Dynamics of the Leonid Meteoroid Stream: a Numerical Approach

We have simulated the evolution of the Leonid stream via numerical integration of 3 million test particles ejected from 55P/Tempel-Tuttle during five perihelion passages of that comet. Using the Whipple ejection velocity formula and a random ejection spread in true anomaly about the parent comet orbit inside 2.3 AU, we have followed the subsequent evolution of Leonid meteoroids differing by over 5 orders of magnitude in mass under the influence of radiation pressure and planetary perturbations. By comparing the model predictions of Leonid activity on a year by year basis with the available observations we have attempted to determine roughly the time of ejection associated with each Leonid storm occurrence and model the observed mass distribution. On the basis of the demonstrated accuracy of the model we make predictions regarding times of peak activity and relative strengths for the Leonid returns for each year during the latter part of the 1990s.

Dynamical Mechanisms for Transferring Comets In and Out of the Oort Cloud

We study scenarios where comets are not original members of the Solar System but have been acquired from the surrounding medium through dynamical evolution. This leads to estimates of the present day number density of comets in the interstellar medium which are not in contradiction with observational upper limits. We also consider the dynamical transfer of Oort Cloud comets into short period comets. The process is very sensitive to the inclination of the comet orbit which leads to strong bias in favour of low inclinations in short comet orbits.

The past orbit of comet Halley and its meteor stream

The present paper studies the structural features of the meteor streams associated with Comet Halley deduced from the observations of its meteor showers, as check points of orbital elements in a deeper history of the comet orbit. Libration of the argument of perihelion of the comet and the corresponding displacement of the nodes, as recognized in the distribution of condensations within the stream, allows to estimate the maximum lifetime of the comet in the inner Solar System at about 2 × 105 years.

4. The Evolution of Comet Orbits as Perturbed by Uranus and Neptune

When the perturbing planets are Uranus and Neptune, the perturbations on comets are so much weaker than with Jupiter and Saturn that a study of the comets’ orbital evolution, using exact numerical integration, would require 200 times more revolutions. This is hardly practical with present computers. Here we describe results with a simulation approach, the “Monte Carlo (random walk) method.” The proper distribution shape for the perturbations in energy are found from a few thousand numerical integrations, then this distribution of perturbations is applied to millions of simulated orbit-revolutions. This method reproduces earlier Jupiter results in 1/500 the former computation time. We find that Neptune can capture near-parabolic comets with perihelia in the range of 30 to 34 AU, increasing their 1/a-values and decreasing their perihelia until they reach a region where Uranus can interact. Uranus in turn passes some of these on to Saturn, who passes some to Jupiter. Ultimately a few reach the orbits of the visible short-period comets. The process requires about 200,000 comet orbit-revolutions, 4 × 108 years, and the efficiency is one in 6000. The rest of the comets are ejected on hyperbolic orbits.

Comet Schwassmann-Wachmann 3 (1930 VI)

The definitive orbit of comet 1930 VI basing on 190 observations has been derived. Investigation of the comet orbit evolution for the time span of 200 yr indicated that the 1882 approach (tappr = 1882 Oct. 22.559; δmin = 0.0057 AU) of the comet to Jupiter resulted in considerable element transformations. The perihelion and aphelion distances reduced from 4.1 AU to 1.2 AU and from 12.2 AU to 5.2 AU, respectively, whereas the period of revolution also underwent a decrease from 23.3 yr to 5.8 yr. The next return of the comet to the perihelion is to be expected in 1974 (T= 1974 March, 17.475).