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Is It a Large Kuiper Object or a Dwarf Planet?
Largest known Kuiper Belt objects
Discovered in 1992, the Kuiper Belt contains numerous objects made of ices—frozen substances such as water, methane and ammonia. These objects orbit the Sun at a distance of approximately 30 to 55 AU (one astronomical unit = distance from Sun to Earth). It is estimated there may be 70,000 objects with a diameter larger than 100 km, and possibly millions of smaller objects as well.
Included among these innumerable Kuiper Belt Objects (KBO) are a handful of comparatively large objects that include Pluto, Eris, Haumea, and Makemake. Scientists speculate, the largest moon of Neptune—Triton—was once a KBO somehow captured by the large gas giant.
In 2005, Eris (originally nicknamed ‘Xena’), was discovered by a team of scientists analyzing pictures taken in 1993 by the Hubble Space Telescope. Eris appears to be larger than Pluto and it has its own orbiting moon, Dysnomia. Additional Kuiper Belt Objects are expected to be of similar or even larger size. It was the discovery of large KBOs that induced scientists to re-evaluate Pluto's status. In 2006 the International Astronomical Union decided to reclassify Pluto as a dwarf planet.
While the majority of the KBOs follow a circular orbit, others have highly elliptical orbits with an aphelion of as much as 100 AU. These, of which Eris is one, are sometimes referred to as Scattered Disc Objects (SDOs). While some scientists feel SDOs and KBOs should be classified independently, others believe in a common origin.
It is hoped much will be learned as the result of an interaction between NASA's "New Horizons" probe (launched January 19, 2006) with Kuiper Belt Objects, if NASA gives final approval after its anticipated fly-by of Pluto in July of 2015. The estimated time of that interaction is 2016-2020.
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The Kuiper Belt and Short-Period Comets
As their name would suggest, "short-period comets" are comets that take less than 200 years to orbit the Sun. These comets are believed to come from the Kuiper Belt. Interaction of some of the KBOs with the gravitational fields of nearby gas giants pulls some of the icy objects into the Solar System. These objects experience orbital modification, and they become comets.
Other comets, called long-period comets, are believed to arise from the much more distant, Oort Cloud.
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References and Resources
NASA: Solar System Exploration: Kuiper Belt & Oort Cloud
New Horizons – NASA’s Pluto-Kuiper Belt Mission
International Astronomical Union: Pluto and the Developing Landscape of Our Solar System
The University of Arizona: Short-Period Comets
Also by Bright Hub: Possibilities for Earth Impact Events: Comets, Asteroids, Meteoroids, by vancepreed