opik
Öpik-Arnold Monte Carlo n-body code from Jay Melosh and Brian Tonks
opik.f
This is a program to follow the orbital evolution of a particle in the solar system statistically, using the method of E. J. Opik. Opik's (1951) treatment assumed that the planets travel in circular orbits and that encounters between particles and planets can be treated using a two-body approximation. The orbital elements a,e,i change only during close encounters (although they may be subject to small periodic perturbations), while the angle to ascending node W and argument of perihelion w are assumed to rotate continuously due to perturbations by other planets. The timescale for this rotation in the Solar System is a few 1E5 years, so the model results are not accurate for smaller intervals. W and w are chosen randomly between 0 and 2*pi in the code. Resonances are ignored, along with possible large changes of a,e,i due to distant perturbations, as occurs in some chaotic systems.
As in Opik's original theory, this program also treats encounters as two-body interactions, but has been significantly improved by the incorporation of a full ellipse-on-ellipse encounter sequence. The lifetime computation still assumes the planets' orbits are basically circular, but is not much in error for somewhat elliptical orbits. Opik's treatment of this portion of the computation has been retained, including his treatment of partially crossing orbits, in which the interaction distance is modified. Speed of the computation has been greatly enhanced using the method
ejectrocks.f
Program to create an input data set of a,e,i orbital parameters for test particles in the statistical orbital mechanical code OPIK.
This code assumes the test particles are ejected with velocity Vrocks from a chosen planet. The position of the planet at ejection and the direction of ejection are assigned randomly. The code computes the velocity of rocks+planet in the invariable coordinate frame, then determines a,e,i and writes them to a file in a format which can then be used by OPIK.
sorthist.f
Program to read orbital evolution output file and output a list of impact histories for each planet suitable for statistical analysis and plotting with Kaliedagraph.
planet.data
Data on sun and planets for program OPIK.