A spinning mass of debris that has been around since the beginning of the solar system can only mean one thing: an Oort cloud.
It all started 4.6 billion years ago after the solar system formed. A cloud of gas and dust started to orbit the sun. It formed next to Neptune and Pluto but started to drift away due to the planets gravitational effects. The Oort cloud is now composed of loose rocks, ice, methane, ammonia, and carbon dioxide. There now are old and new comets in the Oort cloud. Some comets have come from Kuiper Belt, which is like an Oort cloud but smaller and closer to the sun the sun. Others are new and just got captured by the gravitational pull.
Since the Oort cloud is so far away from the sun, it is frigid. It is only a couple more degrees then absolute zero, which is the coldest anything can get. Unlike Earth’s orbit, the Oort cloud orbits the sun at its own pace and takes much longer because it is farther away. At where the Oort cloud is in space, the sun's gravitational pull is weak, which is why parts of debris go flying off and become comets, for example, Jupiter is where comets from the Oort cloud goes from being dark to lighting up with a big tail trailing behind. If the comet reaches near the sun the heat of the sun melts the gases that are with the debris. The gas lights up a bright stream of light which is the comet's tail. After a while, the brightness dims out and goes behind the sun, far into space. After that, the comets ether crash into planets or the sun, but mostly what happens is they get caught in another planet’s orbit.
Astronomers do not exactly know why some debris goes away from the Oort cloud and turns into comets. Their best guess is that they get disturbed because of the gravitational causes from other stars in the galaxy. Even though the Oort cloud makes comets, most of them don't make it to the inner section of the solar system. Comets appear at random times and can't be seen unless they are near Jupiter.
The Oort cloud is unpredictable and can do anything at any moment. Many astronomers are scared that the sun will expose the unpredictable gravitational effect at the edge of our galaxy, that will disrupt the Oort cloud like never before. Others worry about the fact that any moment, a comet, or asteroid can come down to the earth and cause major destruction without warning. For this reason, they created a team of people called the Spacewatch to estimate when the comets will arrive. The Oort cloud is one of the most unpredictable things ever to have existed and is capable of doing anything, at any time.
[Source: Secrets of the Universe]