Scientists call comets “dirty snowballs,” because they are mainly made up of frozen methane, ammonia, and water.
Comets are smaller celestial objects that orbit the Sun with orbits that are very elliptical, often bringing them close to the Sun.
The key characteristic of a comet is that when it does get closer to the Sun, the ice inside begins to melt causing bright features, including the well-known comet “tail.”
Each time a comet becomes warm enough, it “sheds” part of its contents, giving scientists the theory that comets have a limited lifespan.
The scientific community calculates that there are around 3,000 comets, with one occurrence visible from Earth every ten years.
Humans have been viewing comets for thousands of years and, since comets may eventually shed all of its contents, scientists believe that they would have ended their existence a long time ago.
Therefore, there must be a location in the Solar System that is producing comets. Since the outer Solar System is the only place that hasn’t been deeply researched, it’s assumed that this is very likely the birthplace of comets.
Scientists have been studying the orbits of comets and there is evidence that there may possibly be two places in the outer Solar System that are producing comets.
The closer area is the Kuiper Belt, which has already been found to contain a band of comets that share similar shorter orbital traits to those seen in the Asteroid belt.
Further out is a spherical shell called the Oort Cloud and those comets that originate in this area seem to have a longer orbital pattern.
Theories on exactly how comets begin in any of these areas include the idea that they exist as objects and due to collisions with other comets may be knocked into new orbital patterns that are due to the gravity pull of passing interstellar objects, including planets.
When a comet comes close to the Sun and their internal ices begin to melt, they have bright features that show. There are 4 parts to these comets: the nucleus, coma, dust tail, and ion tail.
Over thousands of years astronomers have made note of some of the comets that reappear after durations of time. Some of the most famous include: