Planetary Origins and Evolution at Imperial (2016-2019)

我们是如何从一团尘埃和气体中到达一个能够维持生命的星球的？这是最基本的问题之一，从学生到科学家，每个人都参与其中。我们现在知道了很多答案：我们知道恒星，比如我们的太阳，是由星际尘埃和气体云坍缩形成的。我们知道，像地球这样的行星，是围绕着它们的宿主星星形成的，被称为行星状星云，由尘埃和气体的坍缩云旋转形成。我们知道，45亿年前，在太阳星云中，围绕着年轻的太阳，我们太阳系中的所有物体都是通过一个称为吸积的过程产生的。在所有这些天体中，迄今为止发现的唯一一个生命进化的可居住世界是地球。然而，关于我们的太阳系是如何形成的，我们仍然有很多不知道的东西。例如，为什么所有的行星都如此不同？为什么金星是一个有着厚厚的二氧化碳大气层的地狱，火星是一个有着稀薄大气层的冰冻岩石，而地球是生命的天堂？答案在于这些行星聚集之前发生的事件;它在于星云的早期历史和发生的事件，因为细小的尘埃粘在一起形成称为星子的较大物体;以及这些星子如何通过碰撞，加热和水的影响而改变，成为行星的基石。我们的研究将追踪行星物质的演化，从原行星盘中的第一颗尘埃颗粒的起源，到太阳星云中的星子的聚集，再到这些物体成为行星时和之后的变化。陨石中保存的证据提供了我们太阳系演化的记录。陨石与宇宙尘埃颗粒一起，保留了来自太阳星云的细小尘埃颗粒。这些尘埃颗粒小于百万分之一米，但现代微量分析可以揭示它们的矿物质和成分。我们将研究陨石和宇宙尘埃的细粒成分，以研究细尘如何开始在太阳星云中积累;早期热星云的加热和碰撞产生的重复短暂加热事件如何影响尘埃颗粒的聚集;以及磁场是否有助于控制太阳星云中尘埃的分布。我们还将使用数值模型来模拟第一批蓬松的尘埃聚集体是如何被压缩成岩石的。除了构成行星的岩石和金属材料外，我们的研究还将研究地球水的来源以及对生命起源至关重要的有机材料的命运。通过分析陨石和地球、月球和火星样品中的挥发性元素Zn、Cd和Te的同位素，我们将确定水和其他挥发性物质传递到内太阳系行星的来源和时间。此外，通过新开发的方法，我们可以追溯陨石中有机物质的历史，从它们在星际空间中形成，通过太阳星云到星子。阅读有机物质中高度敏感的记录将揭示宇宙化学如何为太阳系提供生命的原材料。一旦行星最终形成，它们的物质会通过撞击和水流等表面过程继续变化。我们的研究将探讨小行星和彗星的撞击如何塑造行星外壳，以及这种撞击是否危及或有助于生命的出现。我们还将研究火星，它提供了生命可能出现的行星体的第二个例子。火星上古老湖泊的图像将揭示地球历史上的一个关键时期，当时全球气候变化将地球变成了一片干旱的荒地，以评估生物体适应和生存的机会，并为未来的漫游者和样本返回任务确定目标。

How from a cloud of dust and gas did we arrive at a planet capable of supporting life? This is one of the most fundamental of questions, and engages everyone from school children to scientists. We now know much of the answer: We know that stars, such as our Sun, form by the collapse of interstellar clouds of dust and gas. We know that planets, such as Earth, are constructed in a disk around their host star known as the planetary nebula, formed by the rotation of the collapsing cloud of dust and gas. We know that 4.5 billion years ago in the solar nebula, surrounding the young Sun, all the objects in our Solar System were created through a process called accretion. And among all those bodies the only habitable world yet discovered on which life evolved is Earth.There is, however, much that we still do not know about how our Solar System formed. Why, for example, are all the planets so different? Why is Venus an inferno with a thick carbon dioxide atmosphere, Mars a frozen rock with a thin atmosphere, and Earth a haven for life? The answer lies in events that predated the assembly of these planets; it lies in the early history of the nebula and the events that occurred as fine-dust stuck together to form larger objects known as planetesimals; and in how those planetesimals changed through collisions, heating and the effects of water to become the building blocks of planets. Our research will follow the evolution of planetary materials from the origins of the first dust grains in the protoplanetary disk, through the assembly of planetesimals within the solar nebula to the modification of these objects as and after they became planets.Evidence preserved in meteorites provides a record of our Solar System's evolution. Meteorites, together with cosmic dust particles, retain the fine-dust particles from the solar nebula. These dust grains are smaller than a millionth of a metre but modern microanalysis can expose their minerals and compositions. We will study the fine-grained components of meteorites and cosmic dust to investigate how fine-dust began accumulating in the solar nebula; how heating by an early hot nebula and repeated short heating events from collisions affected aggregates of dust grains; and whether magnetic fields helped control the distribution of dust in the solar nebula. We will also use numerical models to simulate how the first, fluffy aggregates of dust were compacted to become rock.As well as the rocky and metallic materials that make up the planets, our research will examine the source of Earth's water and the fate of organic materials that were crucial to the origins of life. By analysing the isotopes of the volatile elements Zn, Cd and Te in meteorites and samples of Earth, Moon and Mars we will establish the source and timing of water and other volatiles delivered to the planets in the inner Solar System. In addition, through newly developed methods we can trace the history of organic matter in meteorites from their formation in interstellar space, through the solar nebula and into planetesimals. Reading the highly sensitive record in organic matter will reveal how cosmic chemistry furnished the Solar System with the raw materials for life. Once the planets finally formed, their materials continued to change by surface processes such as impacts and the flow of water. Our research will examine how impacts of asteroids and comets shaped planetary crusts and whether this bombardment endangered or aided the emergence of life. We will also study the planet Mars, which provides a second example of a planetary body on which life could have appeared. Imagery of ancient lakes on Mars will reveal a crucial period in the planet's history, when global climate change transformed the planet into an arid wasteland, to evaluate the opportunity for organisms to adapt and survive and identify targets for future rover and sample return missions.