CLASSIFICATION OF EIGHT ORDINARY CHONDRITES FROM TEXAS

Based on optical microscopy and electron microprobe analyses, eight previously undescribed or poorly known chondrites were classified into compositional groups, petrologic types, and degree of shock alteration. These chondrites are: Leander, L4b; Nazareth(a), L6d; La Villa, H4b; Mereta, H4c; Gail, H4d; Shafter Lake, H5a; Uvalde, H5d; and Howe, H5d.     

Search for HD in Jupiter and Saturn

Upper limits are placed on the D/H ratio in the observed portions of the atmospheres of Jupiter and Saturn from observations at high S/N over the region of the 5-0 R(1) line of HD. The upper limits of 4 × 10^?5 and 6 × 10^?5 D/H on Jupiter and Saturn, respectively, are not inconsistent with present models for abundance ratios in the primitive solar nebula or with other estimates of this quantity from observations.     

Mass spectrometric study of three-body ion-molecule clustering reactions of CpHq+ ions with N2 or CH4 in N2-CH4 mixtures

Thermochemical data for several ion-molecule clustering of hydrocarbon ions with N2 or CH4 were obtained from clustering equilibria studies in gas mixtures irradiated by alpha-particles. High-pressure mass spectrometry was used to determine the enthalpy and entropy changes of clustering (delta H0 and delta S0, respectively) for the reactions X+(N2)n-1 + 2N2 <==> X(+)(N2)n + N2 with X = CH5, n = 1-2; X = C2H5, n = 1-4; and X = C3H7, n = 1. For X = CH5, the values (delta H0; delta S0) are found to be (-6.8 kcal mol-1; -19.7 cal mol-1 K-1) for n = 1, and (-5.3 kcal mol-1; -15.9 cal mol-1 K-1) for n = 2. For X = C2H5, (delta H0; delta S0) = (-6.9 kcal mol-1; -18.2 cal mol-1 K-1), for n = 1, and (-4.6 kcal mol-1; -20.8 cal mol-1 K-1) for n = 2. From the equilibrium measurements at 129 K, estimates of the thermochemical values could be obtained for n = 3-4. The results obtained for the free energy, delta G0, were -1.4 kcal mol-1 for n = 3, and -1.1 kcal mol-1 for n = 4. For X = C3H7 we found delta G0 = -0.7 kcal mol-1 at 213 K. The association reactions X+ + 2CH4 <==> X+(CH4) + CH4 with X = CH5, C2H5, C2H7, and C3H7 were also studied, resulting in free energy values at 206 K of -3.1, -1.9, -0.5 and -1.3 kcal mol-1, respectively. The results for CH5, C2H5 and C3H7 are compared with previously reported measurements.     

Classification of Six Ordinary Chondrites from Texas

Abstract— Based on optical microscopy, modal and electron microprobe analyses, six ordinary chondrites from Texas preserved in the Monnig Meteorite Collection at Texas Christian University, Fort Worth, Texas, were classified in compositional groups, petrologic types, and shock facies. These meteorites are Comanche (stone), L5c; Haskell, L5c; Deport (a), H4b; Naruna (a), H4b; Naruna (b), H4b; and Clarendon (b), H5d.     

Noble gases and mineralogy of meteorites from China and the Grove Mountains,Antarctica: A 0.05 Ma cosmic ray exposure age of GRV 98004

Abstract— We determined the mineralogical and chemical characteristics and the He, Ne, and Ar isotopic abundances of 2 meteorites that fell in China and of 2 meteorites that were recovered by the 15th Chinese Antarctic Research Expedition. Guangmingshan (H5), Zhuanghe (H5), and Grove Mountain (GRV) 98002 (L5) yield cosmic ray exposure (CRE) ages of 68.7 ± 10.0 Ma, 3.8 ± 0.6 Ma, and 17.0 ± 2.5 Ma, respectively. These ages are within the range typically observed for the respective meteorite types. GRV 98004 (H5) had an extremely short parent body‐Earth transfer time of 0.052 ± 0.008 Ma. Its petrography and mineral chemistry are indistinguishable from other typical H5 chondrites. Only 3 other meteorites exist with similarly low CRE ages: Farmington (L5), Galim (LL6), and ALH 82100 (CM2). We show that several asteroids in Earth‐crossing orbits, or in the main asteroid belt with orbits close to an ejection resonance, are spectrally matching candidates and may represent immediate precursor bodies of meteorites with CRE ages ≤0.1 Ma.     

CLASSIFICATION OF A SECOND GROUP OF ORDINARY CHONDRITES FROM TEXAS

Based on optical microscopy and electron microprobe analyses of mafic minerals, six previously undescribed or poorly known ordinary chondrites from Texas were classified into compositional groups, petrologic types, and shock facies. These meteorites are Junction, L5d; Anton, H4b; Venus, H4d; Dalhart, H5a; Rosebud, H5c; and Cranfills Gap, H6c.     

Some Peculiarities of H-Chondrite Parent Body Evolution

Cosmic-ray exposure ages and gas-retention ages have been calculated for more than 1000 ordinary chondrites. The distributions of meteorites according to ages, local times of fall, and fragment numbers and shapes have been analyzed. The H5-chondrites have been found to differ from H3-, H4-, and H6-chondrites in a number of characteristics: the H5-chondrites lose both cosmogenic and radiogenic gases much more readily; on falling to Earth, H5-chondrites break up into a greater number of fragments, and the parameters that characterize the shape of H5-chondrites (the b/aand c/aratios) likewise appear to differ from the corresponding parameters of H-chondrites of other petrologic types. These features of H5-chondrites are difficult to attribute to their small-perihelion orbits, greater preatmospheric mass, or higher velocity of atmospheric entry. In addition to this, a higher proportion of morning falls is observed among H5-chondrites, especially among meteorites formed in the large-scale event that occurred 7 Myr ago. It is assumed that these distinctive features of H5-chondrites may be due to changes caused in the physical properties (dispersity of mineral components, fracture system, etc.) of the material of the petrologic type 5 of the H-chondrite parent body by the shock effect during megabreccia formation or at a later time. Part of the H5-chondrites segregated from the parent body 7 Myr ago could have been injected deeply into ₆or 3 : 1 resonances, which could have increased the proportion of H5-chondrite morning falls, especially among meteorites with cosmic-ray exposure ages of 4–10 Myr.     

Hα photometry of Abell 2390

We present the results of a search for strong H α emission line galaxies (rest frame equivalent widths greater than 50 Å) in the z ≈0.23 cluster Abell 2390. The survey contains 1189 galaxies over 270 arcmin², and is 50 per cent complete at M _r ≈−17.5+5 log  h . The fraction of galaxies in which H α is detected at the 2 σ level rises from 0.0 in the central regions (excluding the cD galaxy) to 12.5±8 per cent at R ₂₀₀. For 165 of the galaxies in our catalogue, we compare the H α equivalent widths with their [O  ii ] λ 3727 equivalent widths, from the Canadian Network for Observational Cosmology (CNOC1) spectra. The fraction of strong H α emission line galaxies is consistent with the fraction of strong [O  ii ] emission galaxies in the CNOC1 sample: only 2±1 per cent have no detectable [O  ii ] emission and yet significant (>2 σ ) H α equivalent widths. Dust obscuration, non-thermal ionization, and aperture effects are all likely to contribute to this non-correspondence of emission lines. We identify six spectroscopically 'secure' k+a galaxies [ W ₀(O  ii )<5 Å and W ₀(H δ )≳5 Å]; at least two of these show strong signs in H α of star formation in regions that are covered by the slit from which the spectra were obtained. Thus, some fraction of galaxies classified as k+a based on spectra shortward of 6000 Å are likely to be undergoing significant star formation. These results are consistent with a 'strangulation' model for cluster galaxy evolution, in which star formation in cluster galaxies is gradually decreased, and is neither enhanced nor abruptly terminated by the cluster environment.     

Stones from Mohave County,Arizona: Multiple falls in the “Franconia strewn field”

One of the most productive and well‐sampled dense collection areas for meteorites on Earth is the “Franconia strewn field” in Mohave County, Arizona, which since 2002 has yielded hundreds of meteorites in an ellipsoidal area approximately 5 × 16 km across. Based on petrographic, mineral‐chemical, and terrestrial age data, we conclude that among 14 meteorites examined, there are at least 6 and possibly 8 distinct meteorites represented, which fell over a period of approximately 0–20 kyr ago. These include equilibrated H‐chondrites such as Franconia (H5) and Buck Mountains (BM) 001 (H6); H3–6 breccias such as Buck Mountains Wash and BM 004; and L6 chondrites such as BM 002 and BM 003 (which may be paired), Palo Verde Mine, and BM 005. To confidently pair such meteorites often requires thorough petrographic examination, mineral‐chemical analyses, and terrestrial ages. We estimate that 50 ± 10% of the larger specimens in this area are paired, yielding a relatively high value of approximately 2.3–2.9 distinct meteorites km^?2. The meteorite flux estimated for Franconia area is higher than the flux inferred from contemporary fireball data for larger masses. We suggest that one large H3–6 meteoroid fell in the area, most likely that of Buck Mountains Wash approximately 4 kyr ago, which produced an elliptical strewn field with masses generally increasing toward one end, and which raised the meteorite productivity in the recovery area.     

H4 and H5 chondrites from the Rub'al Khali Desert

Abstract Al-Jimshan is a highly weathered 11.45 kg chondrite that was found in 1955 in the Rub' al Khali Desert, Saudi Arabia (20*42′N, 52*50E) about 240 km south-east of the town of al-Hadidah. The main mass is now at UCLA. Based on texture and mineral composition (olivine Fa_17.7 ± 0.4; pyroxene Fs_15.7 ± 1.0 Wo₁₃ ± 0.4), al-Jimshan is classified as an H4 chondrite of shock stage S2. The Bir-Hadi and ad-Dahbubah H chondrites, which also were found in the Rub'al Khali (Holm, 1962), are probably not paired with al-Jimshan. They are classified as H5, shock stage S3 (Fa_18.1 ± 0.5, n = 10; Fs_16.0 ± 0.6, Wo_1.1 ± 0.4, n = 9) and H5, shock stage S2 (Fa_17.9 ± 0.3, n = 10; FS_15.5 ± 0.2 Wo_1.0 ± 0.4, n = 10), respectively.     

The metal homogeneity of the globular star cluster M5

This work is concerned with the precision measurement of the magnitudes of the stars across a large field of the galactic globular cluster M5. The colours of the red giants are subjected to a thorough statistical analysis in order to quantify the extent of any star-to-star variations in metal abundance within the cluster. Use is made of an extensive optical/near-infrared observational data set acquired with a large-array CCD detector and the Johnson V and I filters. The results of this photometry, which is accurate to within a few millimagnitudes for the brighter stars, are used to compile a colour–magnitude diagram.
The analysis finds that in a metal-rich M5 ([Fe/H]=−1.2) the extent of any metal inhomogeneity, Δ[Fe/H], is less than ±0.1 dex, and in a metal-poor M5 ([Fe/H]=−1.5) then     . (The literature contains a range of derived values of metallicity for M5.)     

Photochemistry of the atmosphere of Titan: comparison between model and observations

The photochemistry of simple molecules containing carbon, hydrogen, nitrogen, and oxygen atoms in the atmosphere of Titan has been investigated using updated chemical schemes and our own estimates of a number of key rate coefficients. Proper exospheric boundary conditions, vertical transport, and condensation processes at the tropopause have been incorporated into the model. It is argued that he composition, climatology, and evolution of Titan's atmosphere are controlled by five major processes: (a) photolysis and photosensitized dissociation of CH4; (b) conversion of H to H2 and escape of hydrogen; (c) synthesis of higher hydrocarbons; (d) coupling between nitrogen and hydrocarbons; (e) coupling between oxygen and hydrocarbons. Starting with N2, CH4, and H2O, and invoking interactions with ultraviolet sunlight, energetic electrons, and cosmic rays, the model satisfactorily accounts for the concentrations of minor species observed by the Voyager IRIS and UVS instruments. Photochemistry is responsible for converting the simpler atmospheric species into more complex organic compounds, which are subsequently condensed at the tropopause and deposited on the surface. Titan might have lost 5.6 x 10(4), 1.8 x 10(3), and 4.0 g cm-2, or the equivalent of 8, 0.25, and 5 x 10(-4) bars of CH4, N2, and CO, respectively, over geologic time. Implications of abiotic organic synthesis on Titan for the origin of life on Earth are briefly discussed.     

The Meteoritical Bulletin,No. 83, 1999 July

Abstract— Meteoritical Bulletin No. 83 lists information for 898 newly described meteorites. These include 473 from Antarctica, 341 from the Sahara, and 22 from dry lakes in the southwestern United States. Seven of the meteorites are falls: Kunya-Urgench (H5), Lohawat (howardite), Ourique (H4), Portales Valley (H6), San Pedro de Quiles (L6), Talampaya (eucrite), and Zag (H3-6). Also included are a dozen new iron meteorites; several mesosiderites; a pallasite; several HED meteorites; several ureilites; a variety of CM, CO, CV, CR, and R chondrites; and numerous unequilibrated ordinary chondrites. All shock classifications are after Stöffler et al. (1991) and weathering grades are after Wlotzka (1993), except as noted. All italicized abbreviations refer to addresses tabulated at the end of this document.     

Chemical and oxygen isotopic properties of ordinary chondrites (H5, L6) from Oman: Signs of isotopic equilibrium during thermal metamorphism

Mean bulk chemical data of recently found H5 and L6 ordinary chondrites from the deserts of Oman generally reflect isochemical features which are consistent with the progressive thermal metamorphism of a common, unequilibrated starting material. Relative differences in abundances range from 0.5–10% in REE (Eu = 14%), 6–13% in siderophile elements (Co = 48%), and >10% in lithophile elements (exceptions are Ba, Sr, Zr, Hf, U = >30%) between H5 and L6 groups. These differences may have accounted for variable temperature conditions during metamorphism on their parent bodies. The CI/Mg‐normalized mean abundances of refractory lithophile elements (Al, Ca, Sm, Yb, Lu, V) show no resolvable differences between H5 and L6 suggesting that both groups have experienced the same fractionation. The REE diagram shows subtle enrichment in LREE with a flat HREE pattern. Furthermore, overall mean REE abundances are ~0.6 × CI with enriched La abundance (~0.9 × CI) in both groups. Precise oxygen isotope compositions demonstrate the attainment of isotopic equilibrium by progressive thermal metamorphism following a mass‐dependent isotope fractionation trend. Both groups show a ~slope‐1/2 line on a three‐isotope plot with subtle negative deviation in ?¹⁷O associated with δ¹⁸O enrichment relative to δ¹⁷O. These deviations are interpreted as the result of liberation of water from phyllosilicates and evaporation of a fraction of the water during thermal metamorphism. The resultant isotope fractionations caused by the water loss are analogous to those occurring between silicate melt and gas phase during CAI and chondrule formation in chondrites and are controlled by cooling rates and exchange efficiency.     

Origin and history of chondrite regolith,fragmental and impact-melt breccias from Spain

Abstract— Six ordinary chondrite breccias from the Museo Nacional de Ciencias Naturales, Madrid (Spain), are described and classified as follows: the solar gas-rich regolith breccia Oviedo (H5); the pre-metamorphic fragmental breccias Cabezo de Mayo (type 6, L-LL), and Sevilla (LL4); the fragmental breccias Cañellas (H4) and Gerona (H5); and the impact melt breccia, Madrid (L6). We confirm that chondrites with typical light-dark structures and petrographic properties typical of regolith breccias may (Oviedo) or may not (Cañellas) be solar gas-rich. Cabezo de Mayo and Sevilla show convincing evidence that they were assembled prior to peak metamorphism and were equilibrated during subsequent reheating. These meteorites contain small melt rock clasts that were incorporated into the host chondrite while still molten and/or plastic and cooled rapidly and, yet, are totally equilibrated with their hosts. Compositions of olivine and low-Ca pyroxene in host chondrite and breccia clasts in Cabezo de Mayo are transitional between groups L and LL. It is suggested, based on mineralogic and oxygen isotopic compositions of host and clasts, that the rock formed on the L parent body by mixing, prior to peak metamorphism. This was followed by partial equilibration of two different materials: the indigenous L chondrite host and exotic LL melt rock clasts.     

Search for H2 Emission from Disks around T Tauri and Herbig AE Stars

Preliminary results are presented of observations of the pure rotational lines of H2 toward T Tauri and Herbig Ae stars using the Short Wavelength Spectrometer (SWS) on the Infrared Space Observatory (ISO). The sources are selected to be isolated low- and intermediate-mass young stellar objects, for which the presence of a circumstellar disk has been established by millimeter interferometry. The lowest H2 S(0) and S(1) lines are detected in 3 out of 5 objects. The measured intensities indicate ∼ 0.01 M⊙ of warm (T ≈ 150 K) gas in the ISO beam. It is argued that for at least one case (HD 163296), the emission is probably dominated by the warm gas in the circumstellar disk rather than by shocked- or photon-heated gas in the surrounding envelope. Such observations can provide important constraints on the radial and vertical temperature profiles in circumstellar disks. This revised version was published online in August 2006 with corrections to the Cover Date.     

Weathering in Antarctic H and CR chondrites: Quantitative analysis through Mössbauer spectroscopy

Abstract— Mössbauer spectroscopy is a very useful tool for identifying ferric iron weathering products in meteorites because of the capability to quantify the relative amounts of ferric iron in them. Mössbauer measurements were made of 33 Antarctic H chondrites (predominately H5) and two paired Antarctic CR chondrites. The primary goals of this study are to determine if Mössbauer spectroscopy can be used to determine which phases are weathering in Antarctic meteorites and if the relative amounts of ferric iron correlate with terrestrial age. Determining which minerals are weathering in ordinary chondrites appears very difficult due to variations in composition for different ordinary chondrites of the same meteorite class and possible problems in preparing homogeneous samples. The analysis of the two paired CR chondrites appears to indicate that metallic iron is predominately weathering to produce ferric iron for this class of meteorite. No correlation is seen between the relative amounts of ferric iron and terrestrial age for ordinary chondrites. One Antarctic H5 chondrite (ALHA77294) with a short ¹⁴C age of 135 ± 200 years from the dating of interior carbonate weathering products does have a relatively low amount of ferric iron, which is consistent with this meteorite being exposed on the surface for a relatively short time.     

Magombedze: A new H-chondrite with light-dark structure

Abstract— Magombedze is a light-dark structured H-chondrite breccia that fell in Zimbabwe on 1990 July 2 at 15:30 GMT. White clasts are moderately shocked and have equilibrated mafic silicates (pyroxene Fs_16–18, olivine Fa_18–19) together with clear optically-recognizable plagioclase of variable composition (An_9–13 found); chondrules are distinct but contain no trace of preserved glass. The darker surrounding material contains a higher proportion of fine-grained metal and sulfide than the white clasts, and many of its constituent grains show little evidence of shock. Mafic silicates in the dark lithology are distinctly less-equilibrated (pyroxene Fs_5–21, olivine Fa_11–20) than those in the white clasts, and many chondrules preserve brown devitrified glass; some metamorphic plagioclase of variable composition (An_11–22, found) is present. Some monoclinic pyroxene occurs in both fractions, but it is relatively common in the dark fraction. The white clasts are classified as H5, and the enclosing dark material is H3–5.     

The Cerro los Calvos and La Banderia chondrites

Abstract— The Cerro los Calvos meteorite is a single stone of 68.5 g found in the Nuevo Mercurio strewn field of Zacatecas, Mexico (24°20′N, 102°8′W). It is an unusual H4 chondrite. Its olivine (Fa_12.5) and orthopyroxene (Fs 11.7, Wo 0.8) are reduced relative to typical H chondrites. The La Banderia meteorite of 54.3 g from the same vicinity is an LL5 chondrite of shock classification e.