Effects Of Planetary Perturbations Research Articles

Origin of the ten degree Solar System dust bands

The Solar System dust bands discovered by IRAS are toroidal distributions of dust particles with common proper inclinations. It is impossible for particles with high eccentricity (approximately 0.2 or greater) to maintain a near constant proper inclination as they precess, and therefore the dust bands must be composed of material having a low eccentricity, pointing to an asteroidal origin. The mechanism of dust band production could involve either a continual comminution of material associated with the major Hirayama asteroid families, the equilibrium model (Dermott et al. (1984) Nature 312, 505–509) or random disruptions in the asteroid belt of small, single asteroids (Sykes and Greenberg (1986) Icarus 65, 51–69). The IRAS observations of the zodiacal cloud from which the dust band profiles are isolated have excellent resolution, and the manner in which these profiles change around the sky should allow the origin of the bands, their radial extent, the size-frequency distribution of the material and the optical properties of the dust itself to be determined. The equilibrium model of the dust bands suggests Eos as the parent of the 10° band pair. Results from detailed numerical modeling of the 10° band pair are presented. It is demonstrated that a model composed of dust particles having mean semimajor axis, proper eccentricity and proper inclination equal to those of the Eos family member asteroids, but with a dispersion in proper inclination of 2.5°, produces a convincing match with observations. Indeed, it is impossible to reproduce the observed profiles of the 10° band pair without imposing such a dispersion on the dust band material. Since the dust band profiles are matched very well with Eos, Themis and Koronis type material alone, the result is taken as strong evidence in favor of the equilibrium model. The effects of planetary perturbations are included by imposing the appropriate forced elements on the dust particle orbits (these forced elements vary with heliocentric distance). A subsequent model in which material is allowed to populate the inner solar system by a Poynting-Robertson drag distribution is also constructed. A dispersion in proper inclination of 3.5° provides the best match with observations, but close examination of the model profiles reveals that they are slightly broader than the observed profiles. If the variation of the number density of asteroidal material with heliocentric distance r is given by an expression of the form 1 r τ then these results indicate that γ < 1 compared with γ = 1 expected for a simple Poynting-Robertson drag distribution. This implies that asteroidal material is lost from the system as it spirals in towards the Sun, owing to interparticle collisions.

Toward planets around neutron stars

The two Earth-like mass objects orbiting a 6.2-ms pulsar, PSR1257+25, have survived more than one year of close scrutiny aimed at verifying their existence and remain the most serious candidates to become the first planets detected beyond the Solar System. The analysis of systematic timing measurements of the pulsar made over a 2.5-year period continues to require the presence of two planets with the minimum masses of 3.4 M⊕ and 2.8 M⊕ and the corresponding distances from PSR1257+12 of 0.36 AU and 0.47 AU to correctly predict the pulse arrival times. The presently available 3 μs rms accuracy of this procedure leaves little room for significant contributions to the pulsar’s timing from any mechanisms other than the Keplerian motion. A detection of the effect of planetary perturbations on pulse arrival times which is commonly accepted as the most convincing way to furnish a “100% proof” of the reality of pulsar planets is already possible at a ∼ 2σ level. Intensive searches for millisecond pulsars now under way at various observatories are expected to address a very intriguing question of the frequency of occurrence of neutron star planetary systems.

The structure of the Geminid meteor stream - I. The effect of planetary perturbations

Etude des perturbations gravitationnelles de l'essaim Geminid a l'aide d'un modele simplifie dans lequel Jupiter cause la seule perturbation d'un courant initialement bien defini

Orbit Determination of Comet Ikeya-Seki.

The results of an orbit determination of comet Ikeya-Seki (196Sf) are presented. The observations from several ol~servatories taken prior to the perihelion passages (UlA U Nos. 1923-1933) were the basis for this determination. A differential correction was initiated using a position and velocity estimate derived from Cnnniugham's preliminary orbit (UlA U No. 1928). A Cowell integration program including perturbations from Venus to Saturn was used. Uncertainties in the orbit determination are discussed. With a sparse number of observations, it is shown that the orbital uncertainties can l~e large enough to change an elliptic deten~ination to a hyperbolic one. An estimate of the orbital period is given with an as socited uncertainty. The effect of planetary perturbations on the osculating Kepler period is discussed. The possibility of detecting the effects of mass loss from a change in the angular momentum before and after perihelion passage is also discussed.

The formation and evolution of the Perseid meteor stream.

The formation and evolution of the Perseid meteor stream.