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A KBO is a Kuiper Belt Object, celestial bodies that are located in the Kuiper Belt Region, also known as the Edgeworth-Kuiper Belt. The region extends from Neptune’s orbit to about 55 Astronomical Units (AU). An Astronomical Unit is the distance from the Earth to the Sun. Since Neptune is at 30 AU, the area is 25 AU wide. The Kuiper Belt has been described as a larger version – 20 times as wide and 20 to 200 times as massive – of the asteroid belt, which is located between Mars and Jupiter. Although the Kuiper Belt is much more massive than the asteroid belt, its mass is small compared to the planets. Astronomers say that it is likely around one-tenth the mass of the Earth while some other astronomers put it as low as one-thirtieth of the Earth’s mass. Some astronomers are surprised that there are much fewer Kuiper Belt Objects than they originally believed.
Most of the KBOs are composed of ices; this means that they have a large percentage of ammonia, water ices, and other compounds such as methane. This is the same composition that comets have. Unfortunately, it is difficult for scientists to get an accurate reading on the composition of the Kuiper Belt Objects.
Some of the KBOs are actually quite large. The largest KBO is Pluto, which was reduced to the status of a dwarf planet in 2006 and is also classified as a Kuiper Belt Object. There are also a number of other KBOS that are almost the same size as Pluto and have satellites as well. Thus, some of the other KBOs may be classified as dwarf planets in the future.
Another term used to refer to KBOS is Trans-Neptunian Objects (TNOs), but the terms are not synonymous. Trans-Neptunian Objects include all celestial bodies beyond the orbit of Neptune, thus it also refers to objects in the even more distant Oort Cloud, as well as other objects including those in the scattered disc. Scientists believe that Triton was a Kuiper Belt Object until it was captured by Neptune’s gravity and became its satellite.
More and more Kuiper Belt Objects are being discovered all the time, thanks to advances in technology. Most of these objects do not have names like Pluto does, simply because there are too many of them. Astronomers also believe they have discovered Kuiper Belts around a number of other stars.
Do not forget to check out Astronomy Cast’s episode on Pluto and the icy Solar System.