Planetary Origins and Development

科学家们现在可以探测到遥远的银河系中绕着其他恒星运行的地球大小的行星。然而，行星最初是如何形成，然后发展和功能的许多基本方面是未知的或令人惊讶的不确定。这项提案中的研究将解决科学家在这个迷人的领域寻求答案的一些问题。我们研究的科目是同位素宇宙化学、岩石学、岩石物理学和低温地球化学。四位具有不同背景的首席调查员将共同努力解决五个重大问题。1. 是什么过程产生了构成太阳系的原子？氢和氦主要是138亿年前宇宙大爆炸的产物。但是那些较重的元素，比如钙、钛、铬、镍、锆、钼或钯呢？自20世纪50年代以来，关于这些重元素是如何在大恒星中合成的，已经有了广为接受的理论。现在有证据表明这些理论可能是错误的。我们将测量这些元素的同位素在太阳系中一些最古老的物质中的比例，以检验新的理论。2. 是什么过程控制着类地行星中挥发性元素（如锡）的数量？我们将使用最近建造的熔炉进行实验，以确定熔融的小行星和行星体中这些中等挥发性元素的相对损失和同位素分馏。我们将评估是否是星周盘非常早期的过程造成的，还是大型行星火山进入太空造成的损失。这项工作也可能告诉我们一些热系外行星的大气层。3. 金属岩心是如何形成和分化的？像所有类地行星一样，地球有一个铁核。在地球的情况下，它部分是液体，所以对流，产生磁场。这些核是如何形成并结晶的？我们将测量陨石中钒、铬、镍、钼、钯和钨的同位素变化，再加上实验，将为早期行星胚胎以及更大物体的核心形成和结晶提供新的见解。这些也有望揭示月球形成撞击器Theia.4的性质。岩石行星内部如何对轨道应力做出反应？在地球上，我们知道来自月球的潮汐力会导致行星内部移动。月球形成后不久，它离地球很近——它将占据夜空的三分之一！所以潮汐力要大得多。然而，对于一颗岩石行星如何应对如此巨大的压力，我们知之甚少。我们将进行实验室实验来评估这一点。5. 行星地壳如何影响大气演化？宜居世界的发展最重要的一个方面是大气的形成。然而，对于最重要、最简单的元素之一氢的释放，人们还没有很好地了解。气候模型和生命起源研究中出现了一些想法，我们将通过水和岩石之间相互作用产生氢的新实验和模型研究来验证这些想法。

Scientists can now detect Earth-sized planets orbiting other stars far away in our Milky Way galaxy. Yet, many basic aspects of how planets first form, then develop and function are unknown or surprisingly uncertain. The research in this proposal will address some of the questions to which scientists seek answers in this fascinating area. The subjects in which we work are called isotope cosmochemistry, petrology, rock physics and low temperature geochemistry. Four lead investigators with these different backgrounds will work together to address five big questions. 1. What processes generated the atoms from which our Solar System was built? Hydrogen and helium are mainly the product of the Big Bang 13.8 billion years ago. But what about all the heavier elements like calcium, titanium, chromium, nickel, zirconium, molybdenum or palladium? Since the 1950s there have been well accepted theories for how these heavier elements were synthesised in large stars. Now there is evidence these theories may be wrong. We will measure the proportions of the isotopes of these elements in some of the oldest material in the Solar System to test the new theories. 2. What processes govern the amount of volatile elements like tin in the terrestrial planets? We will perform experiments using a recently-built furnace to determine the relative losses and isotopic fractionation of such moderately volatile elements from molten asteroidal and planetary bodies. We will evaluate whether very early processes in the circumstellar disk were responsible or whether there were losses from large planetary volcanoes into space. This work may also tell us about the atmospheres of some hot exosolar planets. 3. How do metallic cores form and differentiate? The Earth like all terrestrial planets has an iron core. In the case of Earth it is partially liquid, so convects, generating a magnetic field. How do such cores form and then crystallise? We will measure isotopic variations in vanadium, chromium, nickel, molybdenum, palladium and tungsten in meteorites, which together with experiments, will provide new insights into core formation and crystallisation in early planetary embryos as well as larger objects. These are expected to also shed light on the nature of the Moon-forming impactor Theia.4. How do rocky planetary interiors respond to orbital stresses? On Earth we are aware of tidal forces from the Moon that cause the interior of a planet to move. Shortly after the Moon formed it was very close to Earth - it would have occupied a third of the night sky! So the tidal forces would have been vastly bigger. Yet we do not know much about how a rocky planet responds to such huge stresses. We will conduct laboratory experiments to evaluate this. 5. How do planetary crusts influence atmospheric evolution? One of the most important aspects of the development of habitable worlds is the formation of an atmosphere. However, the release of one of the most important and simple of elements, hydrogen, is not well understood. There are ideas emerging from climate modelling and origins of life studies that we will test with new experimental and modelling investigations of hydrogen generation through the interactions between water and rock.