The Motion of Comets 2. The Motion of Comets Comets necessarily obey the same physical laws as every other object. The focus is located a distance ae from the center of the ellipse. Three further constants are required if one wishes to describe the orientation of the ellipse in space relative to some coordinate system, and a fourth quantity is required if one wishes to define the location of a body in that elliptical orbit.
Eccentricity is a mathematical measure of departure from circularity.
A circle has zero eccentricity, and most of the planets have orbits which are nearly circles. Only Pluto and Mercury have eccentricities exceeding 0.1. Comets, however, have very large eccentricities, often approaching one, the value for a parabola. Such highly eccentric orbits are just as possible as circular orbits, as far as the laws of motion are concerned. The solar system consists of the Sun , nine planets, satellites asteroids , comets , and various small debris.