional and geological fingerprint small morphologically fresh impact craters 10 km in diameter on vesta s surface with a photometrically distinct ejecta blanket are expected to represent fresh surface material and thus provide the opportunity to study the composition of the unweathered surface dawn framing camera and visual and infrared spectrometer vir data reveal impact craters with bright dark and mixed i e partly bright and dark ejecta existing on vesta s surface which not only differ in the visible albedo from their surroundings but also in their composition differences in the composition are related to the visible albedo and or the geographic location of the impact craters bright ejecta only seen in the southern vestan hemisphere are dominated by howardite eucrite like material as expected for vesta s upper crust dark ejecta associated with dark impact craters are dominated by a strongly absorbing spectrally neutral compound supporting an origin from carbon rich impactors few impact craters of intermediate albedo in vesta s southern hemisphere contain material resembling diogenites which are expected to exist in the deeper parts of vesta s interior the geological settings suggest that the diogenite like material represents a part of a layer of diogenitic material surrounding the rheasilvia basin or local concentrations of diogenitic material as part of the ejecta excavated during the latter stage of the rheasilvia impact event the spectral differences between eucrite and diogenite dominated materials also could be verified due to spin forbidden absorptions in the visible spectral range which are known from laboratory spectra of pyroxenes but which have been identified in the vir spectra of vesta for the first time