Wikijunior:Solar System/Kuiper Belt
Beyond the orbit of Neptune lies the Kuiper belt. It extends outward an additional three billion kilometers away from the Sun. The belt contains different-sized lumps of icy mixtures. These lumps are called Kuiper belt objects. The biggest are called minor planets or dwarf planets. The Kuiper belt may have formed when the gravity of the young planet Jupiter hurled the objects out to where they are now. The Kuiper belt is named after Gerard Kuiper (rhymes with "viper"), one of several astronomers who hypothesized about a field of small objects beyond Neptune.
What are Kuiper belt objects?
The objects in the Kuiper belt are frozen mixtures of dirt, ice and organic compounds. They are a lot like comets. Some of the objects have a reddish color and others are gray.
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How big are the Kuiper belt objects?
Scientists consider Pluto to be one of the largest Kuiper belt objects. It is 2390 km across and is a dwarf planet. The next largest known Kuiper belt objects are Orcus, 2003 EL61 and 2005 FY9. Orcus is about 1600 km (1,000 miles) across; 2003 EL61 is 70% the size of Pluto and 2005 FY9 is about 50% to 70% of Pluto's size.
Recently, scientists found another dwarf planet named Eris that is even bigger than Pluto. The scientists don't know its exact size, but they think it is about 20% larger than Pluto. At the time it was found, it was almost 100 times further away from the Sun than the Earth. It can come about as close to the Sun as Pluto. Eris has a moon named Dysnomia. The orbit of Eris is tilted almost 45 degrees compared to Earth's orbit. Pluto's orbit is only tilted by 17 degrees.
Other large Kuiper belt objects about or over 1000 km across are Pluto's moon Charon, Quaoar, Varuna, Ixion, 1996 TL66, 2002 TX300, 2002 TC302, 2002 UX25 and 2002 AW197. Ceres, the largest asteroid in the asteroid belt, is about 950 km across.
There are many other Kuiper belt objects that are only a few kilometers or tens of kilometers across.
How many Kuiper belt objects are there?
Over a thousand Kuiper belt objects had been found by astronomers. Scientists think that there might be more than seventy thousand large objects in the Kuiper belt, and some might be almost as big as Earth (although they would be a lot colder). Even though there are so many objects in the Kuiper belt, it is very light, weighing between 1/25 and 1/30 of Earth's mass.
What is it named after?
After the first object in the belt other than Pluto and its moon Charon was spotted from the Mauna Kea Observatory in Hawaii in 1992, the belt was named after the astronomer Gerard Kuiper. Back in 1951 this scientist wrote that he thought this belt might exist, but there was no proof at that time. Other astronomers, including Frederick Leonard, Kenneth Edgeworth, and Julio Fernandez, also thought that the belt existed. For this reason some astronomers call it the Edgeworth-Kuiper belt.
What are the Kuiper belt objects named after?
When an object is discovered in space, it is given a temporary name called a "provisional designation". This temporary name begins with the year the object was discovered, followed by some letters and numbers that tell in what month and in what order it was discovered. Later on, important objects are given formal names, often taken from mythology.
The Kuiper belt objects Orcus, Charon, and Varuna were all named after mythological gods of the underworld. Ixion was named after a mythological person in the underworld. Quaoar was named after a creation god of the Native American Tongva people.