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Largest known Kuiper Belt objects
Credit: NASA
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.
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Eris with its moon, Dysnomia
Credit: NASA
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.
