One question, several references
What lies beyond Neptune?
Kuiper Belt, heliopause and Oort Cloud: understand the references beyond Neptune and their limits.
Try it in the explorer →An orbit is not an empty boundary
Beyond Neptune’s orbit, Solar System regions include populations of small bodies. A belt is an extended region; its depiction does not describe a solid wall.
The Kuiper Belt
The catalogue adopts an outer reference diameter of about 100 astronomical units for the classical belt. Comparing this diameter with a planet’s means comparing an orbital region with a body: the nature of the measurement must remain visible.
The heliopause
The Sun–heliopause reference is a distance of about 120 astronomical units in a reference direction associated with Voyager. This boundary varies and is not a sphere of fixed radius.
The Oort Cloud
Oort Cloud regions are models with highly uncertain boundaries. Catalogue references may help explain their scale, but an illustration is neither a photograph of the cloud nor a measurement of its boundary.
This journey’s references
Sources and method
Dimensions and conventions are those of the fact sheets linked above. Illustrations remain interpretations. Providing a documentary source does not independently certify every catalogue value.