The Oort Cloud is a vast area beyond the Kuiper area that would contain billions of comets.

In 1932 Ernst Öpik, an Estonian astronomer, suggested that the comets came from a cloud outside the Solar System,

In 1950, the idea was again proposed by the Dutch astronomer Jan Oort to explain an apparent contradiction:

The comets are destroyed by several passages in the internal solar system, yet if the comets that we observe existed since the origin of the solar system, all would have been destroyed to this day.

 There must therefore be a source of new comets.

 In addition, Oort's orbital calculions showed that many long-period and random- tilt comets move away from the Sun at distances between 20,000 and 100,000AU at the limits of the Sun's gravitational sphere of influence.

Although no direct observation has been made of such a cloud, astronomers, on the basis of the observations of the orbits and comets, believe that there remains, in the confines of the Solar System,

a vast zone of nuclei Comets, called Cloud of Oort of the name of its discoverer.

This cloud would start at about 10,000/ 30,000 AU and would extend for up to a year-light, see more, and would be stable because the Sun's radiation are too low at this distance.

It could contain a thousand billion core comets and would be the source of most or all comets that enter the solar interior system(some short period comets may come from the Kuiper belt ).

The Oort cloud would be a remnant of the original nebula that collapsed to form the Sun and the planets about 5 billion years ago.

At first, nuclei would have formed by accretion in the Neptune region where matter was sufficient.

Quickly the giant planets would have subjected them to numerous and intense gravitational disturbances, pushing them back to the periphery of the Solar System.

 Occasionally, as a result of external gravitational influences, such as the passage of a nearby star, some of these nuclei would be precipitated into the solar system to become new comets.