Illustration of the Oort cloud, a theorized shell of icy objects that lie beyond the Kuiper Belt, in the outermost reaches of the solar system. It is divided into two regions: a disc-shaped inner Oort cloud and a spherical outer Oort cloud. 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.