Dynamics, Origin, and Activation of Main Belt Comets

The discovery of Main Belt Comets (MBCs) has raised many questions regarding the origin and activation mechanism of these objects. Results of a study of the dynamics of these bodies suggest that MBCs were formed in-situ as the remnants of the break-up of large icy asteroids. Simulations show that similar to the asteroids in the main belt, MBCs with orbital eccentricities smaller than 0.2 and inclinations lower than 25 degrees have stable orbits implying that many MBCs with initially larger eccentricities and inclinations might have been scattered to other regions of the asteroid belt. Among scattered MBCs, approximately 20 percent reach the region of terrestrial planets where they might have contributed to the accumulation of water on Earth. Simulations also show that collisions among MBCs and small objects could have played an important role in triggering the cometary activity of these bodies. Such collisions might have exposed sub-surface water ice which sublimated and created thin atmospheres and tails around MBCs. This paper discusses the results of numerical studies of the dynamics of MBCs and their implications for the origin of these objects. The results of a large numerical modeling of the collisions of m-sized bodies with km-sized asteroids in the outer part of the asteroid belt are also presented and the viability of the collision-triggering activation scenario is discussed.Comment: 9 pages, 4 figures, to appear in the proceedings of IAU Symposium 263: Icy Bodies of the Solar System (Eds. D. Lazzaro, D. Prialnik, o. Schulz and J.A. Fernandez), Cambridge Univ. Pres

On the Dynamical Stability of Gamma Cephei, an S-Type Binary Planetary System

Precision radial velocity measurements of the Gamma Cephei (HR8974) binary system suggest the existence of a planetary companion with a minimum mass of 1.7 Jupiter-mass on an elliptical orbit with a ~2.14 AU semimajor axis and 0.12 eccentricity (hatzes et al. 2003). I present in this paper a summary of the results of an extensive numerical study of the orbital stability of this three-body system for different values of the semimajor axis and orbital eccentricity of the binary, and also the orbital inclination of the planet. Numerical integrations indicate that the system is stable for the planet's orbital inclination ranging from 0 to 60 degrees, and for the binary's orbital eccentricity less than 0.5. The results also indicate that for large values of the inclination, the system may be locked in a Kozai resonance.Comment: 5 pages, 3 figures, to appear in the proceedings of "The Search For Other Worlds." The 14th Annual October Astrophysics Conference in Maryland. Eds. De. Deming and S. Holt (PASP Style

On the Growth of Dust Particles in a Non-Uniform Solar Nebula

A summary of the results of a numerical study of the growth of solid particles in the vicinity of an azimuthally symmetric density enhancement of a protostellar disk are presented. The effects of gas drag and pressure gradients on the rate of growth of dust particles and their settling on the midplane of the nebula are also discussed.Comment: 4 pages, 2 figures, in the proceedings of "The Search For Other Worlds." The 14th Annual October Astrophysics Conference in Maryland. Eds. D. Deming and S. Hol

Partial Averaging Near a Resonance in Planetary Dynamics

Following the general numerical analysis of Melita and Woolfson (1996), I showed in a recent paper that a restricted, planar, circular planetary system consisting of Sun, Jupiter and Saturn would be captured in a near (2:1) resonance when one would allow for frictional dissipation due to interplanetary medium (Haghighipour, 1998). In order to analytically explain this resonance phenomenon, the method of partial averaging near a resonance was utilized and the dynamics of the first-order partially averaged system at resonance was studied. Although in this manner, the finding that resonance lock occurs for all initial relative positions of Jupiter and Saturn was confirmed, the first-order partially averaged system at resonance did not provide a complete picture of the evolutionary dynamics of the system and the similarity between the dynamical behavior of the averaged system and the main planetary system held only for short time intervals. To overcome these limitations, the method of partial averaging near a resonance is extended to the second order of perturbation in this paper and a complete picture of dynamical behavior of the system at resonance is presented. I show in this study that the dynamics of the second-order partially averaged system at resonance resembles the dynamical evolution of the main system during the resonance lock in general, and I present analytical explanations for the evolution of the orbital elements of the main system while captured in resonance.Comment: Plain TeX, 21 Pages, 6 Figures, Submitted to Celest.Mech.Dynamic.Astr

Dynamical Friction and Resonance Trapping in Planetary Systems

A restricted planar circular three-body system, consisting of the Sun and two planets, is studied as a simple model for a planetary system. The mass of the inner planet is considered to be larger and the system is assumed to be moving in a uniform interplanetary medium with constant density. Numerical integrations of this system indicate a resonance capture when the dynamical friction of the interplanetary medium is taken into account. As a result of this resonance trapping, the ratio of orbital periods of the two planets becomes nearly commensurate and the eccentricity and semimajor axis of the orbit of the outer planet and also its angular momentum and total energy become constant. It appears from the numerical work that the resulting commensurability and also the resonant values of the orbital elements of the outer planet are essentially independent of the initial relative positions of the two bodies. The results of numerical integrations of this system are presented and the first-order partially averaged equations are studied in order to elucidate the behavior of the system while captured in resonance.Comment: plainTeX, 30 pages, 18 graphs, accepted by MNRA