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Recently, short-period comets have been subdivided into the Jupiter-type comets, like that of Temple 2 and Encke, which typically have periods of just twenty years; and the Halley-type comets, with intermediate periods of between twenty to about two hundred years.

Experts believed that the Jupiter-type comets are to have originated from the Kuiper Belt that surround the sun at various distances ranging from thirty to fifty astronomical units, or 7.5 billion kilometers to 4.7 billion kilometers. The outer planets Neptune and Uranus and their gravitational influences is thought to affect some objects within the Kuiper belt occasionally, causing them to be flung and be caught up in orbits which characterizes those belonging to the Jupiter family. Halley-type comets on the other hand, together with those considered to be long-period comets, appear to originate from the Oort cloud.

The life spans of short-period comets are influenced by the loss of gas, rocks and dust every time they swing in their orbits around the sun. Many are visibly split into many pieces, while some disintegrate or fall away. Comet’s lives are calculated to be around ten thousand years. But for the average short-period comet, it only takes two hundred trips for its entire lifetime. Based on every 76-year return of Halley’s Comet, experts calculated that it will only live for 15,200 years before it dies out.

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Comets

Periodic Comets are often written with a prefix, which is determined after the second perihelion passage and some of the comets in this category are still unnumbered. The letter P written after the number indicates that the comet is periodic. Some comets have the same name and the prefixes are the only clues to determine that their orbital periods are different. Most comets are named after the people who discovered them and others take the names of those who calculated the orbital periods that some of them engaged in a lifelong career of computing these values. Comets that are considered periodic have already appeared to some observers on Earth and are expected to appear again after completing their orbital periods. The perihelion passage of comets in this category can now be computed with high accuracy.

Some of the most popular periodic comets that have appeared before the eyes of many enthusiasts of the night sky include Halley, Encke, Tempel-Tuttle and Swift-Tuttle. Seeing a comet is a once in a lifetime experience and many night sly observers look forward to seeing one in their own time.

Halleys Comet – A Periodic Comet

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Matter in the Oort cloud is mostly composed of ice particles that vary from water, ethane, hydrogen cyanide, carbon monoxide and methane. Dutch astronomer Jan Oort hypothesized its existence in 1950. He believed that directly observing a cloud cannot be possible with telescopes. This is because the comets that consists it are too minute and far apart. Trillions of comets are projected to be in the Oort cloud, with a total mass of 100 times compared to Earth.

Though its existence has not yet been confirmed, the reality of the Oort cloud is widely embraced by the scientific community. At present, the 0377 Sedna, 2000 CR105, 2006 SQ372, and 2008 KV42 are the known trans-Neptunian objects that are considered probable inner Oort cloud members.

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