Dynamics of the Kuiper Belt: From Planetesimal Formation to Planetary Migration

小行星的埃奇沃斯-柯伊伯带，其中冥王星是已知的最大的成员，提供了一个宏大的测试粒子集合，其轨迹反映了我们行星系统中事件的年表。Eugene Chiang博士的研究项目的学术价值在于，它将详细描述这段历史的三个不同的篇章：(1)星子的形成。原行星盘中面致密粒子层的自引力坍塌有望由尘埃颗粒形成超千米大小的物体。我们将对这一致密层中由Kelvin-Helmholtz不稳定性触发的湍流进行数值流体力学模拟，以评估气体对尘埃施加的湍流应力是否能将尘埃输送到金属丰度不断增加的区域。由于引力不稳定，这些区域形成小行星的时机已经成熟。(2)行星由行星吸积而成。最近发现的海王星特洛伊木马有望为研究海王星的形成环境提供新的见解。理论计算，从详细的数量级估计到使用新的碰撞NBody程序的数值探索，将确定观测到的海王星特洛伊是直接通过碰撞插入还是从较小的天体就地生长。这两个形成通道描绘了海王星诞生时行星小行星盘的截然不同的图景。第一种方法将大部分的圆盘质量放入几十公里宽的物体中，而第二种方法则将厘米大小的物体放入同样的位置。(3)轨道演化。柯伊伯带巨大的轨道倾斜度离散性可以通过引用古代与海王星的近距离接触来理解吗？这一假说只有在散落物体的近日点随后被提升到海王星无法企及的地方时才成立。在存在自引力行星盘的情况下，将首次测试长期共振提升近日点的能力。如果海王星的迁徙负责将柯伊伯带天体捕捉到低阶共振，那么这个过程对与行星交换角动量的行星体的质量谱有什么要求？行星迁移中的随机性程度将通过分析计算和旨在测试分析标度的数值实验来测量。行星迁移是如何填充高阶共振的？N：1共振诊断海王星远古迁移率的潜力将被评估，以期在未来对柯伊伯带进行全天天体测量。这项研究有几个更广泛的影响。从科学上讲，行星迁移和共振捕获问题会影响太阳系外的行星系统，特别是由于行星的引力雕刻而呈现非轴对称的碎片盘系统，以及GJ876a+b等共振行星对。此外，了解行星形成的要求决定了我们对行星系统大小的预期，未来对年轻太阳系的自适应光学成像可能会测量到这个大小。从人力资源的角度来看，江博士将培训两名研究生和一批本科生研究助理，将教授新的研究生和本科生行星系统物理学课程，重点是最近发现的海王星质量巨星，并将继续在研究机构和公共场所演讲。*

AST 0507805ChiangThe Edgeworth-Kuiper Belt of planetesimals, of which Pluto is the largest known member,furnishes a grand ensemble of test particles whose trajectories reflect the chronology of events in our planetary system. The intellectual merit of Dr Eugene Chiang's research project is that it will detail three different chapters in this history: (1) The formation of planetesimals. Self-gravitational collapse of a dense layer of particles at the midplane of the protoplanetary disk promises to form superkilometer-sized objects from dust grains. Numerical hydrodynamical simulations of turbulencetriggered by the Kelvin-Helmholtz instability in this dense layer will be performed to assess whether the turbulent stress exerted by gas on dust can transport dust to regions of ever increasingmetallicity. Such regions are ripe for planetesimal formation by gravitational instability. (2) Theaccretion of planets from planetesimals. New insights into the formation environment of Neptuneare promised from the recent discovery of Neptune Trojans. Theoretical calculations, ranging from detailed order-of-magnitude estimates to numerical explorations with a new collisional Nbody code, will determine whether observed Neptune Trojans were inserted directly by collisions or grew in situ from smaller bodies. These two formation channels paint dramatically different portraits of the planetesimal disk at the time of Neptune's birth. The first places the bulk of the disk mass into objects dozens of kilometers across, while the second does the same for centimeter-sized objects. (3) The evolution of orbits. Can the Kuiper Belt's enormous dispersion of orbital inclinations be understood by appealing to ancient close encounters with Neptune? This hypothesis is valid only if the perihelia of scattered objects can subsequently be raised beyond Neptune's reach. The ability of secular resonances to raise perihelia will be tested, for the first time, in the presence of a self-gravitating disk of planetesimals. If Neptune's migration were responsible for capturing Kuiper Belt objects into low-order resonances, what demands does this process make on the mass spectrum of planetesimals which exchange angular momentum with the planet? The degree of stochasticity in planetary migration will be measured using analytic calculations and numerical experiments designed to test analytic scalings. How are high-order resonances filled by planetary migration? The potential of n:1 resonances to diagnose Neptune's ancient migration rate will be assessed, in anticipation of future all-sky astrometric surveys of the Kuiper Belt.The research has several broader impacts. Scientifically, issues of planetary migrationand resonance capture impact extrasolar planetary systems, particularly debris disk systemsthat exhibit non-axisymmetries attributed to gravitational sculpting by planets, and resonantpairs of planets such as GJ876a+b. Furthermore, understanding the requirements of planetesimalformation determines our expectation for the sizes of planetary systems, sizes that may bemeasured with future adaptive optics imaging of young extrasolar systems. From the perspectiveof human resources, Dr. Chiang will train two graduate students and a cadre of undergraduate research assistants, will teach new graduate and undergraduate classes in the physics of planetary systems, with emphasis on recently discovered Neptune-mass giants, and will continue to deliver lectures at research institutions and at public venues.***