Gas giants are large worlds that have extremely dense atmospheres and very strong gravity. The atmosphere is so dense that it is liquefied and forms a incredibly deep ocean world. It is possible to dive into the ocean of liquefied gasses with a submarine or a submersible spacecraft.
A gas giant can have one large moon in orbit, which is the moon equivalent to a normal planet.
Harvestable Atmospheric Resources
Gas giants are normally rich in various atmospheric resources which can be harvested using harvester bay equipped spacecraft. This is normally also very advantageous as the high atmosphere density means greater harvest yields.
Harvester bay: Atmospheric Condenser Bay
Harvester bay: Particle Collector Bay
The rocky core has the most of the same resources as regular worlds. There are however a few unique resources that are not found anywhere else.