Astronomers in 2005 announced the encounter of a body in the Kuiper Belt understood to be greater in size than Pluto, although later interpretations exposed it was somewhat smaller. The body encountered was acknowledged as Eris, and orbits the sun roughly around once every 580 years, moving nearly one hundred times further from the sun than Earth does. In 2006 after the discovery of Eris, it showed several astronomers the difficulty of labeling Pluto a full-scale planet, and Pluto, Eris, and the biggest asteroid Ceres were now reclassified as dwarf planets.

Due to their insignificant size and withdrawn location, Kuiper Belt Objects are very difficult to notice from Earth.  With the infrared measurements of NASA’s space-based telescopes, Spitzer, it has aided in figuring out sizes for the major objects.

NASA's Hubble Space Telescope has learned the slightest entity ever seen in noticeable light in the Kuiper Belt, an immense ring of icy remains that surround the outer perimeter of the solar system.  The picture below shows the concept of an artist’s idea of the term “the needle-in-a-haystack” this body that was discovered by Hubble is merely 3,200 feet across and 4.2 billion miles away.

 

http://www.space.com/16144-kuiper-belt-objects.html