The Distant Comet Reservoir

From the distribution of long-period comet orbits, Oort argued in 1950 that the Solar System is surrounded by a vast, distant reservoir. Passing stars and Galactic tides can perturb some objects inward.

The Oort Cloud has not been imaged directly as a single structure; it is inferred from comet dynamics and modeled formation histories. Its name marks a powerful explanatory hypothesis rather than a personally observed object.