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3D Numerical Modelling of Impact Cratering in the Solar System

太阳系撞击坑的 3D 数值模拟

基本信息

批准号：
ST/G002452/1
负责人：
Gareth Collins
金额：
$ 22.72万
依托单位：
Imperial College London
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2009
资助国家：
英国
起止时间：
2009 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=ST%2FG002452%2F1
关键词：
3D Numerical Modelling Impact Cratering

项目摘要

The violent collision of asteroids and comets with solid planetary surfaces is a fundamental and ubiquitous process in the solar system. In the early history of our Solar System, small rocky particles collided and accreted to form larger and larger bodies until they grew into the planets we see today. For the Earth, the last of these planetary-scale collisions was a giant impact that ultimately formed the Moon. More recently in solar system history, a catastrophic impact event caused a mass extinction on Earth, including the demise of the dinosaurs. Today, the impact of an asteroid or comet poses a real, if poorly understood threat to humanity. Impact craters are also used to study the solar system. Counts of the number of impact craters on a solid planetary surface are used to distinguish older from younger terrains, and the shapes of large craters provide clues to the near-subsurface structure of a planet. The catastrophic potential of impact cratering, and its far-reaching consequences, make it imperative to understand exactly how the impact process works. Central to this are fundamental equations that relate the size of an impact crater to properties of the impacting object (for example, size and velocity) and conditions on the target body (for example, gravity). In other words, equations that give the answer to the fundamental question: how large will the crater be if a given impactor strikes a given target surface? At present we cannot adequately answer this question, because the equations do not properly include all the important impactor and target-material properties. The first aim of this proposal is to better constrain the relationship between all the important variables in an impact event using computer models. As these equations are fundamental tools for estimating the consequences of impact, this work will advance understanding in many areas of planetary science. The major missing pieces in these impact equations are an understanding of how the growth of the crater is affected by pore space in the target, and the angle at which the impactor strikes the target. The effect of impact angle is important to establish because well-studied vertical impacts are much less likely to occur than impacts at an angle greater than 30 degrees to the vertical, about which far less is known. Impact angle is observed to affect the size and shape of the crater in laboratory impacts, but quantifying the effect in larger impacts can only be established through numerical modelling. Porosity is an important property of asteroids, comets and the near-surface of most Solar System bodies. It is known from laboratory experiments that target rocks with a high porosity reduce the volume of material expelled from the crater during growth, but these effects have not yet been properly quantified. The effect of porous compaction during impact, in particular, may have important implications for the evolution of the solar system. Planets grow by the collision of planetesimals. Quantifying the transfer of energy and momentum in such collisions is therefore of vital importance for understanding the thermal, chemical and physical evolution of the solar system. In most previous work and models, collisions during planetary growth were assumed to be exclusively low-velocity and/or between non-porous planetesimals. However, recent work suggests that early planetesimals had very high porosities (up to 80%), and the growth of planetary embryos would have stirred relative velocities between planetesimals to >1 km/s. Experiments and our own modelling work show that target porosity dramatically affects the consequences of impact: increasing heating and reducing ejected mass. A second aim of this work is therefore to use numerical impact simulations to quantify the effect of planetesimal porosity on heating, compaction and ejection during early planetesimal collisions and assess the implications of this for solar system evolution.

小行星和彗星与固体行星表面的猛烈碰撞是太阳系中一个基本和普遍存在的过程。在我们太阳系的早期历史中，小的岩石颗粒碰撞并吸积形成越来越大的物体，直到它们成长为我们今天看到的行星。对地球来说，最后一次行星级碰撞是一次巨大的撞击，最终形成了月球。最近在太阳系历史上，一次灾难性的撞击事件导致了地球上的大规模灭绝，包括恐龙的灭绝。今天，小行星或彗星的撞击对人类构成了真实的威胁，尽管人们对此知之甚少。撞击坑也被用来研究太阳系。计算固体行星表面上撞击坑的数量可以用来区分较老和较年轻的地形，而大型撞击坑的形状可以为行星的近地表结构提供线索。撞击坑的灾难性可能性及其深远的后果，使得我们必须准确地了解撞击过程是如何运作的。这方面的核心是将弹坑的大小与撞击物体的特性（例如大小和速度）和目标物体的条件（例如重力）联系起来的基本方程。换句话说，这些方程给出了一个基本问题的答案：如果一个给定的撞击物撞击一个给定的目标表面，陨石坑会有多大？目前，我们还不能充分回答这个问题，因为方程没有适当地包括所有重要的撞击物和目标材料的属性。这项建议的第一个目的是利用计算机模型更好地限制撞击事件中所有重要变量之间的关系。由于这些方程是估计撞击后果的基本工具，这项工作将促进对行星科学许多领域的理解。这些撞击方程中主要缺少的部分是理解撞击坑的生长如何受到目标中孔隙空间的影响，以及撞击物撞击目标的角度。确定撞击角度的影响很重要，因为经过充分研究的垂直撞击发生的可能性要比与垂直方向成30度以上角度的撞击小得多，而对垂直方向成30度以上角度的撞击所知要少得多。据观察，撞击角度会影响实验室撞击中弹坑的大小和形状，但只有通过数值模拟才能确定对较大撞击的影响。孔隙度是小行星、彗星和大多数太阳系天体近表面的一个重要特性。从实验室实验中得知，具有高孔隙度的目标岩石减少了在生长过程中从陨石坑排出的物质的体积，但这些影响尚未被适当量化。特别是在撞击过程中的多孔压实效应，可能对太阳系的演化产生重要影响。行星是通过微行星的碰撞而成长的。因此，量化这种碰撞中的能量和动量转移对于了解太阳系的热、化学和物理演化至关重要。在大多数以前的工作和模型中，行星生长过程中的碰撞被假设为完全是低速和/或无孔微行星之间的碰撞。然而，最近的研究表明，早期的微行星具有非常高的孔隙率（高达80%），行星胚胎的生长会将微行星之间的相对速度搅拌到>1 km/s。实验和我们自己的建模工作表明，目标孔隙率显着影响影响的后果：增加加热和减少喷射质量。因此，这项工作的第二个目的是使用数值模拟的影响，以量化的影响，在早期的星子碰撞加热，压实和喷射的星子孔隙度和评估这对太阳系演化的影响。