Characteristics of Icy Comets
Comets look like dirty snowballs, as they are comprised of dust, rocks, and frozen gas. As these comets get closer to the sun and experience its heat, the ice on their surface regions will start to melt. This helps in forming a gas cloud, which is then stretched out by solar winds to create the famous tail of a comet. Shorter-period comets will be the remnants from the formation of the solar system, which took place at least 4.6 billion years ago.
They mainly originated from the icy objects belt beyond Neptune, where they got knocked into an orbit closer to the sun. These shorter-period comets have solar orbits, which are mostly less than 200 years old and seem to be entirely predictable. The longer-period comets might originate from a region, primarily termed as Oort Cloud. It lies around 100,000 times farther away from the sun than the Earth does. So their orbits might take as long as 30 million years, if not more.