Ernst Öpik presented his idea that comets originate in the comet cloud at the outermost edge of the Solar System.

Small bodies of the Solar System constituted Öpik’s most important scientific interests. He presented the idea of the origin of comets at the outermost edge of the Solar System at the distance from 50,000 to 100,000 astronomical units where there was a comet cloud in which the comets, as a result of disturbance, change the orbit and move closer to the Sun. In 1950 the same idea was also put forward by the Dutch astronomer Jan Oort and this is why the cloud is called the Öpik-Oort cloud.

The Öpik-Oort comet cloud