TNO (transneptunian objects)
There are at least 70,000 small bodies with diameters larger
than 100 km orbiting the sun beyond Neptune, in a zone going from
the orbit of Neptune (at 30 AU) to 50 AU. These objects are
called TNOs and mostly occupy a thick band around the ecliptic,
which is generally referred to as the Kuiper Belt. This belt is
the source of the short-period comets, acting as a reservoir for
these bodies in the same way the Oort Cloud acts as a reservoir
for long-period comets.
The Kuiper Belt also deserves some very special attention since the objects that inhabit it are believed to be extremely primitive remnants from the early accretional phases of the solar system.
Astronomers have become aware of TNOs starting from 1992, when D. Jewitt (University of Hawaii) and J. Luu (University of California at Berkeley) reported the discovery of 1992 QB1 a very faint object which is the first TNO ever detected (in the animation: the first images of 1992 QB1).