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| The Kuniper Belt |
Comets are essentially debris left behind during the formation of our Solar System. They are believed to originate from two locations:
The Kuiper Belt - short period comets with orbits less than 100 years
The Oort Cloud - long period comets with orbits greater than 100 years
The Oort Cloud - long period comets with orbits greater than 100 years
Comets have highly elliptical orbits that bring them very close to Earth. When they are far from the Sun, they look like the normal asteroid, however because they are composed of rock and ice (the "dirty snowball" analogy is correct), the grow tails as they encounter Solar Wind. There are actually two tails that are present as the comet approaches the Sun - an Ion tail (gas tail) and a dust tail. It appears as if the heating and energy from the Sun causes jets to form within the comet that results not only in the formation of the tail, but also resulting in debris left behind
Debris from a comets tail are called meteoroids. When we see meteor showers on Earth, this is the Earth passing through the comets debris. There are three terms to know in regards to this debris:
• Meteoroid - the debris as it is in space
• Meteor - the debris as it is seen in the atmosphere
• Meteorite - debris that has survived entry and impact the ground
• Meteor crater - an impact by a meteor creates a crater, called (easy enough) a meteor crater
Meteor impacts on Earth are rare, but hundreds of meteorites are seen every year.
All of the impact craters on the other planets and moons are the result of meteor impacts.
Kuiper Belt Objects:
The Oort Cloud (below) is though to be the origin of long period comets (more than 100 year orbits), but short period comets (less than 100 year orbits) had to originate closer to the Sun. Dutch Astronomer Gerard Kuiper proposed these object came from a new belt of comets just beyond the orbit of Pluto - the Kuiper Belt.
In actuality, all of the icy-rock bodies - like Pluto, Charon and Sedna - beyond the orbit of Neptune are in a classification called Trans-Neptunian Objects or TNO's. The Kuiper Belt Objects and the Oort Cloud are subdivisions within this region.
The theory of the Kuiper Belt was confirmed by the discovery of Sedna, a Pluto-like body with a distance of 13 billion kilometers from the Sun. Its orbital duration is a slow 10,500 year period. This image of Sedna by the Hubble Space Telescope is our clearest image of one of these Kuiper Belt Objects - or KBO's.
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| Oort Cloud |
Oort Cloud:
Dutch Astronomer Jan Oort proposed that our Solar System is surrounded by a vast sphere of debris called the Oort Cloud. This proposition seemed to fit the fact that comets appear to come from all directions, and not just the equatorial plane of the Solar System.
Dutch Astronomer Jan Oort proposed that our Solar System is surrounded by a vast sphere of debris called the Oort Cloud. This proposition seemed to fit the fact that comets appear to come from all directions, and not just the equatorial plane of the Solar System.
This sphere is quite large, and is though to be between 20,000 and 150,000 A.U. - remember that an A.U. is an Astronomical Unit, or the Earth-Sun distance.
Comet Hyakutake and Hale-Bopp are long period comets that originated from the Oort Cloud. 80% of all known comets have the same origins.
