A comet is made of a nucleus (inner core), coma (cloudy envelope around the nucleus), and then a tail. Where exactly do these beautiful, fast-moving cosmic snowballs come from? Scientists are able to trace comets that we see in the inner solar system by retracing their orbits. Through this, scientists believe that comets come from two distinct reservoirs: long-period comets from the Oort Cloud and short-period comets from Kuiper Belt. (A long-period comet is one that takes more than 200 years to complete an orbit around the sun and a short-period comet is one that takes less than 200 years).
The Oort cloud is a theoretical gigantic cloud – found at the outer edges of the solar system beyond Pluto – made of icy planetesimals. Scientists have stated that there could be more than a trillion comets within this cloud. Because of this, it may make up a significant portion of our solar system’s mass. Furthermore, we do not have direct evidence that this cloud exists because it is so far away. Our fastest space probe, Voyager 1, will reach the cloud in ~300 years and it will take another 30,000 years to travel through it!
The second home of comets, the Kuiper belt, is a circumstellar disc that is past the orbit of Neptune. Pluto was actually the first object that was discovered in the Kuiper Belt! The belt contains a vast number of icy bodies which become comets. It is far away, but the Oort Cloud is even further!