With one exception? They were all populated by sentient life. And they had... varying levels of technology, and knowledge of the supernatural.

[Sabriel has... No experience with other worlds beyond the missions, so she can't comment too much on that.]

I have compiled a set of notes on the missions, and you can look through the older files... but one odd trend is that in all cases we've learned of how an orb was first discovered, they were found underground- or in one case, in a volcano.