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[en] Mineral separates from five carbonaceous chondrites were dated by extinct 16 million year 129I, in an attempt to establish the condensation time of the solar nebula. Two Fe3O4 or Fe3O4--FeS samples from the Murchison and Orgueil meteorites are older than any other material dated thus far, and apparently formed within 2 x 105 years of each other. The great age, close isochronism, and primitive nature of the samples suggest that the event recorded was the condensation stage of the solar nebula. It provides a suitable zero point for the chronology of the early solar system. The 129I/127I ratio during condensation of the nebula was (1.46 +- 0.04) x 10-4. The recrystallized C4 chondrite Karoonda began to retain 129Xe 1.8 +- 0.5 million years after the above event. This short cooling time implies rapid accretion (less than or equal to 1 million years) and a shallow origin (less than or equal to 10 km) below the surface of its parent body. (U.S.)
[en] We measured the abundances of Sr and rare earth elements (REEs) in the matrices of five CV3 carbonaceous chondrites: Meteorite Hills (MET) 00430, MET 01070, La Paz ice field (LAP) 02206, Asuka (A) 881317 and Roberts Massif (RBT) 04143. In the MET 00430 and MET 01074 matrices, the Sr/CI and light REE (LREE, La–Nd)/CI ratios positively correlate with the amounts of Ca-rich secondary minerals, which formed during aqueous alteration in the CV3 chondrite parent body. In contrast, in the LAP 02206 and RBT 04143 matrices, although the Sr/CI ratios correlate with the amounts of Ca-rich secondary minerals, the LREE/CI ratios vary independently from the amounts of any secondary minerals. This suggests that the LREE/CI ratios in these matrices were produced prior to the parent body alteration, probably in the solar nebula. The LREE/CI ratios of the LAP 02206 and RBT 04143 matrices reveal the mixing process of matrix minerals prior to the accretion of the CV3 chondrite parent body. The mixing degrees of matrix minerals might be different between these two matrices. Because solid materials would be mixed over time according to the radial diffusion model of a turbulent disk, the matrix minerals consisting of LAP 02206 and RBT 04143 matrices might be incorporated into their parent body with different timing. .
[en] True relative Sr isotopic compositions, determined by the double-spike technique, are reported for 8 olivine chondrules from Allende and a single chondrule from Richardton. The Richardton chondrule has an Sr composition identical with the whole meteorite, but the Allende chondrules are up to 1.4% per mass unit light-isotope enriched, closely similar to Ca-Al inclusions (CAI) from the same individual stone. The correspondence of the patterns for chondrules and CAI suggests that both groups of objects derived their fractionated Sr in similar ways. The lack of any detectable non-linear Sr isotopic anomaly in the objects suggests that their Sr compositions did not have some exotic or extrasolar origin, but were derived from normal system Sr by mass fractionation. The consistent light-Sr enrichment of Allende objects may be explained by several schemes, and all are heavily model-dependent. Most plausible to the author is that the CAI and chondrules derived their fractionated Sr from a region of the nebula made isotopically light by partial kinetic mass separation of elements in the vapour phase. Later, the solid objects may have moved to an isotopically more normal region, where the Allende matrix accreted. (orig.)
[en] We study the influence of transport processes on the chemical evolution of DM Tau-like protoplanetary disks. Turbulent transport of gases and ices is implicitly modeled in full two dimensions (2D), using the mixing-length approximation, along with the time-dependent chemistry. We find that turbulent transport enhances abundances and column densities of many gas-phase species and ices, particularly, complex ones. The influence of turbulent mixing on disk chemistry is more pronounced in the inner, planet-forming disk region where gradients of temperature and high-energy radiation intensities are steeper than in the outer region. The molecules that are unresponsive to transport include, e.g., C2H, C+, CH4, CN, CO, HCN, HNC, H2CO, OH, as well as water and ammonia ice. Their column densities computed with the laminar and 2D mixing model differ by a factor of ∼< 2-5. Molecules whose vertical column densities in the laminar and dynamical models differ by up to two orders of magnitude include, e.g., C2H2, some carbon chains, CS, H2CS, H2O, HCO+, HCOOH, HNCO, N2H+, NH3, CO ice, H2CO ice, CH3OH ice, and electrons. Molecules whose column densities are altered by diffusion by more than two orders of magnitude include, e.g., C2S, C3S, C6H6, CO2, O2, SiO, SO, SO2, long carbon chain ices, CH3CHO ice, HCOOH ice, O2 ice, and OCN ice. We indicate several observable or potentially detectable tracers of transport processes in protoplanetary disks and the solar nebula, such as heavy hydrocarbon ices, complex organics, CO2, O2, SO, SO2, C2S, C3S compared to CO and water ice.
[en] The hydrodynamical axially symmetric collapse of a 3 M -cloud with an initial density of 10-20 g cm-3 has been investigated. In order to first arrive at an equilibrium configuration a temperature of 15K has been assumed. During about 9 free-fall times the cloud has artificially been cooled down to the (Jeans-) critical temperature of 8K. Thus, the dynamical collapse studied in this paper starts from an equilibrium configuration following a slow quasi-hydrostatic contraction. Two sequences corresponding to a different choice of the initial angular velocity Ωi = 10-14 sec-1 (Case A) and Ωi = 10-15 sec-1 (Case B) have been computed. In both cases a fast spinning, optically thick disk-like core of low mass and temperature forms for which fission into two or even more pieces is very likely to occur. (orig.)
[de]Der hydrodynamische, axialsymmetrische Kollaps einer Wolke mit 3M(Sonne) und einer urspruenglichen Dichte von 10-20 g/cm3 wurde untersurcht. Um zuerst eine Gleichgewichtskonfiguration zu erreichen, wurde eine Temperatur von 15K angenommen. Waehrend etwa der neunfachen Zeit des freien Falls wird die Wolke kuenstlich auf die kritische (Jeans-) Temperatur von 8K heruntergekuehlt. Deshalb beginnt der in dieser Arbeit untersuchte dynamische Kollaps mit einer Gleichgewichtskonfiguration, gefolgt von einer Phase langsamer quasi-hydrostatischer Kontraktion. Fuer zwei verschiedene Anfangswerte der Winkelgeschwindigkeit Ωi = 10-14 sec-1 (Fall A) und Ωi = 10-15 sec-1 (Fall B) wird die Entwicklung berechnet. In beiden Faellen bildet sich ein schnell rotierender, optisch dicker scheibenfoermiger Core geringer Masse und niedriger Temperatur der mit grosser Wahrscheinlichkeit in zwei oder noch mehr Stuecke zerfaellt. (orig.)
[en] The aggregation, fragmentation and thermal processing of dust in protoplanetary disks is believed to be the first step on the long road from dust to planets. Models of this process in the literature have so far been applied mostly to the early solar system, and were mostly limited to a static 'minimum mass solar nebula' model of the protoplanetary disk. We present the initial results of a campaign to extend such a modeling to evolving protoplanetary disks, to improve the realism and detail of coagulation/fragmentation models compared to models in the literature so far and to link these models to observations
[en] The appearance of an inner edge to the Oort comet cloud at a semimajor axis of a = (1--2) x 104 AU is an observational artifact. Stellar perturbations are frequent enough and strong enough to assure that a constant fraction of the comets with semimajor axes greater than this are in orbits which bring them within the planetary region. Only infrequent, close stellar encounters are able to repopulate the planet-crossing orbits of comets with smaller semimajor axes. Owing to their relatively short orbital periods which return them frequently to the planetary system, the comets in these more tightly bound orbits will be deflected by Jupiter into drastically different orbits or be destroyed by solar heating before another close stellar passage repopulates their numbers. Comets with semimajor axes less than 2 x 104 AU appear in the inner solar system only in intense bursts or showers which last for a few orbital periods after the close passage of a star to the Sun. This is followed by a much longer span of time during which only comets with a>2 x 104 AU enter the planetary system. The theoretically determined location of the boundary between the semimajor axes of those comets which enter the planetary system only in bursts or showers and those which arrive in a steady stream is very abrupt and falls at the observed inner edge of the Oort cloud. We propose that the comets formed in the outer parts of the collapsing protosun, which had a radius of less than 5 x 103 AU. If this produced a first-generation comet cloud with a radius of 103 AU or greater, the coupled dynamical perturbations of passing stars and Jupiter will, of necessity, lead to the formation of a comet cloud similar that of the observed Oort comet cloud
[en] The clustering of fine particles by mutual thermal collisions is investigated experimentally. Fine particles are prepared in an argon gas atmosphere by the gas evaporation technique. Mass distributions of clusters of the particles are obtained from micrographs of specimen grids placed at different heights above the evaporating source. The cluster growth is clearly seen in the change of mass distribution with height. A comparison of the experimental results with a theoretical model indicates that the cluster of fine particles does not grow in the spherical manner usually assumed, but in a planar manner. As an important consequence of the conclusion to the primordial solar nebula, the sedimentation time of the grains sinking towards the equatorial plane of the solar disk becomes longer than the value previously adopted because of the large ratio of surface to volume of a planar cluster. This longer time should alter the scenario of the evolution of the solar system after sedimentation. (Auth.)
[en] A general form of the planetary distance law has been proposed based on the distance relation in the Solar System derived by Rawal (1989) from the 'modern Laplacian theory' of the formation of the Solar System discussed by Prentice (1978) together with the concept of Roche limit. 5 refs