The Oort Cloud in the Galactic Context

由于奥尔特彗星云延伸到离最近恒星距离的1/3处，因此银河系环境和该彗星云的演化之间有很强的联系。事实上，观测到的新彗星的半长轴分布的尖峰是由于更遥远的彗星被经过的恒星和银河潮汐作为一个整体产生了更显著的扭转。鉴于这种联系，由于太阳在银河系中的轨道和太阳从其形成环境中漂移而导致的银河系环境的变化将对奥尔特云中彗星的分布以及随后这些彗星向内太阳系的输送产生重大影响。在这个研究项目中，托马斯·奎因博士和他的同事们将首先研究奥尔特云在太阳系45亿年历史中的形成和演化，假设有许多不同的恒星形成环境。太阳很可能是在一个密集的星团中形成的，但实际的密度和离开星团的时间尺度是不确定的。这项工作将考虑许多恒星密度和星团耗散时间尺度，并将得到的奥尔特云和随后的彗星阵雨强度与没有星团环境的控制情况进行比较。然而，太阳系在银河系中并不是一个静止的位置。因此，随着太阳在银河系中轨道的演变，研究将继续纳入银河扰动的变化。这将在通过冷暗物质（CDM）宇宙中的分层合并形成的星系的宇宙学动机模型的背景下完成。这个模型是用研究小组的大规模平行宇宙学代码“汽油”计算出来的，这个模型已经被证明产生了许多观察到的螺旋星系的特征。奥尔特云的演化将被计算，因为它感受到来自星系模型中存在的圆盘、旋臂和其他亚结构的气体、恒星和暗物质的扰动。这项研究将特别关注随后进入太阳系内部的彗星通量的变化以及对地球撞击率的可能后果。自从人们把白垩纪末期的大灭绝事件与彗星撞击联系起来之后，人们就把彗星与古生物学和地质学联系起来。奎因博士和获得该奖项的研究生都是华盛顿大学天体生物学项目的一部分，因此，他们的研究将与该项目中生物学家和地质学家的工作联系起来。轨道动力学和彗星之间的联系也吸引了广大公众。我们的行星系统的起源问题，它如何融入整个银河系以及对生命的影响是吸引公众进入动力学研究结果的问题。奎因博士和这位研究生将把他们的研究结果纳入他们的本科课程和公开讲座中

AST 0709191QuinnSince the Oort comet cloud extends to 1/3 the distance to the nearest stars, there is a strong connection between the galactic environment and the evolution of this cloud. Indeed the spike in semi-major axis distribution of observed new comets is due to the more significant torquing of more distant comets by passing stars and the Galactic tide as a whole. Given this connection, changes in the Galactic environment due to the orbit of the Sun in the Galaxy and drifting of the Sun from its formation environment will have significant effect on the distribution of comets in the Oort cloud and the subsequent delivery of those comets to the inner Solar System.In this research program, Dr. Thomas Quinn and colleagues will first study the formation and evolution of the Oort Cloud over the 4.5 billion years of the Solar System's history assuming a number of different star forming environments. It is quite likely that the Sun formed in a dense stellar cluster, but the actual densities and timescale for leaving the cluster are uncertain. The work will consider a number of stellar densities and cluster dissipation timescales and compare the resulting Oort Cloud and subsequent comet shower strength with a control case with no cluster environment. The Solar System, however, does not occupy a static place within the Galaxy. The research will therefore go on to incorporate changes in Galactic perturbations as the orbit of the Sun in the Galaxy evolves. This will be accomplished in the context of a cosmologically motivated model of the Galaxy formed via hierarchical merging in a Cold Dark Matter (CDM) Universe. This model has been calculated using the research group's massively parallel cosmological code, GASOLINE, and the model has been shown to produce many observed characteristics of spiral galaxies. The evolution of the Oort Cloud will be calculated as it feels the perturbations of the gas, stars, and dark matter from the disk, spiral arms and other substructure that exists in the galaxy model. The study will pay particular attention to the subsequent changes to the comet flux into the inner Solar System and possible consequences for impact rates on the Earth.Ever since the connection was made between the extinction event at the end of the Cretaceous and a comet impact, a strong connection has been made between comets and the disciplines of Paleontology and Geology. Both Dr. Quinn and the graduate student supported on this award are part of the University of Washington's Astrobiology program and therefore, will be connecting their research to work done by biologists and geologists in that program. The connection between orbital dynamics and comets also engages the public at large. The issues of the origin of our planetary system, how it fits into the galaxy as a whole and the implications for life are issues that draw the public into the results of dynamical research. Dr. Quinn and the graduate student will incorporate their results into their undergraduate classes and public lectures.***