Kinetic model of ammonia synthesis in the solar nebula

The synthesis of ammonia in the primitive solar nebula was probably catalyzed by metallic iron grains because the gas phase reaction is kinetically inhibited. A preliminary kinetic model predicts a maximum of 3% of the nitrogen in the form of ammonia at the time of planetary accretion. Rates of reaction were derived from industrial data on ammonia iron catalysts. Due to the low rates of reaction, molecular nitrogen remains the dominant species even at the low temperatures where chemical equilibrium favors ammonia formation. Thus planetary atmospheres formed from a reservoir composed largely of molecular nitrogen. The non-equilibrium volatile gases (CO and N₂) suggested to comprise most of the carbon and nitrogen in comets is consistent with the model.     

Evaporation metamorphism of primitive dust material in the early solar nebula

An evaporation experiment on matrix material of the Murchison (C2) meteorite up to 1900°C in vacuo has revealed the evaporation sequence of primitive dust material and the associated evolution of residual solid phases from hydrous silicates through magnesium silicates and iron-metal to calcium-aluminum oxides. The comparison with primitive meteorites suggests that the evaporation metamorphism coupled with the re-condensation may have played an important role in the generation of diverse primitive meteorites in the early solar nebula.     

Carbon isotopic fractionation in the process of Fischer-Tropsch reaction in primitive solar nebula

Carbon isotopic fractionation of low-weight molecules of the products of Fischer-Tropsch reaction under the conditions of Earth's accumulation region in primitive solar nebula has been experimentally studied. Among the reaction products, carbon dioxide has the heaviest isotopic composition; carbon isotopic composition of methane has a large variation; different from biogenic natural gases, carbon isotopic compositions among ethane, propane and butane yield a reverse distribution pattern. It suggests that primordial hydrocarbons that were captured in the interior of the Earth during its accretion possess a reverse carbon isotopic distribution pattern. Project supported by the National Natural Science Foundation of China (Grant No. 49233060).     

On the formation of meteoritic chondrules by aerodynamic drag heating in the solar nebula

During the formation of the solar nebula interstellar grains were fallling into the nebula with velocities of the order of 10 km/s at the radial distance where the meteorites were to form. This kinetic energy is 20 times the amount of thermal energy needed to melt the grains. The grains were decelerated by aerodynamic drag in the nebula. Where grain-rich parcels of interstellar material fell into the nebula, heat generated by drag could not be radiated away because of the opacity imparted to the system by the grains, and high temperatures were reached. In this situation presolar aggregations of grains would melt to form chondrules. Many of the properties of chondrules (and also CAI's) are consistent with their formation by this means. The infall heating concept provides a new framework in which the formation and significance of chondritic meteorites can be understood.     

Magnetic fields of the solar nebula as recorded in chondrules from the Allende meteorite

The natural remanent magnetization (NRM) in individual chondrules from the Allende meteorite was measured. These had previously been oriented relative to each other. The NRM directions of the chondrules are not initially random, but they become scattered after either alternating field (AF) or thermal demagnetization. The NRM is less stable than anhysteretic remanent magnetization (ARM) against AF-demagnetization.

The bulk of the NRM in the matrix is erased by 300°C. For the larger chondrules it is erased by 550°C, but for the smaller chondrules and the white inclusion a substantial decrease in NRM occurs by 350°C leaving about 20% up to 600°C. The behavior of the laboratory-induced ARM and the NRM under alternating field demagnetization suggest that the NRM of the chondrules consists of at least two components of TRM. One is a high-temperature component which was acquired when the individual chondrules were cooled through the Curie temperature and before they were assembled into the Allende meteorite. The other is a low-temperature component which was probably acquired in a field of about 1 Oe when the meteorite experienced thermal metamorphism or during the assembly of the meteorite.     

On the vertical transport of angular momentum in the atmosphere

Summary The possible modes of vertical transport of angular momentum in the atmosphere are considered. Momentum balance calculations for both hemispheres show the possibility of countergradient transport by vertical eddies in the region of the mid-latitude jet. As a consequence, it is pointed out that the transport of momentum downward from the region of maximum westerlies would have to be accomplished by the mean meridional motions, through the action of Coriolis torques. The same mechanism may account for a large part of the upward transport in the tropics. The very approximate nature of the calculations must, however, be borne clearly in mind.     

Zirconium isotope evidence for incomplete admixing of r-process components in the solar nebula

Isotopic anomalies in Mo and Zr have recently been reported for bulk chondrites and iron meteorites and have been interpreted in terms of a primordial nucleosynthetic heterogeneity in the solar nebula. We report precise Zr isotopic measurements of carbonaceous, ordinary and enstatite chondrites, eucrites, mesosiderites and lunar rocks. All bulk rock samples yield isotopic compositions that are identical to the terrestrial standard within the analytical uncertainty. No anomalies in ⁹²Zr are found in any samples including high Nb/Zr eucrites and high and low Nb/Zr calcium-aluminum-rich inclusions (CAIs). These data are consistent with the most recent estimates of <10⁻⁴ for the initial ⁹²Nb/⁹³Nb of the solar system. There exists a trace of isotopic heterogeneity in the form of a small excess of r-process ⁹⁶Zr in some refractory CAIs and some metal-rich phases of Renazzo. A more striking enrichment in ⁹⁶Zr is found in acetic acid leachates of the Allende CV carbonaceous chondrite. These data indicate that the r- and s-process Zr components found in presolar grains were well mixed on a large scale prior to planetary accretion. However, some CAIs formed before mixing was complete, such that they were able to sample a population of r-process-enriched material. The maximum amount of additional r-process component that was added to the otherwise well-mixed Zr in the molecular cloud or disk corresponds to ∼0.01%.     

Evidence for successive episodes of condensation at high temperature in a part of the solar nebula

A centimeter-sized CaAl-rich inclusion, CAI 3643, in the Allende meteorite has preserved a record of its multiple stages of growth by condensation at high temperature. It consists of three distinct, concentric layers—core, mantle and crust. The open-textured core is composed of hibonite laths, interstitial melilite and voids, grains of alumina, and OsIr metal nuggets in the inner core that are complementary in composition to RuPt-rich nuggets in the outer core. The core formed out of rapidly-aggregated crystals from two episodes of condensation in the same gaseous reservoir. Mo and W depletions in the nuggets indicate condensation from a relatively oxidizing gas, with 60 times higherH/₂OH₂ than solar gas. The compact mantle of coarse melilite contains perovskite inclusions and rare NiFe metal and sulfide grains. The compact, fine-grained crust consists of melilite, hibonite, spinel, perovskite, and opaques similar to those in the mantle. Neither mantle nor crust has been molten; each grew by condensation of solids directly onto the surface of the CAI. The formed CAI experienced some metamorphic recrystallization of melilite, and volatile alteration producing grossular, feldspathoids and hercynite. Trace element analyses of perovskites and a bulk sample show the mantle and crust to be depleted in refractory elements (i.e. Group II) and complementary to the ultra-refractory core. Despite differences in texture and composition, the core, mantle and crust display a continuity in their modal mineralogical compositions, their extreme Al₂O₃ enrichments (53–69% cf. 25–45% for other CAI's) and their trace element complementarity. This implies that all the layers of 3643 formed from the same cooling gaseous reservoir within a limited interval of time and space, consistent with an origin in a local, transient heating event in the CV chondrite formation region of the nebula.     

High temperature rims around chondrules in primitive chondrites: evidence for fluctuating conditions in the solar nebula

Rims or rim sequences surrouding chondrules have been identified in carbonaceous and unequilibrated ordinary chondrites. These chondrule rims include three chemical subtypes: Fe,Ca-rich and Fe,Ni-metal-rich rims, which occur predominantly in Kainsaz (CO3), and ferromagnesian rims which occur in Kainsaz (CO3), Allende (CV3), Renazzo (CR2), Chainpur (LL3), Semarkona (LL3), Krymaka (L3), and Tieschitz (H3). The compositions of minerals in these rims are often drastically different from those in the underlying chondrule cores, indicating that the solar nebula was chemically heterogeneous. In many cases the compositions of the rims require an environment that was much more oxidizing than a solar composition gas. Particularly interesting is that some of the Fe,Ca-rich chondrule rims are remarkably similar to some of the rims around refractory inclusions, suggesting that chondrules and refractory inclusions experienced late, coeval processing. The textures of the chondrule rims suggest they formed at high temperatures and that they accreted onto chondrules that had already solidified. The lengthscale of the thermal heterogeneities necessary to make available hot material that could accrete to cold chondrules has been calculated to be less than 10 km, implying there were localized heat sources in the solar nebula.     

Turbulent transport of angular momentum and differential rotation

Abstract

With the help of simplifying approximations, we have derived expressions for the non-diffusive fluxes of the angular momentum which are brought about by the action of Coriolis forces on the convective motion. The original turbulence, which is not perturbed by the Coriolis forces, is considered given and weakly anisotropic, the anisotropy having a preferred radial direction. The eddy viscosities are evaluated. Hence, a closed equation for the angular velocity is derived, and then solved for the case of slow rotation. It is shown that the differential rotation is generated most effectively in the case of moderate rotation when the Rossby number is of order unity. At small Rossby numbers, the rotation differentiality is inhibited. A negative eddy viscosity is suggested for the case of rapid rotation. Some implications for the Sun and other astrophysical objects are discussed.     

Fractionation in the solar nebula,II. Condensation of Th,U, Pu,and Cm

Reasonable assumptions concerning activity coefficients allow the calculation of the relative volatility of the actinide elements under conditions expected during the early history of the solar system. Several of the light rare earths have volatilities similar to Pu and Cm and can be used as indicators of the degree of fractionation of these extinct elements. Uranium is considerably more volatile than either Pu or Cm, leading to fractionations of about a factor of 50 and 90 in the Pu/U and Cm/U ratio in the earliest condensates from the solar nebula. Ca, Al-rich inclusions from the Allende meteorite, including the coarse-grained inclusions, have a depletion of U relative to La of about a factor of three, suggesting that these inclusions may have been isolated from the nebular gas before condensation of U was complete. The inclusions, however, can be used to determine solar Pu/U and Cm/U ratios if the rare earth patterns are determined in addition to the other normal measurements.     

On cumulus-scale transport of horizontal momentum in monsoon depression over India

A diagnostie method of cumulus parameterization is suggested in which vertical transport of horizontal momentum by cumulus-scale is derived by making use of large-scale vorticity as well as divergence budget equations. Data for composite monsoon depression over India available from our earlier studies used to test the method. As a first approximation, the results are obtained using only the vorticity budget equation.The results show that in the southwest sector of the monsoon depression, which is characterized by maximum cloudiness and precipitation, there is an excess of cyclonic vorticity in the lower troposphere and anticyclonic vorticity in the upper troposphere associated with the large-scale motion. The distribution of eddy vertical transport of horizontal momentum is such that anticyclonic vorticity is generated in the lower troposphere and cyclonic vorticity aloft. Cumulus-scale eddies thus work against the large-scale system and tend to off-set the large-scale imbalance in vorticity.     

Turbulent transport of angular momentum in magnetized fluids and torsional oscillations of the sun

Abstract

Fluxes of angular momentum produced by turbulence in rotating fluids are derived with the effects of a magnetic field included. It is assumed that the rotation is slow but that the magnetic field is of arbitrary strength. A mean magnetic field is shown to produce qualitative changes of the sources of the differential rotation rather than the quenching of differential rotation usually expected. A new equatorward flux of angular momentum arises through the influence of the toroidal magnetic field. The possibility of interpreting the torsional oscillations of the Sun as a consequence of the magnetic perturbations of the turbulent angular momentum fluxes is discussed.     

Spectral characteristics of the meridional transport of angular momentum in the mid-troposhere of the Southern Hemisphere

Summary The wavenumber-frequency spectra of the meridional flux of angular momentum at 20°, 30°, 40°, 50°, 60° and 70°S, at 500 mb, show a definite domain of wave interactions between the zonal and meridional components of the velocity at various latitudes. In middle latitudes, the spectral band of the meridional flux of angular momentum is oriented from a region of low wavenumbers and low frequencies to a region of high wavenumbers and negative frequencies assigned for waves moving from west to east. In low latitudes, however, the spectral domain is confined to a narrow band centered near the zero frquency.In contrast to the meridional flux of angular momentum in the Northern Hemisphere in which the intensity in winter is about twice that in Summer, in the Southern Hemisphere the meridional flux shows same intensity for all seasons.In the Southern Hemisphere, most of the meridional flux of angular momentum is directed toward the south pole and is accomplished by the eastward moving waves. In the Northern Hemisphere, however, most of the meridional flux is directed toward the north pole and is contributed by the stationary waves.The National Center for Atmospheric Research, Boulder, Colorado 80302, (USA).     

Arrival of the first relativistic solar protons and conditions in the solar corona

When solar cosmic rays (SCRs) can be observed with ground-based equipment (ground-level enhancements, GLEs), events are often characterized by a rapid increase in the relativistic proton intensity during the initial phase, which makes it possible to estimate the time of particle escape from the solar corona. This phase attracts attention of researchers owing to its closeness in time to the instant of particle acceleration. It is known that the observed SCR characteristics bear traces of many physical processes, including different acceleration mechanisms the relative role of which is still unclear. Flare processes and acceleration by a shock, related to coronal mass ejection (CME), are the main pretenders to the role of SCR accelerator. Several powerful solar proton events during cycle 23 are considered in the work, and the release time of the first particles from the corona and the dynamics of CMEs have been estimated. The time series of the X-ray and radio bursts, close in time to particle escape, are analyzed. The conclusion have been drawn that the first relativistic particles were most probably accelerated during flare processes.     

Diagnostics of solar wind streams and their sources in the solar corona

The studies are based on the experimental mass sounding of the interplanetary plasma near the Sun at radial distances of R = 4−70 R _S, performed at Pushchino RAO, Russian Academy of Sciences, and on the calculated magnetic fields in the solar corona based on the magnetic field strength and structure measured on the Sun’s surface at J. Wilcox Solar Observatory, United States. The experimental data make it possible to localize the position of the boundary closest to the Sun of the transition transonic region of the solar wind in the near-solar space (R ≈ 10−20 R _S) and to perform an interrelated study of the solar wind structure and its sources, namely, the magnetic field components in the solar corona based on these data. An analysis of the evolution of the flow types in 2000–2007 makes it possible to formulate the physically justified criterion responsible for the time boundaries of different epochs in the solar activity cycle.     

Observing solar phenomenas with the large solar vacuum telescope

The large solar vacuum telescope (LSVT) was designed to study solar phenomenas with high spatial and spectral resolution. Due to the large size of the telescope, its real spatial resolution may be as high as ≈0.4 arcsec, which makes it possible to observe fine-structure solar phenomenas like Ellerman bombs and pores. At present, the main subjects of investigation are solar flares. The LSVT research methods—spectral, spectropolarimetric, and filter—provide valuable information on the physical parameters in the phenomenas under study. Spectra and images of the Sun are recorded through an birefringent filter by two CCD cameras.     

Magnetic coupling in the solar system

Sarah Matthews, Danielle Bewsher and Chris Davis discuss the complexities of the solar magnetic field, informed by data from Hinode and STEREO.