Oblivio is a volcanic hell world with a large expanse of lava across the entire landscape, cooler regions of black magma are located on the surface as well. This is because the moon is subjected to immense tidal forces constantly inflicted upon it by its parent planet, creating extreme volcanic activity on the surface. Much like Jupiter's moon Io before it was terraformed, albeit much more potent.
This causes the moon's temperature to rise extremely high, and with its thick atmosphere barely any heat escapes and is trapped within itself. The radiation produced by the gas giant also causes this effect. The atmosphere is so thick the moon does not experience any form of night, always existing in a permanent state of day light.
This volcanic activity leaves the surface very smooth, the moon has very few mountains. It also has piratically no impact craters with most asteroids incinerate before reaching the surface, if one manages to reach the ground, the crater ls consumed by the shifting landscape.
The moon serves as the "sun" of the Solum System due to it being the only body in the system that produces natural light, and with the moon being tidally locked with its parent planet, the gas giant is dimly illuminated constantly. This causes the other moons of the system to have a strange day-night cycle, with three standard hours of daylight and three standard hours of night.
Before it became the hell world we know today, the moon was a temperate Oceania world with multi-cellular organisms existing within its waters. However, after Solum's ejection from its home system the moon flew much closer in orbit around its parent planet and it became subject to extreme tidal forces. This evaporated Oblivio's oceans causing a runaway greenhouse effect and covered the surface with thick molten lava.
It is also responsible for Etiamteamo surface oceans. The smaller moon orbits in very close proximity to Oblivio, causing its sister moon to keep a warm enough climate for surface liquid.
Oblivio formed along with its parent planet Solum around 4,127,010,000 BCE. Originally it was a cold ice world, however the moon would be bombarded by dwarf moons in orbit around Solum, melting the surface and forming a thin oxygen atmosphere. Life began to arise shortly after this event.
Around 3,999,666,333 BCE, Solum would be ejected from its home system and become a rogue planet of the Mid Arm. This caused the ocean moon to be hurled into very close to Solum. With this, the moon was battered by the gas giant's extreme tidal forces and radiation. This almost instantly evaporated its water causing the moons now thick atmosphere. These tidal forces created extreme volcanic activity across the entirety of the moon, increasing its temperature a thousand fold.
With this volcanic activity and increase in temperature, the moon's thick atmosphere began to glow a hellish orange color. This glow was so luminance that it provided sun like light and energy to its sister worlds against the darkness of space. This also provided the moon closest to it, Etiamteamo, with warmth powerful enough to melt its frozen oceans, turning the world to the temperate Terra it once was.
Much like the rest of the Solum System, Oblivio was unknown to any Ambrosian civilization until the Ugnara discovered it while radar mapping stars around the capital of their enemy, the Hope System during the Ugnara wars in 10465 CE. Once it was discovered, a small fleet of robotic probes were launched to map out the system, discovering the volcanic moon and its sister worlds, including Etiamteamo. With this, the Ugnara would use the Oblvio's home system as a staging ground to launch a surprise invasion on the Human Alliance of Ambrosia's capital star system, Hope. However, the Ugnara were defeated before these plans came to fruition.
After the Ugnara's defeat, and eventual joining of the Ambrosia Alliance of United Systems, the Solum System would be further colonized by the Ugnara as a sort of checkpoint for those who want to enter the Hope System. Small groups of humans would migrate to the system as well.
While its sister moon Etiamteamo was majorly focused on, a smaller colony was built in Oblivio's upper atmosphere where the blistering heat is bearable to organic life in 10489 CE. This colony, named Infernium, would continue to grow larger and larger until becoming a functional city with a population of around five million in 10500 CE.