Oort Cloud Definition

What is this comet-filled cloud in our solar system?

The Oort cloud is a giant sphere of icy cometary nuclei that surrounds our solar system. Its maximum distance is 1.9 light years away from the Sun, which is as far as the Sun’s gravitational influence extends.

In 1950, Dutch astronomer Jan Oort developed the concept of this cloud as the origin of comets. It was created during the formation of the solar system, when planetesimal bodies gathered to form planets or moons. The gravitational influence of Uranus and Neptune sent some of these planetesimals outwards to form the Oort cloud.

Over time the gravitational effects of the Sun, planets in the solar system and even nearby stars have caused objects to actually leave the Oort cloud. They then either turn up in the form of comets in the inner solar system, or they are sent completely out of our system’s influence altogether. Just as objects are lost from the cloud, new ones from outside the solar system can also be attracted into it.


Oort Cloud DefinitionEvidence of the Oort cloud’s existence is supported by the discovery on 14 November 2003 of the furthest object in the solar system. Named Sedna, it is currently 13 billion kilometres away from Earth. Its highly elliptical orbit around the Sun takes 11,250 years and to a maximum distance of 130 billion kilometres.

Sedna has a diameter of between 1,180 to 1,800 kilometres, making it larger than an asteroid but smaller than a planet. It is the second reddest object in the solar system after Mars, and its surface temperature is a rather cold -240”C.

A sticking point is that it is much closer than the predicted position of the Oort cloud. One suggestion is that millions of years ago a rogue star passed by, causing comets and bodies like Sedna to form an inner Oort cloud.