The Kuiper Belt

The Kuiper Belt is a thick disk of icy rocks beyond the orbit of Neptune. The disk of material is roughly in line with the orbits of the planets in our Solar System. It's a bit like the asteroid belt but much larger. There are at least 100,000 icy and rocky objects in the Kuiper Belt. In fact, some moons of Saturn and Neptune are thought to have come from there. 

Pluto and many of the other dwarf planets in our Solar System are part of the Kuiper belt. In 2015, the New Horizons mission became the first spacecraft to explore the Kuiper belt.

The Oort Cloud

The Oort Cloud is a huge sphere of icy rocks beyond the Kuiper Belt. It is thought to surround the entire Solar Solar System. The Oort Cloud is about 2 light years away from Earth. This means it takes light - travelling at 300,000 kilometres every second - 2 years to reach Earth from the Oort cloud! The Oort Cloud is sometimes used to mark the edge of our Solar System. 

We think most of the comets in our Solar System come from the Oort Cloud, but we do not know much else about it. Because it is so far from the Sun, the objects in the Oort Cloud are too dark for astronomers to observe. The Voyager spacecraft have travelled further than any other space probe. Voyager 1 and Voyager 2 left Earth in 1977. It will take them about 300 years to reach the inner edge of the Oort Cloud. It could take 30,000 years to fly past it!