The Oort Cloud and the Kuiper Belt

The Oort cloud is the spherical area of leftover debris from the beginning of the Solar System, including mainly asteroids, and some comets.  The Kuiper belt also contains this debris but it is a lot closer to the Sun, its inner limit being the orbit of Neptune.  In total, millions of asteroid-like bodies have been discovered in these areas, some of which being big enough to be moons, and one, called Eris, is classified as a dwarf planet and is larger than Pluto.  Eris, and a few other relatively large bodies also have moons in orbit around them (one body, discovered in 2003, has two moons!).  Also, comets orbiting elliptically around the sun usually pass through the Kuiper belt.  Periodical comets, ones that orbit continuously around the sun can travel out to the Oort cloud, and some escape the sun's gravity floating free into space.  New Horizons, a spacecraft that flew by Pluto in July 2015, also will explore some objects in the Kuiper belt objects from 2016-2020.  Many secrets of these zones are still waiting to be discovered.