[Show abstract][Hide abstract] ABSTRACT: The data from the analysis of samples returned by Hayabusa from asteroid 25143 Itokawa are used to constrain the preaccretion history, the geological activity that occurred after accretion, and the dynamical history of the asteroid from the main belt to near-Earth space. We synthesize existing data to pose hypotheses to be tested by dynamical modeling and the analyses of future samples returned by Hayabusa 2 and OSIRIS-REx. Specifically, we argue that the Yarkosky-O'Keefe-Radzievskii-Paddack (YORP) effect may be responsible for producing geologically high-energy environments on Itokawa and other asteroids that process regolith and essentially affect regolith gardening.
[Show abstract][Hide abstract] ABSTRACT: Concentrations of trace elements in four Late Pleistocene lake sediment sequences across Lithuania were studied using inductively coupled plasma-mass spectrometry (ICP-MS). Such elements as Cr, Cu, Eu, La, Ni, Zn, Zr, and platinum group elements were used for constraints. The studied sediments deposited during the time interval from Bølling to Allerød and to Younger Dryas. Material for sediments of the Dengtiltis and Krokšlys sequences was delivered from the same or very similar source. Geochemical features of the sediments are consistent with the presence of extraterrestrial material in at least two horizons separated by ∼2000 years, and resulted from two separate events. The younger horizon is detected in all studied sequences and corresponds to the age of ca. 11.0–11.5 ka BP. Its geochemical features are suggested to result from a local meteorite impact/bolide explosion tentatively related to the Velnio Duobės meteorite crater. The older horizon detected only for the Ūla-2 sequence corresponds to the age of ca. 13.5 ka BP and is due to the bolide airburst. There is also suggested meteoritic material in sediments dated as ca. 12.9 ka BP. The presence of volcanic materials related to the volcanic activity in the French Massif Central (a volcano of ca. 15.3 ka BP), and Laacher See volcano in Germany (12.88 ka BP) are suggested for some sedimentary layers of the studied sequences.
Full-text · Article · Nov 2015 · Quaternary International
[Show abstract][Hide abstract] ABSTRACT: Ongoing spectroscopic reconnaissance of the OSIRIS-REx target Asteroid (101955) Bennu was performed in July 2011 and May 2012. Near-infrared spectra taken during these apparitions display slightly more positive (“redder”) spectral slopes than most previously reported measurements. While observational systematic effects can produce such slope changes, and these effects cannot be ruled out, we entertain the hypothesis that the measurements are correct. Under this assumption, we present laboratory measurements investigating a plausible explanation that positive spectral slopes indicate a finer grain size for the most directly observed sub-Earth region on the asteroid. In all cases, the positive spectral slopes correspond to sub-Earth latitudes nearest to the equatorial ridge of Bennu. If confirmed by OSIRIS-REx in situ observations, one possible physical implication is that if the equatorial ridge is created by regolith migration during episodes of rapid rotation, that migration is most strongly dominated by finer grain material. Alternatively, after formation of the ridge (by regolith of any size distribution), larger-sized equatorial material may be more subject to loss due to centrifugal acceleration relative to finer grain material, where cohesive forces can preferentially retain the finest fraction (Rozitis, B., Maclennan, E., Emery, J.P. . Nature 512, 174–176).
[Show abstract][Hide abstract] ABSTRACT: In September of 2016, the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith EXplorer) spacecraft will depart for asteroid (101955) Bennu, and when it does, humanity will turn an important corner in the exploration of the Solar System. After arriving at the asteroid in the Fall of 2018, it will undertake a program of observations designed to select a site suitable for retrieving a sample that will be returned to the Earth in 2023. The third mission in NASA's New Frontiers program, OSIRIS-REx will obtain a minimum of 60 g of a primitive asteroid's surface, the largest sample of extra-terrestrial material returned to the Earth since the end of the Apollo lunar missions (Figure 1). OSIRIS-REx will also return a separate sample of the fine-grained surface material that is <1 mm in diameter.
No preview · Article · Jun 2015 · IEEE Aerospace Conference Proceedings
[Show abstract][Hide abstract] ABSTRACT: We used ground-based photometric phase curve data of the OSIRIS-REx target asteroid (101955) Bennu and low phase angle data from asteroid (253) Mathilde as a proxy to fit Bennu data with Minnaert, Lommel-Seeliger, (RObotic Lunar Orbiter) ROLO, Hapke, and McEwen photometric models, which capture the global light scattering properties of the surface and subsequently allow us to calculate the geometric albedo, phase integral, spherical Bond albedo, and the average surface normal albedo for Bennu. We find that Bennu has low reflectance and geometric albedo values, such that multiple scattering is expected to be insignificant. Our photometric models relate the reflectance from Bennu’s surface to viewing geometry as functions of the incidence, emission, and phase angles. Radiance Factor functions (RADFs) are used to model the disk-resolved brightness of Bennu. The Minnaert, Lommel-Seeliger, ROLO, and Hapke photometric models work equally well in fitting the best ground-based photometric phase curve data of Bennu. The McEwen model works reasonably well at phase angles from 20o to 70o. Our calculated geometric albedo values of , and for the Minnaert, the Lommel-Seeliger, and the ROLO models respectively are consistent with the geometric albedo of 0.045±0.015 computed by Emery et al. (2014) and Hergenrother et al. (2014). Also, our spherical Bond albedo values of , and for the Minnaert model, Lommel-Seeliger, and ROLO models respectively are consistent with the value of 0.017±0.002 presented by Emery et al. (2014). On the other hand, the semi-physical models such as the Hapke model, where several assumptions and approximations were necessary, and the McEwen model are not supported by the global disk-integrated data, indicating that disk-resolved measurements will be necessary to constrain these models, as expected.
[Show abstract][Hide abstract] ABSTRACT: Exogenous delivery of amino acids and other organic molecules to planetary surfaces may have played an important role in the origins of life on Earth and other solar system bodies. Previous studies have revealed the presence of indigenous amino acids in a wide range of carbon-rich meteorites, with the abundances and structural distributions differing significantly depending on parent body mineralogy and alteration conditions. Here we report on the amino acid abundances of seven type 3–6 CK chondrites and two Rumuruti (R) chondrites. Amino acid measurements were made on hot water extracts from these meteorites by ultrahigh-performance liquid chromatography with fluorescence detection and time-of-flight mass spectrometry. Of the nine meteorites analyzed, four were depleted in amino acids, and one had experienced significant amino acid contamination by terrestrial biology. The remaining four, comprised of two R and two CK chondrites, contained low levels of amino acids that were predominantly the straight chain, amino-terminal (n-ω-amino) acids β-alanine, and γ-amino-n-butyric acid. This amino acid distribution is similar to what we reported previously for thermally altered ureilites and CV and CO chondrites, and these n-ω-amino acids appear to be indigenous to the meteorites and not the result of terrestrial contamination. The amino acids may have been formed by Fischer–Tropsch-type reactions, although this hypothesis needs further testing.
No preview · Article · Mar 2015 · Meteoritics & planetary science
[Show abstract][Hide abstract] ABSTRACT: Asteroid (101955) Bennu, the target of NASA’s OSIRIS-REx sample return mission, is a km diameter low albedo near-Earth object. It has a spectral signature consistent with primitive carbonaceous chondrites, and an orbit similar to that of the Earth. A plausible evolution scenario for Bennu is that it migrated inward across the inner main belt from a low albedo family by Yarkovsky thermal forces over many hundreds of Myr. Eventually, it entered a resonance that took it into the terrestrial planet region, where a combination of planetary encounters and resonances took it to its current orbit over a few Myr to tens of Myr. When it departed the main belt, Bennu probably had an eccentricity and an inclination . Several low albedo families have the appropriate dynamical, color, albedo, and broad spectral characteristics to produce Bennu: Clarissa, Erigone, Eulalia, New Polana, and Sulamitis.
[Show abstract][Hide abstract] ABSTRACT: The primary objective of the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission is to return pristine samples of carbonaceous material from the surface of a primitive asteroid. The target asteroid, near-Earth object (101955) Bennu, is the most exciting, accessible, and volatile- and organic-rich remnant from the early Solar System. OSIRIS-REx returns a minimum of 60 g of bulk regolith and a separate 26 cm2of fine-grained surface material from this body. Analyses of these samples provide unprecedented knowledge about presolar history, from the initial stages of planet formation to the origin of life. Prior to sample acquisition, OSIRIS-REx performs comprehensive global mapping of the texture, mineralogy, and chemistry of Bennu, resolving geological features, revealing its geologic and dynamic history, and providing context for the returned samples. The instruments also document the regolith at the sampling site in situ at scales down to the sub-centimeter. In addition, OSIRIS-REx studies the Yarkovsky effect, a non-Keplerian force affecting the orbit of this potentially hazardous asteroid (PHA), and provides the first ground truth for telescopic observations of carbonaceous asteroids.
[Show abstract][Hide abstract] ABSTRACT: To better understand the formation conditions of ferromagnesian chondrules from the Renazzo-like carbonaceous (CR) chondrites, a systematic study of 210 chondrules from 15 CR chondrites was conducted. The texture and composition of silicate and opaque minerals from each observed FeO-rich (type II) chondrule, and a representative number of FeO-poor (type I) chondrules, were studied to build a substantial and self-consistent data set. The average abundances and standard deviations of Cr2O3 in FeO-rich olivine phenocrysts are consistent with previous work that the CR chondrites are among the least thermally altered samples from the early solar system. Type II chondrules from the CR chondrites formed under highly variable conditions (e.g., precursor composition, redox conditions, cooling rate), with each chondrule recording a distinct igneous history. The opaque minerals within type II chondrules are consistent with formation during chondrule melting and cooling, starting as S- and Ni-rich liquids at 988–1350 °C, then cooling to form monosulfide solid solution (mss) that crystallized around olivine/pyroxene phenocrysts. During cooling, Fe,Ni-metal crystallized from the S- and Ni-rich liquid, and upon further cooling mss decomposed into pentlandite and pyrrhotite, with pentlandite exsolving from mss at 400–600 °C. The composition, texture, and inferred formation temperature of pentlandite within chondrules studied here is inconsistent with formation via aqueous alteration. However, some opaque minerals (Fe,Ni-metal versus magnetite and panethite) present in type II chondrules are a proxy for the degree of whole-rock aqueous alteration. The texture and composition of sulfide-bearing opaque minerals in Graves Nunataks 06100 and Grosvenor Mountains 03116 suggest that they are the most thermally altered CR chondrites.
[Show abstract][Hide abstract] ABSTRACT: We review the results of an extensive campaign to determine the physical, geological, and dynamical properties of asteroid (101955) Bennu. This investigation provides information on the orbit, shape, mass, rotation state, radar response, photometric, spectroscopic, thermal, regolith, and environmental properties of Bennu. We combine these data with cosmochemical and dynamical models to develop a hypothetical timeline for Bennu's formation and evolution. We infer that Bennu is an ancient object that has witnessed over 4.5 Gyr of solar system history. Its chemistry and mineralogy were established within the first 10 Myr of the solar system. It likely originated as a discrete asteroid in the inner Main Belt approximately 0.7–2 Gyr ago as a fragment from the catastrophic disruption of a large (approximately 100-km), carbonaceous asteroid. It was delivered to near-Earth space via a combination of Yarkovsky-induced drift and interaction with giant-planet resonances. During its journey, YORP processes and planetary close encounters modified Bennu's spin state, potentially reshaping and resurfacing the asteroid. We also review work on Bennu's future dynamical evolution and constrain its ultimate fate. It is one of the most Potentially Hazardous Asteroids with an approximately 1-in-2700 chance of impacting the Earth in the late 22nd century. It will most likely end its dynamical life by falling into the Sun. The highest probability for a planetary impact is with Venus, followed by the Earth. There is a chance that Bennu will be ejected from the inner solar system after a close encounter with Jupiter. OSIRIS-REx will return samples from the surface of this intriguing asteroid in September 2023.
[Show abstract][Hide abstract] ABSTRACT: The low-temperature form of CuFe2S3, cubanite, has been identified in the CI chondrite and NASA Stardust mission collections. The presence of this mineral constrains the maximum temperature to 210 °C since the time of its formation. However, until now, the conditions under which cubanite forms were less well constrained. In order to refine the history of the time-varying, low-temperature fluids which existed on the CI-chondrite parent body and Comet 81P/Wild 2 (Wild 2), we synthesized cubanite. The experimental synthesis of this mineral was achieved, for the first time, under low-temperature aqueous conditions relevant to the CI-chondrite parent body. Using a variant of in situ hydrothermal recrystallization, cubanite formed in aqueous experiments starting with temperatures of 150 and 200 °C, pH approximately 9, and oxygen fugacities corresponding to the iron-magnetite buffer. The composition and structure of the cubanite were determined using electron microprobe and transmission electron microscopy techniques, respectively. The combined compositional, crystallographic, and experimental data allow us to place limits on the conditions under which the formation of cubanite is feasible, which in turn constrains the nature of the fluid phase on the CI-chondrite parent body and Wild 2 when cubanite was forming.
[Show abstract][Hide abstract] ABSTRACT: Here, we report the mineralogy, petrography, C-N-O-stable isotope compositions, degree of disorder of organic matter, and abundances of presolar components of the chondrite Roberts Massif (RBT) 04133 using a coordinated, multitechnique approach. The results of this study are inconsistent with its initial classification as a Renazzo-like carbonaceous chondrite, and strongly support RBT 04133 being a brecciated, reduced petrologic type >3.3 Vigarano-like carbonaceous (CV) chondrite. RBT 04133 shows no evidence for aqueous alteration. However, it is mildly thermally altered (up to approximately 440 °C); which is apparent in its whole-rock C and N isotopic compositions, the degree of disorder of C in insoluble organic matter, low presolar grain abundances, minor element compositions of Fe,Ni metal, chromite compositions and morphologies, and the presence of unequilibrated silicates. Sulfides within type I chondrules from RBT 04133 appear to be pre-accretionary (i.e., did not form via aqueous alteration), providing further evidence that some sulfide minerals formed prior to accretion of the CV chondrite parent body. The thin section studied contains two reduced CV3 lithologies, one of which appears to be more thermally metamorphosed, indicating that RBT 04133, like several other CV chondrites, is a breccia and thus experienced impact processing. Linear foliation of chondrules was not observed implying that RBT 04133 did not experience high velocity impacts that could lead to extensive thermal metamorphism. Presolar silicates are still present in RBT 04133, although presolar SiC grain abundances are very low, indicating that the progressive destruction or modification of presolar SiC grains begins before presolar silicate grains are completely unidentifiable.
[Show abstract][Hide abstract] ABSTRACT: The Late Pleistocene climate oscillation (Younger Dryas, or YD, cooling) is connected predominantly to a sharp decrease of thermohaline circulation in the Atlantic Ocean, affecting the salinity in the areas where north Atlantic deep water is formed [1-3]. Recently, however, a hypothesis was proposed relating the YD cooling to an extraterrestrial (ET) bolide impact . This hypothesis suggested that just before the onset of the YD cooling (12.9 ka), a large bolide (~4 km in the diameter) exploded over the North American Laurentide Ice Sheet. The consequences of such an event (“impact winter”) led to an abrupt climate change. If the impact occurred over North America, transportation of the impact cloud eastward by the dominating movement of the air masses could have delivered impactrelated material as far to the east as Europe (Fig. 1) . Lake sediments, where undisturbed, proved to preserve reliable paleorecords on environmental, geochemical, and biotic changes [e.g., 7]. Continuing sedimentation in lakes of North-Central Europe started in Allerød and continued during the YD [3,8], covering a period of the suggested ET impact . Therefore, geochemical fingerprints of the ET event can be preserved in paleolimnological records. There is not much data existing on the geochemistry of lake sediments in Europe in terms of the possible presence of the ET fingerprints. It is likely due to the fact that the event was very short and the layers carrying such fingerprints are very thin and, secondly, that nobody really searched for such geochemical anomalies.
An increase of the concentration of elements which are in much higher abundances in meteorites than in terrestrial materials (“meteoritic” elements), especially in the platinum group elements (PGE), is accepted to be a clear indicator of a contribution of a meteoritic component to the terrestrial environment . For the present study, the authors applied inductively coupled plasma-mass spectrometry (ICP-MS) in order to check the presence of geochemical anomalies (including the ETrelated anomalies) in Late Glacial sediments from a few lakes in Belgium, the Netherlands, Lithuania and NW Russia. All studied sedimentary sequences are dated either by radiocarbon, or thermoluminescence, or pollen methods, providing the time frames for a search for geochemical anomalies.
Our study revealed that in spite of different local lithologies, some samples of Late Glacial lake sediments collected from the horizons corresponding to the age of ca. 12.9 ka display simultaneous enrichment in at least a few “meteoritic” elements (some PGE, Ni, Co, Cr). If enrichment in any of the “meteoritic” elements alone could be due to the influence of some terrestrial processes (e.g., changes in a source of sedimentary material; influence of biotic activity), simultaneous enrichment in a few “meteoritic” elements should raise suspicion about the potential presence of the ET material.
Enrichment in “meteoritic” elements was observed only for very thin sedimentary layers in lakes of different parts of Europe. That points out that the event responsible for the enrichment was very short, which is consistent with the influence of the ET impact. Therefore, we suggest that elevated concentrations of “meteoritic” elements in the Late Pleistocene lake sediments are due to the presence of microparticles related to the ET event. Interestingly enough, some sedimentary horizons (ca. 12.9 ka) enriched in “meteoritic” elements also display enrichment in “volcanic” (such as REE, Zr, Hf, Sr, and Ti, i.e., elements common in products of volcanic eruptions) elements. We connect such a “double” enrichment with the presence of material from both the eruption of the Laacher See volcano (ca. 12.9 ka)  and a possible pre-YD ET event.
Because of only patchy and weakly-pronounced occurrences of suggestively ET geochemical fingerprints in paleolimnological records of Europe, we hypothesize that the post-impact cloud did not completely blanket the sky over Europe; instead, the majority of the impact-related material deposited in North America, Greenland and North Atlantic. Therefore the influence of the pre-YD impact-related processes on the climate, if pronounced, should be restricted mostly by the Western Hemisphere, and be very limited in the Eastern Hemisphere.
[Show abstract][Hide abstract] ABSTRACT: The Design Reference Asteroid (DRA) is a compilation of all that is known
about the OSIRIS-REx mission target, asteroid (101955) Bennu. It contains our
best knowledge of the properties of Bennu based on an extensive observational
campaign that began shortly after its discovery, and has been used to inform
mission plan development and flight system design. The DRA will also be
compared with post-encounter science results to determine the accuracy of our
Earth-based characterization efforts. The extensive observations of Bennu in
1999 has made it one of the best-characterized near-Earth asteroids. Many
physical parameters are well determined, and span a number of categories:
Orbital, Bulk, Rotational, Radar, Photometric, Spectroscopic, Thermal, Surface
Analog, and Environment Properties. Some results described in the DRA have been
published in peer-reviewed journals while others have been reviewed by
OSIRIS-REx Science Team members and/or external reviewers. Some data, such as
Surface Analog Properties, are based on our best knowledge of asteroid
surfaces, in particular those of asteroids Eros and Itokawa. This public
release of the OSIRIS-REx Design Reference Asteroid is a annotated version of
the internal OSIRIS-REx document OREX-DOCS-04.00-00002, Rev 9 (accepted by the
OSIRIS-REx project on 2014-April-14). The supplemental data products that
accompany the official OSIRIS-REx version of the DRA are not included in this
release. We are making this document available as a service to future mission
planners in the hope that it will inform their efforts.
[Show abstract][Hide abstract] ABSTRACT: We report in situ O isotope and chemical compositions of magnetite and olivine in chondrules of the carbonaceous chondrites Watson-002 (anomalous CK3) and Asuka (A)-881595 (ungrouped C3). Magnetite in Watson-002 occurs as inclusion-free subhedral grains and rounded inclusion-bearing porous grains replacing Fe,Ni-metal. In A-881595, magnetite is almost entirely inclusion-free and coexists with Ni-rich sulfide and less abundant Ni-poor metal. Oxygen isotope compositions of chondrule olivine in both meteorites plot along carbonaceous chondrite anhydrous mineral (CCAM) line with a slope of approximately 1 and show a range of Δ17O values (from approximately −3 to −6‰). One chondrule from each sample was found to contain O isotopically heterogeneous olivine, probably relict grains. Oxygen isotope compositions of magnetite in A-881595 plot along a mass-dependent fractionation line with a slope of 0.5 and show a range of Δ17O values from −2.4‰ to −1.1‰. Oxygen isotope compositions of magnetite in Watson-002 cluster near the CCAM line and a Δ17O value of −4.0‰ to −2.9‰. These observations indicate that magnetite and chondrule olivine are in O isotope disequilibrium, and, therefore, not cogenetic. We infer that magnetite in CK chondrites formed by the oxidation of pre-existing metal grains by an aqueous fluid during parent body alteration, in agreement with previous studies. The differences in Δ17O values of magnetite between Watson-002 and A-881595 can be attributed to their different thermal histories: the former experienced a higher degree of thermal metamorphism that led to the O isotope exchange between magnetite and adjacent silicates.
[Show abstract][Hide abstract] ABSTRACT: Stereo-photoclinometry (SPC) has been used extensively to determine the shape and topog- raphy of various asteroids from image data. This technique will be used as one of two main approaches for de- termining the shape and topography of the asteroid Bennu, the target of the Origins Spectral Interpretation Resource Identification Security-Regolith Explorer (OSIRIS-REx) mission. The purpose of this study is to evaluate the quality of SPC products derived from the Near-Earth Asteroid Rendezvous (NEAR) mission, whose suite of imaging data resembles that to be collected by OSIRIS-REx. We make use of the NEAR laser range-finder (NLR) to independently assess SPC’s accuracy and precision.
[Show abstract][Hide abstract] ABSTRACT: Concentration and distribution of trace elements across the sequence of the Late Pleistocene sediments from the lake Medvedevskoye suggest the addition of materials other than those from a common source for the lake sediments of the region. The sediments of the lake Medvedevskoye carry some geochemical fingerprints which could be related the ET event that occurred at ca. 12.9 ka. Because such fingerprints are extremely subtle, the NW Russia can be considered to be the most remote eastern region of the extent of the Late Pleistocene airborne ET material. The sediments of the lake Medvedevskoye can also contain volcanic material from the eruption of the Laacher See (Germany) volcano and probably from other Late Pleistocene volcanoes of Western Europe and/or Iceland.
[Show abstract][Hide abstract] ABSTRACT: Concentration and distribution of trace elements across the sequence of the Late Pleistocene sediments from the lake Medvedevskoye suggest the addition of materials other than those from a common source for the lake sediments of the region. The sediments of the lake Medvedevskoye carry some geochemical fingerprints which could be related the ET event that occurred at ca. 12.9 ka. Because such fingerprints
are extremely subtle, the NW Russia can be considered to be the most remote eastern region of the extent of the Late Pleistocene airborne ET material. The sediments of the lake Medvedevskoye can also contain volcanic material from the eruption of the Laacher See (Germany) volcano and probably from other Late Pleistocene volcanoes of Western Europe and/or Iceland.
[Show abstract][Hide abstract] ABSTRACT: The NASA New Frontiers Origins Spectral Interpretation Resource Identification Security Regolith Explorer (OSIRIS-REx) mission will be the first to sample the B-type asteroid (101955) Bennu . This asteroid is thought to be primitive and carbonaceous, and is probably closely related to CI and/or CM meteorites . The OSIRIS-REx mission hopes to better understand both the physical and geochemical origin and evolution of carbonaceous asteroids through its investigation of Bennu. The OSIRIS- REx spacecraft will launch in September 2016, and arrive at Bennu two years later. The Canadian Space Agency is contributing a scanning lidar system known as the OSIRIS-REx Laser Altimeter (OLA), to the OSIRIS-REx Mission. The OLA instrument is part of suite of onboard instruments  including cameras (OCAMS) , a visible and near- infrared spectrometer (OVIRS) , a thermal emission spectrometer (OTES), and an X-ray imaging spectrometer (REXIS) .