The first Kuiper Belt Object was discovered in 1992, proving that Kuiper’s theory was correct. Detecting them is difficult because they are very faint and move so slowly. It takes hundreds of years for these objects to complete one orbit around the Sun. The objects are probably left-overs from the birth of the planets. They were ejected to this remote outer region by interactions with the giant planets.

Which planet is the largest member of the Kuiper Belt?

Further out are the comets of the Oort Cloud. These are so far away that they are invisible in even the largest telescopes. Every so often one of these comets is disturbed and heads towards the Sun. It then becomes visible in the night sky.