Augustus is a large gas giant gas giant, home of the extinct Zarennasen. It is the 3rd planet in the Kenna System, and is under the jurisdiction of the Amanian Federation.
The atmosphere of Augustus is different than most gas giants in that it is made of oxygen, not the typical helium and hydrogen of most gas giants. However, there are bands of hydrogen within the planet's atmosphere. Unusual flying creatures have adapted to life there, but life originally didn't exist in Augustus' atmosphere.
Life came from Augustus' moon Nocoma, a cool temperate world with basic unicellular life. Billions of years ago, Nocoma was struck by an asteroid which wiped out all life save for some hardy microorganisms that eventually made it to Augustus where they began to evolve in their new environment.
The bacteria became multicellular organisms. Them majority of life on the planet appear have a slightly bug-like appearance. They breath in the small amount of helium in the planet's atmosphere, and use it in large bladders to stay afloat. Some also have wings, though it is hard to fly through the dense atmosphere. Some life has adapted harder exoskeletons and have migrated to the lower regions of the gas giant where the pressure is so high that the gas turns into a liquid of oxygen and helium. The creatures 'swim' through the honey-like substance, and produce bioluminescence.
With the passage of time, the creatures began to slowly evolve. The Augustians soon established something akin to a tribal system. As the Amanians continued to expand their floating cities on Augustus, the flying creatures evolved without them knowing. They then began to peer out at the stars and wonder what was out there. But they were stuck floating with no land to build cities on and materials to build floating cities.
Then, a mutation occurred. An Augustian was born with a harder exoskeleton then the normal creatures, and could store the helium for long trips instead of constantly having to breath in more. The creature was fascinated by the stars, attempted to fly out of the planet's atmosphere and succeeded. He told his companions about the discoveries he had made. The creature eventually had 3 children, and they had carried down that gene of strength exoskeletons and respiratory endurance. He took his young out for flights around the planet. Eventually, they grew up and passed on their genes to other creatures. The genome spread throughout the planet.
The creatures were no longer bound to the atmosphere. They could experience the cosmos at will. But they still couldn't go that far out, and needed to return to their planet for more helium. Then one named Aydo. flew to one of the planet's moons, a barren selena. She was the first of their kind to go to a different stellar object. But she did not make it back in time to get more helium. Aydo was remembered as a very strong figure in their culture.
After Amanians had pretty much covered Augustus's surface with mega-cities, they decided to return to the Augustinians and check on them. They were amazed to see how they had evolved in such a short period of time. Amanians called them Zarennasen, old Amanian for 'skywalker.' The Amanians helped the Zarennasen by building them a large city to live in the atmosphere. The Zarennasen had the intelligence of 60000 CE Amanians at this time and formed a peace with Amanians, but under one rule: the Amanians should not interfere with their evolution beyond this point.
Thus, the Zarennasen were left alone to live on the city. They used the technology in the city to invent their first rockets, and were able to fly to Augustus's largest moon, the same moon that Aydo had discovered and died on. The Zarennasen built a lunar base there. Their technology continued to improve, and eventually they colonized a few other planets in the Kenna System. This was just in time to take part in the Amanian Civil War, their participation in which made the side they were not on detonate thousands of nuclear bombs over their planet and any colonies they had, driving them to total extinction.