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In the tandem planet formation regime,planets form at two distinct sites where solid particles are densely accumulated due to the on/off state of the magnetorotational instability(MRI).We found that tandem planet formation can reproduce the solid component distribution of the Solar System and tends to produce a smaller number of large planets through continuous pebble flow into the planet formation sites.In the present paper,we investigate the dependence of tandem planet formation on the vertical magnetic field of the protoplanetary disk.We calculated two cases of B_Z 3.4 × 10~(-3) G and B_Z = 3.4 × 10~(-5) G at 100 AU as well as the canonical case of B_Z = 3.4 × 10~(-4) G.We found that tandem planet formation holds up well in the case of the strong magnetic field(B_Z 3.4 × 10~(-3) G).On the other hand,in the case of a weak magnetic field(B_Z= 3.4 × 10~(-5) G) at 100 AU,a new regime of planetary growth is realized:the planets grow independently at different places in the dispersed area of the MRl-suppressed region of r-8-30 AU at a lower accretion rate of M 10~(-7.4)M_⊙yr~(-1).We call this the "dispersed planet formation" regime.This may lead to a system with a larger number of smaller planets that gain high eccentricity through mutual collisions. 相似文献
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We studied the particle growth in a protoplanetary disk in a high-ionization environment and found that icy planet formation is inactive for a disk with an ionization rate 100 times higher than that of the present Solar System. In particular, in the case of M 10~(-7.4)M_☉yr~(-1), only rocky planet formation occurs. In such a case, all the solid materials in the disk drift inward, eventually reach the inner MRI front,and accumulate there. They form a dense, thin sub-disk of solid particles, which undergoes gravitational instability to form rocky planetesimals. The planetesimals rapidly grow into a planet through pebble accretion. Consequently, rocky planets tend to be much larger than planets formed through other regimes(tandem planet formation regime and dispersed planet formation regime), in which icy planet formation actively takes place. These rocky planets may evolve into hot Jupiters if they grow fast enough to the critical core mass of the runaway gas accretion before the dispersal of the disk gas, or they may evolve into super-Earths if the gas dispersed sufficiently early. 相似文献
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Fabrice Fraysse Oleg S. Pokrovsky Jacques Schott Jean-Dominique Meunier 《Chemical Geology》2009,258(3-4):197-206
In order to better understand the reactivity of plant phytoliths in soil solutions, we determined the solubility, surface properties (electrophoretic mobilities and surface charge) and dissolution kinetics of phytoliths extracted from fresh biomass of representative plant species (larch tree and elm, horsetail, fern, and four grasses) containing significant amount of biogenic silica. The solubility product of larch, horsetail, elm and fern phytoliths is close to that of amorphous silica and soil bamboo phytoliths. Electrophoretic measurements yield isoelectric point pHIEP = 0.9, 1.1, 2.0 and 2.2 for four grasses, elm, larch and horsetail phytoliths respectively, which is very close to that of quartz or amorphous silica. Surface acid–base titrations allowed generation of a 2-pK surface complexation model (SCM) for larch, elm and horsetail phytoliths. Phytoliths dissolution rates, measured in mixed-flow reactors at far from equilibrium conditions at 1 ≤ pH ≤ 8, were found to be very similar among the species, and close to those of soil bamboo phytoliths. Mechanistic treatment of all plant phytoliths dissolution rates provided three-parameters equation sufficient to describe phytoliths reactivity in aqueous solutions:Alternatively, the dissolution rate dependence on pH can be modeled within the concept of surface coordination theory assuming the rate proportional to concentration of > SiOH2+, > SiOH0 and > SiO? species. In the range of Al concentration from 20 to 5000 ppm in the phytoliths, we have not observed any correlation between their Al content and solubility, surface acid–base properties and dissolution kinetics.It follows from the results of this study that phytoliths dissolution rates exhibit a minimum at pH ～ 3. Mass-normalized dissolution rates are similar among all four types of plant species studied and these rates are an order of magnitude higher than those of typical soil clay minerals. The minimal half life time of larch and horsetail phytoliths in the interstitial soil solution ranges from 10–12 years at pH = 2–3 to < 1 year at pH above 6, comparable with mean residence time of phytoliths in soil from natural observations. 相似文献
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Previous paleoenvironmental studies reported the δD values of a mixture of coeluting alkenones. Here, we present a semi-preparative normal-phase high-performance liquid chromatography–mass spectrometry (NP-HPLC–MS) method for purifying long chain (C37 and C38) unsaturated methyl and ethyl ketones (alkenones) on the basis of chain length and degree of unsaturation.The method was applied to purify alkenones in suspended particles and surface sediments from a site in Chesapeake Bay, eastern USA. The hydrogen isotopic composition of di- and triunsaturated C37 and C38 alkenones differed significantly on the basis of chain length and the degree of unsaturation, demonstrating the importance of gas chromatography–isotope ratio-mass spectrometry (GC–irMS) analysis of individual alkenones for accurate paleoenvironmental reconstruction. Constant fractionation factors between alkenones with different chain length but the same degree of unsaturation () and those with the same chain length but different degree of unsaturation () in all samples suggest that the values may represent hydrogen isotope fractionation associated with elongation and desaturation during alkenone biosynthesis. 相似文献
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Frédéric Béjina Misha Bystricky Nicolas Tercé Matthew L. Whitaker Haiyan Chen 《Comptes Rendus Geoscience》2019,351(2-3):86-94
In situ X-ray diffraction was used to measure the isothermal bulk modulus at room conditions (KT0) of synthetic olivines with different iron contents. The chemical formulae of the olivine samples were with x = 0.45; 0.64; 0.82; 1, with 1% standard deviation (referenced as Fa45, Fa64, Fa82 and Fa100, respectively). All experiments were performed in the multi-anvil apparatus installed at NSLS beamline X17B2, to pressures up to about 7 GPa. Unit-cell volumes under hydrostatic conditions and differential stresses present in the samples were calculated using the method developed by Singh et al. (1998), and pressures measured using NaCl as a standard were then corrected for these stresses. Using a second-order Birch–Murnaghan equation of state, we obtained the isothermal bulk modulus of each composition: GPa, GPa, GPa and GPa. These values combined with data available in the literature show that the KT0 of Fe-rich olivines increases very slowly with the Fe content, but possibly not in a simple linear trend. 相似文献
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