Dynamics of Extrasolar Planets and the Kuiper Belt

太阳系外行星和海王星外天体的埃奇奥尔-柯伊伯带构成了行星天文学的两个强有力的驱动力。自从这些天体在不到十年前被发现以来，对它们的动力学特征的理论理解仍然难以捉摸。为什么太阳系外行星的轨道偏心率与太阳系气体巨星相比如此之大？在太阳中心距离为47 Au的地方，是什么造成了经典柯伊伯带的明显边缘？经典腰带天体的轨道倾角是如何急剧膨胀的？ 加州大学伯克利分校的尤金·蒋博士及其同事将研究一系列直接解决这些问题的理论动力学问题。他将研究这两类看似不同的物体如何参与许多相同的动力学过程，最显着的轨道迁移和共振相互作用。行星在它们纳塔尔气盘中是非常移动的。已知的太阳系外行星质量足够大，以至于它们在轨道周围的圆盘物质中清除了环形间隙。一个有间隙的行星受制于其宿主盘的粘性演化。磁流体动力学湍流盘的粘性扩散时间随着与星星距离的减小而缩短。因此，两颗行星向它们的母星星迁移，使得外行星的周期与内行星的周期之比增加。该比率的发散意味着一系列平均运动共振将被交叉。每个共振交叉可以在迁移体中产生相当大的轨道偏心率。蒋博士和他的合作者将探索这一机制，以获得令人兴奋的怪癖。将计算原行星盘的粘性、热和质量分布，以确定行星迁移的时间尺度。共振交叉的天体力学将通过一系列的分析和数值轨道积分进行研究。将进行行星-盘相互作用的数值流体动力学模拟，以测试共振通道的有效性。太阳系巨星轨道的圆形性可能与太阳系外行星轨道的极端拉长相一致，在原行星盘的框架内，其粘性随距离的增加而急剧下降;这个框架表明外太阳系的轨道结构可能确实是普通的。海王星最外层最强的2：1平均运动共振在多大程度上引力塑造了经典柯伊伯带将被确定。当海王星在晚期重撞击时期向外迁移时，它的共振向外扫过，并将柯伊伯带天体捕获到振动的轨道上。蒋博士和他的合作者将通过分析和数值计算来解释在2：1共振中振动的有限质量的物体。一个大规模的，迁移的2：1共振可能会泄漏到经典带域的对象;共振捕获和保留的不完善的效率决定了居住在2：1的身体和身体组成的非共振经典带的比例。对经典带状天体的偏心、倾斜2：1微扰的动力学加热程度进行了测量。这项研究将最终预测2：1共振内的质量，可以通过蒋博士已经积极参与的专门观测进行测试。

AST 0205892ChiangExtrasolar planets and the Edgeworth-Kuiper Belt of trans-Neptunian bodies constitute twopowerful drivers of planetary astronomy. Since the discovery of these objects less than a decadeago, theoretical understanding of their dynamical characteristics remains elusive. Why are theorbital eccentricities of extrasolar planets so large compared to those of Solar System gas giants?What is responsible for delineating an apparent edge to the Classical Kuiper Belt at a heliocentricdistance of 47 AU? How did the orbital inclinations of Classical Belt objects become dramaticallyinflated? Dr. Eugene Chiang and colleagues, at the University of California at Berkeley, will investigate a series of theoretical dynamical problems that directly address these issues. He will examine how these two seemingly disparate classes of objects participate in many of the same dynamical processes, most notably orbital migration and resonant interaction. Planets can be remarkably mobile while embedded in their natal gaseous disks. Known extrasolar planets are sufficiently massive that they clear annular gaps in disk material about their orbits. A gap-opening planet is slaved to the viscous evolution of its host disk. Viscous diffusion times of magnetohydrodynamically turbulent disks shorten with decreasing distance from the star. Thus, two gap-opening planets migrate towards their parent star such that the ratio of the period of the outer planet to that of the inner planet grows. The divergence of this ratio implies that a series of mean motion resonances will be crossed. Each resonance crossing can generate substantial orbital eccentricities in the migrating bodies. Dr. Chiang and his collaborators will explore this mechanism for exciting eccentricities. The viscous, thermal, and mass profiles of protoplanetary disks will be computed to determine planetary migration timescales. The celestial mechanics of resonance crossings will be investigated through a series of analytic and numerical orbit integrations. Numerical hydrodynamic simulations of planet-disk interactions will be undertaken to test the effectiveness of resonance passages. The circularity of orbits of Solar System giants may be reconciled with the extreme elongations of extrasolar planetary orbits within the framework of protoplanetary disks whose viscosities decrease dramatically with distance; this framework indicates that the orbital architecture of the outer Solar System may indeed be commonplace.The extent to which Neptune's outermost, strongest 2:1 mean-motion resonance gravitationally sculpted the Classical Kuiper Belt will be ascertained. As Neptune migrated outwards duringthe era of late heavy bombardment, its resonances swept outward and captured Kuiper Belt Ob-jects into librating orbits. Dr. Chiang and his collaborators will account for, through analytic andnumerical calculations, the finite masses of bodies librating within the 2:1 resonance. A massive,migrating 2:1 resonance may leak objects into the Classical Belt domain; imperfect efficiencies ofresonant capture and of retainment determine the fraction of bodies that reside in the 2:1 and thefraction of bodies that comprise the non-resonant Classical Belt. The degree of dynamical heatingby eccentric, inclined 2:1 perturbers on Classical Belt Objects will be gauged. This study willculminate in predictions for the mass within the 2:1 resonance that can be tested by dedicatedobservations in which Dr. Chiang is already actively involved.***