Formation and evolution of small planets and moons

小行星和卫星的形成和演化

基本信息

批准号：
ST/T000163/1
负责人：
Lidunka Vocadlo
金额：
$ 50.06万
依托单位：
University College London
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2020
资助国家：
英国
起止时间：
2020 至无数据
项目状态：
未结题

来源：
https://gtr.ukri.org/projects?ref=ST%2FT000163%2F1
关键词：
Formation evolution small planets moons

项目摘要

Our research aims to aid understanding of the formation and evolution of smaller terrestrial planetary cores (e.g., Mercury, the Moon, Mars and Ganymede) and the icy moons and smaller bodies of the outer solar system. We shall do this in the following ways: (i) by investigating core crystallisation processes (Project 1), (ii) by determining the physical properties of core-forming materials under the relevant conditions of pressure and temperature (Project 2) and (iii) by investigating the physical properties of icy materials (including their vibrational spectra) at high pressures and very low temperatures (Project 3).Key observables from recent and future missions are surface morphologies, spectroscopic observations, magnetic fields, gravity data and, for the Moon and for Mars (via the current InSight mission) seismic observations. The generation of magnetic fields relies on energy sources which include the release of gravitational energy and latent heat of crystallisation. Detailed understanding of these energy sources in small planetary cores is currently uncertain, as it is not even known whether they crystallise from the bottom up or from the top down, and this has first order implications for dynamo driving mechanisms; these are the main issues to be addressed by Project 1. Key deliverables of this project will be ab initio predictions over the entire pressure-temperature range relevant to the cores of Mercury, Ganymede, Mars and the Moon of: i) the adiabatic temperature gradients and melting curves of iron-alloys, which will allow us to determine the mode of core crystallisation, ii) the densities of the liquids and the liquid-solid density contrast, which contributes to gravitational energy release, and iii) the latent heat of fusion in iron alloy systems.Project 2 is predominantly experimental, and addresses major gaps in our knowledge of the fundamental physical properties of iron alloys and related materials at the conditions found within the smaller planetary cores. If we are to understand planetary evolution, geophysical modelling of planetary interiors - the outputs of which can be tested against data from spacecraft and ground-based observations - is essential, but these geophysical models will be reliable only if the physical properties of the constituent core-forming materials (essentially iron and iron alloys) are accurately known in the relevant pressure and temperature ranges. At present, this is often not the case for the conditions expected in the interiors of the Moon, Mercury, Mars and Ganymede. Surprisingly, even for the simplest approximation - a core of pure iron - the data currently available are inadequate. Key deliverables of the project will be the determination of the phase diagrams and physical properties of iron alloys, especially ternary systems such as Fe-Ni-Si and Fe-S-Si, at pressures up to ~40 GPa. Project 3 addresses a different class of materials - water ice and hydrated sulphate salts - which form the mantles of the icy bodies of the outer solar system. Application of pressure to these readily induces changes in crystal structure and, in the case of the hydrated sulphate salts, can lead to expulsion of water and transformation to a lower hydration state. The consequence of these structural changes is to produce a layered structure within the icy body. In addition, the large volume changes accompanying dehydration may result in global expansion and rifting and/or global contraction and crumpling of the surface. Key deliverables of this project include the phase diagrams, equations of state and thermal and electrical conductivities of these icy materials under the relevant conditions of pressure and temperature. In addition to this we shall determine the vibrational spectra of these various phases which will allow direct comparison with mission data.

我们的研究旨在帮助了解较小的地球行星核心（例如水星、月球、火星和木卫三）以及冰冷的卫星和外太阳系较小天体的形成和演化。我们将通过以下方式做到这一点：（i）通过研究核心结晶过程（项目1），（ii）通过在相关压力和温度条件下确定核心形成材料的物理性质（项目2）和（iii））通过研究高压和极低温度下冰材料的物理特性（包括其振动光谱）（项目 3）。近期和未来任务的关键观测数据是表面形态、光谱观测、磁场、重力数据，以及月亮以及火星（通过当前的洞察号任务）地震观测。磁场的产生依赖于能源，包括重力能和结晶潜热的释放。目前对小行星核心中这些能源的详细了解尚不确定，因为甚至不知道它们是从下往上结晶还是从上往下结晶，这对发电机驱动机制具有一阶影响；这些是项目 1 要解决的主要问题。该项目的主要交付成果将是对与水星、木卫三、火星和月球核心相关的整个压力-温度范围的从头预测： i) 绝热温度梯度和铁合金的熔化曲线，这将使我们能够确定核心结晶的模式，ii）液体的密度和液固密度对比，这有助于引力能释放，以及 iii) 铁合金系统中的熔化潜热。项目 2 主要是实验性的，并解决了我们在较小行星核心内发现的条件下铁合金和相关材料的基本物理特性的知识中的主要差距。如果我们要了解行星演化，行星内部的地球物理建模（其输出可以根据来自航天器和地面观测的数据进行测试）至关重要，但只有构成核心的物理特性正确时，这些地球物理模型才是可靠的- 成形材料（主要是铁和铁合金）在相关压力和温度范围内准确已知。目前，月球、水星、火星和木卫三内部的预期情况通常并非如此。令人惊讶的是，即使对于最简单的近似——纯铁核心——目前可用的数据也是不够的。该项目的主要成果是确定铁合金的相图和物理性能，特别是三元体系，如 Fe-Ni-Si 和 Fe-S-Si，在高达约 40 GPa 的压力下。项目 3 涉及不同类别的材料——水冰和水合硫酸盐——它们形成了太阳系外冰体的地幔。对它们施加压力很容易引起晶体结构的变化，并且在水合硫酸盐的情况下，可以导致水的排出并转变为较低的水合状态。这些结构变化的结果是在冰体内产生层状结构。此外，伴随脱水的大体积变化可能导致表面的整体膨胀和裂开和/或整体收缩和皱缩。该项目的主要成果包括这些冰材料在相关压力和温度条件下的相图、状态方程以及热导率和电导率。除此之外，我们还将确定这些不同阶段的振动光谱，这将允许与任务数据进行直接比较。