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Archaeology of Exo-Terrestrial Planetary Systems and a Search for Water

地外行星系统考古学和寻找水源

基本信息

批准号：
ST/J003344/3
负责人：
Jay Farihi
金额：
$ 40.53万
依托单位：
University College London
依托单位国家：
英国
项目类别：
Fellowship
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%2FJ003344%2F3
关键词：
Archaeology Exo Terrestrial Planetary Systems

项目摘要

The research I propose will, uniquely, constrain the frequency and bulk chemical composition of terrestrial planets around other stars. Critically, my research program has the potential to detect the signature of water within rocky planetary bodies and thereby constrain the potential for oceans and habitats for life. This is made possible by stars at the end of their lives called white dwarfs. Over 95% of all stars in the Milky Way, including our Sun, will end their lives as white dwarfs, gently shedding their outer layers, then shrinking to Earth-sized, slowly cooling embers. By studying rocky planetary systems at white dwarfs, one sees a glimpse into the future of the Earth. In the search for terrestrial planetary systems around other stars, white dwarfs offer a unique advantage. Owing to high gravities, heavy elements sink rapidly to the interior, leaving behind pure hydrogen or helium atmospheres. Those white dwarfs with rocky planetary systems can become contaminated by the infall of small, but detectable amounts of heavy elements such as silicon, magnesium, and iron (termed simply 'metals' by astronomers). Only recently, a number of white dwarfs polluted by rocky planetary debris have been discovered, and I have played a lead role in identifying and understanding these stars and their environments. These systems arose analogously to the rings of Saturn; a large asteroid or moon passing too close to the star was torn apart by gravity and now resides as a disk of material orbiting the white dwarf. This ring of debris gradually falls onto the star, contaminating its otherwise-pristine atmosphere with metals. I will use white dwarfs polluted by metals to infer the masses, basic chemical compositions, and water content of their surviving rocky planetary systems. The proposed project has two parts: 1) to observe the rocky debris itself in orbit about the star, and 2) to measure the chemical content of this debris as it pollutes the star, broken down into its constituent elements. The first part requires infrared and submillimeter observations to detect warm orbiting dust at these metal-polluted stars. The basic goal of this work is to unambiguously correlate orbiting rocky debris with the polluted stellar atmospheres, and firmly establish the material as planetary. The long-wavelength light from the warm dust provides a measure of the spatial distribution, temperature, size, and composition of the orbiting particles, thus constraining the nature of the now destroyed, rocky asteroid, moon, or planet. I will significantly increase the number of known white dwarfs with debris rings to gain a superior statistical understanding of the frequency of terrestrial planetary systems around other stars. The second step is to use the star itself to determine the bulk chemical composition of the planetary debris falling onto and polluting its atmosphere. I will measure the relative elemental abundances of several to two dozen heavy elements in each of these stars using optical and ultraviolet observations. In doing so, it will be possible to establish the basic makeup of terrestrial planets around other stars, as well as catalog their diversity. Water can be identified by searching for oxygen in excess of that carried by rocks alone; a simple accounting of each detected metal as an oxide can reveal extra oxygen delivered as H2O. In this way I will determine the mass of water in rocky asteroids and moons, and compare these findings with water-rich Solar System bodies

我提议的研究将独一无二地限制围绕其他恒星的类地行星的频率和大量化学成分。关键的是，我的研究计划有可能探测到岩石行星体内的水的特征，从而限制海洋和生命栖息地的潜力。这是由被称为白矮星的末期恒星实现的。银河系中超过95%的恒星，包括我们的太阳，将以白矮星的形式结束它们的生命，轻轻地剥离它们的外层，然后收缩成地球大小的慢慢冷却的余烬。通过研究白矮星上的岩石行星系统，人们可以一窥地球的未来。在寻找围绕其他恒星的类地行星系统时，白矮星提供了独特的优势。由于高重力，重元素迅速下沉到内部，留下纯氢或氦大气。那些拥有岩石行星系统的白矮星可能会受到少量但可检测到的重元素的污染，如硅、镁和铁(天文学家将其简称为金属)。直到最近，才发现了一些被岩石行星碎片污染的白矮星，我在识别和了解这些恒星及其环境方面发挥了带头作用。这些系统的形成类似于土星的光环；一颗大的小行星或月亮太靠近恒星时被引力撕裂，现在作为一个围绕白矮星运行的物质圆盘存在。这个碎片环逐渐落到这颗恒星上，用金属污染了它原本纯净的大气。我将使用被金属污染的白矮星来推断它们幸存的岩石行星系统的质量、基本化学成分和水含量。拟议中的项目包括两个部分：1)在围绕恒星的轨道上观察岩石碎片本身，2)测量这些碎片污染恒星时的化学含量，这些碎片被分解成组成元素。第一部分需要红外和亚毫米观测，以探测这些被金属污染的恒星的温暖轨道尘埃。这项工作的基本目标是明确地将轨道上的岩石碎片与受污染的恒星大气联系起来，并牢固地确立这种物质是行星物质。来自温暖尘埃的长波长光提供了轨道粒子的空间分布、温度、大小和组成的测量，从而限制了现在被摧毁的岩石小行星、月球或行星的性质。我将大幅增加具有碎片环的已知白矮星的数量，以更好地从统计上了解其他恒星周围的类地行星系统的频率。第二步是利用恒星本身来确定落在其大气层上并污染其大气的行星碎片的主要化学成分。我将使用光学和紫外线观测来测量每一颗恒星中几到二十多种重元素的相对元素丰度。通过这样做，将有可能建立围绕其他恒星的类地行星的基本构成，以及对它们的多样性进行分类。水可以通过寻找超过岩石本身携带的氧气来识别；简单地计算每一种被探测到的金属作为氧化物就可以发现额外的氧气以H2O的形式提供。通过这种方式，我将确定岩石小行星和卫星中的水的质量，并将这些发现与富含水的太阳系天体进行比较