本文提出后处理工具Differentiated Body Composition Tracker，基于50次REBOUND模拟追踪碰撞中核幔物质转移，揭示非均匀核物质分布与巨型撞击可形成富铁行星。
摘要：
以往研究表明，在行星形成后期，行星胚胎与星子之间的撞击往往可以决定组成一个系统中新形成行星的核与幔物质比例。此前研究曾尝试将这些碰撞改变成分的效应纳入行星形成的N体模拟，且通常以后处理代码的形式实现。在本文中，我们提出了Differentiated Body Composition Tracker（分化天体成分追踪器），这是一种新的后处理工具，利用从N体积分器REBOUND收集的碰撞数据，确定撞击过程中碰撞天体与所产生碎片之间转移的核物质和幔物质数量。我们使用来自50次REBOUND行星形成模拟的数据展示该代码的工作方式，并探讨代码参数如何影响这些模拟中留存天体的核质量分数。随后，我们研究初始星盘中核物质的非均匀分布如何影响行星最终的核质量分数。在理想条件下，我们发现，巨型撞击与富含核物质的行星胚胎相结合，可能形成一些已被发现的富铁行星。
英文摘要：
Previous research suggests that impacts between planetary embryos and planetesimals during the late stages of planet formation can often determine the percentages of core and mantle material that compose the newly formed planets in a system. Previous studies have attempted to include the composition-changing effects of these collisions in N-body simulations of planet formation, often as post-processing codes. In this paper, we present the Differentiated Body Composition Tracker, a new post-processing tool that uses collisional data collected from the N-body integrator REBOUND to determine the amount of core and mantle material that is transferred between colliding objects and the resulting fragments during an impact. We demonstrate how this code works using the data from 50 REBOUND simulations of planet formation and explore how the parameters in the code affect the core mass fractions of the remaining objects from these simulations. We then investigate how non-uniform distributions of core material across an initial disc affect the final core mass fractions of planets. Under ideal conditions, we find that a combination of giant impacts and planetary embryos enriched in core material could create some of the iron-rich planets that have been discovered.
The creep tide theory is used to establish the basic equations of the tidal evolution of differentiated bodies formed by aligned homogeneous layers in co-rotation. The mass concentration of the body is given by the fluid Love number $k_f$. The formulas are given by series expansions valid for high eccentricity systems. They are equivalent to Darwin's equations, but formally more compact. An application to the case of Enceladus, with $k_f=0.942$, is discussed.
Self-consistent-field method for triaxial differentiated bodies in hydrostatic equilibrium
Université Paris Cité, CNRS, Institut de Physique du Globe de Paris（巴黎西岱大学、法国国家科学研究中心、巴黎地球物理研究所）；Université de Bordeaux, CNRS, Laboratoire d’Astrophysique de Bordeaux（波尔多大学、法国国家科学研究中心、波尔多天体物理实验室）
We present a fragmentation module and a composition tracking code for the $n$-body code REBOUND. Our fragmentation code utilises previous semi-analytic models and follows an implementation method similar to fragmentation for the $n$-body code MERCURY. In our $n$-body simulations with fragmentation, we decrease the collision and planet formation timescales by inflating the particle radii by an expansion factor $f$ and experiment with various values of $f$ to understand how expansion factors affect the collision history and final planetary system. As the expansion factor increases, so do the rat…
We introduce here our new approach to modeling particle cloud evolution off surface of small bodies (asteroids and comets), following the evolution of ejected particles requires dealing with various time and spatial scales, in an efficient, accurate and modular way. In order to improve computational efficiency and accuracy of such calculations, we created an N-body modeling package as an extension to the increasingly popular orbital dynamics N-body integrator Rebound. Our code is currently a stand-alone variant of the Rebound code and is aimed at advancing a comprehensive understanding of indi…
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
Dynamical models of Solar System evolution have suggested that P-/D-type volatile-rich asteroids formed in the outer Solar System and may be genetically related to the Jupiter Trojans, the comets and small KBOs. Indeed, their spectral properties resemble that of anhydrous cometary dust. High-angular-resolution images of P-type asteroid (87) Sylvia with VLT/SPHERE were used to reconstruct its 3D shape, and to study the dynamics of its two satellites. We also model Sylvia's thermal evolution. The shape of Sylvia appears flattened and elongated. We derive a volume-equivalent diameter of 271 +/- 5…
Necroplanetology: Simulating the Tidal Disruption of Differentiated Planetary Material Orbiting WD 1145+017
WD 1145+017系统显示出不规则的凌日特征，这与体积密度为$< 4$ g cm $^{-3}$和体积质量为$\lesssim 10^{21}$ kg的分化小行星的潮汐破裂相一致（Veras等人，2017; arXiv：1610.06926）。我们使用开源的N体代码REBOUND（Rein and Liu，2011; arXiv：1110.4876）来模拟这种具有不同内部结构的破坏：改变内核体积分数，地幔/内核密度比，以及存在/不存在薄的低密度地壳。我们允许碎石堆部分中断和捕获光变曲线在特定的点，在中断的节奏可比的地面测光。作为概念验证，我们表明，随着小行星被破坏，改变这些结构参数对过境光变曲线有观测上可区分的影响，并将模拟生成的光变曲线与Gary等人的数据进行比较，2017年（arXiv：1608.00026）。需要说明的是，我们的模拟没有详细模拟升华或解释其对轨道演化的影响，我们发现低核心分数和低地幔/核心密度比的小行星与2016年4月左右存在多周的稳定过境特征最一致（在Gary等人中称为G6121，2017（arXiv：1608.00026）和Hallakoun等人的A1，2017（arXiv：1702.05483）.将潮汐扰动模拟与测光相结合，可以揭示出系外行星体的内部结构和组成特征，这些信息只有在我们观测到行星系正在死亡时才有可能。像TESS和LSST这样的全天巡天任…
Volatile compositions of asteroids provide information on the Solar System history and the origins of Earth's volatiles. Visible to near-infrared observations at wavelengths of $<2.5\ {\rm μm}$ have suggested a genetic link between outer main belt asteroids located at $2.5$-$4\ {\rm au}$ and carbonaceous chondrite meteorites (CCs) that show isotopic similarities to volatile elements on Earth. However, recent longer wavelength data for large outer main belt asteroids show $3.1\ {\rm μm}$ absorption features of ammoniated phyllosilicates that are absent in CCs and cannot easily form from materia…
The interest in the structure of ice-rich planetary bodies, in particular the differentiation between ice and rock, has grown due to the discovery of Kuiper belt objects and exoplanets. We thus carry out a parameter study for a range of planetary masses $M$, yielding radii $50 \aplt R \aplt 3000$~km, and for rock/ice mass ratios between 0.25 and 4, evolving them for 4.5~Gyr in a cold environment, to obtain the present structure. We use a thermal evolution model that allows for liquid and vapor flow in a porous medium, solving mass and energy conservation equations under hydrostatic equilibrium…
Metallic bodies that were the cores of differentiated bodies are sources of iron meteorites and are considered to have formed early in the terrestrial planet region before migrating to the main asteroid belt. Surface temperatures and mutual collision velocities differ between the terrestrial planet region and the main asteroid belt. To investigate the dependence of crater shape on temperature, velocity and impactor density, we conducted impact experiments on room- and low-temperature iron meteorite and iron alloy targets (carbon steel SS400 and iron-nickel alloy) with velocities of 0.8-7 km/s.…
Magnetic fields provide an important probe of the thermal, material, and structural history of planetary and sub-planetary bodies. Core dynamos are a potential source of magnetic fields for differentiated bodies, but evidence of magnetization in undifferentiated bodies requires a different mechanism. Here we study the amplified field provided by the stellar wind to an initially unmagnetized body using analytic theory and numerical simulations, employing the resistive MHD AstroBEAR adaptive mesh refinement (AMR) multiphysics code. We obtain a broadly applicable scaling relation for the peak mag…
On The Effect of Giant Planets on the Scattering of Parent Bodies of Iron Meteorite from the Terrestrial Planet Region into the Asteroid Belt: A Concept Study
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)…
碰撞演化是星子形成的关键过程，分米天体在不同的模型中起着关键作用。然而，两个尘土飞扬的分米物体之间的碰撞结果从未被实验研究过。因此，我们在不来梅落塔中进行了微重力碰撞实验。团聚体由具有不规则形状的微米级颗粒的石英组成，并且平均体积填充因子为0.437 $\pm$ 0.004。骨料为高12 cm、直径12 cm的圆柱体，典型质量为1.5 kg。这些是迄今为止在碰撞中研究的最大和最大的尘埃聚集体。在0.8 - 25.7 cm s $^{-1}$之间的速度范围内，我们观察到回弹和碎裂，但没有粘附。团聚体分裂的临界破碎速度为16.2 $\pm$ 0.4 cm s $^{-1}$。在较低的速度下，聚集体彼此反弹。在此速度范围内，恢复恢复系数随碰撞速度的增加而从0.8减小到0.3。虽然聚集体非常弱，但碎裂的临界比动能$Q_{μ=1}$比预期大6倍。大型天体在原行星盘中的碰撞应该快得多，并且很可能产生较小的碎片。在行星环中，碰撞速度大约为几厘米/秒$^{-1}$，因此在这些实验中研究的范围内。行星环中常见的尘埃团块和风化层覆盖的冰粒的恢复系数是相似的。
In order to link infrared observations of dust formed during planet formation in debris disks to mid-infrared spectroscopic data of planetary materials from differentiated terrestrial and asteroidal bodies, we obtained absorption spectra of a representative suite of terrestrial crustal and mantle materials, and of typical Martian meteorites. A series of debris disk spectra characterized by a strong feature in the 9.0-9.5 micron range (HD23514, HD15407a, HD172555 and HD165014), is comparable to materials that underwent shock, collision or high temperature events. These are amorphous materials s…
Accretion processes in protoplanetary disks produce a diversity of small bodies that played a crucial role in multiple reshuffling events throughout the solar system and in both early and late accretion of planets. Application of thermo-chronometers to meteorites provides precise dating of the formation age of mineralogical components. Nucleosynthetic anomalies indicating a dichotomy between NC and C meteorites and precise parent body (PB) chronology can be combined with thermal evolution models to constrain the timescale of accretion and dynamical processes in the early solar system. Achondri…
According to adaptive-optics observations by Ferrais et al., (22) Kalliope is a 150-km, dense and differentiated body. Here, we interpret (22) Kalliope in the context of bodies in its surroundings. While there is a known moon Linus, with a 5:1 size ratio, no family has been reported in the literature, which is in contradiction with the existence of the moon. Using the hierarchical clustering method (HCM) along with physical data, we identified the Kalliope family. Previously, it was associated to (7481) San Marcello. We then used various models (N-body, Monte-Carlo, SPH) of its orbital and col…
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…
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…
Universität Bern（伯尔尼大学）；Institut für Geologie, Universität Bern（伯尔尼大学地质研究所）；Universität Münster（明斯特大学）；Institut für Planetologie, Universität Münster（明斯特大学行星研究所）；Max Planck Institute for Solar System Research（马克斯·普朗克太阳系统研究所）；Thermo Fisher Scientific（赛默飞世尔科技）
An experimental study of low-velocity impacts into granular material in reduced gravity
为了提高我们对着陆小天体和小行星演化的理解，我们使用新型落塔设施进行了低速（2-40 cm s^-1）、浅撞击实验，将直径10 cm的铝球在低有效重力（~0.2-1 m s^-2）下撞击石英砂。使用现场加速度计，我们测量的加速度曲线的影响，并确定峰值加速度，碰撞持续时间和最大穿透深度。我们发现，穿透深度与碰撞速度成线性比例，但在实验范围内测试的有效重力是独立的，并且碰撞持续时间是独立的有效重力和碰撞速度。在任何实验中都没有观察到反弹。我们的低重力实验结果表明，从准静态制度的惯性制度的过渡发生的碰撞能量两个数量级小于在地球重力下的类似的碰撞实验。较低的能量状态变化可能是由于在我们的实验中表面材料的流体动力学阻力增加，但也可能支持准静态状态随着有效重力变低而减少的概念。
Impact-induced erosion of the Earth's early crust during accretion of terrestrial bodies can significantly modify the primordial chemical composition of the Bulk Silicate Earth (BSE, that is, the composition of the crust added to the present-day mantle). In particular, it can be particularly efficient in altering the abundances of elements having a strong affinity for silicate melts (i.e. incompatible elements) as the early differentiated crust was preferentially enriched in those. Here, we further develop an erosion model (EROD) to quantify the effects of collisional erosion on the final comp…
