Basaltic Asteroids Research Articles

Dynamical evolution of basaltic asteroids outside the Vesta family in the inner main belt

Context. Basaltic V-type asteroids are leftovers from the formation and evolution of differentiated planetesimals. They are thought to originate from mantles and crusts of multiple different parent bodies. Identifying the links between individual V-type asteroids and multiple planetesimals is challenging, especially in the inner part of the main asteroid belt, where the majority of V-type asteroids are expected to have originated from a single planetesimal, namely, (4) Vesta. Aims. In this work, we aim to trace the origin of a number of individual V-type asteroids from the inner part of the main asteroid belt. The main goal is to identify asteroids that may not be traced back to (4) Vesta and may therefore originate from other differentiated planetesimals. Methods. We performed a 2 Gyr backward numerical integration of the orbits of the selected V-type asteroids. For each asteroid, we used 1001 clones to map the effect of orbital uncertainties. In the integration, we use information on physical properties of the considered V-type asteroids such as pole orientation, rotational period, and thermal parameters. Results. The majority of the studied objects can be traced back to the Vesta family within 2 Gyr of integration. The number of objects of the low-inclination V-types did not reach the boundary of the Vesta family during the integration time. Two asteroids, namely, (3307) Athabasca and (17028) 1999 FJ5, do not show a dynamic link to (4) Vesta. Increasing the integration time for these objects leads to further separation from (4) Vesta. Conclusions. The majority of V-types in the inner main belt outside the Vesta family are clearly Vesta fugitives. Two objects, namely, (3307) Athabasca and (17028) 1999 FJ5, show no clear dynamical link to (4) Vesta. Together with (809) Lundia (from our previous work), these objects could represent the parent bodies of anomalous HED meteorites such as the Banbura Rockhole. Furthermore, some objects of the low-inclination population cannot be traced back to (4) Vesta within the 2 Gyr integration.

Spins and shapes of basaltic asteroids and the missing mantle problem

Basaltic V-type asteroids are common in the inner part of the Main Asteroid Belt and much less abundant in the mid and outer parts. They are of scientific interest because they sample crusts and mantles of theoretically plentiful differentiated planetesimals that existed in the Solar System four billion years ago. Some Solar System theories suggest that those objects formed in the terrestrial planet region and were then implanted in the main asteroid belt. In consequence, we should observe a large number of fragments of multiple differentiated planetesimals in the inner Main Belt. That region of the Asteroid Belt is filled with V-type fragments; however, they are difficult to tell apart from typical Vestoids and Vesta fugitives. In this work, we focus on physical and dynamical characterization of V-types in the inner Main-Belt and aim to reconcile those properties with the planetesimal formation and evolution theories.We conducted an observing campaign over the years 2013–2022 and obtained photometric observations of V-type asteroids located mostly outside the Vesta family at specific locations of the inner Main Belt (the so-called Cells I and II). The total number of partial dense photometric lightcurves obtained in this study was ∼ 2910. We were able to model ∼100 V-types. We further supplement those data with 133 spins of V-types from the DAMIT database and 237 objects derived from Gaia DR3 (Ďurech & Hanuš 2023). We found 78%±11% and 38%±13% retrograde rotators in Cell I and II, respectively. This statistic is remarkably consistent with the numerical simulations of the escape paths of Vesta fugitives that predict 81% retrograde rotators in Cell I and 40% in Cell II after the dynamical integration of 2 Gys. Based on our statistics we conclude that if there are non-Vestoids in the inner main belt, they are likely to be very few. This is consistent with the small fraction of anomalous HED meteorites in meteorite collections, small number of non-Vestoids in the middle and outer Main Belt and points to planetesimal formation location close to the Sun.

Spectral analysis of basaltic asteroids observed by the Gaia space mission

ABSTRACT There is a great deal of scientific interest in characterizing the basaltic asteroids (spectrally classified as V-types), as they are the key to understanding planetesimal formation and evolution in the early Solar system. These have long been recognized as parts of the crusts of fully differentiated planetesimals. Thus, their multiplicity, distribution, and physical characteristics are crucial for providing context for and constraining the theoretical evolution models of the Solar system. In this work, we perform spectral analysis with an extended data set of spectral measurements from the ESA Gaia mission Data Release 3, thus increasing the sample size of the analysed V-types by more than three times as compared to the literature. Using the data provided by Gaia, we identified ∼2000 possible V-type asteroids. About 350 of them successfully pass our data validation criteria. This sample includes 31 new V-type asteroids beyond 2.5 au and 6 in the Phocaea region. We confirm that the V-type asteroids in the middle and outer part of the main belt show distinct spectral properties compared to typical vestoids. In the inner main belt, we found a great diversity of spectral parameters among the V-types in all populations. Number of asteroids show band depths even greater than that of (1459) Magnya. Furthermore, some objects present 0.9 μm band-centres more than one standard deviation away from the typical value for vestoids. However since the DR3 band centres are often overestimated, those findings are to be confirmed. Overall our results indicate that the inner main belt may contain remnants of multiple differentiated planetesimals, not just (4) Vesta.

Spectral characterisation of 14 V-type candidate asteroids from the MOVIS catalogue

Most of the currently known basaltic (V-type) asteroids are believed to be past or present members of the Vesta dynamical family. The rising discoveries of V-type asteroids that are not linked to the Vesta family dynamically suggest that a number of major basaltic bodies may have been present during the early stages of the solar system. Using the near-infrared (NIR) colour data in the Moving Objects from VISTA Survey (MOVIS) catalogue, a list of 477 V-type candidates was compiled, with more than half of them outside the Vesta family. In this work, we aim to provide a spectral analysis of 14 V-type candidates of various dynamical types. The computed visible and NIR spectral parameters are used to investigate evidence of space-weathering or mineralogical differences from the expected basaltic composition. Based on the analysis of their visible spectra, we confirm 11 new V-type asteroids: six low-i asteroids – (3188) Jekabsons, (3331) Kvistaberg, (4693) Drummond, (7223) Dolgorukij, (9007) James Bond, and (29733) 1999 BA4; along with four inner-other asteroids – (5524) Lecacheux, (19983) 1990 DW, (51742) 2001 KE55, and (90023) 2003 BD13; as well as one fugitive – (2275) Cuitlahuac. Additionally, we analysed three peculiar outer main belt V-type candidates based on their visible + NIR spectra. We confirm the diogenite-like composition of (2452) Lyot. The spectrum of asteroid (7302) is not consistent with a basaltic composition and likely reflects an S-type body. The spectrum of (14390) 1990 QP10is similar to a V-type but it shows unique spectral features that suggest a peculiar composition. Overall, our results demonstrate the efficiency of the MOVIS catalogue in identifying V-type objects, with a success rate of over 85%. The identification of V-types in the inner main-belt is more likely due to the presence of the Vesta family and other nearby asteroids that had escaped from the family. In the middle and outer main belt, where the amount of data is more limited, the proportion of false positives increases.

Distribution and spectrophotometric classification of basaltic asteroids

ABSTRACTWe aim to determine the distribution of basaltic asteroids (classified as V-types) based on the spectrophotometric data reported in the MOVIS-C catalogue. A total of 782 asteroids were identified. The observations with all four filters (Y, J, H, Ks), available for 297 of these candidates, allow a reliable comparison with the laboratory data of howardite, eucrite, and diogenite meteorites. We found that the majority of the basaltic candidates (≈95${{\ \rm per\ cent}}$) are located in the inner main belt, while only 29 (≈4${{\ \rm per\ cent}}$) and 8 (≈1${{\ \rm per\ cent}}$) are located in the middle (MMB) and outer main belt (OMB), respectively. A fraction of ≈33${{\ \rm per\ cent}}$ from the V-type candidates is associated with the Vesta family (with respect to AstDyS). We also identified four MMB V-type candidates belonging to (15) Eunomia family, and another four low inclination ones corresponding to (135) Hertha. We report differences between the colour indices and albedo distributions of the V-type candidates located in the inner main belt compared to those from the MMB and OMB. These results support the hypothesis of a different origin for the basaltic asteroids with a semimajor axis beyond 2.5 au. Furthermore, lithological differences are present between the vestoids and the inner low inclination basaltic asteroids. The data allow us to estimate the unbiased distribution of basaltic asteroids across the main asteroid belt. We highlight that at least 80${{\ \rm per\ cent}}$ of the ejected basaltic material from (4) Vesta is missing or is not yet detected because it is fragmented in sizes smaller than 1 km.

Investigating magmatic processes in the early Solar System using the Cl isotopic systematics of eucrites

Generally, terrestrial rocks, martian and chondritic meteorites exhibit a relatively narrow range in bulk and apatite Cl isotope compositions, with δ37Cl (per mil deviation from standard mean ocean chloride) values between −5.6 and +3.8‰. Lunar rocks, however, have more variable bulk and apatite δ37Cl values, ranging from ∼−4 to +40‰. As the Howardite-Eucrite-Diogenite (HED) meteorites represent the largest suite of crustal and sub-crustal rocks available from a differentiated basaltic asteroid (4 Vesta), studying them for their volatiles may provide insights into planetary differentiation processes during the earliest Solar System history.Here the abundance and isotopic composition of Cl in apatite were determined for seven eucrites representing a broad range of textural and petrological characteristics. Apatite Cl abundances range from ∼25 to 4900 ppm and the δ37Cl values range from −3.98 to +39.2‰. Samples with lower apatite H2O contents were typically also enriched in 37Cl but no systematic correlation between δ37Cl and δD values was observed across samples. Modelled Rayleigh fractionation and a strong positive correlation between bulk δ66Zn and apatite δ37Cl support the hypothesis that Cl degassed as metal chlorides from eucritic magmas, in a hydrogen-poor environment. In the case of lunar samples, it has been noted that δ37Cl values of apatite positively correlate with bulk La/Yb ratio. Interestingly, most eucrites show a negative correlation with bulk La/Yb ratio. Recently, isotopically light Cl values have been suggested to record the primary solar nebular signature. If this is the case then 4 Vesta, which accreted rapidly and early in Solar System history, could also record this primary nebular signature corresponding to the lightest Cl values measured here. The significant variation in Cl isotope composition observed within the eucrites are likely related to degassing of metal chlorides.

Oxygen isotopes in HED meteorites and their constraints on parent asteroids

The howardite, eucrite and diogenite (HED) clan of meteorites are usually regarded as Vesta meteorites, but there is still serious controversy over whether Vesta is the only parent body for HEDs. Different numbers of HED parent asteroids have been proposed in previous studies of oxygen isotopes. The main controversy is whether the anomalous oxygen isotopic compositions in some HEDs are caused by factors such as terrestrial weathering, addition of exogenous material during brecciation, or a possible primary isotopic heterogeneity of Vesta. To readdress the questions of whether all HED meteorites are from the same parent body, or to constrain the possible number of multiple parent asteroids, the oxygen isotopic data of 166 HED meteorites from the literature are compiled and reviewed here. Among them, 146 HED meteorites have similar Δ17O values of −0.240 ± 0.020‰ (2σ), and the remaining 20 meteorites show oxygen isotopic anomalies (Δ17O values fall outside 3σ from the above mean). Fifteen HED meteorites have anomalous oxygen isotope compositions that cannot be accounted for by terrestrial weathering or the addition of exogenous material, while the oxygen isotope anomalies in the remaining 5 HEDs are caused by the above factors. Based on studies of a number of isotopic and trace element systems, HED meteorites should form from a magma ocean, thus their parent asteroid is highly likely to be homogeneous. This implies that the oxygen isotope variability of HEDs suggest multiple parent bodies for these meteorites, which is supported by arguments from astrophysical and other geochemical studies such as Zn and Cr. In summary, according to the Δ17O values and a number of other observations, we believe that HED meteorites most likely originate from at least 6 different basaltic asteroids.

Color study of asteroid families within the MOVIS catalog

The aim of this work is to study the compositional diversity of asteroid families based on their near-infrared colors, using the data within the MOVIS catalog. As of 2017, this catalog presents data for 53 436 asteroids observed in at least two near-infrared filters (Y,J,H, orKs). Among these asteroids, we find information for 6299 belonging to collisional families with bothY−JandJ−Kscolors defined. The work presented here complements the data from SDSS and NEOWISE, and allows a detailed description of the overall composition of asteroid families. We derived a near-infrared parameter, theML*, that allows us to distinguish between four generic compositions: two different primitive groups (P1 and P2), a rocky population, and basaltic asteroids. We conducted statistical tests comparing the families in the MOVIS catalog with the theoretical distributions derived from ourML*in order to classify them according to the above-mentioned groups. We also studied the background populations in order to check how similar they are to their associated families. Finally, we used this parameter in combination with NEOWISE and SDSS to check for possible bimodalities in the data. We found 43 families withML*err< 0.071 and with at least 8 asteroids observed: 5 classified as P1, 10 classified as P2, 19 families associated with the rocky population, and 9 families that were not linked to any of the previous populations. In these cases, we compared our samples with different combinations of these theoretical distributions to find the one that best fits the family data. We also show, using the data from MOVIS and NEOWISE, that the Bapistina family presents a two-cluster distribution in the near-infrared albedo vs.ML*parameter space that might be related to a common differentiated parent body. Finally, we show that the backgrounds we defined seem to be linked to their associated families.

Basalt or Not? Near-infrared Spectra, Surface Mineralogical Estimates, and Meteorite Analogs for 33 Vp-type Asteroids

Abstract Investigations of the main asteroid belt and efforts to constrain that population’s physical characteristics involve the daunting task of studying hundreds of thousands of small bodies. Taxonomic systems are routinely employed to study the large-scale nature of the asteroid belt because they utilize common observational parameters, but asteroid taxonomies only define broadly observable properties and are not compositionally diagnostic. This work builds upon the results of work by Hardersen et al., which has the goal of constraining the abundance and distribution of basaltic asteroids throughout the main asteroid belt. We report on the near-infrared (NIR: 0.7 to 2.5 μm) reflectance spectra, surface mineralogical characterizations, analysis of spectral band parameters, and meteorite analogs for 33 Vp asteroids. NIR reflectance spectroscopy is an effective remote sensing technique to detect most pyroxene group minerals, which are spectrally distinct with two very broad spectral absorptions at ∼0.9 and ∼1.9 μm. Combined with the results from Hardersen et al., we identify basaltic asteroids for ∼95% (39/41) of our inner-belt Vp sample, but only ∼25% (2/8) of the outer-belt Vp sample. Inner-belt basaltic asteroids are most likely associated with (4) Vesta and represent impact fragments ejected from previous collisions. Outer-belt Vp asteroids exhibit disparate spectral, mineralogical, and meteorite analog characteristics and likely originate from diverse parent bodies. The discovery of two additional likely basaltic asteroids provides additional evidence for an outer-belt basaltic asteroid population.

Basaltic material in the main belt: a tale of two (or more) parent bodies?

The majority of basaltic objects in the main belt are dynamically connected to Vesta, the largest differentiated asteroid known. Others, due to their current orbital parameters, cannot be easily dynamically linked to Vesta. This is particularly true for all the basaltic asteroids located beyond 2.5 au, where lies the 3:1 mean motion resonance with Jupiter. In order to investigate the presence of other V-type asteroids in the middle and outer main belt (MOVs) we started an observational campaign to spectroscopically characterize in the visible range MOV candidates. We observed 18 basaltic candidates from TNG and ESO - NTT between 2015 and 2016. We derived spectral parameters using the same approach adopted in our recent statistical analysis and we compared our data with orbital parameters to look for possible clusters of MOVs in the main belt, symptomatic for a new basaltic family. Our analysis seemed to point out that MOVs show different spectral parameters respect to other basaltic bodies in the main belt, which could account for a diverse mineralogy than Vesta; moreover, some of them belong to the Eos family, suggesting the possibility of another basaltic progenitor. This could have strong repercussions on the temperature gradient present in the early Solar System, and on our current understanding of differentiation processes.

REMOTE SENSING OBSERVATIONS AND NUMERICAL SIMULATION FOR MARTIAN LAYERED EJECTA CRATERS

Abstract. To understand past Martian climates, it is important to know the distribution and nature of water ice on Mars. Impact craters are widely used ubiquitous indicators for the presence of subsurface water or ice on Mars. Remote sensing observations and numerical simulation are powerful tools for investigating morphological and topographic features on planetary surfaces, and we can use the morphology of layered ejecta craters and hydrocode modeling to constrain possible layering and impact environments. The approach of this work consists of three stages：Firstly, the morphological characteristics of the Martian layered ejecta craters are performed based on Martian images and DEM data. Secondly, numerical modeling layered ejecta are performed through the hydrocode iSALE (impact-SALE). We present hydrocode modeling of impacts onto targets with a single icy layer within an otherwise uniform basalt crust to quantify the effects of subsurface H2O on observable layered ejecta morphologies. The model setup is based on a layered target made up of a regolithic layer (described by the basalt ANEOS), on top an ice layer (described by ANEOS equation of H2O ice), in turn on top of an underlying basaltic crust. The bolide is a 0.8 km diameter basaltic asteroid hitting the Martian surface vertically at a velocity of 12.8 km/s. Finally, the numerical results are compared with the MOLA DEM profile in order to analyze the formation mechanism of Martian layered ejecta craters. Our simulations suggest that the presence of an icy layer significantly modifies the cratering mechanics, and many of the unusual features of SLE craters may be explained by the presence of icy layers. Impact cratering on icy satellites is significantly affected by the presence of subsurface H2O.

The compositional diversity of non-Vesta basaltic asteroids

We present near-infrared (0.78–2.45 µm) reflectance spectra for nine middle and outer main belt (a > 2.5 AU) basaltic asteroids. Three of these objects are spectrally distinct from all classifications in the Bus-DeMeo system and could represent spectral end members in the existing taxonomy or be representatives of a new spectral type. The remainder of the sample are classified as V- or R-type. All of these asteroids are dynamically detached from the Vesta collisional family, but are too small to be intact differentiated parent bodies, implying that they originated from differentiated planetesimals which have since been destroyed or ejected from the solar system. The 1- and 2-µm band centers of all objects, determined using the Modified Gaussian Model (MGM), were compared to those of 47 Vestoids and fifteen HED meteorites of known composition. The HEDs enabled us to determine formulas relating Band 1 and Band 2 centers to pyroxene ferrosilite (Fs) compositions. Using these formulas we present the most comprehensive compositional analysis to date of middle and outer belt basaltic asteroids. We also conduct a careful error analysis of the MGM-derived band centers for implementation in future analyses. The six outer belt V- and R-type asteroids show more dispersion in parameter space than the Vestoids, reflecting greater compositional diversity than Vesta and its associated bodies. The objects analyzed have Fs numbers which are, on average, between five and ten molar percent lower than those of the Vestoids; however, identification and compositional analysis of additional outer belt basaltic asteroids would help to confirm or refute this result. Given the gradient in oxidation state which existed within the solar nebula, these results tentatively suggest that these objects formed at either a different time or location than 4 Vesta.

V-type candidates and Vesta family asteroids in the Moving Objects VISTA (MOVIS) catalogue

Basaltic asteroids (V-types) are believed to be fragments of large differentiated bodies. The majority of them are found in the inner part of the asteroid belt, and are current or past members of the Vesta family. Recently, some V-type asteroids have been discovered far from the Vesta family supporting the hypothesis of the presence of multiple basaltic asteroids in the early solar system. The discovery of basaltic asteroids in the outer belt challenged the models of the radial extent and the variability of the temperature distribution in the early solar system. We aim to identify new basaltic V-type asteroids using near-infrared colors of ~40000 asteroids observed by the VHS-VISTA survey and compiled in the MOVIS-C catalogue. We also want to study their near-infrared colors and to study the near-infrared color distribution of the Vesta dynamical family. We performed a search in the MOVIS-C catalogue of all the asteroids with (Y-J) and (J-Ks) in the range (Y-J) > 0.5 and (J-Ks) < 0.3, associated with V-type asteroids, and studied their color distribution. We have also analyzed the near-infrared color distribution of 273 asteroid members of the Vesta family and compared them with the albedo and visible colors from WISE and SDSS data. We determined the fraction of V-type asteroids in the family. We found 477 V-type candidates in MOVIS-C, 244 of them outside the Vesta dynamical family. We identified 19 V-type asteroids beyond the 3:1 mean motion resonance, 6 of them in the outer main belt, and 16 V-types in the inner main belt with proper inclination i_p < 3.0deg, well below the inclination of the Vesta family. We computed that ~85% of the members of the Vesta dynamical family are V-type asteroids, and only 1-2% are primitive class asteroids and unlikely members of the family. This work almost doubles the sample of basaltic asteroid candidates in regions outside the Vesta family.

V‐type near‐Earth asteroids: Dynamics, close encounters and impacts with terrestrial planets

BackgroundAsteroids colliding with planets vary in composition and taxonomical type. Among Near‐Earth Asteroids (NEAs) are the V‐types, basaltic asteroids that are classified via spectroscopic observations.Materials and Methodswe performed numerical simulations and statistical analysis of close encounters and impacts between V‐type NEAs and the terrestrial planets over the next 10 Myr. We study the probability of V‐ type NEAs colliding with Earth, Mars and Venus, as well as the Moon. We perform a correlational analysis of possible craters produced by V‐type NEAs, using available catalogs for terrestrial impact craters.ResultsThe results suggest that V‐type NEAs can have many close encounters below 1 LD and even some of them impacts with all the terrestrial planets, the Earth in particular. There are four candidate craters on Earth that were likely caused by V‐type NEAs.ConclusionAt least 70% of the V‐type NEAs can have close encounters with the terrestrial planets (and 58% with the Moon) . They can collide with all the terrestrial planets. In particular for the Earth the average rate is one every ∼12 Myr. The two craters with the highest probability of being generated by an impact with a basaltic impactor are: the Strangways crater (24 km diameter) in Australia and the Nicholson crater (12.5 km diameter) in Canada.

VESTOIDS, PART II: THE BASALTIC NATURE AND HED METEORITE ANALOGS FOR EIGHTVp-TYPE ASTEROIDS AND THEIR ASSOCIATIONS WITH (4) VESTA

Improving constraints on the abundance of basaltic asteroids in the main asteroid belt is necessary for better understanding the thermal and collisional environment in the early solar system, for more rigorously identifying the genetic family for (4) Vesta, for determining the effectiveness of Yarkovsky/YORP in dispersing asteroid families, and for better quantifying the population of basaltic asteroids in the outer main belt (a greater than 2.5 AU) that are likely unrelated to (4) Vesta. NIR spectral observations in this work were obtained for the Vp-type asteroids (2011) Veteraniya, (5875) Kuga, (8149) Ruff, (9147) Kourakuen, (9553) Colas, (15237) 1988 RL6, (31414) Rotaryusa, and (32940) 1995 UW4 during August and September 2014 utilizing the SpeX spectrograph at the NASA Infrared Telescope Facility (IRTF), Mauna Kea, Hawaii. Spectral band parameter (band centers, Band Area Ratios) and mineralogical analysis (pyroxene chemistry) for each average asteroid NIR reflectance spectrum suggests a howardite-eucrite-diogenite (HED) meteorite analog for each asteroid. (5875) Kuga is most closely associated with the eucrite meteorites, (31414) Rotaryusa is most closely associated with the diogenites, and the remaining other six asteroids are most closely associated with the howardite meteorites. Along with orbital locations in the inner main belt and in the vicinity of (4) Vesta, the existing evidence suggests that these eight Vp-type asteroids are also likely Vestoids.

Pole and shape of (1459) Magnya, the outer main belt basaltic asteroid

Pole and shape of (1459) Magnya, the outer main belt basaltic asteroid

Near infrared spectroscopy of HED meteorites: Effects of viewing geometry and compositional variations

The howardite, eucrite and diogenite (HED) meteorites are genetically related and represent the most voluminous group of achondrites. They are the closest analog materials to Vesta and V-type asteroids. Many of these meteorites were the focus of intense petrologic and visible to near infrared spectral studies. As ground-based and orbital observations of basaltic asteroids have increased, an improved understanding of HEDs is needed. For this study, we investigated 24 HED samples, mainly new finds from Northwest Africa (NWA). Visible to near infrared (up to 2.5μm) spectral measurements under varying illumination and observation geometries were acquired for 4 samples. Phase reddening and bluing (i.e., increase and decrease in spectral slope) is observed for the visible slope as phase angle increase. Monotonic phase reddening can occur for the near infrared slope as phase angle increase. Non-systematic changes with phase angle are found for the Band Area Ratio parameter. At phase angles higher than ∼60°, the decrease of reflectance and decrease of pyroxene bands depth are undistinguishable from admixture of low albedo material to HED samples. To assess the precision of empirical equations relating spectral properties and composition, the pyroxenes, feldspar, and olivine chemistry of the samples was determined. Using previous calibrations, systematic overestimations of the ferrosilite (Fs) and wollastonite (Wo) contents are found, especially in the 15–40 Fs range. To overcome such discrepancies, a new set of empirical equations is proposed. For an application of the new calibration, we selected two compositional end-member areas on Vesta on the basis of their iron content. For the iron-poor terrain we found an average pyroxene composition of Fs30Wo5 and for the iron-rich terrain an average of Fs47Wo14.

Overview of the composition of asteroid 4 Vesta: Constraints from the Dawn spacecraft mission and HEDs

Overview of the composition of asteroid 4 Vesta: Constraints from the Dawn spacecraft mission and HEDs

Dawn completes its mission at 4 Vesta

AbstractThe 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.

Mineralogical investigation of severalQpasteroids and their relation to the Vesta family

Context. To take advantage of the large dataset provided by the SDSS data, recently a new taxonomic scheme was proposed designed to be compatible with previous taxonomies. One interesting feature in this distribution is the large number of Q p asteroids scattered all around the main belt with a marked concentration in the Vesta region, where the V p are found most frequently. Since the mineralogy and thermal evolution traditionally related to the classical Q- and V-type taxonomic classes (and by construction the Q p and V p ), this finding was quite surprising.Aims. We aim to observationally determine the mineralogy of a sample of Q p asteroids of and outside the Vesta family to test whether the Q p of the Vesta family are indeed basaltic, and whether the difference in band depth implied by the SDSS spectra relates to diffences in mineralogy with respect to the V p . Moreover, we aim to determine whether the Q p outside Vesta family have an ordinary chondrite (OC) mineralogy and whether their spectra indeed correspond to Q-class asteroids.Methods. We observed a sample of asteroids classified as Q p -type in the literature, mainly located in the Vesta family and neighborhood, to confirm their mineralogy. Spectroscopic observations of 11 asteroids were obtained at the SOAR and IRTF telescopes in the visible and near-infrared region. Thermal observations of three objects were also carried out at the Gemini South telescope in order to determine the albedo of the asteroids.Results. The analysis indicated that all observed asteroids in the Vesta vicinity have a basalt-rich mineralogy, with no clear difference from other Vesta family members in terms of silicate composition. From our study it is not clear why these particular basaltic asteroids have a relatively suppressed band I so that they are classified as Q p . Two asteroids with an OC-compatible mineralogy were identified in the external part of the main belt, at around 2.8−2.9 AU. This discovery suggests new dynamical routes for the transport of Q-type asteroids to the near-Earth region and of OC meteorites to the Earth.