Formation of the earliest solids: Clues from 26Al

最早固体的形成：来自 26Al 的线索

基本信息

批准号：
ST/G002983/1
负责人：
Sara Russell
金额：
$ 29.47万
依托单位：
Natural History Museum
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2009
资助国家：
英国
起止时间：
2009 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=ST%2FG002983%2F1
关键词：
Formation earliest solids Clues 26Al

项目摘要

We know that the solar system formed about four and a half billion years ago when a cloud of dust and gas collapsed to form the Sun and planets. As the Sun formed, a swirling dusty disk evolved around it, called the accretion disk. Left over material from this disk eventually became the planets. We can learn about the solar system when it was at this stage by studying some meteorites that date from this era, the chondrites. If you look at chondritic meteorites you can see that they contain little round balls with a diameter of about 0.1 to 1 mm, called chondrules. These formed in the accretion disk around the nascent sun. Chondrule formation is an important step in the hierarchy of grain growth from interstellar, nanometer sized grains that made up the accretion disk to planets, which are thousands of kilometres in diameter. Chondrules obtained their round shape when they were molten for only a few minutes at very high temperatures of up to >2000 degree C. Although the formation of an individual chondrule was brief, there is some first evidence that the process causing this 'flash' heating was active for 1-2 Million years. One aim of this study is to constrain the time interval during which chondrule formation was an active process in the accretion disk. There is also some indication that chondrules with a different chemical compositions formed at different times. This would be an exciting finding, as it would document a chemical evolution of the accretion disk with time, recorded in chondrules. This would help us understand how the accretion disk changed with time as the planet forming process progressed. However, the data available so far are still ambiguous. A focus of the study is therefore to determine both the chemical composition and the age of a single chondrule and verify whether there is a correlation between them. We can learn about all this using a radioactive isotope, 26Al. Aluminium-26 was present in the early solar system, but since it is radioactive with a very short half-life it decayed away and so the quantity lessened to essentially zero about 10 Million years after the beginning of the solar system. However, if a mineral formed early within this 10 Million years and incorporated 26Al, its decay product 26Mg can be measured today and we can re-calculate how much 26Al was initially in the chondrule. This may then give us an idea of its age. There is a complication in that some chondrules may contain fragments of older materials and addition of this may affect the 26Al data. We will look for this by studying the chondrule visually and making chemical measurements on it.

我们知道，太阳系是在大约四亿五亿年前形成的，当时一团尘埃和气体坍塌形成了太阳和行星。当太阳形成时，围绕它演化出一个旋转的尘埃盘，称为吸积盘。这个圆盘留下的物质最终变成了行星。我们可以通过研究这个时代的一些陨石（球粒陨石）来了解太阳系在这个阶段的情况。如果观察球粒陨石，您会发现它们含有直径约为 0.1 至 1 毫米的小圆球，称为球粒。它们是在新生太阳周围的吸积盘中形成的。球粒的形成是颗粒生长层次中的重要一步，从构成吸积盘的星际纳米颗粒到直径数千公里的行星。当球粒在高达 >2000 摄氏度的高温下仅熔化几分钟时，就获得了圆形形状。虽然单个球粒的形成很短暂，但有一些初步证据表明，导致这种“闪蒸”加热的过程活跃了1-2百万年。这项研究的目的之一是限制吸积盘中球粒形成活跃过程的时间间隔。还有一些迹象表明，具有不同化学成分的球粒是在不同时间形成的。这将是一个令人兴奋的发现，因为它将记录记录在球粒中的吸积盘随时间的化学演化。这将有助于我们了解随着行星形成过程的进展，吸积盘如何随时间变化。然而，迄今为止可获得的数据仍然不明确。因此，研究的重点是确定单个球粒的化学成分和年龄，并验证它们之间是否存在相关性。我们可以使用放射性同位素 26Al 了解这一切。铝26存在于早期太阳系中，但由于它具有放射性，半衰期很短，因此它会衰变，因此在太阳系开始后约1000万年，其数量基本上减少到零。然而，如果一种矿物在这 1000 万年之内形成并含有 26Al，那么今天就可以测量其衰变产物 26Mg，并且我们可以重新计算球粒中最初有多少 26Al。这也许能让我们了解它的年龄。存在一个复杂情况，即某些球粒可能包含旧材料的碎片，添加这些碎片可能会影响 26Al 数据。我们将通过目视研究球粒并对它进行化学测量来寻找这一点。