What is the Oort cloud?

What is the is region of space at the edge of the Solar System?


Asked by Neil McDonald

The Oort cloud is a spherical ‘cloud’ of frozen objects at the very edge of our solar system. You can imagine it a bit like a fishbowl, with the Solar System at the centre, and the spherical cloud of icy bodies on the edge.

Named after the astronomer Jan Oort who hypothesised its existence in 1950, the Oort cloud has still not been directly observed. However scientists believe that the majority of comets originate from here. By studying the orbits of long period comets and projecting them back to the point of origin, they seem to have a common starting distance.

The current best estimates for the region of space that this ‘spherical comet halo’ occupies is from 5000 to 50 000 AU (with 1 AU being the distance from the Sun to the Earth) so it is truly a vast volume of space.

It shares a classification with another region of ‘space bodies’ – the Kuiper belt. Both have orbits beyond that of Neptune and as such are known as Trans Neptunian Objects (TNOs).

Unfortunately, being so far away, it will be a long time before we get to explore this massive region of space.

Answered by Sophie Allan from the National Space Centre

Image courtesy of NASA

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