Steampunk, Space and Aliens

[Dr. Beckenstein]

What if the inhabitants were planted there in the distant past?

They could be human - and alien - descendants of people who lived there when the galactic society collapsed and the long night started. After thousands of years, the humans have build a steampunkish society, maybe based on old tales and novels (the holy Sherlock) and discover old spaceships from pre-collapse that help them to conquer the system.

And what if the whole system was build by an ancient race?
A gas giant with one habitable world is unlikely, and one is a few is almost impossible...