[SunkenCiv]

In the case of the planets, a single explosive event could account for it; I was thinking today about the supposed Oort cloud, which is said to look like this:

Mostly I regard the Oort cloud as a hypothetical construct made necessary by theory rather than detected through observation (iow, a kludge), but a spherical concentric cloud doesn't seem too likely -- although it might have got there (if it is found to exist) when an earlier version of the Sun blew up.

[RightWhale]

Maybe the Oort cloud is the source of the background microwave radiation.