Chemical Composition Of Meteorites Research Articles

Photoluminescence of silicon‐vacancy defects in nanodiamonds of different chondrites

AbstractPhotoluminescence spectra show that silicon impurity is present in lattice of some nanodiamond grains (ND) of various chondrites as a silicon‐vacancy (SiV) defect. The relative intensity of the SiV band in the diamond‐rich separates depends on chemical composition of meteorites and on size of ND grains. The strongest signal is found for the size separates enriched in small grains; thus, confirming our earlier conclusion that the SiV defects preferentially reside in the smallest (≤2 nm) grains. The difference in relative intensities of the SiV luminescence in the diamond‐rich separates of individual meteorites are due to variable conditions of thermal metamorphism of their parent bodies and/or uneven sampling of nanodiamond populations. Annealing of separates in air eliminates surface sp2‐carbon; consequently, the SiV luminescence is enhanced. Strong and well‐defined luminescence and absorption of the SiV defect is a promising feature to locate cold (<250 °C) nanodiamonds in space.

Our astrochemical heritage

Our Sun and planetary system were born about 4.5 billion years ago. How did this happen and what is our heritage from these early times? This review tries to address these questions from an astrochemical point of view. On the one hand, we have some crucial information from meteorites, comets and other small bodies of the Solar System. On the other hand, we have the results of studies on the formation process of Sun-like stars in our Galaxy. These results tell us that Sun-like stars form in dense regions of molecular clouds and that three major steps are involved before the planet formation period. They are represented by the pre-stellar core, protostellar envelope and protoplanetary disk phases. Simultaneously with the evolution from one phase to the other, the chemical composition gains increasing complexity. In this review, we first present the information on the chemical composition of meteorites, comets and other small bodies of the Solar System, which is potentially linked to the first phases of the Solar System's formation. Then we describe the observed chemical composition in the pre-stellar core, protostellar envelope and protoplanetary disk phases, including the processes that lead to them. Finally, we draw together pieces from the different objects and phases to understand whether and how much we inherited chemically from the time of the Sun's birth.

Asteroid (21) Lutetia as a remnant of Earth’s precursor planetesimals

Isotopic and chemical compositions of meteorites, coupled with dynamical simulations, suggest that the main belt of asteroids between Mars and Jupiter contains objects formed in situ as well as a population of interlopers. These interlopers are predicted to include the building blocks of the terrestrial planets as well as objects that formed beyond Neptune (Bottke et al. 2006, Levison et al. 2009, Walsh et al. 2011). Here we report that the main belt asteroid (21) Lutetia – encountered by the Rosetta spacecraft in July 2010 – has spectral (from 0.3 to 25μm) and physical (albedo, density) properties quantitatively similar to the class of meteorites known as enstatite chondrites. The chemical and isotopic compositions of these chondrites indicate that they were an important component of the formation of Earth and other terrestrial planets. This meteoritic association implies that Lutetia is a member of a small population of planetesimals that formed in the terrestrial planet region and that has been scattered in the main belt by emerging protoplanets (Bottke et al. 2006) and/or by the migration of Jupiter (Walsh et al. 2011) early in its history. Lutetia, along with a few other main-belt asteroids, may contains part of the long-sought precursor material (or closely related materials) from which the terrestrial planets accreted.

Models of the Internal Structure of Callisto

Models of the internal structure of Callisto were constructed and the extent of its differentiation was determined based on geophysical information from the Galileo spacecraft (the mass, the radius, the mean density, and the moment of inertia), geochemical data (the chemical composition of meteorites), and the equations of state of water, ices, and meteoritic material. The thickness and the phase state of the water-ice shell were defined as well as the ice concentrations in the rock-ice mantle and the bulk concentration of H2O. The constraints on the density distribution in the mantle and the size of the rock-iron core were derived. We considered models of the internal structure of Callisto in which the presence of a continuous ice shell was assumed (models without ocean) and models with an internal ocean. We demonstrated that it is possible to apply three-layer models with an icy shell up to 320 km in thickness and a rock-iron core in different combinations with a rock-ice mantle. These models do not reject a two-layer structure of Callisto (an ice lithosphere plus a rock-ice mantle or a rock-ice mantle plus a rock-iron core) and a one-layer model of the satellite composed only of a rock-ice mantle with an ice concentration that is variable in depth. Taking into account the chemically bound water, the bulk content of H2O in the satellite is found to be 49–55 wt %. For the model with an internal ocean, the geophysically allowed thickness of the water-ice shell of Callisto was estimated to be 270–315 km with thicknesses of the icy crust and the underlying water layer of 135–150 and 120–180 km, respectively. The results of reconstruction of the composition and structure of the regular satellites of Jupiter allow us to conclude that they were possibly formed from material whose composition was close to ordinary L/LL chondrites at relatively low temperatures, lower than the temperature of evaporation of iron and Fe-Mg silicates.

Core Sizes and Internal Structure of Earth's and Jupiter's Satellites

Models of the internal structure of the Moon and Galilean satellites of Jupiter—Io, Europa, and Ganymede—based on the geophysical (the mass and moment of inertia from recent Lunar Prospector and Galileo gravity measurements, and seismic velocities for the Moon), geochemical (the chemical composition of meteorites), and thermodynamic (modeling of phase relations and physical properties in the Na 2O–TiO 2–CaO–FeO–MgO–Al 2O 3–SiO 2–Fe–FeS system) constraints are constructed. Bulk composition of the Moon (enrichment in SiO 2, FeO, and refractories, and depletion in MgO) resembles neither the terrestrial matter nor the material of chondrites and achondrites. The radii of a lunar core are estimated to be 310–320 km for the Fe core, and 430–440 km for the eutectic Fe–FeS core. The Moon has the lowest Fe tot/Si weight ratio, 0.40–0.47, among the terrestrial planets, chondrites, and satellites of the outer Solar System. The correspondence between the density and moment of inertia values for bulk Io and rock–iron cores of Europa and Ganymede shows that their bulk compositions are, in general, similar and may be described by the composition close to L and LL chondrites. For such composition and density models, radii of the Fe core and eutectic Fe–FeS core are estimated to be R(Fe core)=590–630 km and R(Fe–FeS core)=830–875 km for Io, R(Fe core)=420–510 km and R(Fe–FeS core)=610–710 km for Europa, and R(Fe core)=580–650 km and R(Fe–FeS core)=820–900 km for Ganymede with an outer shell composed of the ice solid phases. The results of modeling support the hypothesis that Io, Europa, and Ganymede have a massive metallic core in which a magnetic field may be produced. Thickness of an ice–liquid outer shell in Europa is estimated to be 120–140 km (7–8% of total mass); thickness of a solid ice outer shell in Ganymede is expected to be 890–920 km (46–48% of total mass). Models showing the outer shell of Ganymede to consist of a mixture of water and ice are considered, and the thickness of an outer water-ice shell (780–850 km) and Fe–FeS core radii are estimated. The possibility of an inner liquid–water layer beneath the icy surface of Ganymede cannot be ruled out if the bulk composition of its rock–iron core were close to the composition of LL (rather than L) chondrites.

AN H4–6 CHONDRITE: MOTTA DI CONTI

The mineralogical and chemical compositions of meteorites from the Motta di Conti, Vercelli, Italy, shower (February 29, 1868) have been determined. Microprobe analyses, of olivine (Fa19,6) and orthopyroxene (Fs17,8), as well as the bulk chemical composition, particularly the ratios of SiO2/MgO (1.50), Fe°/Ni° (11.03), Fetotal/SiO2 (0.81), Fe°/Fetotal (0.70) and the content of Fetotal (28.60%) classify the meteorite as an H‐group chondrite. The percentage of total metallic nickel‐iron (22.06%) is somewhat higher than the average in H‐group chondrites. The texture of our stone shows evidence of metamorphism. The integration between matrix and chondrules is advanced and may suggest a high petrographic grade, but the identification of several microscopic features (e.g. small grains of monoclinic twinned pyroxene, FeNi‐FeS intergrowths, globules and mosaic) leads to the conclusion that a variety of petrographic types (4–6) are present. Metamorphic equilibration in chondrites is discussed and a preliminary hypothesis for H4–6 chondrites is suggested.

Report of the Committee on Meteorites

Several monographs and collections of papers were published in Meteoritics during 1967 to 1969 (Chirvinskij, 1967; Vdovykin, 1967; Wood, 1968; Cikulin, 1969; Anders et al, 1967; Stanjukovič, 1968). Extensive work on meteorites is continuing in the Meteorite Committee of the Academy of Sciences of U.S.S.R. Fesenkov and Krinov continued publishing the journal Meteoritika, where most of the papers of scientists of the U.S.S.R. are published. Hoffleit continued publishing Meteoritics of the Meteorite Society. Javnel’ continued editing a bibliography on meteorites. A bibliography on the isotopic and chemical composition of meteorites was published by Kielbasinski and Wanat. The UNESCO working group on meteorites under the chairmanship of Orcel edited the Directory of Meteorite Collections and Meteorite Research in 1968.The Meteorite Committee of the Academy of Sciences of the U.S.S.R. organized its 13th meteorite conference in 1968. The Meteorite Society had its 30th to 32nd annual meetings during 1967 to 1969. The International Atomic Agency in cooperation with UNESCO and five other international scientific unions and organizations including the IAU represented by Millman, prepared a Symposium on Meteorite Research in Vienna, Austria, 7-13 August, 1968, initiated by the UNESCO Working Group on Meteorites. More than 70 papers were presented at this Symposium, showing the interests of various sciences in meteorites. The Symposium volume appeared very soon after the sessions were closed in the series Astrophysics and Space Science Library, published by D. Reidel Publishing Company, Dordrecht, Holland, under the title Meteorite Research edited by P. M. Millman (1969, 940 pages).

Chemische unterschiede bei uredelgashaltigen steinmeteoriten

So far differences in the chemical composition of meteorites with light-dark structure have only been found for the trace elements C, Bi, and primordial rare gases. In this work further chemical analyses of stony meteorites with sharp boundaries between the light and dark structure have been performed. Large differences have been found in the achondrites Kapoeta and Staroe Pesjanoe. Chondrites show this difference to a smaller extent. In all cases, however, C is enriched in the dark phases by a factor of 2 to 3. The primordial rare gases show a similar behaviour. It is difficult to interpret the chemical differences by the shock and solar wind hypotheses alone. The dark phases have specific similarities with carbonaceous chondrites and can rather be understood as an admixture of carbonaceous chondritic material to the light phases.