Dynamics of Extrasolar Planets and the Kuiper Belt

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

AST 0205892 Chiang Extrasolar planets and the Edgeworth-Kuiper Belt of trans-Neptunian bodies constitute two powerful drivers of planetary astronomy. Since the discovery of these objects less than a decade ago, theoretical understanding of their dynamical characteristics remains elusive. Why are the orbital 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 heliocentric distance of 47 AU? How did the orbital inclinations of Classical Belt objects become dramatically inflated? 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 during the 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 and numerical 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 of resonant capture and of retainment determine the fraction of bodies that reside in the 2:1 and the fraction of bodies that comprise the non-resonant Classical Belt. The degree of dynamical heating by eccentric, inclined 2:1 perturbers on Classical Belt Objects will be gauged. This study will culminate in predictions for the mass within the 2:1 resonance that can be tested by dedicated observations in which Dr. Chiang is already actively involved. ***