Caption: A schematic diagram of the orbits of comets. The orbits are all highly elliptical orbits.

Features:

1. Short-period comets have orbital periods less than 200 years and have orbital planes somewhat concentrated near the ecliptic plane. It is thought that short-period comets originate as Kuiper Belt objects (KBOs) that astronomical perturbations perturb into highly elliptical orbits.

2. Long-period comets have orbital periods ranging from 200 years to thousands of years and their orbital planes have a spherically symmetric distribution. It is thought that long-period comets originate as Oort Cloud objects (OCOs) that astronomical perturbations perturb into highly elliptical orbits.

3. The Oort cloud is a hypothetical spherically symmetric population of rocky-icy bodies extending from perhaps from 2000 AU to 200,000 AU from the Sun (see Wikipedia: Oort cloud: Structure and composition). No OCO has ever been detected since they are very hard to detect: they are very dim, tiny, slow-moving far-off astronomical objects.

4. The Oort cloud must exist to resupply long-period comets which can't live forever. A long-period comet evaporates all its ices after a few passes close to the Sun (i.e., a few perihelions) and eventually impacts some other Solar System astro-body or, via a gravitational assist, is launched back into an orbit entirely beyond the Neptune orbit or ejected from the Solar System on an escape trajectory (AKA escape orbit): i.e., a parabolic trajectory or hyperbolic trajectory.