Oort Cloud

The Oort Cloud is a vast, spherical region of icy objects and comets that surrounds our solar system at a distance of roughly 2,000 to 100,000 au (astronomical units). It's considered the distant reservoir of cometary bodies, originating from the early solar system. The Oort Cloud's objects are mostly composed of ice, dust, and rock, and they can be knocked loose from their orbits by gravitational influences from passing stars or galactic tides, sending comets careening toward the inner solar system. While unobservable directly, it plays a key role in supplying long-period comets that occasionally visit Earth.