As the dwarf planet of Pluto is left behind, we are already within the next region of the Solar System; the Kuiper Belt. It begins just outside the orbit of Neptune and encompasses the orbit of Pluto. The Kuiper Belt is a flat disc consisting of rocks and ice boulders of many sizes. They vary from the very small up to the dwarf planet of Eris which is larger than Pluto.
We are now about 7.4 billion miles (12 billion kilometres) from the Sun and, as such, it takes the majority of objects about 250 years to make one orbit. Over a thousand of these objects are thought to be comet-like. They are termed short-period comets because there is a relatively short period of time between returns.
The outer edge of the Kuiper Belt merges with the last region of interest within the Solar System. This is the Oort Cloud and it consists of a huge area which surrounds the Solar System. It stretches out to about 1.6 light years which is nearly half-way to the nearest star, Proxima Centauri at approximately 4.25 light years distance.
It is believed that the Oort Cloud is home to about one trillion comets; that is 1,000,000,000,000. This doesn’t mean to say that if we were able to train a powerful enough telescope on the Oort Cloud we would see millions of comets with their bright tails. Comets only display a tail when they are close to the Sun.
However, some of them get “bumped” out of the Oort Cloud and are sent on a journey which will take them close to the Sun. And it is at this point that we may have a chance of observing them with a bright tail.
That completes our tour of the Solar System. New topics to feed the curious mind will follow in due course.
John Pullen 