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List of hyperbolic comets
The following is a list of parabolic and hyperbolic comets in the Solar System. Many of these comets may come from the Oort cloud, or perhaps even have interstellar origin. Due to the Oort Cloud not being gravitationally attracted enough to the Sun to form into a fairly thin disk, like the inner Solar System, comets originating from it can come from roughly any orientation, and many even orbit retrograde. By definition, a hyperbolic orbit means that the comet will only travel through the Solar System once, with the Sun acting as a gravitational slingshot, sending the comet hurtling out of the Solar System entirely unless its eccentricity is otherwise changed. Comets orbiting in this way still originate from the Solar System, however. Typically comets in the Oort Cloud are thought to have roughly circular orbits around the Sun, but their orbital velocity is so slow that they are easily perturbed by passing stars and the galactic tide.
Prior to finding a well-determined orbit for comets, the JPL Small-Body Database and the Minor Planet Center list comet orbits as having an assumed eccentricity of 1.0. In the list below, a number of comets discovered by the SOHO space telescope have eccentricities of exactly 1.0, because most orbits are based on only an observation arc of several hours or minutes. The SOHO satellite observes the corona of the Sun and the area around it, and as a result often observes sungrazing comets, including the Kreutz sungrazers. Although officially given an assumed eccentricity of 1.0, the Kreutz sungrazers have an orbital period of roughly 750 years, and originate from the progenitor of the Great Comet of 1106. Many of the Kreutz sungrazers additionally don't survive perihelion, as they are quite literally "sungrazers" – on average their perihelion distance is roughly 0.0050 astronomical unit (AU), and the radius of the Sun is 0.0046 AU.
The Kreutz sungrazers have a perihelion distance of ~0.0050 AU, an inclination of 144 degrees, and an orbital period of roughly 750 years. Three other sungrazing groups, the Meyer, Marsden, and Kracht groups, have a perihelion distance of 0.035, 0.044, and 0.049 AU, an inclination of 72, 13, and 26 degrees, and a period of at least a decade, 5.6, and 3–4 years.
Some comets in this list are designated with an X-designation. This is for comets whose orbits have not been calculated for various reasons, often that they were observed so long ago that nobody bothered writing down the location of them well enough for an orbit to be determined, or that they were observed in modern times over such a short period that their long-term orbit was too uncertain to calculate.
== List ==
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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