The Oort cloud is a theoretical spherical shell or cloud of icy planetesimals hypothesized to surround the solar system at immense distances. It is thought to be the source of long-period comets, which are bodies that follow highly elliptical orbits and are believed to originate from this region. This cloud extends far beyond the orbits of the known planets and major minor bodies, potentially extending from tens of thousands to hundreds of thousands of astronomical units from the sun. The cloud is primarily composed of primordial, volatile-rich material and helps define the outer boundary of the solar system's stable gravitational influence.