Jupiter-family comet

…into two dynamical groups: the short-period comets with orbital periods shorter than 200 years and the long-period comets with orbital periods longer than 200 years. The short-period comets were split into two groups, the Jupiter-family comets with periods shorter than about 20 years and the Halley-type comets with periods longer…

For Jupiter-family comets, the mean time between comet impacts is 28 million years. For Halley-type comets, the mean time between comet impacts is 521 million years. Note that the impact frequency for both Jupiter-family and Halley-type comets may be higher if there are yet undiscovered members…

Short-period comets complete their orbits in less than 200 years and so likely have been observed before; they generally approach along the plane of the solar system, near which lie the orbits of most of the planets, including Earth. Like short-period comets, most known Earth-approaching…

…like Encke’s Comet, was a short-period comet; it had a period of about 6.75 years. It was only the third periodic comet to be confirmed. It was identified with a comet observed by French astronomers Jacques Lebaix Montaigne and Charles Messier in 1772 and by Pons in 1805, and it…

…account for the number of short-period comets then known. Also, no comets had ever been observed on truly hyperbolic orbits. Some long-period comets did have orbit solutions that were slightly hyperbolic, barely above an eccentricity of 1.0. But a truly hyperbolic comet approaching the solar system with the Sun’s velocity…

Marsden found that for a short-period comet, the magnitude of the rocket force was typically only a few hundred-thousandths of the solar gravitational attraction, but that was enough to change the time when the comet would return. Later, Marsden and colleagues computed the rocket forces for long-period comets and found…

…a good source for the short-period comets. Up until that time it was thought that short-period comets were long-period comets from the Oort cloud that had dynamically evolved to short-period orbits because of planetary perturbations, primarily by Jupiter. But astronomers who tried to simulate that process on computers found that…

…key element in understanding the short-period comets was their relatively low-inclination orbits. Typical short-period comets have orbital inclinations up to about 35°, whereas long-period comets have completely random orbital inclinations from 0° to 180°. Fernández suggested that the easiest way to produce a low-inclination short-period comet population was to start…

…will eventually be seen as short-period comets, while most others will be thrown into long-period orbits or even ejected to interstellar space.

_… sublimation—an unexpected result, given that short-period comets are expected to lose their near-surface CO₂ early during their many passages close to the Sun. The other half of the nucleus was far less active and only showed evidence of water ice sublimation. The active half of the comet also appeared to…

…only a few percent, for short-period, Jupiter-family comets, which have made hundreds of returns, on average.