bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact‐induced microbial endolithic habitats
Authors: Cockell Charles S. , Lee Pascal , Osinski Gordon , Horneck Gerda , Broady Paul
Published: January 2010

Abstract— Asteroid and comet impacts on Earth are commonly viewed as agents of ecosystem destruction, be it on local or global scales. However, for some microbial communities, impacts may represent an opportunity for habitat formation as some substrates are rendered more suitable for colonization when processed by impacts. We describe how heavily shocked gneissic crystalline basement rocks exposed at the Haughton impact structure, Devon Island, Nunavut, Arctic Canada, are hosts to endolithic photosynthetic microorganisms in significantly greater abundance than lesser‐shocked or unshocked gneisses. Two factors contribute to this enhancement: (a) increased porosity due to impact fracturing and differential mineral vaporization, and (b) increased translucence due to the selective vaporization of opaque mineral phases. Using biological ultraviolet radiation dosimetry, and by measuring the concentrations of photoprotective compounds, we demonstrate that a covering of 0.8 mm of shocked gneiss can provide substantial protection from ultraviolet radiation, reducing the inactivation of Bacillus subtilis spores by 2 orders of magnitude. The colonisation of the shocked habitat represents a potential mechanism for pioneer microorganisms to invade an impact structure in the earliest stages of post‐impact primary succession. The communities are analogous to the endolithic communities associated with sedimentary rocks in Antarctica, but because they occur in shocked crystalline rocks, they illustrate a mechanism for the creation of microbial habitats on planetary surfaces that do not have exposed sedimentary units. This might have been the case on early Earth. The data have implications for the microhabitats in which biological signatures might be sought on Mars.
Properties of chondrules in EL3 chondrites, comparison with EH3 chondrites, and the implications for the formation of enstatite chondrites
Authors: Schneider D. M. , Symes S. J. K. , Benoit P. H. , Sears D. W. G.
Published: January 2010

Abstract— The study of chondrules provides information about processes occurring in the early solar system. In order to ascertain to what extent these processes played a role in determining the properties of the enstatite chondrites, the physical and chemical properties of chondrules from three EL3 chondrites and three EH3 chondrites have been examined by optical, cathodoluminescence (CL), and electron microprobe techniques. Properties examined include size, texture, CL, and composition of both individual phases and bulk chondrules. The textures, distribution of textures, and composition of silicates of the EL3 chondrules resemble those of EH3 chondrules. However, the chondrules from the two classes differ in that (1) the size distribution of the EL chondrules is skewed to larger values than EH chondrules, (2) the enstatite in EL chondrules displays varying shades of red CL due to the presence of fine‐grained sulfides and metal in the silicates, and (3) the mesostasis of EH chondrules is enriched in Na relative to that of EL chondrules. The similarities between the chondrules of the two classes suggest similar precursor materials, while the differences suggest that there was not a single reservoir of meteoritic chondrules, but that their origin was fairly local. The differences in the size distribution of chondrules in EH and EL chondrites may be explained by aerodynamic and gravitational sorting during accumulation of the meteoric material, while differences in CL and mesostasis properties may reflect differences in formation conditions and cooling rate following chondrule formation. We argue that our observations are consistent with the formation of enstatite chondrites in a thick dynamic regolith on their parent body.
Yamato 792947, 793408 and 82038: The most primitive H chondrites, with abundant refractory inclusions
Authors: Kimura M. , Hiyagon H. , Palme H. , Spettel B. , Wolf D. , Clayton R. N. , Mayeda T. K. , Sato T. , Suzuki A. , Kojima H.
Published: January 2010

Abstract— In this paper we report petrological and chemical data of the unusual chondritic meteorites Yamato (Y)‐792947, Y‐93408 and Y‐82038. The three meteorites are very similar in texture and chemical composition, suggesting that they are pieces of a single fall. The whole‐rock oxygen isotopes and the chemical compositions are indicative of H chondrites. In addition, the mineralogy, and the abundances of chondrule types, opaque minerals and matrices suggest that these meteorites are H3 chondrites. They were hardly affected by thermal and shock metamorphism. The degree of weathering is very low. We conclude that these are the most primitive H chondrites, H3.2–3.4 (S1), known to date. On the other hand, these chondrites contain extraordinarily high amounts of refractory inclusions, intermediate between those of ordinary and carbonaceous chondrites. The distribution of the inclusions may have been highly heterogeneous in the primitive solar nebula. The mineralogy, chemistry and oxygen isotopic compositions of inclusions studied here are similar to those in CO and E chondrites.
The geology of 433 Eros
Authors: Robinson M. S. , Thomas P. C. , Veverka J. , Murchie S. L. , Wilcox B. B.
Published: January 2010

Abstract— The global high‐resolution imaging of asteroid 433 Eros by the Near‐Earth Asteroid Rendezvous (NEAR) Shoemaker spacecraft has made it possible to develop the first comprehensive picture of the geology of a small S‐type asteroid. Eros displays a variety of surface features, and evidence of a substantial regolith. Large scale facets, grooves, and ridges indicate the presence of at least one global planar structure. Directional and superposition relations of smaller structural features suggest that fracturing has occurred throughout the object. As with other small objects, impact craters dominate the overall shape as well as the small‐scale topography of Eros. Depth/diameter ratios of craters on Eros average ∼0.13, but the freshest craters approach lunar values of ∼0.2. Ejecta block production from craters is highly variable; the majority of large blocks appear to have originated from one 7.6 km crater (Shoemaker). The interior morphology of craters does not reveal the influence of discrete mechanical boundaries at depth in the manner of craters formed on lunar mare regolith and on some parts of Phobos. This lack of mechanical boundaries, and the abundant evidence of regolith in nearly every high‐resolution image, suggests a gradation in the porosity and fracturing with depth. The density of small craters is deficient at sizes below ∼200 m relative to predicted slopes of empirical saturation. This characteristic, which is also found on parts of Phobos and lunar highland areas, probably results from the efficient obliteration of small craters on a body with significant topographic slopes and a thick regolith. Eros displays a variety of regolith features, such as debris aprons, fine‐grained “ponded” deposits, talus cones, and bright and dark streamers on steep slopes indicative of efficient downslope movement of regolith. These processes serve to mix materials in the upper loose fragmental portion of the asteroid (regolith). In the instance of “ponded” materials and crater wall deposits, there is evidence of processes that segregate finer materials into discrete deposits. The NEAR observations have shown us that surface processes on small asteroids can be very complex and result in a wide variety of morphologic features and landforms that today seem exotic. Future missions to comets and asteroids will surely reveal still as yet unseen processes as well as give context to those discovered by the NEAR Shoemaker spacecraft.
Cosmogenic nuclides in the Brenham pallasite
Authors: Honda M. , Caffee M. W. , Miura Y. N. , Nagai H. , Nagao K. , Nishiizumi K.
Published: January 2010

Abstract— Cosmic‐ray‐produced (cosmogenic) nuclides were studied in fragments of the Brenham pallasite, a large stony iron meteorite. The contents of light noble gases (He, Ne, and Ar) and long‐lived radionuclides (10Be, 26Al, 36Cl, and 53Mn), produced by nuclear reactions with cosmic rays, were measured in the separated metal and olivine phases from numerous samples representing a wide range of shielding conditions in the meteoroid. The distribution of cosmogenic nuclide concentrations in the metal follows patterns similar to that observed in large iron meteorites. Shielding effects were estimated from the relative proportions of low‐ and high‐energy reaction products. The production rates varied, from surface to interior, by a factor of more than several hundred. The 36Cl‐36Ar cosmic‐ray exposure age of Brenham is 156 ± 8 Myr. This determination is based on a multiple nuclide approach that utilizes cosmogenic nuclide pairs. This approach not only yields a “shielding independent” exposure age but also demonstrates that the production of cosmogenic nuclides occurred in a single stage. The depth profiles of 10Be in the stone phase and 53Mn in the metal phase are shown superimposed on corresponding profiles from the Apollo 15 long drill core.

Surprisingly low abundances of lithophile elements, such as K, U, and Th, provided a unique opportunity to examine the production systematics of those nuclides whose inventories typically have significant contributions from non‐cosmogenic sources, particularly radiogenic contributions. The U and Th contents of the olivine samples are extremely low, allowing detection of cosmogenic 4He production from oxygen, magnesium, silicon, and iron.
Modeling the Ries‐Steinheim impact event and the formation of the moldavite strewn field
Authors: Stöffler Dieter , Artemieva Natalia A. , Pierazzo Elisabetta
Published: January 2010

Abstract— Using detailed geological, petrographic, geochemical, and geographical constraints we have performed numerical modeling studies that relate the Steinheim crater (apparent diameter Da = 3.8 km), the Ries crater (Da = 24 km) in southern Germany, and the moldavite (tektite) strewn field in Bohemia and Moravia (Czech Republic), Lusatia (East Germany), and Lower Austria. The moldavite strewn field extends from ∼200 to 450 km from the center of the Ries to the east‐northeast forming a fan with an angle of ∼57°. An oblique impact of a binary asteroid from a west‐southwest direction appears to explain the locations of the craters and the formation and distribution of the moldavites. The impactor must have been a binary asteroid with two widely separated components (some 1.5 and 0.15 km in diameter, respectively). We carried out a series of three‐dimensional hydrocode simulations of a Ries‐type impact. The results confirm previous results suggesting that impacts around 30–50° (from the horizontal) are the most favorable angles for near‐surface melting, and, consequently for the formation of tektites. Finally, modeling of the motion of impact‐produced tektite particles through the atmosphere produces, in the downrange direction, a narrow‐angle distribution of the moldavites tektites in a fan like field with an angle of ∼75°. An additional result of modeling the motion of melt inside and outside the crater is the preferred flow of melt from the main melt zone of the crystalline basement downrange towards the east‐northeast rim. This explains perfectly the occurrence of coherent impact melt bodies (some tens of meters in size) in a restricted zone of the downrange rim of the Ries crater. The origin of these melt bodies, which represent chemically a mixture of crystalline basement rocks similar to the main melt mass contained (as melt particles <0.5 m in size) in the suevite, do not occur at any other portion of the Ries crater rim and remained enigmatic until now. Although the calculated distribution of moldavites still deviates to some degree from the known distribution, our results represent an important step toward a better understanding of the origin and distribution of the high‐velocity surface melts and the low‐velocity, deep‐seated melt resulting from an oblique impact on a stratified target.
Infrared observations of asteroids from space: The past and future
Authors: Price Stephan D.
Published: January 2010

Abstract— Infrared observations from space have large sensitivity and total instantaneous field of view advantages over ground‐based measurements. The limits to telescope performance from thermal emission from the atmosphere and sky noise are eliminated in space and the instrument can be cooled to temperatures where the photon noise from the zodiacal background provides the fundamental limit to the sensitivity of the system. Furthermore, the entire thermal infrared spectral range is available; the atmospheric is virtually opaque at the wavelengths of molecular absorption bands from water vapor and CO2 to ground‐based observations. Space‐based infrared radiometry from the experiments described in this article supplied the basis for the largest, consistent set of derived diameters and albedos of asteroids. Radiometry over a large spectral range and a large span of phase angles provides essential information of the detailed thermal properties of a body. Infrared measurements resolve the ambiguity of whether a visual observation is of a small highly reflective object or a large dark one. Infrared spectroscopy obtained by the previous space‐based experiments, and the spectral capability of two infrared missions to be flown within the next several years, is a powerful remote sensing tool to assay the mineralogy of a surface. A description is given of what knowledge has been and will be gained from past and future infrared missions on the physical characteristics of asteroids. Why the database derived from previous satellites remains the major source of new radiometric measurements is explained and the benefits to be had from a space‐based infrared spectrometer/photometer dedicated to studying small bodies in the solar system presented.
Probing the interior of asteroids and comets using radio reflection tomography
Authors: Safaeinili A. , Gulkis S. , Hofstadter M. D. , Jordan R. L.
Published: January 2010

Abstract— Asteroids and comets are of great scientific interest: their interior structure and composition, which are poorly known, provide information about conditions and processes that occurred during the early stages of solar system development. They are also of interest for social and economic reasons. Their proximity to Earth and abundance in the solar system make them potential sources of raw materials as well as a threat, as evidenced by past catastrophic impacts. Information on their composition and structure is therefore important to assess both the potential benefit of these objects and mitigate the potential risk they pose. This paper describes the use of radio reflection tomography for studying the interiors of asteroids and comets. We discuss technical issues regarding benefits and challenges of implementing a radio reflection tomography instrument and present potential solutions. This paper addresses a range of topics including (1) data collection scenarios, (2) data processing and inversion, and (3) instrument implementation. A “strawman” instrument capable of imaging the full interior of an asteroid or a comet with dimensions of a few kilometers is presented. Such an instrument can play a significant role in studying the near‐Earth objects, both for scientific and socio‐economic purposes.
The role of sticky interstellar organic material in the formation of asteroids
Authors: Kudo T. , Kouchi A. , Arakawa M. , Nakano H.
Published: January 2010

Abstract— Collision experiments and measurements of viscoelastic properties were performed involving an interstellar organic material analogue to investigate the growth of organic grains in the protosolar nebula. The organic material was found to be stickiest at a radius of between 2.3 and 3.0 AU, with a maximum sticking velocity of 5 m s−1 for millimeter‐size organic grains. This stickiness is considered to have resulted in the very rapid coagulation of organic grain aggregates and subsequent formation of planetesimals in the early stage of the turbulent accretion disk. The planetesimals formed in this region appear to be represent achondrite parent bodies. In contrast, the formation of planetesimals at <2.1 and >3.0 AU begins with the establishment of a passive disk because silicate and ice grains are not as sticky as organic grains.
Ion microprobe U‐Th‐Pb dating of phosphates in martian meteorite ALH 84001
Authors: Terada Kentaro , Monde Tsuyoshi , Sano Yuji
Published: January 2010

Abstract— Phosphates in martian meteorites are important carriers of trace elements, although, they are volumetrically minor minerals. PO4 also has potential as a biomarker for life on Mars. Here, we report measurements of the U‐Th‐Pb systematics of phosphates in the martian meteorite ALH 84001 using the Sensitive High Resolution Ion MicroProbe (SHRIMP) installed at Hiroshima University, Japan. Eleven analyses of whitlockites and 1 analysis of apatite resulted in a total Pb/U isochron age of 4018 ± 81 Ma in the 238U/206Pb‐207Pb/206Pb‐204Pb/206 Pb 3‐D space, and a 232Th‐208Pb age of 3971 ± 860 Ma. These ages are consistent within a 95% confidence limit. This result is in agreement with the previously published Ar‐Ar shock age of 4.0 ± 0.1 Ga from maskelynite and other results of 3.8–4.3 Ga but are significantly different from the Sm‐Nd age of 4.50 ± 0.13 Ga based on the whole rock and pyroxene. Taking into account recent studies on textural and chemical evidence of phosphate, our result suggests that the shock metamorphic event defines the phosphate formation age of 4018 ± 81 Ma, and that since then, ALH 84001 has not experienced a long duration thermal metamorphism, which would reset the U‐Pb system in phosphates.
Ferric iron in SNC meteorites as determined by Mössbauer spectroscopy: Implications for martian landers and martian oxygen fugacity
Authors: DYAR M. Darby
Published: January 2010

Abstract— Mössbauer spectra of martian meteorites are currently of great interest due to the Mössbauer spectrometers on the Athena mission MER rovers as well as the European Space Agency Mars Express mission, with its Beagle 2 payload. Also, considerable current effort is being made to understand the oxygen fugacity of martian magmas because of the effect of fO2 on mineral chemistry and crystallization processes. For these 2 reasons, the present study was conceived to acquire room temperature Mössbauer spectra of mineral separates and whole rock samples of 10 SNC meteorites. The results suggest that mineral identification using remote application of this technique will be most useful when the phases present have distinctive parameters arising from Fe in very different coordination polyhedra; for example, pyroxene coexisting with olivine can be discriminated easily, but opx versus cpx cannot. The MER goal of using Mössbauer spectroscopy to quantify the relative amounts of individual mineral species present will be difficult to satisfy if silicates are present because the lack of constraints on wt% FeO contents of individual silicate phases present will make modal calculations impossible. The remote Mössbauer spectroscopy will be most advantageous if the rocks analyzed are predominantly oxides with known stoichiometries, though these phases are not present in the SNCs. As for the detection of martian oxygen fugacity, no evidence exists in the SNC samples studied of a relationship between Fe3+ content and fO2 as calculated by independent methods. Possibly, all of the Fe3+ observed in olivine is the result of dehydrogenation rather than oxidation, and this process may also be the source of all the Fe3+ observed in pyroxene. The observed Fe3+ in pyroxene also likely records an equilibrium between pyroxene and melt at such low fO2 that little or no Fe3+ would be expected.
Magnetic fields of lunar multi‐ring impact basins
Authors: Halekas J. S. , Lin R. P. , Mitchell D. L.
Published: January 2010

Abstract— We survey the magnetic fields of lunar multi‐ring impact basins using data from the electron reflectometer instrument on the Lunar Prospector spacecraft. As for smaller lunar craters, the primary signature is a magnetic low that extends to ˜1.5–2 basin radii, suggesting shock demagnetization of relatively soft crustal magnetization. A secondary signature, as for large terrestrial basins, is the presence of central magnetic anomalies, which may be due to thermal remanence in impact melt rocks and/or shock remanence in the central uplift. The radial extent of the anomalies may argue for the former possibility, but the latter or a combination of the two are also possible. Central anomaly fields are absent for the oldest pre‐Nectarian basins, increase to a peak in early Nectarian basins, and decrease to a low level for Imbrian basins. If basin‐associated anomalies provide a good indication of ambient magnetic fields when the basins formed, this suggests the existence of a “magnetic era” (possibly due to a lunar core dynamo) similar to that implied by paleointensity results from returned lunar samples. However, the central basin anomalies suggest that the fields peaked in early Nectarian times and were low in Imbrian times, while samples provide evidence for high fields in Nectarian and early Imbrian times.
Solar wind and other gases in the regoliths of the Pesyanoe parent object and the moon
Authors: Mathew K. J. , Marti K.
Published: January 2010

We report new data from Pesyanoe‐90,1 (dark lithology) on the isotopic signature of solar wind (SW) Xe as recorded in this enstatite achondrite which represents a soil‐breccia of an asteroidal regolith. The low temperature (≤800°C) steps define the Pesyanoe‐S xenon component, which is isotopically consistent with SW Xe reported for the lunar regolith. This implies that the SW Xe isotopic signature was the same at two distinct solar system locations and, importantly, also at different times of solar irradiation. Further, we compare the calculated average solar wind “SW‐Xe” signature to Chass‐S Xe, the indigenous Xe observed in SNC (Mars) meteorites. Again, a close agreement between these compositions is observed, which implies that a mass‐dependent differential fractionation of Xe between SW‐Xe and Chass‐S Xe is >1.5%o per amu. We also observe fractionated (Pesyanoe‐F) Xe and Ar components in higher temperature steps and we document a fission component due to extinct 244Pu. Interestingly, the Pesyanoe‐F Xe component is revealed only at the highest temperatures (>1200°C). The Pesyanoe‐F gas reveals Xe isotopic signatures that are consistent with lunar solar energetic particles (SEP) data and may indicate a distinct solar energetic particle radiation as was inferred for the moon. However, we cannot rule out fractionation processes due to parent body processes. We note that ratios 36Ar/38Ar≤5 are also consistent with SEP data. Calculated abundances of the fission component correlate well with radiogenic 40Ar concentrations, revealing rather constant 244Pu/K ratios in Pesyanoe, and separates thereof, and indicate that both components were retained. We identify a nitrogen component (δ15N = 44%o) of non‐solar origin with an isotopic signature distinct from indigenous N (δ15N = −33%o). While large excesses at 128Xe and 129Xe are observed in the lunar regolith samples, these excesses in Pesyanoe are small. On the other hand, significant 126Xe isotopic excesses, comparable to relative excesses observed in lunar soils and breccias, are prominent in the intermediate temperature steps of Pesyanoe‐90,1.
The Kaidun meteorite: Clasts of alkaline‐rich fractionated materials
Authors: Ivanov Andrei V. , Kononkova Nataliya N. , Yang S. Vincent , Zolensky Michael E.
Published: January 2010

Abstract— Clasts of alkaline (the second find in meteorites) and subalkaline rocks were found in the Kaidun meteorite. One of them (#d4A) is a large crystal of albite with inclusions of fluorapatite, arfvedsonite, aenigmatite, and wilkinsonite. The two latter minerals were previously unknown in meteorites. Another clast (#d[3–5]D) has a melt crystallization texture of mainly feldspar (oligoclase) composition and contains relict grains of both high‐Ca and low‐Ca pyroxene and fluorapatite. The mineralogical characteristics of these clasts suggest a genetic relationship and an origin from the same parent body. The textural and mineralogical characteristics of the clasts indicate origin by extensive igneous differentiation. Such processes most likely took place in a rather large differentiated body. The material of clast #d(3–5)D is similar in some mineralogical respects to basaltic shergottites.
Redistribution of elements in the heavily shocked Yanzhuang chondrite
Authors: Kong Ping , Xie Xiande
Published: January 2010

Abstract— Compositions of metal, sulfide, olivine, pyroxene, and plagioclase/plagioclase glass were studied for the melted and unmelted parts of the heavily shocked H6(S6) chondrite‐Yanzhuang. We found that the partitioning of some trace elements significantly changed between the 2 parts; compared with the corresponding minerals in the unmelted part, Ga is enriched in the metal, Co, Cr, and Zn are enriched in the sulfide, Cr is enriched in olivine and pyroxene, and Ti is enriched in the plagioclase glass of the melt pocket. These detailed studies of the mineral phases put constraints on 3 important parameters (temperature, pressure, and duration) associated with the post‐shock melting process. The coexistence of melted and unmelted olivine in the melt pocket of Yanzhuang implies a peak temperature after shock that approaches the melting point of olivine. The lack of Ni in the olivine crystallized from a melt suggests crystallization of olivine at pressures below 10 kbar. The resetting of Ga partitioning between metal and silicate in the melt pocket indicates that the interval from the peak temperature after shock to the crystallization of metal‐sulfide and plagioclase glass in the melted part of Yanzhuang is longer than 500 sec.
Noble gases in Muong Nong‐type tektites and their implications
Authors: MIZOTE Sayaka , MATSUMOTO Takuya , MATSUDA Jun‐ichi , KOEBERL Christian
Published: January 2010

Abstract— We have the elemental abundances and isotopic compositions of noble gases in Muong Nong‐type tektites from the Australasian strewn field by crushing and by total fusion of the samples. We found that the abundances of the heavy noble gases are significantly enriched in Muong Nong‐type tektites compared to those in normal splash‐form tektites from the same strewn field. Neon enrichments were also observed in the Muong Nong‐type tektites, but the Ne/Ar ratios were lower than those in splash‐form tektites because of the higher Ar contents in the former. The absolute concentrations of the heavy noble gases in Muong Nong‐type tektites are similar to those in impact glasses. The isotopic ratios of the noble gases in Muong Nong‐type tektites are mostly identical to those in air, except for the presence of radiogenic 40Ar. The obtained K‐Ar ages for Muong Nong‐type tektites were about 0.7 Myr, similar to ages of other Australasian tektites. The crushing experiments suggest that the noble gases in the Muong Nong‐type tektites reside mostly in vesicles, although Xe was largely affected by adsorbed atmosphere after crushing. We used the partial pressure of the heavy noble gases in vesicles to estimate the barometric pressure in the vesicles of the Muong Nong‐type tektites. Likely, Muong Nong‐type tektites solidified at the altitude (between the surface and a maximum height of 8–30 km) lower than that for splash‐form tektites.
Detection of terrestrial fluorine by proton induced gamma emission (PIGE): A rapid quantification for Antarctic meteorites
Authors: Noll K. , Döbeli M. , Krähenbühl U. , Grambole D. , Herrmann F. , Koeberl C.
Published: January 2010

Abstract— The enrichment of fluorine on the surface of Antarctic meteorites is investigated by applying the nuclear reactions 19F(p, αγ)16O or 19F(p, p'γ)19F with the proton induced gamma emission (PIGE) technique, a class of nuclear reaction analysis (NRA). Results for the Antarctic meteorites ALHA77294, TIL 82409, LEW 86015, ALHA77003, and ALH 83108 are presented. Possible sources of terrestrial F are: volcanic exhalation, tephra layers (volcanic glass), continental soil dust, or sea spray. Material from blue‐ice dust‐band samples also shows concentrations of F that are significantly higher than the bulk concentrations of meteorites. Finally, a quick investigation for Antarctic meteorites by external PIGE is proposed, leading to a F‐contamination index that supplements the qualitative ABC‐weathering index.
Noble gases in ureilites released by crushing
Authors: Okazaki Ryuji , Nakamura Tomoki , Takaoka Nobuo , Nagao Keisuke
Published: January 2010

Abstract— Noble gases in two ureilites, Kenna and Allan Hills (ALH) 78019, were measured with two extraction methods: mechanical crushing in a vacuum and heating. Large amounts of noble gases were released by crushing, up to 26.5% of 132Xe from ALH 78019 relative to the bulk concentration. Isotopic ratios of the crush‐released Ne of ALH 78019 resemble those of the trapped Ne components determined for some ureilites or terrestrial atmosphere, while the crush‐released He and Ne from Kenna are mostly cosmogenic. The crush‐released Xe of ALH 78019 and Kenna is similar in isotopic composition to Q gas, which indicates that the crush‐released noble gases are indigenous and not caused by contamination from terrestrial atmosphere. In contrast to the similarities in isotopic composition with the bulk samples, light elements in the crush‐released noble gases are depleted relative to Xe and distinct from those of each bulk sample. This depletion is prominent especially in the 20Ne/132Xe ratio of ALH 78019 and the 36Ar/132Xe ratio of Kenna. The values of measured 3He/21Ne for the gases released by crushing are significantly higher than those for heating‐released gases. This suggests that host phases of the crush‐released gases might be carbonaceous because cosmogenic Ne is produced mainly from elements with a mass number larger than Ne.

Based on our optical microscopic observation, tabular‐foliated graphite is the major carbon mineral in ALH 78019, while Kenna contains abundant polycrystalline graphite aggregates and diamonds along with minor foliated graphite. There are many inclusions at the edge and within the interior of olivine grains that are reduced by carbonaceous material. Gaps can be seen at the boundary between carbonaceous material and silicates. Considering these petrologic and noble gas features, we infer that possible host phases of crush‐released noble gases are graphite, inclusions in reduction rims, and gaps between carbonaceous materials and silicates.

The elemental ratios of noble gases released by crushing can be explained by fractionation, assuming that the starting noble gas composition is the same as that of amorphous carbon in ALH 78019. The crush‐released noble gases are the minor part of trapped noble gases in ureilites but could be an important clue to the thermal history of the ureilite parent body. Further investigation is needed to identify the host phases of the crush‐released noble gases.
The parameterization of solid metal‐liquid metal partitioning of siderophile elements
Authors: CHABOT Nancy L. , JONES John H.
Published: January 2010

Abstract— Many solar system processes involve a metallic liquid, and the composition of the metallic liquid, such as the liquid's concentrations of S, P, and C, will influence the partitioning of elements during such processes. We present a method for parameterizing solid metal‐liquid metal partition coefficients for siderophile (metal‐loving) elements as a function of the metallic liquid composition. Our parameterization method is based on an older theory of Jones and Malvin (1990), which stated that the metallic liquid is composed of metal and non‐metal‐bearing domains, and the domains are the dominant influence on the partitioning behavior. By revising the means by which the metal domains are calculated, our revised parameterization method is able to match experimental partitioning data from the Fe‐Ni‐S, Fe‐Ni‐P, Fe‐Ni‐S‐P, and Fe‐Ni‐C systems. Mathematical expressions were derived for the solid metal‐liquid metal partitioning of 13 siderophile elements. Elements that are chalcophile (S‐loving), P‐loving, or C‐loving prefer the non‐metal‐bearing domains in the metallic liquid and, consequently, aren't fit by the parameterization method presented here. Possible applications for our parameterization method include modeling the crystallization of iron meteorites, planetary differentiation, and the solidification of Earth's inner core.
New noble gas data of primitive and differentiated achondrites including Northwest Africa 011 and Tafassasset
Authors: PATZER Andrea , SCHULTZ Ludolf , FRANKE Luitgard
Published: January 2010

Abstract— This work reports on the noble gas inventory of 3 new acapulcoites, 3 brachinites, 2 new eucrites from the Dar al Gani region in Libya, the unique achondrite Dar al Gani (DaG) 896 from the same locality, the new eucrite‐like achondrite Northwest Africa (NWA) 011, and the controversial sample Tafassasset.

We determined cosmic ray exposure and gas retention ages, evaluated shielding conditions, and discuss the trapped noble gas component of the specimens. All exposure ages are within the known range of stony meteorites and partly confirm previously established age clusters. Shielding conditions vary, suggesting substantial shielding for all 3 brachinites and Tafassasset. We cannot exclude, however, that the Mg‐rich composition of brachinites simply simulates heavy shielding. Regarding the trapped component, we found Q‐like compositions only for the acapulcoite Thiel Mountains (TIL) 99002. The brachinite Elephant Moraine (EET) 99402 yields a high, subsolar 36Ar/132Xe ratio of ˜400 along with a slightly elevated 84Kr/132atio, indicating minor atmospheric contamination. All the other samples, particularly the eucrite DaG 983, are characterized by clearly elevated Ar/Kr/Xe ratios due to significant terrestrial alteration.

Tafassasset exhibits noble gas parameters that are different from those of CR chondrites, including a relatively high cosmic ray exposure age, the absence of a solar component, low 132Xe concentrations, a low trapped 36Ar/132Xe ratio of ˜30, and a noticeable amount of radiogenic 129Xe. Similar attributes have been observed for some primitive achondrites. These attributes are also consistent with the metamorphic character of the sample. We, therefore, consider Tafassasset's noble gas record to be inconclusive as to its classification (primitive achondrite versus metamorphosed CR chondrite).
The petrogenesis of type B1 Ca‐Al‐rich inclusions: The spinel perspective
Authors: CONNOLLY Harold C. , BURNETT D. S. , McKEEGAN Kevin D.
Published: January 2010

Abstract— Minor element variations in MgAl2O4 spinel from the type B1 calcium‐aluminum‐rich inclusion (CAI) Allende TS‐34 confirm earlier studies in showing correlations between the minor element chemistry of spinels with their location within the inclusion and with the chemistry of host silicate phases. These correlations result from a combination of crystallization of a liquid produced by re‐melting event(s) and local re‐equilibration during subsolidus reheating. The correlation of the Ti and V in spinel inclusions with the Ti and V in the adjacent host clinopyroxene can be qualitatively explained by spinel and clinopyroxene crystallization prior to melilite, following a partial melting event. There are, however, difficulties in quantitative modeling of the observed trends, and it is easier to explain the Ti correlation in terms of complete re‐equilibration. The correlation of V in spinel inclusions with that in the adjacent host clinopyroxene also cannot be quantitatively modeled by fractional crystallization of the liquid produced by re‐melting, but it can be explained by partial re‐equilibration. The distinct V and Ti concentrations in spinel inclusions in melilite from the edge regions of the CAI are best explained as being affected by only a minor degree of re‐equilibration. The center melilites and included spinels formed during crystallization of the liquid produced by re‐melting, while the edge melilites and included spinels are primary. The oxygen isotope compositions of TS‐34 spinels are uniformly 16O‐rich, regardless of the host silicate phase or its location within the inclusion. Similar to other type B1 CAIs, clinopyroxene is 16O‐rich, but melilite is relatively 16O‐poor. These data require that the oxygen isotope exchange in TS‐34 melilite occurred subsequent to the last re‐melting event.
Precursors of Mars: Constraints from nitrogen and oxygen isotopic compositions of martian meteorites
Authors: MOHAPATRA Ratan K. , MURTY S. V. S.
Published: January 2010

Abstract— We present an approach to assess the nature of materials involved in the accretion of Mars by the planet's nitrogen (δ15N) and oxygen (Δ17O) isotopic compositions as derived from data on martian meteorites. δ15N for Mars has been derived from nitrogen and xenon systematics, while Δ17O has been taken from the literature data. These signatures indicate that Mars has most probably accreted from enstatite and ordinary chondritic materials in a ratio of 74:26 and may not have a significant contribution from the carbonaceous (CI, CM, or CV) chondrites. This is consistent with the chromium isotopic (ɛ53Cr) signatures of martian meteorites and the bulk planet Fe/Si ratio for Mars as suggested by the moment of inertia factor (I/MR2) obtained from the Mars Pathfinder data. Further, a simple homogeneous accretion from the above two types of materials is found to be consistent with the planet's moment of inertia factor and the bulk composition of the mantle. But, it requires a core with 6.7 wt% Si, which is consistent with the new results from the high pressure and temperature melting experiments and chemical data on the opaque minerals in enstatite chondrites.
Acid‐susceptive material as a host phase of argon‐rich noble gas in the carbonaceous chondrite Ningqiang
Authors: NAKAMURA Tomoki , ZOLENSKY Michael , SEKIYA Minoru , OKAZAKI Ryuji , NAGAO Keisuke
Published: January 2010

Abstract— A fine‐grained dark inclusion in the Ningqiang carbonaceous chondrite consists of relatively pristine solar nebular materials and has high concentrations of heavy primordial rare gases. Trapped 36Ar concentration amounts to 6 times 10−6 cc STP/g, which is higher than that of Ningqiang host by a factor of three. Light HF‐HCl etching of the dark inclusion removed 86, 73, and 64% of the primordial 36Ar, 84Kr, and 132Xe, respectively. Thus, the majority of the noble gases in this inclusion are located in very acid‐susceptive material. Based on the elemental composition, the noble gases lost from the dark inclusion during the acid‐treatments are Ar‐rich, and the noble gases remaining in the inclusion are Q and HL gases. Transmission electron microscopy showed that the acid treatments removed thin Si, Mg, and Fe‐rich amorphous rims present around small olivine and pyroxene grains in the dark inclusion, suggesting that the Ar‐rich gases reside in the amorphous layers. A possible origin of the Ar‐rich gases is the acquisition of noble‐gas ions with a composition fractionated relative to solar abundance favoring the heavy elements by the effect of incomplete ionization under plasma conditions at 8000 K electron temperature.
Magnetic classification of stony meteorites: 1. Ordinary chondrites
Authors: ROCHETTE Pierre , SAGNOTTI Leonardo , BOUROT‐DENISE Michèle , CONSOLMAGNO Guy , FOLCO Luigi , GATTACCECA Jérôme , OSETE Maria Luisa , PESONEN Lauri
Published: January 2010

Abstract— We present a database of magnetic susceptibility measurements on 971 ordinary chondrites. It demonstrates that this parameter can be successfully used to characterize and classify ordinary chondrite meteorites. In ordinary chondrites, this rapid and non‐destructive measurement essentially determines the amount of metal in the sample, which occurs in a very narrow range for each chondrite class (though terrestrial weathering can result in a variable decrease in susceptibility, especially in finds). This technique is particularly useful not only for a rapid classification of new meteorites, but also as a check against curation errors in large collections (i.e., unweathered meteorites, the measured susceptibility of which lies outside the expected range, may well be misclassified or misidentified samples). Magnetic remanence, related to magnetic field measurements around asteroids, is also discussed.
Quantifying hydrogen‐deuterium exchange of meteoritic dicarboxylic acids during aqueous extraction
Authors: FULLER Megan , HUANG Yongsong
Published: January 2010

Abstract— Hydrogen isotope ratios of organic compounds in carbonaceous chondrites provide critical information about their origins and evolutionary history. However, because many of these compounds are obtained by aqueous extraction, the degree of hydrogen‐deuterium (H/D) exchange that occurs during the process needs to be quantitatively evaluated. This study uses compound‐specific hydrogen isotopic analysis to quantify the H/D exchange during aqueous extraction. Three common meteoritic dicarboxylic acids (succinic, glutaric, and 2‐methyl glutaric acids) were refluxed under conditions simulating the extraction process. Changes in δD values of the dicarboxylic acids were measured following the reflux experiments. A pseudo‐first order rate law was used to model the H/D exchange rates which were then used to calculate the isotope exchange resulting from aqueous extraction. The degree of H/D exchange varies as a result of differences in molecular structure, the alkalinity of the extraction solution and presence/absence of meteorite powder. However, our model indicates that succinic, glutaric, and 2‐methyl glutaric acids with a δD of 1800%***o would experience isotope changes of 38o, 10o, and 6o, respectively during the extraction process. Therefore, the overall change in δD values of the dicarboxylic acids during the aqueous extraction process is negligible. We also demonstrate that H/D exchange occurs on the chiral α‐carbon in 2‐methyl glutaric acid. The results suggest that the racemic mixture of 2‐methyl glutaric acid in the Tagish Lake meteorite could result from post‐synthesis aqueous alteration. The approach employed in this study can also be used to quantify H/D exchange for other important meteoritic compounds such as amino acids.
Magnetic remanence in the Murchison meteorite
Authors: KLETETSCHKA Gunther , KOHOUT Tomas , WASILEWSKI Peter J.
Published: January 2010

Abstract— The Murchison meteorite is a carbonaceous chondrite containing a small amount of chondrules, various inclusions, and matrix with occasional porphyroblasts of olivine and/or pyroxene. It also contains amino acids that may have served as the necessary components for the origin of life. Magnetic analyses of Murchison identify an ultrasoft magnetic component due to superparamagnetism as a significant part of the magnetic remanence. The rest of the remanence may be due to electric discharge in the form of lightning bolts that may have formed the amino acids. The level of magnetic remanence does not support this possibility and points to a minimum ambient field of the remanence acquisition. We support our observation by showing that normalized mineral magnetic acquisition properties establish a calibration curve suitable for rough paleofield determination. When using this approach, 1–2% of the natural remanence left in terrestrial rocks with TRM and/or CRM determines the geomagnetic field intensity irrespective of grain size or type of magnetic mineral (with the exception of hematite). The same method is applied to the Murchison meteorite where the measured meteorite remanence determines the paleofield minimum intensity of 200–2000 nT during and/or after the formation of the parent body.
Fassaites in compact type A Ca‐Al‐rich inclusions in the Ningqiang carbonaceous chondrite: Evidence for partial melting in the nebula
Authors: LIN Yangting , KIMURA Makoto , WANG Daode
Published: January 2010

Abstract— Fassaite is a major component of Ca‐Al‐rich inclusions (CAIs) of Types B and C that crystallized from liquids. In contrast, this mineral is rarely reported in Type A inclusions and has been much less studied. In this paper, we report highly Ti‐, Al‐enriched fassaite that occurs as rims on perovskite in two compact Type A inclusions from the Ningqiang meteorite. In addition, one of the inclusions contains an euhedral grain of Sc‐fassaite (16.4 wt% Sc2O3) isolated in melilite. The occurrence and mineral chemistry of the fassaite rims can be explained by a reaction of pre‐existing perovskite with CAI melts. Hence, such rims may serve as an indicator for partial melting of Type A inclusions. The Sc‐fassaite is probably a relict grain. A third spherical CAI contains several euhedral grains of V‐fassaite (4.8–5.4 wt% V2O3) enclosed in a melilite fragment. The high V content of fassaite cannot be related to any Fremdlinge, magnetite, or metallic Fe‐Ni, because these phases are absent in the inclusion. In the same CAI, other fassaites intergrow with spinel and minor perovskite, filling voids inside of the melilite and space adjacent to the Wark‐Lovering rim. The fassaite intergrown with spinel is almost V‐free. The coexistence of two types of fassaite suggests that this CAI has not been completely melted.
Estimated optical constants of the Tagish Lake meteorite
Authors: ROUSH Ted L.
Published: January 2010

Abstract— The visible, near‐infrared, and mid‐infrared (0.3–25 μm) real and imaginary indices of refraction are derived from reflectance measurements of the Tagish Lake meteorite. These are compared to some real and imaginary indices of refraction of the individual minerals composing the Tagish Lake meteorite. From this comparison, it is clear that the imaginary indices of several individual minerals contribute to the estimated imaginary index of this meteorite.