The Oort cloud is a vast, roughly spherical swarm of icy bodies surrounding the Solar System, so large that the planets’ orbits shrink to a speck at its centre.
About The Oort cloud
Some comets fall towards the Sun from every direction on orbits so long that they must come from far beyond the planets. The Dutch astronomer Jan Oort argued that they come from an enormous reservoir of icy bodies surrounding the Sun, loosely held by its gravity, and the cloud bears his name.
Its members are thought to be leftovers from the formation of the planets, flung outward by the giant planets’ gravity. Out there, the pull of passing stars and the tide of the Galaxy itself nudge some of them inward, sending new comets towards the Sun. The outer cloud reaches a good part of the way to the nearest stars.
What you see in the piece
This is where the scale of the zoom first becomes hard to believe: the whole planetary system collapses to a point inside the cloud, and the size you see is the size it really is.
Measured or modelled
No body in the Oort cloud has ever been seen in place. Its existence, shape and extent are inferred from the orbits of long-period comets and from models of the early Solar System, and the piece draws it as such a model.
Questions
Has the Oort cloud been observed?
Not directly. Its objects are too small, dark and distant to see; its existence is inferred from comets arriving from all directions on very long orbits.
How big is the Oort cloud compared with the Solar System?
Vastly bigger than the planets’ orbits. Its outer edge reaches a substantial fraction of the way to the nearest stars.