• Book Review: New Cosmic Horizons, David Leverington

      Clark, C. E. (The Meteoritical Society, 2002-01-01)
    • Molecular and isotopic analyses of Tagish Lake alkyl dicarboxylic acids

      Pizzarello, Sandra; Huang, Yongsong (The Meteoritical Society, 2002-01-01)
      The Tagish Lake meteorite soluble organic suite has a general composition that differs from those of both CI- and CM chondrites. These differences suggest that distinct processes may have been involved in the formation of different groups of organics in meteorites. Tagish Lake alkyl dicarboxylic acids have a varied, abundant distribution and are, with carboxylated pyridines, the only compounds to have an occurrence comparable to that of the Murchison meteorite. This study has undertaken their molecular and isotopic characterization, with the aim to understand their origin and to gain insights into the evolutionary history of the meteorite parent body. Tagish Lake alkyl dicarboxylic acids are present as a homologous series of saturated and unsaturated species with three through ten-carbon atom chain length. Linear saturated acids are predominant and show decreasing amounts with increasing chain length. A total of forty-four of these compounds were detected with the most abundant, succinic acid, present at ~40 nmoles/g. met. Overall the molecular distribution of Tagish Lake dicarboxylic acids shows a remarkable compound to compound correspondence with those observed in the Murchison and Murray meteorites. In both Tagish Lake and Murchison, the imides of the more abundant dicarboxylic acids were also observed. All delta-D and delta-13C values for Tagish Lake acids are positive and show a substantial isotopic enrichment. delta-D values vary from, approximately, +1120 ppm for succinic acid to +1530 ppm for methyl glutaric acid. delta-13C values ranged from +12.6 ppm for methyl glutaric acid to +22.9 ppm for glutaric acid, with adipic acid having a significantly lower value (+5.5 ppm). Murchison dicarboxylic acid showed similar isotopic values: their delta-13C values were generaly higher by an average 17% and delta-D values were lower for succinic and glutaric acids, possibly due to contamination. The molecular and isotopic data collected for these compounds restrict their possible origin to processes, either interstellar or of very cold nebular regions, that produced significant isotopic enrichments. Saturated or partially unsaturated nitriles and dinitriles appear to be good precursor candidates as their hydrolysis, upon water exposure, would produce dicarboxylic acids and other carboxylated species found in Tagish Lake. This evolutionary course could possibly include pre-accretionary processes.
    • Amino acids in the Tagish Lake Meteorite

      Kminek, G.; Botta, O.; Glavin, D. P.; Bada, J. L. (The Meteoritical Society, 2002-01-01)
      High performance liquid chromatography (HPLC) based amino acid analysis of a Tagish Lake meteorite sample recovered three months after the meteorite fell to Earth have revealed that the amino acid composition of Tagish Lake is strikingly different from that of the CM and CI carbonaceous chondrites. We found that the Tagish Lake meteorite contains only trace levels of amino acids (total abundance = 880 parts per billion, ppb), which is much lower than the total abundance of amino acids in the CI Orgueil (4,100 ppb) and the CM Murchison (16,900 ppb). Because most of the same amino acids found in the Tagish Lake meteorite are also present in the Tagish Lake ice melt water, we conclude that the amino acids detected in the meteorite are terrestrial contamination. We found that the exposure of a sample of Murchison to cold water lead to a substantial reduction over a period of several weeks in the amount of amino acids that are not strongly bound to the meteorite matrix. However, strongly bound amino acids that are extracted by direct HCl hydrolysis, are not affected by the leaching process. Thus even if there had been leaching of amino acids from our Tagish Lake meteorite sample during its three month residence in Tagish Lake ice and melt water, a Murchison type abundance of endogenous amino acids in the meteorite would have still been readily detectable. The low amino acid content of Tagish Lake indicates that this meteorite originated from a different type of parent body than the CM's and CI's. The parent body was apparently devoid of the reagents such as aldehyldes/ketones, HCN and ammonia needed for the effective abiotic synthesis of amino acids. Based on reflectance spectral measurements, Tagish Lake has been associated with P or D- type asteroids. If the Tagish Lake meteorite was indeed derived from these types of parent bodies, our understanding of these primitive asteroids needs to be re-evaluated with respect to their potential inventory of biologically important organic compounds.
    • From the Editors

      Brown, P. G.; Hildebrand, A. R.; Zolensky, M. E. (The Meteoritical Society, 2002-01-01)
    • The Mazapil meteorite: From paradigm to periphery

      Beech, M. (The Meteoritical Society, 2002-01-01)
      The remarkable fact about the Mazapil meteorite is that it fell on the same night, in 1885, that the Andromedid meteor shower underwent a spectacular outburst. The simultaneity of these two events has driven speculation ever since. From ~1886 to ~1950 the circumstances of the Mazapil fall were taken, by a number of researchers, as the paradigm that demonstrated the fact that comets were actually swarms of meteoritic boulders. Beginning ~1950, however, most researchers began to adopted the stance that the timing of the Mazapil fall was nothing more than pure coincidence. The reason behind this change in interpretation stemmed from, amongst other factors, the fact that none of the prominent annual meteor showers could be clearly shown to deliver meteorites. Also, with the introduction of the icy-conglomerate model for cometary nuclei, by F. Whipple in the early 1950s, it became increasingly clear that only exceptional circumstances would allow for the presence of large meteoritic bodies in cometary streams. Further, by the mid 1960s it had been shown that meteorites could, in fact, be delivered to the Earth from the main belt asteroid region via gravitational resonances. With the removal of the dynamical 'barrier' against the delivery of meteorites from the asteroid region, the idea that the Mazapil meteorite could have been part of the Andromedid stream fell into complete disfavor. This being said, we nonetheless present the results of a study concerning the possible properties of the parent object to the Mazapil meteorite based upon the assumption that it was a member of the Andromedid stream. This study is presented to illustrate the point that while cometary showers do not yield meteorites on the ground, this does not, in fact, substantiate the argument that no meteoritic bodies reside in cometary streams. Indeed, we find no good reason to suppose that an object with the characteristics of the Mazapil meteorite could not have been delivered from the Andromedid stream. However, we argue that upon the basis of the actual reported observations and upon the scientific maxim of minimized hypothesis and least assumption it must be concluded that the timing of the fall of the Mazapil meteorite and the occurrence of the Andromedid outburst were purely coincidental.
    • An entry model for the Tagish Lake fireball using seismic, satellite and infrasound records

      Brown, P. G.; ReVelle, D. O.; Tagliaferri, E.; Hildebrand, A. R. (The Meteoritical Society, 2002-01-01)
      We present instrumental observations of the Tagish Lake fireball and interpret the observed characteristics in the context of two different models of ablation. From these models we estimate the pre‐atmospheric mass of the Tagish Lake meteoroid to be ~56 tonnes and its porosity to be between 37 and 58%, with the lowest part of this range most probable. These models further suggest that some 1300 kg of gram‐sized or larger Tagish Lake material survived ablation to reach the Earth's surface, representing an ablation loss of 97% for the fireball. Satellite recordings of the Tagish Lake fireball indicate that 1.1 x 10^12 J of optical energy were emitted by the fireball during the last 4 s of its flight. The fraction of the total kinetic energy converted to light in the satellite pass band is found to be 16%. Infrasonic observations of the airwave associated with the fireball establish a total energy for the event of 1.66 +/- 0.70 kT TNT equivalent energy. The fraction of this total energy converted to acoustic signal energy is found to be between 0.10 and 0.23%. Examination of the seismic recordings of the airwave from Tagish Lake have established that the acoustic energy near the sub‐terminal point is converted to seismic body waves in the upper‐most portion of the Earth's crust. The acoustic energy to seismic energy coupling efficiency is found to be near 10^(-6) for the Tagish Lake fireball. The resulting energy estimate is near 1.7 kT, corresponding to a meteoroid 4 m in diameter. The seismic record indicates extensive, nearly continuous fragmentation of the body over the height intervals from 50 to 32 km. Seismic and infrasound energy estimates are in close agreement with the pre‐atmospheric mass of 56 tonnes established from the modeling. The observed flight characteristics of the Tagish Lake fireball indicate that the bulk compressive strength of the pre‐atmospheric Tagish Lake meteoroid was near 0.25 MPa, while the material compressive strength (most appropriate to the recovered meteorites) was closer to 0.7 MPa. These are much lower than values found for fireballs of ordinary chondritic composition. The behavior of the Tagish Lake fireball suggests that it represents the lowest end of the strength spectrum of carbonaceous chondrites or the high end of cometary meteoroids. The bulk density and porosity results for the Tagish Lake meteoroid suggest that the low bulk densities measured for some small primitive bodies in the solar system may reflect physical structure dominated by microporosity rather than macroporosity and rubble‐pile assemblages.
    • Magnetic study of magnetite in the Tagish Lake meteorite

      Thorpe, A. N.; Senftle, F. E.; Grant, J. R. (The Meteoritical Society, 2002-01-01)
      The saturation magnetization, saturation remanent magnetization, the coercive, and remanent coercive force were determined at room and liquid nitrogen temperatures for three pieces of the Tagish Lake meteorite. The results are compared to similar data for four other chondrites (Allende, Murray, Orgueil, and Murchison). The data suggests that the Tagish Lake meteorite is magnetically homogeneous, and is not as magnetically hard as the comparison chondrites. The magnetization measurements indicate that it contains about 10-11% multi-domain magnetite. Magnetic susceptibility measurements on all the samples from 77 K to room temperature showed a Verwey transition for all the samples which contain a significant amount of multi-domain magnetite. The coercive force data further indicate that the magnetite in Tagish Lake is multi-domain and that the grain size is small and approximately 4-9 micrometers.
    • Mineralogy of Tagish Lake: An ungrouped type 2 carbonaceous chondrite

      Zolensky, M. E.; Nakamura, K.; Gounelle, M.; Mikouchi, T.; Kasama, T.; Tachikawa, O.; Tonui, E. (The Meteoritical Society, 2002-01-01)
      In this paper we describe the recovery, handling and preliminary mineralogical investigation of the Tagish Lake meteorite. Tagish Lake is a type 2 carbonaceous chondrite which bears similarities to CI1 and CM chondrite groups, but is distinct from both. Abundant phyllosilicates as well as chondrules (however sparse) and common olivine grains in the matrix preclude any other classification. The bulk density of Tagish Lake (1.67 g/cc), which is far lower than CI or CM chondrites (2.2-2.3 and 2.6-2.9 g/cc, respectively), or any other meteorite for that matter. We have identified two lithologies: a dominant carbonate-poor lithology and a less-abundant carbonate-rich lithology. The meteorite is a breccia at all scales. We have noted similarities between Tagish Lake and some clasts within the enigmatic meteorite Kaidun; possibly there are genetic relationships here worth exploring. In the paper we describe a clast of CM1 material within Tagish Lake which is very similar to a major lithology in Kaidun.
    • Light element geochemistry of the Tagish Lake CI2 chondrite: Comparison with CI1 and CM2 meteorites

      Grady, Monica M.; Verchovsky, A. B.; Franchi, I. A.; Wright, I. P.; Pillinger, C. T. (The Meteoritical Society, 2002-01-01)
      We have studied the carbon and nitrogen stable isotope geochemistry of a small pristine sample of the Tagish Lake carbonaceous chondrite by high resolution stepped combustion mass spectrometry, and compared the results with data from the Orgueil (CI1), EET 83334 (CM1) and Murchison (CM2) chondrites. The small chip of Tagish Lake analysed herein had a higher carbon abundance (5.81 wt%) than any other chondrite, and a nitrogen content (~1220 ppm) between that of CI1 and CM2 chondrites. Owing to the heterogeneous nature of the meteorite, the measured carbon abundance might be artificially high: the carbon inventory and whole rock carbon isotopic composition (delta-13C is approximately equal to +24.4 ppm) of the chip was dominated by 13C-enriched carbon from the decomposition of carbonates (between 1.29 and 2.69 wt%; delta-13C is approximately equal to +67 ppm and delta-18O is approximately equal to +35 ppm, in the proportions ~4:1 dolomite to calcite). In addition to carbonates, Tagish Lake contains organic carbon (~2.6 wt%; delta-13C is approximately equal to -9 ppm; 1033 ppm N, delta-15N is approximately equal to +77 ppm), a level intermediate between CI and CM chondrites. Around 2% of the organic material is thermally labile and solvent soluble. A further ~18% of the organic species are liberated by acid hydrolysis. Tagish Lake also contains a complement of presolar grains. It has a higher nanodiamond abundance (~3650-4330 ppm) than other carbonaceous chondrites, along with ~8 ppm silicon carbide. Whilst carbon and nitrogen isotope geochemistry is not diagnostic, the data are consistent with classification of Tagish Lake as a CI2 chondrite.
    • Comparison of the trace element composition of Tagish Lake with other primitive carbonaceous chondrites

      Friedrich, Jon M.; Wang, Ming-Sheng; Lipschutz, Michael E. (The Meteoritical Society, 2002-01-01)
      A meteorite fall on 18 January 2000 was detected by U.S. Defense Department satellites which established its pre-impact orbit. Fresh samples were collected from frozen Tagish Lake in British Columbia a week later and some properties of these samples reveal it to be a unique meteorite. We characterized Tagish Lake and 8 other samples using ICPMS and RNAA: data for 47 elements reveal that each of 9 carbonaceous chondrites of different type exhibit the Orgueil-normalized plateaus expected for members of such types. Trends evident in Tagish Lake differ from all other carbonaceous chondrites, including CI and CM. Samples of Tagish Lake collected later show similar patterns affected by weathering.
    • Mineralogy and petrology of melt rocks from the Popigai impact structure, Siberia

      Whitehead, J.; Grieve, R. A. F.; Spray, J. G. (The Meteoritical Society, 2002-01-01)
      The late Eocene Popigai impact structure of Siberia comprises an approximately 0.5-1.5 km thick, ~100 km diameter sequence of clast-rich and clast-poor andesitic to rhyolitic impact melt rocks and impact breccias, underlain by Archean to Proterozoic crystalline basement and Proterozoic to Phanerozoic sedimentary rocks. The fine-grained to cryptocrystalline texture of the more melt-rich rocks, despite their occurrence in bodies locally in excess of 800 m thick and 28 km long, suggests that the melt crystallized in response to: (1) cooling by the clast load, and/or; (2) rapid nucleation on finely brecciated clasts, which have since been assimilated and/or; (3) crystallization enhanced by the relatively low water contents of the melts. Rapid crystallisation of the melt is indicated by the lack of zoning in minerals, the presence of glass, the lack of strain recovery features in clasts and the lack of evidence for fractionation in the major and trace elements, including the rare-earth elements. Optical and analytical electron microscopy reveal that the previously reported division of the melt rocks into high- and low-temperature variants based on hand sample appearance, or glass content, is not warranted. Clasts within the melt-rich rocks exhibit a wide range of shock metamorphic features, though they are not distributed in the impact melts in a systematic manner. This indicates that the melt-rich rocks were well mixed during their formation, thus juxtaposing unshocked with shocked material. Injection of mesostasis melt into partially melted checkerboard plagioclase and orthopyroxene clasts also occurred during this mixing stage.
    • Geochemistry of the ungrouped carbonaceous chondrite Tagish Lake, the anomalous CM chondrite Bells, and comparison with CI and CM chondrites

      Mittlefehldt, David W.; Killgore, Marvin; Lee, Michael T. (The Meteoritical Society, 2002-01-01)
      I have determined the composition via INAA of a bulk pristine sample of the Tagish Lake carbonaceous chondrite fall, along with bulk samples of the CI chondrite Orgueil and of several CM chondrites. Tagish Lake has a mean of refractory lithophile element/Cr ratios like those of CM chondrites, and distinctly higher than the CI chondrite mean. Tagish Lake exhibits abundances of the moderately volatile lithophile elements Na and K that are slightly higher than those of mean CM chondrites. Refractory through moderately volatile siderophile element abundances in Tagish Lake are like those of CM chondrites. Tagish Lake is distinct from CM chondrites in abundances of the most volatile element. Mean CI-normalized Se/Co, Zn/Co and Cs/Co for Tagish Lake are 0.68 +/- 0.01, 0.71 +/- 0.07 and 0.76 +/- 0.02, while for all available CM chondrite determinations, these ratios lie between 0.31-0.61, 0.32-0.58 and 0.39-0.74, respectively. Considering petrography, and oxygen isotopic and elemental compositions, Tagish Lake is an ungrouped member of the carbonaceous chondrite clan. The overall abundance pattern is similar to those of CM chondrites, indicating that Tagish Lake and CMs experienced very similar nebular fractionations. Bells is a CM chondrite with unusual petrologic characteristics. Bells has a mean CI-normalized refractory lithophile element/Cr ratio of 0.96, lower than for any other CM chondrite, but shows CI-normalized moderately volatile lithophile element/Cr ratios within the ranges of other CM chondrites, except for Na which is low. Iridium, Co, Ni and Fe abundances are like those of CM chondrites, but the moderately volatile siderophile elements, Au, As and Sb, have abundances below the ranges for CM chondrites. Abundances of the moderately volatile elements Se and Zn of Bells are within the CM ranges. Bells is best classified as an anomalous CM chondrite.