Orbit Of Comets

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When you talk about the orbit of comets there are two main types: short period and long period. Most comets have elongated oval shaped (elliptical) orbits that take them close to the Sun for a part of their orbit, and then out into the further reaches of the Solar System for the remainder. Comets are often classified according to the length of their orbital period. The longer the period the more elongated the ellipse. Based on their orbital characteristics, short-period comets are thought to originate from the centaurs, Kuiper belt, or the scattered disc. The source of long-period comets is thought to be the far more distant, spherical Oort cloud.

Short period comets are generally defined as having orbital periods of less than 200 years. They usually orbit more-or-less in the ecliptic plane in the same direction as the planets. Their orbits typically take them out to the region of the outer planets, beyond Jupiter, at aphelion. Short-period comets are further divided into the Jupiter family which have orbital periods less than 20 years and Halley family which have orbital periods between 20 and 200 years.

Long-period comets have highly elongated (eccentric) orbits and periods ranging from 200 years to thousands or even millions of years. Despite their long orbital periods, they remain gravitationally bound to the Sun. Their orbits take them far beyond the outer planets at aphelia, and the plane of their orbits need not lie near the ecliptic. Those comets that are ejected from the solar system due to close passes by major planets are no longer properly considered as having “periods”.

There is a third class of orbit of comets. The single apparition comets. Single-apparition comets are similar to long-period comets, but have parabolic or hyperbolic trajectories which will cause them to permanently exit the solar system after passing the Sun one time. A parabolic trajectory is a Kepler orbit with the eccentricity equal to 1. When moving away from the source it is called an escape orbit.
Under standard assumptions a body traveling along an escape orbit will coast to infinity. A hyperbolic trajectory is a Kepler orbit with the eccentricity greater than 1. Under standard assumptions a body traveling along this trajectory will coast to infinity.

Here is a good article on the orbit of comets. Berkeley offers a nice piece on the topic. Here on Universe Today we have a great article on a comet’s route that takes it away from an Earth impact. Astronomy Cast has a tight article about Roche limits and black holes.

Source: NASA

Tagged as: long period comets, orbit of comets, short period comets, single apparition comets