Final answer:
Long-period comets are believed to primarily come from the Oort Cloud, a spherical collection of icy bodies far beyond the main planetary region of our solar system. They have unpredictable orbits and can appear in the inner solar system after their paths are altered by gravitational interactions. The Oort Cloud is distinct from the Kuiper belt, which contains short-period comets and is closer to the Sun.
Step-by-step explanation:
Long-period comets are thought to reside mainly in the Oort Cloud, a vast spherical shell surrounding our solar system. This cloud extends up to approximately 50,000 astronomical units (AU) from the Sun, which is about the edge of the Sun's gravitational influence. The Oort Cloud is believed to contain between one trillion (10ⁱ²) and ten trillion (10ⁱ³) comets, which are essentially icy bodies left over from the formation of the solar system. Comets from the Kuiper belt, a disk-shaped region beyond Neptune's orbit, also contribute to the comet population within our inner solar system. However, the Kuiper belt comets typically have shorter orbital periods, while long-period comets from the Oort Cloud are known for their infrequent and unpredictable visits to the inner solar system.
Once a comet from the Oort Cloud is diverted towards the inner solar system, its volatile materials begin to sublimate due to the Sun's warmth, causing it to exhibit a visible glow and tail. While some of these comets manage to survive multiple perihelion passes, they eventually lose their volatiles after a few thousand passes and may come to a dramatic end—as in the case of comet Shoemaker-Levy 9, which broke apart and collided with Jupiter. The study of comets from both the Oort Cloud and Kuiper belt offers astronomers insights into the primitive conditions of the early solar system.