Artwork representing the Oort Cloud. This is a vast cloud found at a distance of about two light years from the Sun (upper centre right) which contains billions of cometary nuclei, remnants of the primordial solar system nebula. The existence of the Oort Cloud was suggested by the Dutch astronomer Jan Oort in 1950 to explain the origin of the long-period comets. These are bodies in the Oort cloud which are sent in a closer orbit to the Sun by perturbations with the gravitational field of nearby stars and molecular clouds or by the tidal field of the galactic disc.