Impacts between differentiated planetesimals are ubiquitous in protoplanetary discs and may mix materials from the core, mantle, and crust of planetesimals, thus forming stony-iron meteorites. The surface composition of the asteroid (16) Psyche represents a mixture of metal and non-metal components. However, the velocities, angles, and outcome regimes of impacts that mixed metal and silicate from different layers of planetesimals are debated. Our aim is to investigate the impacts between planetesimals that can mix large amounts of metal and silicate, and the mechanism of stony-iron meteorite formation. We used smooth particle hydrodynamics to simulate the impacts between differentiated planetesimals with various initial conditions that span different outcome regimes. In our simulations, the material strength was included and the effects of the states of planetesimal cores were studied. Using a statistical approach, we quantitatively analysed the distributions of metal and silicate after impacts. Our simulations modelled the mass, depth, and sources of the metal-silicate mixture in different impact conditions. Our results suggest that the molten cores in planetesimals could facilitate mixing of metal and silicate. Large amounts of the metal-silicate mixture could be produced by low-energy accretional impacts and high-energy erosive impacts in the largest impact remnant, and by hit-and-run and erosive impacts in the second-largest impact remnant. After impact, most of the metal-silicate mixture was buried at depth, consistent with the low cooling rates of stony-iron meteorites. Our results indicate that mesosiderites potentially formed in an erosive impact, while pallasites potentially formed in an accretional or hit-and-run impact. The mixing of metal and non-metal components on Psyche may also be the result of impacts.
Formation of Cosmic Crystals in Highly-Supersaturated Silicate Vapor Produced by Planetesimal Bow Shocks
一些证据表明，在原始陨石和行星际尘埃颗粒（IDP）中观察到的细硅酸盐晶体在过饱和硅酸盐蒸气中成核，然后结晶生长。我们研究了$μ$ m大小的硅酸盐颗粒的蒸发和结晶硅酸盐从蒸汽中的冷凝，从而产生的弓形激波产生的小行星轨道在早期太阳星云的气体加热。我们对激波加热的数值模拟表明，当弓形激波强到足以使球粒前体尘埃颗粒熔化时，这些微米级颗粒几乎完全蒸发。我们发现，硅酸盐蒸汽冷却非常迅速的膨胀到周围的无冲击星云区域，冷却速率估计，例如，高达2000 K s $^{-1}$的蒸汽加热的弓激波与半径为1公里的星子。蒸汽的快速冷却导致尘埃的非平衡气相冷凝，其温度远低于平衡冷凝的预期温度。结果发现，冷凝温度低于几百K或更多的平衡温度。这解释了最近硅酸盐蒸汽冷凝实验研究的结果，即在如此大的过冷度下的冷凝再现了与陨石中发现的硅酸盐晶体相似的形态。我们的研究结果强烈地表明，在早期太阳系中，星子弓形激波不仅是球粒形成的可能场所之一，而且也是其他宇宙晶体形成的可能场所之一。
Sticking Properties of Silicates in Planetesimal Formation Revisited
在过去，实验室实验和理论计算表明，在星子形成的背景下，硅酸盐的衍生粘附性能不匹配。Kimura等人（2015）提出，这种不匹配是由于假设的表面能值，据推测与颗粒表面上不同厚度的水层的存在或缺乏有关。我们目前的抗拉强度测量粉尘聚集体具有不同的水含量在这里。结果支持Kimura et al.（2015）的建议。干样品显示出比湿样品高出10倍的强度。$γ= 0.2 J/m^2$的高值可能适用于原行星盘的干燥低压条件，将来应该使用。
Context: The formation of rocky planetesimals is a long-standing problem in planet formation theory. One of the possibilities is that it results from gravitational instability as a result of pile-up of small silicate dust particles released from sublimating icy pebbles that pass the snow line. Aims: We want to understand and quantify the role of the water snow line for the formation of rock-rich and ice-rich planetesimals. In this paper, we focus on the formation of rock-rich planetesimals. A companion paper examines the combined formation of both rock-rich and ice-rich planetesimals. Methods:…
Around the snow line, icy pebbles and silicate dust may locally pile-up and form icy and rocky planetesimals via streaming instability and/or gravitational instability. We perform 1D diffusion-advection simulations that include the back-reaction to radial drift and diffusion of icy pebbles and silicate dust, ice sublimation, release of silicate dust, and their recycling through recondensation and sticking onto pebbles outside the snow line. We use a realistic description of the scale height of silicate dust obtained from Ida et al. and that of pebbles including the effects of a Kelvin-Helmholt…
During the formation of terrestrial planets, volatile loss may occur through nebular processing, planetesimal differentiation, and planetary accretion. We investigate iron meteorites as an archive of volatile loss during planetesimal processing. The carbon contents of the parent bodies of magmatic iron meteorites are reconstructed by thermodynamic modelling. Calculated solid/molten alloy partitioning of C increases greatly with liquid S concentration and inferred parent body C concentrations range from 0.0004 to 0.11 wt.%. Parent bodies fall into 2 compositional clusters characterized by cores…
Long-lived thermal dynamo generation on differentiated, impact-disrupted planetesimals
organization= Centre for Planetary Habitability , addressline= Department of Geosciences, University of Oslo , city= Oslo , country= Norway；organization= Department of Earth Sciences , addressline= University of Oxford, South Parks Road , city= Oxford , postcode= OX1 3AN , country= UK
Giant planet migration is an important phenomenon in the evolution of planetary systems. Recent works have shown that giant planet growth and migration can shape the asteroid belt, but these works have not considered interactions between planetesimals. We have calculated the evolution of planetesimal disks, including planetesimal-planetesimal collisions, during gas giant growth and migration. The numbers, locations, and impact velocities of these collisions depend on the specific growth and migration path. We find that giant planet growth alone has little effect on impact velocities, and most …
The ungrouped iron meteorite Nedagolla is the first meteorite with bulk Mo, Ru, and Ni isotopic compositions that are intermediate between those of the non-carbonaceous (NC) and carbonaceous (CC) meteorite reservoirs. The Hf-W chronology of Nedagolla indicates that this mixed NC-CC isotopic composition was established relatively late, more than 7 million years after Solar System formation. The mixed NC-CC isotopic composition is consistent with the chemical composition of Nedagolla, which combines signatures of metal segregation under more oxidizing conditions (relative depletions in Mo and W)…
Metal-Silicate Segregation During Planetary Accretion: Limited Iron Emulsification through intermediate Impacts
School of Science and Engineering, Tulane University（杜兰大学科学与工程学院）；Department of Physics, University of Louisiana at Lafayette（路易斯安那拉斐特大学物理系）；School of Earth and Atmospheric Sciences, Queensland University of Technology（昆士兰科技大学地球与大气科学学院）
As part of our ongoing initiative on accurately calculating the accretion rate of planetesimals in the core-accretion model, we demonstrated in a recent article that when the calculations include the gravitational force of the Sun (the original core-accretion model did not include solar gravity), results change considerably [ApJ, 899:45]. In this paper, we have advanced our previous study by including the effect of Saturn. To maintain focus on the effect of this planet, and in order to be consistent with previous studies, we did not include the effect of the nebular gas. Results demonstrated t…
Accretion and differentiation of the terrestrial planets with implications for the compositions of early-formed Solar System bodies and accretion of water
Carbon is an essential element for the existence and evolution of life on Earth. Its abundance in Earth's crust and mantle (the Bulk Silicate Earth, BSE) is surprisingly high given that carbon is strongly siderophile (metal-loving) at low pressures and temperatures, and hence should have segregated almost completely into Earth's core during accretion. Estimates of the concentration of carbon in the BSE lie in the range 100-260 ppm and are much higher than expected based on simple models of core-mantle differentiation. Here we show through experiments at the putative conditions of Earth's core …
We assess whether chondrules, once-molten mm-sized spheres filling the oldest meteorites, could have formed from super-km/s collisions between planetesimals in the solar nebula. High-velocity collisions release hot and dense clouds of silicate vapor which entrain and heat chondrule precursors. Thermal histories of CB chondrules are reproduced for colliding bodies $\sim$10--100 km in radius. The slower cooling rates of non-CB, porphyritic chondrules point to colliders with radii $\gtrsim$ 500 km. How chondrules, collisionally dispersed into the nebula, agglomerated into meteorite parent bodies …
Collision and disruption processes of proto-planetary bodies in the early solar system are key to understanding the genesis of diverse types of main-belt asteroids. Mesosiderites are stony-iron meteorites that formed by mixing of howardite-eucrite-diogenite-like crust and molten core materials and provide unique insights into the catastrophic break-up of differentiated asteroids. However, the enigmatic formation process and the poorly constrained timing of metal-silicate mixing complicate the assignment to potential parent bodies. Here we report high-precision uranium-lead dating of mesosideri…
Mesosiderites are a type of stony-iron meteorites composed of a mixture of silicates and Fe-Ni metals. The mesosiderite silicates and metals are considered to have originated from the crust and metal core, respectively, of a differentiated asteroid. In contrast, mesosiderites rarely contain the olivine that is mainly included in a mantle. Although a giant impact onto a differentiated asteroid is considered to be a probable mechanism to mix crust and metal materials to form mesosiderites, it is not obvious how such a giant impact can form mesosiderite-like materials without including mantle mat…
