Structure and dynamics of small planets and moons

小行星和卫星的结构和动力学

• 批准号: ST/K000934/1
• 负责人: Ian Wood
• 金额: $ 84.3万
• 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: 2013
• 资助国家: 英国
• 起止时间: 2013 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=ST%2FK000934%2F1
• 关键词: Structure; dynamics; small; planets; moons

The proposed research aims to understand the interior structure and evolution of smaller planetary bodies, both icy (e.g., the Jovian moons) and rocky (e.g., the planet Mercury).Icy moons:Orbiting the gas-giant planets are many icy moons, which vary in size from 10s of kilometres across to >2500 km, larger than the planet Mercury. The three largest icy moons are Ganymede and Callisto (orbiting Jupiter), and Titan (orbiting Saturn); they have similar radii and bulk densities, but have experienced radically different geological histories. Callisto appears not to have evolved at all, its interior is a near uniform mixture of rock and ice, and the surface geology is dominated by impact craters. Ganymede's metal, rock, and ice components have separated out to form an iron core, a rocky mantle, and a thick icy shell, which has rifted the crust and caused the eruption of liquid water - an icy equivalent to Earth's volcanic magma. Titan has also undergone internal segregation to form a dense core coated by a thick icy shell. Unlike Ganymede, Titan may still be active. The most remarkable discovery is that all of these large icy bodies have global oceans of liquid water beneath icy crusts 10-200 km thick. These oceans are possible niches for extraterrestrial life in the outer reaches of our solar system.To understand why icy bodies of otherwise similar size and composition have led such different lives, we must construct mathematical models of the internal structure and heat flow. This modelling relies upon knowledge of how the icy layer transports heat from the core to the surface. Under the high pressures in the interior of an icy body, water-ice exists in several different crystalline forms, each with very different thermo-physical properties. In addition, there are likely to be abundant water-rich hydrates of various molecules, such as ammonia, and many soluble sulfates. These compounds often have a smaller thermal conductivity than water ice; just as a thick winter quilt will keep you warm in bed, a low-thermal-conductivity planetary crust will keep the interior much warmer than it would be otherwise, allowing subsurface oceans to stay liquid throughout geological history. For most of ices and hydrates, the physical properties we need to construct accurate models are not known at relevant pressures and temperatures. In this project we will measure properties such as the thermal expansion, thermal conductivity and specific heat capacity, supporting our measurements with computer simulation. We shall then incorporate the results into our planetary models and thus investigate the internal structure and evolution of the icy moons.MercuryMercury is the target of two orbital missions, MESSENGER (current) and Bepi-Columbo (2019) both of which have instruments on board to study its internal structure, composition and magnetic field. Mercury is only slightly less dense than the Earth but is much smaller and therefore the material within its interior is not as strongly compressed. For Mercury to have such a high density, its core must be large (>40% by volume, <70% by mass) and iron-rich (~70% Fe, ~30% silicate). Mercury's small size also suggests it must have cooled more rapidly than the Earth and therefore will have a distinct chemistry and evolutionary history. The presence of a magnetic field suggests that Mercury has a molten region, although fast cooling means that this may be confined to a rather thin shell. As a result of these differences, it is possible that the dynamo that supports the magnetic field of Mercury differs substantially from the Earth's dynamo. Understanding Mercury's interior requires us to construct geophysical models of its internal structure and evolution. To do this we must know the physical properties of the materials that make up its interior; these can be obtained through calculations based on quantum mechanics for both solid and liquid iron alloys at high pressures and temperatures.

拟议中的研究旨在了解较小行星体的内部结构和演化，这些行星体都是冰冷的（例如，木星的卫星）和岩石（例如，冰卫星：围绕着气态巨行星运行的是许多冰卫星，其大小从10公里到2500公里不等，比水星大。三颗最大的冰卫星是木卫三和木卫四（绕木星运行），以及土卫六（绕土星运行）;它们有相似的半径和体积密度，但经历了截然不同的地质历史。木卫四似乎根本没有进化，它的内部是一个近乎均匀的岩石和冰的混合物，表面地质主要是撞击坑。木卫三的金属、岩石和冰的成分已经分离出来，形成了一个铁核、一个岩石地幔和一个厚厚的冰壳，这使地壳裂开，导致液态水的喷发--一种相当于地球火山岩浆的冰。土卫六也经历了内部分离，形成了一个被厚厚的冰壳覆盖的致密核心。与木卫三不同，土卫六可能仍然活跃。最引人注目的发现是，所有这些大型冰体在10 - 200公里厚的冰壳下都有全球液态水海洋。这些海洋可能是太阳系外围的地外生命的栖息地，要理解为什么大小和成分相似的冰体会有如此不同的生命，我们必须构建内部结构和热流的数学模型。这种建模依赖于冰层如何将热量从核心传输到表面的知识。在冰体内部的高压下，水冰以几种不同的结晶形式存在，每种结晶形式都具有非常不同的热物理性质。此外，可能存在大量的各种分子的富含水的水合物，如氨和许多可溶性硫酸盐。这些化合物的热导率通常比水冰小;就像一床厚厚的冬季被子会让你在床上保持温暖一样，低热导率的行星地壳会让内部比其他情况下温暖得多，从而使地下海洋在整个地质历史中保持液态。对于大多数冰和水合物，我们需要建立精确的模型的物理性质是未知的，在相关的压力和温度。在这个项目中，我们将测量热膨胀，导热系数和比热容等性能，并通过计算机模拟来支持我们的测量。水星水星是两个轨道任务的目标，信使（当前）和Bepi-Columbo（2019），这两个任务都有仪器来研究其内部结构，组成和磁场。水星的密度只比地球稍小，但体积小得多，因此其内部的物质没有强烈的压缩。水星要有如此高的密度，它的核心必须是大的（体积大于40%，质量小于70%）和富铁的（约70%的铁，约30%的硅酸盐）。水星的小尺寸也表明它必须比地球更快地冷却，因此将有一个独特的化学和进化历史。磁场的存在表明水星有一个熔化的区域，尽管快速冷却意味着这可能局限于一个相当薄的壳。由于这些差异，支持水星磁场的发电机可能与地球的发电机有很大不同。了解水星的内部需要我们构建其内部结构和演化的地球物理模型。要做到这一点，我们必须知道组成其内部的材料的物理性质;这些可以通过基于量子力学的计算在高压和高温下获得固体和液体铁合金。

项目成果

MgSO4·11H2O and MgCrO4·11H2O based on time-of-flight neutron single-crystal Laue data.

MgSO4·11H2O 和 MgCrO4·11H2O 基于飞行时间中子单晶劳厄数据。

• DOI: 10.1107/s0108270113005751
• 发表时间: 2013
• 期刊: Acta crystallographica. Section C, Crystal structure communications
• 作者: Fortes AD

P - V - T equation of state of synthetic mirabilite (Na 2 SO 4 ·10D 2 O) determined by powder neutron diffraction

粉末中子衍射测定合成芒硝(Na 2 SO 4 ·10D 2 O)的P-V-T状态方程

• DOI: 10.1107/s0021889813001362
• 发表时间: 2013
• 期刊: Journal of Applied Crystallography
• 影响因子: 6.1
• 作者: Fortes A

High-resolution neutron-diffraction measurements to 8 kbar

高达 8 kbar 的高分辨率中子衍射测量

• DOI: 10.1080/08957959.2017.1386183
• 发表时间: 2017
• 期刊: High Pressure Research
• 影响因子: 2
• 作者: Bull C

Partitioning of Co2+ and Mn2+ into meridianiite (MgSO4·11H2O): Ternary solubility diagrams at 270 K; cation site distribution determined by single-crystal time-of-flight neutron diffraction and density functional theory

Co2 和 Mn2 分配成子午线石 (MgSO4·11H2O)：270 K 时的三元溶解度图；

• DOI: 10.1016/j.fluid.2017.01.005
• 发表时间: 2017
• 期刊: Fluid Phase Equilibria
• 影响因子: 2.6
• 作者: Fortes A

Crystal structures of deuterated sodium molybdate dihydrate and sodium tungstate dihydrate from time-of-flight neutron powder diffraction.

• DOI: 10.1107/s2056989015011354
• 发表时间: 2015-07-01
• 期刊: Acta crystallographica. Section E, Crystallographic communications
• 作者: Fortes AD