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Showing papers in "Meteoritics & Planetary Science in 2014"


Journal ArticleDOI
TL;DR: In this article, the authors explore the hypothesis that small rubble pile asteroids have a small but non-zero cohesive strength, which creates a scale dependence with relative strength increasing as size decreases.
Abstract: We explore the hypothesis that, due to small van der Waals forces between constituent grains, small rubble pile asteroids have a small but non-zero cohesive strength. The nature of this model predicts that the cohesive strength should be constant independent of asteroid size, which creates a scale dependence with relative strength increasing as size decreases. This model counters classical theory that rubble pile asteroids should behave as scale-independent cohesionless collections of rocks. We explore a simple model for asteroid strength that is based on these weak forces, validate it through granular mechanics simulations and comparisons with properties of lunar regolith, and then explore its implications and ability to explain and predict observed properties of small asteroids in the NEA and Main Belt populations, and in particular of asteroid 2008 TC3. One conclusion is that the population of rapidly rotating asteroids could consist of both distributions of smaller grains (i.e., rubble piles) and of monolithic boulders.

198 citations


Journal ArticleDOI
TL;DR: In this article, the authors identified three types of surface modification probably formed by space weathering on the surfaces of Itokawa particles: redeposition rims, composite rims and composite vesicular rims.
Abstract: On the basis of observations using Cs-corrected STEM, we identified three types of surface modification probably formed by space weathering on the surfaces of Itokawa particles. They are (1) redeposition rims (2–3 nm), (2) composite rims (30–60 nm), and (3) composite vesicular rims (60–80 nm). These rims are characterized by a combination of three zones. Zone I occupies the outermost part of the surface modification, which contains elements that are not included in the unchanged substrate minerals, suggesting that this zone is composed of sputter deposits and/or impact vapor deposits originating from the surrounding minerals. Redeposition rims are composed only of Zone I and directly attaches to the unchanged minerals (Zone III). Zone I of composite and composite vesicular rims often contains nanophase (Fe,Mg)S. The composite rims and the composite vesicular rims have a two-layered structure: a combination of Zone I and Zone II, below which Zone III exists. Zone II is the partially amorphized zone. Zone II of ferromagnesian silicates contains abundant nanophase Fe. Radiation-induced segregation and in situ reduction are the most plausible mechanisms to form nanophase Fe in Zone II. Their lattice fringes indicate that they contain metallic iron, which probably causes the reddening of the reflectance spectra of Itokawa. Zone II of the composite vesicular rims contains vesicles. The vesicles in Zone II were probably formed by segregation of solar wind He implanted in this zone. The textures strongly suggest that solar wind irradiation damage and implantation are the major causes of surface modification and space weathering on Itokawa.

132 citations


Journal ArticleDOI
TL;DR: In this article, the authors look at the relationship between the value of e54Cr in bulk meteorites and the time (after calcium-aluminum-rich inclusion, CAI) when their parent bodies accreted.
Abstract: We look at the relationship between the value of e54Cr in bulk meteorites and the time (after calcium-aluminum-rich inclusion, CAI) when their parent bodies accreted. To obtain accretion ages of chondrite parent bodies, we estimated the maximum temperature reached in the insulated interior of each parent body, and estimated the initial 26Al/27Al for this temperature to be achieved. This initial 26Al/27Al corresponds to the time (after CAI formation) when cold accretion of the parent body would have occurred, assuming 26Al/27Al throughout the solar system began with the canonical value of 5.2 × 10−5. In cases of iron meteorite parent bodies, achondrite parent bodies, and carbonaceous chondrite parent bodies, we use published isotopic ages of events (such as core formation, magma crystallization, and growth of secondary minerals) in each body's history to obtain the probable time of accretion. We find that e54Cr correlates with accretion age: the oldest accretion ages (1 ± 0.5 Ma) are for iron and certain other differentiated meteorites with e54Cr of −0.75 ± 0.5, and the youngest ages (3.5 ± 0.5 Ma) are for hydrated carbonaceous chondrites with e54Cr values of 1.5 ± 0.5. Despite some outliers (notably Northwest Africa [NWA] 011 and Tafassasset), we feel that the correlation is significant and we suggest that it resulted from late, localized injection of dust with extremely high e54Cr.

125 citations


Journal ArticleDOI
TL;DR: In this article, a petrographic and mineralogical survey of Paris, a CM chondrite considered to be the least-altered CM identified so far, is presented. But the results of the survey are limited to a single sample and only mild thermal metamorphism.
Abstract: -We report a petrographic and mineralogical survey of Paris, a new CM chondrite considered to be the least-altered CM identified so far (Hewins et al. 2014). Compared to other CMs, Paris exhibits (1) a higher concentration of Fe-Ni metal beads, with nickel contents in the range 4.1-8.1 wt%; (2) the systematic presence of thin lamellae and tiny blebs of pentlandite in pyrrhotite grains; and (3) ubiquitous tochilinite/cronstedtite associations with higher FeO/SiO2 and S/SiO2 ratios. In addition, Paris shows the highest concentration of trapped 36Ar reported so far for a CM chondrite (Hewins et al. 2014). In combination with the findings of previous studies, our data confirm the reliability of (1) the alteration sequence based on the chemical composition of tochilinite/cronstedtite associations to quantify the fluid alteration processes and (2) the use of Cr content variability in type II ferroan chondrule olivine as a proxy of thermal metamorphism. In contrast, the scales based on (1) the Fe3+ content of serpentine in the matrix to estimate the degree of aqueous alteration and (2) the chemical composition of Fe-Ni metal beads for quantifying the intensity of the thermal metamorphism are not supported by the characteristics of Paris. It also appears that the amount of trapped 36Ar is a sensitive indicator of the secondary alteration modifications experienced by chondrites, for both aqueous alteration and thermal metamorphism. Considering Paris, our data suggest that this chondrite should be classified as type 2.7 as it suffered limited but significant fluid alteration and only mild thermal metamorphism. These results point out that two separated scales should be used to quantify the degree of the respective role of aqueous alteration and thermal metamorphism in establishing the characteristics of CM chondrites

79 citations


Journal ArticleDOI
TL;DR: The results of a multitechnique study of the bulk properties of insoluble organic material (IOM) from the Tagish Lake meteorite, including four lithologies that have undergone different degrees of aqueous alteration was presented in this paper.
Abstract: Here, we present the results of a multitechnique study of the bulk properties of insoluble organic material (IOM) from the Tagish Lake meteorite, including four lithologies that have undergone different degrees of aqueous alteration. The IOM C contents of all four lithologies are very uniform and comprise about half the bulk C and N contents of the lithologies. However, the bulk IOM elemental and isotopic compositions vary significantly. In particular, there is a correlated decrease in bulk IOM H/C ratios and dD values with increasing degree of alteration—the IOM in the least altered lithology is intermediate between CM and CR IOM, while that in the more altered lithologies resembles the very aromatic IOM in mildly metamorphosed CV and CO chondrites, and heated CMs. Nuclear magnetic resonance (NMR) spectroscopy, C X-ray absorption near-edge (XANES), and Fourier transform infrared (FTIR) spectroscopy confirm and quantitate this transformation from CR-like, relatively aliphatic IOM functional group chemistry to a highly aromatic one. The transformation is almost certainly thermally driven, and probably occurred under hydrothermal conditions. The lack of a paramagnetic shift in 13 C NMR spectra and 1s-r* exciton in the C-XANES spectra, both typically seen in metamorphosed chondrites, shows that the temperatures were lower and/or the timescales were shorter than experienced by even the least metamorphosed type 3 chondrites. Two endmember models were considered to quantitatively account for the changes in IOM functional group chemistry, but the one in which the transformations involved quantitative conversion of aliphatic material to aromatic material was the more successful. It seems likely that similar processes were involved in producing the diversity of IOM compositions and functional group chemistries among CR, CM, and CI chondrites. If correct, CRs experienced the lowest temperatures, while CM and CI chondrites experienced similar more elevated temperatures. This ordering is inconsistent with alteration temperatures based on mineralogy and O isotopes.

78 citations


Journal ArticleDOI
TL;DR: In 2010, the PMSCF/JAXA was established in Sagamihara, Kanagawa, Japan, to curate planetary material samples returned from space in conditions of minimum terrestrial contaminants as discussed by the authors.
Abstract: – The Planetary Material Sample Curation Facility of JAXA (PMSCF/JAXA) was established in Sagamihara, Kanagawa, Japan, to curate planetary material samples returned from space in conditions of minimum terrestrial contaminants. The performances for the curation of Hayabusa-returned samples had been checked with a series of comprehensive tests and rehearsals. After the Hayabusa spacecraft had accomplished a round-trip flight to asteroid 25143 Itokawa and returned its reentry capsule to the Earth in June 2010, the reentry capsule was brought back to the PMSCF/JAXA and was put to a series of processes to extract recovered samples from Itokawa. The particles recovered from the sample catcher were analyzed by electron microscope, given their ID, grouped into four categories, and preserved in dimples on quartz slide glasses. Some fraction of them has been distributed for initial analyses at NASA, and will be distributed for international announcement of opportunity (AO), but a certain fraction of them will be preserved in vacuum for future analyses.

66 citations


Journal ArticleDOI
TL;DR: Novato L6 chondrite fragmental breccia fell in California on 17 October 2012, and was recovered after the Cameras for Allsky Meteor Surveillance (CAMS) project determined the meteor's trajectory between 95 and 45 km altitude as mentioned in this paper.
Abstract: The Novato L6 chondrite fragmental breccia fell in California on 17 October 2012, and was recovered after the Cameras for Allsky Meteor Surveillance (CAMS) project determined the meteor's trajectory between 95 and 45 km altitude. The final fragmentation at 33 1 km altitude was exceptionally well documented by digital photographs. The first sample was recovered before rain hit the area. First results from a consortium study of the meteorite's characterization, cosmogenic and radiogenic nuclides, origin and conditions of the fall are presented. Some meteorites did not retain fusion crust and show evidence of spallation. Before entry, the meteoroid was 35+/-5 cm in diameter (mass 80+/-35 kg) with a cosmic ray exposure age of 9+/-1 Ma, if it had a one-stage exposure history. However, based on the cosmogenic nuclide inventory, a two-stage exposure history is more likely, with lower shielding in the last few Ma. Thermoluminescence data suggest a collision event within the last approx. 0.1 Ma. Novato likely belonged to the class of shocked L chondrites that have a common shock age of 470 Ma, based on the U,Th-He age of 460+/-220 Ma. The measured orbits of Novato, Jesenice and Innisfree are consistent with a proposed origin of these shocked L chondrites in the Gefion asteroid family, but leave open the possibility that they came to us directly from the 5:2 mean motion resonance with Jupiter. Novato experienced a stronger compaction than did other L6 chondrites of shock-stage S4. Despite this, a freshly broken surface shows a wide range of organic compounds.

66 citations


Journal ArticleDOI
TL;DR: In this article, the H and Cl systematics in apatite from four brecciated lunar meteorites were investigated, and the results showed that apatites in the first group contain ∼700-2500 ppm H2O with δD values averaging around ∼0 ± 100‰.
Abstract: We have investigated the H and Cl systematics in apatite from four brecciated lunar meteorites. In Northwest Africa (NWA) 4472, most of the apatites contain ∼2000–6000 ppm H2O with δD between −200 and 0‰, except for one grain isolated in the matrix, which contains ∼6000 ppm H2O with δD of ∼500–900‰. This low-δD apatite contains ∼2500–7500 ppm Cl associated with δ37 Cl of ∼15–20‰, while the high-δD grain contains ∼2500 ppm Cl with δ37 Cl of ∼7–15‰. In NWA 773, apatites in a first group contain ∼700–2500 ppm H2O with δD values averaging around ∼0 ± 100‰, while apatites in a second group contain ∼5500–16500 ppm H2 O with δD ∼250 ± 50‰. In Sayh al Uhaymir (SaU) 169 and Kalahari (Kal) 009, apatites are similar in terms of their H2O contents (∼600–3000 ppm) and δD values (−100 to 200‰). In SaU 169, apatites contain ∼6000–10,000 ppm Cl, characterized by δ37 Cl of ∼5–12‰. Overall, most of the analyzed apatite grains have δD within the range reported for carbonaceous chondrites, similar to apatite analyzed in ancient (>3.9 Ga) lunar magmatic. One grain in NWA 4472 has H and Cl isotope compositions similar to apatite from mare basalts. With an age of 4.35 Ga, this grain could be a representative of the oldest known lunar volcanic activity. Finally, since numerous evolved clasts in NWA 773 formed through silicate liquid immiscibility, the apatite grains with extremely high H2 O contents, reaching pure hydroxylapatite composition, could provide insights into the effects of such process on the evolution of volatiles in lunar magmas.

64 citations


Journal ArticleDOI
TL;DR: In this paper, a data set of magnetic hysteresis properties of 91 ordinary chondrite falls is presented, and it is shown that these properties can be explained by a mixture of multidomain kamacite that dominates the induced magnetism and tetrataenite.
Abstract: Magnetic properties are sensitive proxies to characterize FeNi metal phases in meteorites. We present a data set of magnetic hysteresis properties of 91 ordinary chondrite falls. We show that hysteresis properties are distinctive of individual meteorites while homogeneous among meteorite subsamples. Except for the most primitive chondrites, these properties can be explained by a mixture of multidomain kamacite that dominates the induced magnetism and tetrataenite (both in the cloudy zone as single-domain grains, and as larger multidomain grains in plessite and in the rim of zoned taenite) dominates the remanent magnetism, in agreement with previous microscopic magnetic observations. The bulk metal contents derived from magnetic measurements are in agreement with those estimated previously from chemical analyses. We evidence a decreasing metal content with increasing petrologic type in ordinary chondrites, compatible with oxidation of metal during thermal metamorphism. Types 5 and 6 ordinary chondrites have higher tetrataenite content than type 4 chondrites. This is compatible with lower cooling rates in the 650-450 °C interval for higher petrographic types (consistent with an onion-shell model), but is more likely the result of the oxidation of ordinary chondrites with increasing metamorphism. In equilibrated chondrites, shock-related transient heating events above approximately 500 °C result in the disordering of tetrataenite and associated drastic change in magnetic properties. As a good indicator of the amount of tetrataenite, hysteresis properties are a very sensitive proxy of the thermal history of ordinary chondrites, revealing low cooling rates during thermal metamorphism and high cooling rates (e.g., following shock reheating or excavation after thermal metamorphism). Our data strengthen the view that the poor magnetic recording properties of multidomain kamacite and the secondary origin of tetrataenite make equilibrated ordinary chondrites challenging targets for paleomagnetic study.

64 citations


Journal ArticleDOI
TL;DR: In this paper, three different sample preparation protocols were developed for the APT analysis of meteoritic nanodiamonds at sub-nm resolution and present carbon isotope peak ratios of both synthetic and meteoritic nano-diamonds.
Abstract: Atom-probe tomography (APT) is currently the only analytical technique that, due to its spatial resolution and detection efficiency, has the potential to measure the carbon isotope ratios of individual nanodiamonds. We describe three different sample preparation protocols that we developed for the APT analysis of meteoritic nanodiamonds at sub-nm resolution and present carbon isotope peak ratios of meteoritic and synthetic nanodiamonds. The results demonstrate an instrumental bias associated with APT that needs to be quantified and corrected to obtain accurate isotope ratios. After this correction is applied, this technique should allow determination of the distribution of 12C/13C ratios in individual diamond grains, solving the decades-old question of the origin of meteoritic nanodiamonds: what fraction, if any, formed in the solar system and in presolar environments? Furthermore, APT could help us identify the stellar sources of any presolar nanodiamonds that are detected.

64 citations


Journal ArticleDOI
TL;DR: Using the Rb-Sr and Sm-Nd isotopic systems, Tissint, a depleted shergottite, has a crystallization age of 574 20 Ma, an initial e 143 Nd =+ 42.2 0.5, and an initial 87 Sr/ 86 Sr = 0.700760 11.5 as discussed by the authors.
Abstract: The recent witnessed fall of the meteorite Tissint represents the delivery of a pristine new sample from the surface of Mars. This meteorite provides an unprecedented opportunity to study a variety of aspects about the planet's evolution. Using the Rb-Sr and Sm-Nd isotopic systems, we determined that Tissint, a depleted shergottite, has a crystallization age of 574 20 Ma, an initial e 143 Nd =+ 42.2 0.5, and an initial 87 Sr/ 86 Sr = 0.700760 11. These initial Nd and Sr isotopic compositions suggest that Tissint originated from a mantle source on Mars that is distinct from the source reservoirs of the other Martian meteorites. The known crystallization ages, geochemical characteristics, ejection ages, and ejection dynamics of Tissint and other similarly grouped Martian meteorites suggest that they are likely derived from a source crater up to approximately 90 km in diameter with an age of approximately 1 Ma that is located on terrain that is approximately 600 million years old.

Journal ArticleDOI
TL;DR: In this article, four samples from the pristine collection of the Tagish Lake meteorite, an ungrouped C2 chondrite, were studied to characterize and understand its alteration history using EPMA, XRD, and TEM.
Abstract: Four samples (TL5b, TL11h, TL11i, and TL11v) from the pristine collection of the Tagish Lake meteorite, an ungrouped C2 chondrite, were studied to characterize and understand its alteration history using EPMA, XRD, and TEM. We determined that samples TL11h and TL11i have a relatively smaller proportion of amorphous silicate material than sample TL5b, which experienced low-temperature hydrous parent-body alteration conditions to preserve this indigenous material. The data suggest that lithic fragments of TL11i experienced higher degrees of aqueous alteration than the rest of the matrix, based on its low porosity and high abundance of coarse- and fine-grained sheet silicates, suggesting that TL11i was present in an area of the parent body where alteration and brecciation were more extensive. We identified a coronal, “flower”-like, microstructure consisting of a fine-grained serpentine core and coarse-grained saponite-serpentine radial arrays, suggesting varied fluid chemistry and crystallization time scales. We also observed pentlandite with different morphologies: an exsolved morphology formed under nebular conditions; a nonexsolved pentlandite along grain boundaries; a “bulls-eye” sulfide morphology and rims around highly altered chondrules that probably formed by multiple precipitation episodes during low-temperature aqueous alteration (≥100 °C) on the parent body. On the basis of petrologic and mineralogic observations, we conclude that the Tagish Lake parent body initially contained a heterogeneous mixture of anhydrous precursor minerals of nebular and presolar origin. These materials were subjected to secondary, nonpervasive parent-body alteration, and the samples studied herein represent different stages of that hydrous alteration, i.e., TL5b (the least altered) < TL11h < TL11i (the most altered). Sample TL11v encompasses the petrologic characteristics of the other three specimens.

Journal ArticleDOI
TL;DR: In this article, the 3D microstructure of 48 Itokawa regolith particles was examined by synchrotron microtomography at SPring-8 during the preliminary examination of Hayabusa samples.
Abstract: In this study, the three-dimensional (3-D) microstructure of 48 Itokawa regolith particles was examined by synchrotron microtomography at SPring-8 during the preliminary examination of Hayabusa samples. Moreover, the 3-D microstructure of particles collected from two LL6 chondrites (Ensisheim and Kilabo meteorites) and an LL5 chondrite (Tuxtuac meteorite) was investigated by the same method for comparison. The modal abundances of minerals, especially olivine, bulk density, porosity, and grain size are similar in all samples, including voids and cracks. These results show that the Itokawa particles, which are surface materials from the S-type asteroid Itokawa, are consistent with the LL chondrite materials in terms of not only elemental and isotopic composition of the minerals but also 3-D microstructure. However, we could not determine whether the Itokawa particles are purely LL5, LL6, or a mixture of the two. No difference between the particles collected from Rooms A and B of the sample chamber, corresponding to the sampling sequence of the spacecraft's second and first touchdowns, respectively, was detected because of the statistically small amount of particles from Room B.

Journal ArticleDOI
TL;DR: This paper conducted a geochemical, petrologic, mineralogic and Sm-Nd, Rb-Sr, and Ar-Ar isotopic study of NWA 4734 to constrain the origin of young mare basalts.
Abstract: Northwest Africa (NWA) 4734 is an unbrecciated basaltic lunar meteorite that is nearly identical in chemical composition to basaltic lunar meteorites NWA 032 and LaPaz Icefield (LAP) 02205. We have conducted a geochemical, petrologic, mineralogic, and Sm-Nd, Rb-Sr, and Ar-Ar isotopic study of these meteorites to constrain their petrologic relationships and the origin of young mare basalts. NWA 4734 is a low-Ti mare basalt with a low Mg* (36.5) and elevated abundances of incompatible trace elements (e.g., 2.00 ppm Th). The Sm-Nd isotope system dates NWA 4734 with an isochron age of 3024 ± 27 Ma, an initial eNd of +0.88 ± 0.20, and a source region 147Sm/144Nd of 0.201 ± 0.001. The crystallization age of NWA 4734 is concordant with those of LAP 02205 and NWA 032. NWA 4734 and LAP 02205 have very similar bulk compositions, mineral compositions, textures, and ages. Their source region 147Sm/144Nd values indicate that they are derived from similar, but distinct, source materials. They probably do not sample the same lava flow, but rather are similarly sourced, but isotopically distinct, lavas that probably originate from the same volcanic complex. They may have experienced slightly different assimilation histories in route to eruption, but can be source-crater paired. NWA 032 remains enigmatic, as its source region 147Sm/144Nd definitively precludes a simple relationship with NWA 4734 and LAP 02205, despite a similar bulk composition. Their high Ti/Sm, low (La/Yb)N, and Cl-poor apatite compositions rule out the direct involvement of KREEP. Rather, they are consistent with low-degree partial melting of late-formed LMO cumulates, and indicate that the geochemical characteristics attributed to urKREEP are not unique to that reservoir. These and other basaltic meteorites indicate that the youngest mare basalts originate from multiple sources, and suggest that KREEP is not a prerequisite for the most recent known melting in the Moon.

Journal ArticleDOI
TL;DR: The most commonly accepted age of the Imbrium impact is 3770 to 3920 Ma, with the latter being the most widely accepted age for basin-forming events.
Abstract: Previous age estimates of the Imbrium impact range from 3770 to 3920 Ma, with the latter being the most commonly accepted age of this basin-forming event. The occurrence of Ca-phosphates i ...

Journal ArticleDOI
TL;DR: In this paper, the authors used 2D and 3D finite-difference numerical models to determine the formation time, initial radius of the parent body of the acapulcoite-lodranite meteorites, and their formation depth inside the body by applying available geochronological, thermal, and textural constraints to numerical data.
Abstract: The acapulcoite-lodranite meteorites are members of the primitive achondrite class. The observation of partial melting and resulting partial removal of Fe-FeS indicates that this meteorite group could be an important link between achondrite and iron meteorites, on the one hand, and chondrite meteorites, on the other. Thus, a better understanding of the thermomechanical evolution of the parent body of this meteorite group can help improve our understanding of the evolution of early planetesimals. Here, we use 2-D and 3-D finite-difference numerical models to determine the formation time, initial radius of the parent body of the acapulcoite-lodranite meteorites, and their formation depth inside the body by applying available geochronological, thermal, and textural constraints to our numerical data. Our results indicate that the best fit to the data can be obtained for a parent body with 25–65 km radius, which formed around 1.3 Ma after calcium-aluminum-rich inclusions. The 2-D and 3-D results considering various initial temperatures and the effect of porosity indicate possible formation depths of the acapulcoite-lodranite meteorites of 9–19 and 14–25 km, respectively. Our data also suggest that other meteorite classes could form at different depths inside the same parent body, supporting recently proposed models (Elkins-Tanton et al. 2011; Weiss and Elkins-Tanton 2013).

Journal ArticleDOI
TL;DR: The Orgueil meteorite was found to contain a large diversity of carbon-rich compounds, which help address the question of organo-synthesis in the early solar system.
Abstract: The goal of this paper is to summarize 150 yr of history of a very specialmeteorite. The Orgueil meteorite fell near Montauban in southwestern France on May 14,1864. The bolide, which was the size of the full Moon, was seen across Western France, andalmost immediately made the news in local and Parisian newspapers. Within a few weeks ofthe fall, a great diversity of analyses were performed under the authority of Gabriel AugusteDaubree, geology professor at the Paris Museum, and published in the Comptes Rendus del’Academie des Sciences. The skilled scientists reported the presence of iron sulfides,hydrated silicates, and carbonates in Orgueil. They also characterized ammonium saltswhich are now gone, and observed sulfates being remobilized at the surface of the stone.They identified the high water and carbon contents, and noted similarities with the Alaismeteorite, which had fallen in 1806, 300 km away. While Daubree and his colleagues notedthe similarity of the Orgueil organic matter with some terrestrial humus, they were cautiousnot to make a direct link with living organisms. One century later, Nagy and Claus wereless prudent and announced the discovery of “organized” elements in some samples ofOrgueil. Their observations were quickly discredited by Edward Anders and others who alsodiscovered that some pollen grains were intentionally placed into the rock back in the1860s. Orgueil is now one of the most studied meteorites, indeed one of the most studiedrocks of any kind. Not only does it contain a large diversity of carbon-rich compounds,which help address the question of organo-synthesis in the early solar system but itschemical composition is also close to that of the Sun’s photosphere and serves as a cosmicreference. Secondary minerals, which make up 99% of the volume of Orgueil, wereprobably formed during hydrothermal alteration on the parent-body within the first fewmillion years of the solar system; their study is essential to our understanding of fluid–rockinteraction in asteroids and comets. Finally, the Orgueil meteorite probably originated froma volatile-rich “cometary” outer solar system body as indicated by its orbit. Because it bearsstrong similarities to other carbonaceous chondrites that originated on dark asteroids, thiscometary connection supports the idea of a continuum between dark asteroids and comets

Journal ArticleDOI
TL;DR: Two petrographic settings of carbonaceous components, mainly filling open fractures and occasionally enclosed in shock-melt veins, were found in the recently fallen Tissint Martian meteorite as mentioned in this paper.
Abstract: Two petrographic settings of carbonaceous components, mainly filling open fractures and occasionally enclosed in shock-melt veins, were found in the recently fallen Tissint Martian meteorite. The presence in shock-melt veins and the deuterium enrichments (delta D up to +1183 parts per thousand) of these components clearly indicate a pristine Martian origin. The carbonaceous components are kerogen-like, based on micro-Raman spectra and multielemental ratios, and were probably deposited from fluids in shock-induced fractures in the parent rock of Tissint. After precipitation of the organic matter, the rock experienced another severe shock event, producing the melt veins that encapsulated a part of the organic matter. The C isotopic compositions of the organic matter (delta C-13 = -12.8 to -33.1 parts per thousand) are significantly lighter than Martian atmospheric CO2 and carbonate, providing a tantalizing hint for a possible biotic process. Alternatively, the organic matter could be derived from carbonaceous chondrites, as insoluble organic matter from the latter has similar chemical and isotopic compositions. The presence of organic-rich fluids that infiltrated rocks near the surface of Mars has significant implications for the study of Martian paleoenvironment and perhaps to search for possible ancient biological activities on Mars.

Journal ArticleDOI
TL;DR: Scherst et al. as discussed by the authors pointed out that the evidence reported in these papers does not comply with established recognition criteria for impact (see, e.g., French and Koeberl [2010] and references therein; Reimold et al., 2013).
Abstract: We were surprised to see the cover of the August 2013 issue of Meteoritics & Planetary Science (MAPS) adorned by a field image of a Greenlandic migmatite. The caption refers to the Maniitsoq structure in Greenland and explains that the lithology shown on the cover “is interpreted as due to a crustal-scale hydrothermal convection cell in a now deeply exhumed Archean impact structure” (Scherst en and Garde 2013). We found this statement surprising, as the Maniitsoq structure (Garde et al. 2012, 2013) has not been widely accepted as an impact structure, because the evidence reported in these papers does not comply with established recognition criteria for impact (see, e.g., French and Koeberl [2010] and references therein; Reimold et al. 2013). Garde and colleagues assert that, when established criteria “do not work,” new ones can be devised. To present such a statement as that related to the MAPS cover—highlighting this structure, in our view gives unnecessary credit to a (as we insist on calling) proposed but unconfirmed impact structure. The article by Scherst en and Garde (2013), to which this cover refers, contains high-quality U-Pb data for zircon, which are interpreted as hydrothermal re-equilibration of the isotope systems as the result of an impact event. Reimold et al. (2013) recommended a detailed investigation of Maniitsoq zircon grains to investigate the possible presence of impact evidence in the form of planar fractures, shock-induced granular texture, or twinning in zircon. The numerous zircon images shown in Scherst en and Garde (2013), however, fail to illustrate any textural evidence of shock deformation. While we explicitly appreciate the high-quality U-Pb ages, we must insist that there is still no tangible evidence for impact at Maniitsoq. Nor does the circumstantial evidence preclude alternatives, such as magmatic/tectonic explanations, for the observations and data reported so far from Maniitsoq. Let us assume that Maniitsoq could be a deeply eroded impact structure with a diameter of some 150 km. This would place Maniitsoq within the range of “large, old, eroded impact structures,” such as Sudbury (Canada) or Vredefort (South Africa). In these cases, and especially in that of the long controversial, deeply eroded Vredefort Structure, the ultimate proof of impact origin came from the discovery of shatter cones and planar deformation features (PDFs) in quartz, as well as the presence of a meteoritic component in impact melt rocks, all of which are accepted in the impact community as unambiguous proof of impact origin. The often annealed and/or decorated planar deformation features in Vredefort quartz were shown by Leroux et al. (1994) through detailed TEM analysis to represent bona fide shock deformation in the form of basal Brazil twins and decorated, higher order PDFs. Only with this proof in hand—further supported by unambiguous evidence for shock deformation in zircon (planar fractures and granular zircon texture)—were various authors able to later interpret breccia bodies, structural observations, and morphometric data within an impact context. Planar is the key term in planar deformation features, so that the description of “commonly curved, coarsened, and partially annealed” features as “planar features” (p. 1474) by Scherst en and Garde (2013) is not consistent with the published definitions. Their features are not imperfectly preserved, but have never been planar. Hence, we consider that they cannot provide evidence for a shock event. They also state “Proven but imperfectly preserved PDFs in known impact structures are only rarely reported in the literature,” which represents another obscure finding—as “imperfectly preserved” (in their sense referring to curved) features only rarely would be recognized as impact-diagnostic PDFs. As further emphasized below, “decorated PDFs” are still planar, even if their traces in thin section only represent straight fluid inclusion trails. Maniitsoq is just one of several recent instances where the impact origin of geological structures was proposed based on evidence unrelated to the commonly accepted criteria for impact. These recognized criteria include the presence of evidence of shock metamorphism (such as shatter cones—Figs. 1a and 1b, or planar deformation features [PDFs—see Fig. 2] in various minerals), and remnants or chemical traces of extraterrestrial projectiles (e.g., see the recent reviews by French and Koeberl [2010] and Koeberl [2014]). In the Maniitsoq case, Garde and coworkers developed their own criteria for shock metamorphism by interpreting Meteoritics & Planetary Science 49, Nr 5, 723–731 (2014) doi: 10.1111/maps.12284

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed brightness variation with ecliptic longitude and using the Lowell Observatory photometric database, they estimate spin-axis longitudes for more than 350,000 asteroids.
Abstract: By analyzing brightness variation with ecliptic longitude and using the Lowell Observatory photometric database, we estimate spin-axis longitudes for more than 350,000 asteroids. Hitherto, spin-axis longitude estimates have been made for fewer than 200 asteroids. We investigate longitude distributions in different dynamical groups and asteroid families. We show that asteroid spin-axis longitudes are not isotropically distributed as previously considered. We find that the spin-axis longitude distribution for Main Belt asteroids is clearly nonrandom, with an excess of longitudes from the interval 30°–110° and a paucity between 120° and 180°. The explanation of the nonisotropic distribution is unknown at this point. Further studies have to be conducted to determine if the shape of the distribution can be explained by observational bias, selection effects, a real physical process, or other mechanism.

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TL;DR: The Meteoritical Bulletin 100 contains 1943 meteorites including 8 falls (Boumdeid [2011], Huaxi, Kosice, Silistra, Soltmany, Sutter's Mill, Thika, Tissint), with 1575 ordinary chondrites, 139 carbonaceous chondites, 96 HED achondrie, 25 ureilites, 18 primitive achonderes, 17 iron meteorites, 15 enstatite chondrieres, 11 lunar meteorite, 10 mesosiderites, 10 ungrouped ach
Abstract: Meteoritical Bulletin 100 contains 1943 meteorites including 8 falls (Boumdeid [2011], Huaxi, Kosice, Silistra, Soltmany, Sutter's Mill, Thika, Tissint), with 1575 ordinary chondrites, 139 carbonaceous chondrites, 96 HED achondrites, 25 ureilites, 18 primitive achondrites, 17 iron meteorites, 15 enstatite chondrites, 11 lunar meteorites, 10 mesosiderites, 10 ungrouped achondrites, 8 pallasites, 8 Martian meteorites, 6 Rumuruti chondrites, 3 enstatite achondrites, and 2 angrites, and with 937 from Antarctica, 592 from Africa, 230 from Asia, 95 from South America, 44 from North America, 36 from Oceania, 6 from Europe, and 1 from an unknown location. This will be the last Bulletin published in the current format. Information about approved meteorites can be obtained from the Meteoritical Bulletin Database (MBD) available online at http://www.lpi.usra.edu/meteor/

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TL;DR: The authors determined the abundances and enantiomeric compositions of amino acids in Sutter's Mill fragment #2 (designated SM2) recovered prior to heavy rains that fell April 25-26, 2012, and two other meteorite fragments, SM12 and SM51, that were recovered postrain.
Abstract: We determined the abundances and enantiomeric compositions of amino acids in Sutter's Mill fragment #2 (designated SM2) recovered prior to heavy rains that fell April 25–26, 2012, and two other meteorite fragments, SM12 and SM51, that were recovered postrain. We also determined the abundance, enantiomeric, and isotopic compositions of amino acids in soil from the recovery site of fragment SM51. The three meteorite stones experienced terrestrial amino acid contamination, as evidenced by the low d/l ratios of several proteinogenic amino acids. The d/l ratios were higher in SM2 than in SM12 and SM51, consistent with rain introducing additional l-amino acid contaminants to SM12 and SM51. Higher percentages of glycine, β-alanine, and γ-amino-n-butyric acid were observed in free form in SM2 and SM51 compared with the soil, suggesting that these free amino acids may be indigenous. Trace levels of d+l-β-aminoisobutyric acid (β-AIB) observed in all three meteorites are not easily explained as terrestrial contamination, as β-AIB is rare on Earth and was not detected in the soil. Bulk carbon and nitrogen and isotopic ratios of the SM samples and the soil also indicate terrestrial contamination, as does compound-specific isotopic analysis of the amino acids in the soil. The amino acid abundances in SM2, the most pristine SM meteorite analyzed here, are approximately 20-fold lower than in the Murchison CM2 carbonaceous chondrite. This may be due to thermal metamorphism in the Sutter's Mill parent body at temperatures greater than observed for other aqueously altered CM2 meteorites.

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TL;DR: Sutter's Mill is a unique regolith breccia consisting mainly of various CMlithologies as discussed by the authors, which can be used to predict what will be found on the surfaces of C class asteroids such as Ceres and thetarget asteroids of the OSIRIS-REx and Hayabusa 2 sample return missions (which willvisit predominantly primitive asteroids).
Abstract: Based upon our characterization of three separate stones by electron and X-raybeam analyses, computed X-ray microtomography, Raman microspectrometry, and visible-IR spectrometry, Sutter’s Mill is a unique regolith breccia consisting mainly of various CMlithologies. Most samples resemble existing available CM2 chondrites, consisting ofchondrules and calcium-aluminum-rich inclusion (CAI) set within phyllosilicate-dominatedmatrix (mainly serpentine), pyrrhotite, pentlandite, tochilinite, and variable amounts of Ca-Mg-Fe carbonates. Some lithologies have witnessed sufficient thermal metamorphism totransform phyllosilicates into fine-grained olivine, tochilinite into troilite, and destroycarbonates. One finely comminuted lithology contains xenolithic materials (enstatite, Fe-Crphosphides) suggesting impact of a reduced asteroid (E or M class) onto the main Sutter’sMill parent asteroid, which was probably a C class asteroid. One can use Sutter’s Mill tohelp predict what will be found on the surfaces of C class asteroids such as Ceres and thetarget asteroids of the OSIRIS-REx and Hayabusa 2 sample return missions (which willvisit predominantly primitive asteroids). C class asteroid regolith may well contain a mixtureof hydrated and thermally dehydrated indigenous materials as well as a significantadmixture of exogenous material would be essential to the successful interpretation ofmineralogical and bulk compositional data.

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TL;DR: Novato, a newly observed fall in the San Francisco Bay area, is a shocked and brecciated L6 ordinary chondrite containing dark and light lithologies as discussed by the authors.
Abstract: Novato, a newly observed fall in the San Francisco Bay area, is a shocked and brecciated L6 ordinary chondrite containing dark and light lithologies. We have investigated the U-Pb isotope systematics of coarse Cl-apatite grains of metamorphic origin in Novato with a large geometry ion microprobe. The U-Pb systematics of Novato apatite reveals an upper intercept age of 4472 ± 31 Ma and lower intercept age of 473 ± 38 Ma. The upper intercept age is within error identical to the U-Pb apatite age of 4452 ± 21 Ma measured in the Chelyabinsk LL5 chondrite. This age is interpreted to reflect a massive collisional resetting event due to a large impact associated with the peak arrival time at the primordial asteroid belt of ejecta debris from the Moon-forming giant impact on Earth. The lower intercept age is consistent with the most precisely dated Ar-Ar ages of 470 ± 6 Ma of shocked L chondrites, and the fossil meteorites and extraterrestrial chromite relicts found in Ordovician limestones with an age of 467.3 ± 1.6 Ma in Sweden and China. The lower intercept age reflects a major disturbance related to the catastrophic disruption of the L chondrite parent body most likely associated with the Gefion asteroid family, which produced an initially intense meteorite bombardment of the Earth in Ordovician period and reset and degassed at least approximately 35% of the L chondrite falls today. We predict that the 470 Ma impact event is likely to be found on the Moon and Mars, if not Mercury.

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TL;DR: The results from the preliminary examination of this collection, the Stardust Interstellar Preliminary Examination (ISPE), were presented in this article, where extraterrestrial materials were found in two tracks in aerogel whose trajectories and morphology are consistent with an origin in the interstellar dust stream, and in residues in four impacts in the aluminum foil collectors.
Abstract: With the discovery of bona fide extraterrestrial materials in the Stardust Interstellar Dust Collector, NASA now has a fundamentally new returned sample collection, after the Apollo, Antarctic meteorite, Cosmic Dust, Genesis, Stardust Cometary, Hayabusa, and Exposed Space Hardware samples. Here, and in companion papers in this volume, we present the results from the Preliminary Examination of this collection, the Stardust Interstellar Preliminary Examination (ISPE). We found extraterrestrial materials in two tracks in aerogel whose trajectories and morphology are consistent with an origin in the interstellar dust stream, and in residues in four impacts in the aluminum foil collectors. While the preponderance of evidence, described in detail in companion papers in this volume, points toward an interstellar origin for some of these particles, alternative origins have not yet been eliminated, and definitive tests through isotopic analyses were not allowed under the terms of the ISPE. In this summary, we answer the central questions of the ISPE: How many tracks in the collector are consistent in their morphology and trajectory with interstellar particles? How many of these potential tracks are consistent with real interstellar particles, based on chemical analysis? Conversely, what fraction of candidates are consistent with either a secondary or interplanetary origin? What is the mass distribution of these particles, and what is their state? Are they particulate or diffuse? Is there any crystalline material? How many detectable impact craters (> 100 nm) are there in the foils, and what is their size distribution? How many of these craters have analyzable residue that is consistent with extraterrestrial material? And finally, can craters from secondaries be recognized through crater morphology (e.g., ellipticity)?

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TL;DR: In this paper, the Sutter's Mill dolomite is estimated to have formed by precipitation from an aqueous fluid on the parent body within several million years of accretion.
Abstract: Radiometric dating of secondary minerals can be used to constrain the timing of aqueous alteration on meteoritic parent bodies. Dolomite is a well-documented secondary mineral in CM chondrites, and is thought to have formed by precipitation from an aqueous fluid on the CM parent body within several million years of accretion. The petrographic context of crosscutting dolomite veins indicates that aqueous alteration occurred in situ, rather than in the nebular setting. Here, we present 53Mn-53Cr systematics for dolomite grains in Sutter's Mill section SM51-1. The Mn-Cr isotope data show well-resolved excesses of 53Cr correlated with 55Mn/52Cr ratio, which we interpret as evidence for the in situ decay of radioactive 53Mn. After correcting for the relative sensitivities of Mn and Cr using a synthetic Mn- and Cr-bearing calcite standard, the data yield an isochron with slope corresponding to an initial 53Mn/55Mn ratio of 3.42 ± 0.86 × 10−6. The reported error includes systematic uncertainty from the relative sensitivity factor. When calculated relative to the U-corrected Pb-Pb absolute age of the D'Orbigny angrite, Sutter's Mill dolomites give a formation age between 4564.8 and 4562.2 Ma (2.4–5.0 Myr after the birth of the solar system). This age is contemporaneous with previously reported ages for secondary carbonates in CM and CI chondrites. Consistent carbonate precipitation ages between the carbonaceous chondrite groups suggest that aqueous alteration was a common process during the early stages of parent body formation, probably occurring via heating from internal 26Al decay. The high-precision isochron for Sutter's Mill dolomite indicates that late-stage processing did not reach temperatures that were high enough to further disturb the Mn-Cr isochron.

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TL;DR: In this paper, a previously unrecognized correlation exists between meteorite bulk permeabilities and porosities with the speciation of the Ca-, Fe-rich silicates (pyroxenes, andradite, kirschsteinite) among the CVox and CVred meteorites.
Abstract: CV (Vigarano type) carbonaceous chondrites, comprising Allende-like (CVoxA) and Bali-like (CVoxB) oxidized and reduced (CVred) subgroups, experienced differing degrees of fluid-assisted thermal and shock metamorphism. The abundance and speciation of secondary minerals produced during asteroidal alteration differ among the subgroups: (1) ferroan olivine and diopside–hedenbergite solid solution pyroxenes are common in all CVs; (2) nepheline and sodalite are abundant in CVoxA, rare in CVred, and absent in CVoxB; (3) phyllosilicates and nearly pure fayalite are common in CVoxB, rare in CVred, and virtually absent in CVoxA; (4) andradite, magnetite, and Fe-Ni-sulfides are common in oxidized CVs, but rare in reduced CVs; the latter contain kirschsteinite instead. Thus, a previously unrecognized correlation exists between meteorite bulk permeabilities and porosities with the speciation of the Ca-, Fe-rich silicates (pyroxenes, andradite, kirschsteinite) among the CVox and CVred meteorites. The extent of secondary mineralization was controlled by the distribution of water ices, permeability, and porosity, which in turn were controlled by impacts on the asteroidal parent body. More intense shock metamorphism in the region where the reduced CVs originated decreased their porosity and permeability while simultaneously expelling intergranular ices and fluids. The mineralogy, petrography, and bulk chemical compositions of both the reduced and oxidized CV chondrites indicate that mobile elements were redistributed between Ca,Al-rich inclusions, dark inclusions, chondrules, and matrices only locally; there is no evidence for large-scale (>several cm) fluid transport. Published 53Mn-53Cr ages of secondary fayalite in CV, CO, and unequilibrated ordinary chondrites, and carbonates in CI, CM, and CR chondrites are consistent with aqueous alteration initiated by heating of water ice-bearing asteroids by decay of 26Al, not shock metamorphism.

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TL;DR: In this article, thermal models were constructed to investigate the effect of metal-troilite melting on the thermal history of the parent asteroids of the H, L, and LL parent asteroids.
Abstract: Ordinary chondrite meteorites contain silicates, Fe,Ni-metal grains, and troilite (FeS). Conjoined metal-troilite grains would be the first phase to melt during radiogenic heating in the parent body, if temperatures reached over approximately 910–960 °C (the Fe,Ni-FeS eutectic). On the basis of two-pyroxene thermometry of 13 ordinary chondrites, we argue that peak temperatures in some type 6 chondrites exceeded the Fe,Ni-FeS eutectic and thus conjoined metal-troilite grains would have begun to melt. Melting reactions consume energy, so thermal models were constructed to investigate the effect of melting on the thermal history of the H, L, and LL parent asteroids. We constrained the models by finding the proportions of conjoined metal-troilite grains in ordinary chondrites using high-resolution X-ray computed tomography. The models show that metal-troilite melting causes thermal buffering and inhibits the onset of silicate melting. Compared with models that ignore the effect of melting, our models predict longer cooling histories for the asteroids and accretion times that are earlier by 61, 124, or 113 kyr for the H, L, and LL asteroids, respectively. Because the Ni/Fe ratio of the metal and the bulk troilite/metal ratio is higher in L and LL chondrites than H chondrites, thermal buffering has the greatest effect in models for the L and LL chondrite parent bodies, and least effect for the H chondrite parent. Metal-troilite melting is also relevant to models of primitive achondrite parent bodies, particularly those that underwent only low degrees of silicate partial melting. Thermal models can predict proportions of petrologic types formed within an asteroid, but are systematically different from the statistics of meteorite collections. A sampling bias is interpreted to explain these differences.

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TL;DR: In this article, a detailed analysis of the Kosice meteorite fall is conducted to derive a reliable law describing the mass distribution among the recovered fragments, and the authors conclude that two to three larger fragments of 500 to 1000 kg each should exist, but were either not recovered or not reported by illegal meteorite hunters.
Abstract: In this study, we conduct a detailed analysis of the Kosice meteorite fall (February 28, 2010), to derive a reliable law describing the mass distribution among the recovered fragments. In total, 218 fragments of the Kosice meteorite, with a total mass of 11.285 kg, were analyzed. Bimodal Weibull, bimodal Grady, and bimodal lognormal distributions are found to be the most appropriate for describing the Kosice fragmentation process. Based on the assumption of bimodal lognormal, bimodal Grady, bimodal sequential, and bimodal Weibull fragmentation distributions, we suggest that, prior to further extensive fragmentation in the lower atmosphere, the Kosice meteoroid was initially represented by two independent pieces with cumulative residual masses of approximately 2 and 9 kg, respectively. The smaller piece produced about 2 kg of multiple lightweight meteorite fragments with the mean around 12 g. The larger one resulted in 9 kg of meteorite fragments, recovered on the ground, including the two heaviest pieces of 2.374 kg and 2.167 kg with the mean around 140 g. Based on our investigations, we conclude that two to three larger fragments of 500–1000 g each should exist, but were either not recovered or not reported by illegal meteorite hunters.

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TL;DR: Kamil is a 45 m diameter impact crater identified in 2008 in southern Egypt and was generated by the hypervelocity impact of the Gebel Kamil iron meteorite on a sedimentary target, namely layered sandstones with subhorizontal bedding as discussed by the authors.
Abstract: Kamil is a 45 m diameter impact crater identified in 2008 in southern Egypt. It was generated by the hypervelocity impact of the Gebel Kamil iron meteorite on a sedimentary target, namely layered sandstones with subhorizontal bedding. We have carried out a petrographic study of samples from the crater wall and ejecta deposits collected during our first geophysical campaign (February 2010) in order to investigate shock effects recorded in these rocks. Ejecta samples reveal a wide range of shock features common in quartz-rich target rocks. They have been divided into two categories, as a function of their abundance at thin section scale: (1) pervasive shock features (the most abundant), including fracturing, planar deformation features, and impact melt lapilli and bombs, and (2) localized shock features (the least abundant) including high-pressure phases and localized impact melting in the form of intergranular melt, melt veins, and melt films in shatter cones. In particular, Kamil crater is the smallest impact crater where shatter cones, coesite, stishovite, diamond, and melt veins have been reported. Based on experimental calibrations reported in the literature, pervasive shock features suggest that the maximum shock pressure was between 30 and 60 GPa. Using the planar impact approximation, we calculate a vertical component of the impact velocity of at least 3.5 km s � 1 . The wide range of shock features and their freshness make Kamil a natural laboratory for studying impact cratering and shock deformation processes in small impact structures.