Planetary Origins and Development (OxPOD)

根据对陨石中最古老粒子的放射性测年，太阳系是由大约45.7亿年前由气体和尘埃组成的扁平圆盘形成的。随着太阳处于中心，经历了最早、最猛烈的发展阶段，氢、氦、水氨和甲烷等气体被扫到小行星带之外的最外层，在那里它们被浓缩成木星、土星、天王星和海王星等巨行星。内太阳系主要由尘埃组成，这些尘埃在S几千年的10‘年中逐渐聚集在一起，成长为大量大小为10-100公里的天体。在300万到3000万年的时间里，这些小天体相互碰撞并成长为内行星、水星、金星、地球和火星，留下了小行星带中较小的小行星作为行星形成之前的残余物。这个项目旨在通过对陨石的研究和旨在模拟太阳系最早历史时期行星生长条件的实验相结合的方法，了解发生在小行星上和行星成长过程中的一些最重要的过程。我们特别感兴趣的是，内行星是如何获得硫、氯、锌和铅等所谓“中等挥发性元素”的库存的，以及这些元素和其他挥发性元素，特别是惰性气体氦、氦、氩、氪和氙气是如何被脱气到大气层并循环到行星内部的。我们还在建设实验模拟太阳系外行星天王星和海王星深处的条件的能力，据信这两颗行星含有大量甲烷。我们的5个相互关联的项目可以单独总结如下：a.解决太阳系内行星如何获得硫和氯等中等挥发性非金属的当前浓度的问题，并询问获得机制是否与获得挥发性金属如锌、铅、锑和铜的机制不同。这包括在大约1300摄氏度的温度下熔化含有这些元素的岩石，并确定不同元素在大气层中损失的速度。b.硫通过木卫一内部循环的物理和化学途径是什么？木卫一是木星的卫星，是太阳系中火山活动最活跃的天体，它的大气层不断地得到火山释放的富硫气体的补充。这个项目使用计算机模拟来解决硫被排放到大气中，在表面冷凝，然后再循环到内部的方式。c.火星表面的水化是如何导致挥发物的循环的，包括水、惰性气体、氯、溴和碘？这些气体被锁定在一种常见的矿物角闪石中，从而固定在火星表面。这个项目的目的是通过高压实验来确定这些元素在多大程度上可以被捕获在角闪石中并循环到火星内部。d.向富碳小行星添加水是如何导致磁铁矿的生长的？很大一部分碳质陨石在其母体上经历了水蚀变，磁铁矿是其中涉及的过程的重要线索。这个项目的目的是在实验室中实验模拟导致观察到的类型磁铁矿的转化过程。E.天王星和海王星内部极端压力和温度条件下甲烷和水的性质是什么？该项目的目的是确定甲烷和水的化合物在这些巨大行星的内部是稳定的，并提供数据，以便能够对行星性质进行模拟。

Based on radioactive dating of the oldest particles in meteorites, the solar system formed from a flattened disk of gas and dust about 4.57 billion years ago. With the sun at the centre going through its earliest, violent stages of development, gases such as hydrogen, helium, water ammonia and methane were swept to the outermost parts, beyond the asteroid belt, where they were condensed into the giant planets Jupiter, Saturn, Uranus and Neptune. The inner solar system consisted predominantly of dust and this dust gradually clumped together over 10's of thousands of years and grew into a large number of bodies of 10-100 km in size. Over periods of 3 to 30 million years these small bodies collided and grew into the inner planets, Mercury, Venus, Earth and Mars, leaving the smaller asteroids of the asteroid belt as remnants of the period before the planets grew.This project is aimed at the understanding of some of the most important processes which took place on small asteroids and during growth of the planets using a combination of studies of meteorites and experiments aimed at simulating conditions on growing planets during the earliest history of the solar system. We are particularly interested in how the inner planets acquired their inventories of the so-called "moderately volatile elements" such as sulphur, chlorine, zinc and lead, and how these and other volatile elements, notably the noble gases Helium, Neon, Argon, Krypton and Xenon, are degassed to the atmosphere and recycled to the planet's interior. We are also building the capacity to simulate experimentally the conditions deep within the outer solar system planets Uranus and Neptune, which are believed to contain significant amount of methane. Individually our 5 inter-related projects may be summarised as follows:A. Addresses the question of how the planets of the inner solar system obtained their current concentrations of moderately volatile non-metals such as sulphur and chlorine and asks if the mechanisms of acquisition are different from those in which the volatile metals such as zinc, lead antimony and copper were acquired. This involves melting rocks containing these elements at temperatures of about 1300oC and determining the rates at which the different elements are lost to the atmosphere.B. What are the physical and chemical pathways by which sulphur is cycled through Io's interior? Io, a moon of Jupiter, is the most volcanically active body in the solar system and its atmosphere is being continually replenished by sulphur-rich gases emitted by volcanoes. This project uses computer modelling to address the ways in which sulphur is emitted to the atmosphere, condensed on the surface and then recycled to the interior.C. How has hydration of the martian surface led to recycling of volatiles including water, the noble gases, chlorine, bromine and iodine? These gases become fixed on Mars' surface by being locked into a common mineral, amphibole. The aim of this project is to determine, by high pressure experiment, the extents to which these elements can be trapped in amphibole and recycled to the martian interior.D. How did addition of water to carbon-rich asteroids lead to the growth of magnetite? A large proportion of carbonaceous meteorites have undergone aqueous alteration on their parent bodies and magnetite is an important clue to the processes involved. This project is aimed at experimentally simulating in the laboratory the transformation processes which lead to magnetite of the types observed.E. What are the properties of methane and water under the extreme pressure and temperature conditions in the interiors of Uranus and Neptune? This project is aimed at determining which compounds of methane and water are stable in the interiors of these giant planets and providing data to enable modelling of the planetary properties.