<P> The outer limit of the Oort cloud defines the cosmographical boundary of the Solar System and the extent of the Sun's Hill sphere . The outer Oort cloud is only loosely bound to the Solar System, and thus is easily affected by the gravitational pull both of passing stars and of the Milky Way itself . These forces occasionally dislodge comets from their orbits within the cloud and send them toward the inner Solar System . Based on their orbits, most of the short - period comets may come from the scattered disc, but some may still have originated from the Oort cloud . </P> <P> Astronomers conjecture that the matter composing the Oort cloud formed closer to the Sun and was scattered far into space by the gravitational effects of the giant planets early in the Solar System's evolution . Although no confirmed direct observations of the Oort cloud have been made, it may be the source of all long - period and Halley - type comets entering the inner Solar System, and many of the centaurs and Jupiter - family comets as well . </P> <P> In 1932 the Estonian astronomer Ernst Öpik postulated that long - period comets originated in an orbiting cloud at the outermost edge of the Solar System . The Dutch astronomer Jan Oort independently revived the idea in 1950 as a means to resolve a paradox: </P> <Ul> <Li> Over the course of the Solar System's existence the orbits of comets are unstable and eventually dynamics dictate that a comet must either collide with the Sun or a planet or else be ejected from the Solar System by planetary perturbations . </Li> <Li> Moreover, their volatile composition means that as they repeatedly approach the Sun, radiation gradually boils the volatiles off until the comet splits or develops an insulating crust that prevents further outgassing . </Li> </Ul>

The oort cloud may be the source of this icy object