Avalon
Currently unofficial lore, and in progress.
 Weather Satellite image of Avalon | |
| Orbital characteristics | |
|---|---|
| 771568 km | |
| Eccentricity | 0.01 |
| 5.322 days (127.7 h) | |
Average orbital speed | 10.53 km/s |
| Inclination | 0° |
| Satellite of | Valaya |
| Star | Solakku |
| Physical characteristics | |
| |
| Circumference | 13,238 kilometres (8,226 mi) |
| |
| Mass |
|
| 2.452 m/s2 (0.25 g) | |
| 3.22 km/s | |
| Tidally locked | |
| Albedo | 0.45 |
Avalon is the fourth and largest moon of Valaya, and the only celestial body orbiting Solakku known to naturally harbor life and one of only three with exposed bodies of liquid on its surface. It is mostly barren, with a majority of the surface taken up by cold deserts, though heavily vegetated areas can be found in coastal regions, with the density of vegetation increasing towards the equator.
Avalon holds on to a thick atmosphere, which consists mostly of nitrogen and oxygen. It plays a vital role on sustaining the habitable surface conditions, as it generates a greenhouse effect that maintains the average surface temperature of −50 °C (−58 °F). Evaporation occuring in Avalon’s oceans generate a consistent cloud cover in the atmosphere, as well as powering global precipitation.
Most notably, Avalon is one of just a few worlds in the galaxy where intelligent life has evolved. Avali have come to inhabit every geographical region of Avalon, having had a profound impact on its biosphere.
Natural History
Avalon formed approximately 2.31 billion years ago, shortly after its parent planet. Similarly to the planets, it coalesced out of a disk of gas and dust, though it formed inside a smaller disk orbiting Valaya, rather than the larger protoplanetary disk surrounding Solakku, with the material composing the former having been captured from the latter.
The atmosphere of Avalon didn’t form until after the moon’s formation. Sourced from volcanic activity and outgassing, its initial thickness was thinner than it is today. After this initial activity, Avalon’s surface rapidly cooled, causing volatile ices, including water and ammonia, to freeze solid. However, pockets of water, having condensed out of the atmosphere during this cooling process, formed underground, where they were kept liquid by tidal heating and geothermal heat.
These underground oceans were left isolated until 1.6 billion years ago, during which time the first Prokaryotic cells developed around geothermal vents and spread out from there. At the same time, Solakku’s luminosity had been slowly increasing, all the while volcanic activity enriched the atmosphere of Avalon with greenhouse gases, leading to temperatures rising to above the melting point of ammonia. Eventually, geological activity caused the thus forming ammonia surface oceans to make contact with the underground water oceans, causing them to mix. This process is known as The Great Nitrification event and lasted until 1.3 billion years ago, when Avalon’s surface temperature largely stabilized and the two sets of oceans became evenly mixed with each other.
At the time, the average composition of the oceans would’ve been more skewed towards a higher ammonia content than today, with geological evidence suggesting a ammonia content as high as 83%. The early, water-based life would’ve been forced to adapt to the sudden presence of Ammonia, a toxic substance for those early cells, causing a mass-extinction event out of which the first ammonia-based single-celled organisms emerged, alongside rare ammonia-tolerant, water-based species. The former went on to form the first Prokaryotes that then became the common ancestor to all modern life on Avalon.
It is believed that a number of these cells left their natural environment, floating upwards through the tunnels connecting the oceans until reaching the surface, where they quickly adapted to make use of starlight from Solakku as an energy source. These photosynthetic cells produced oxygen as a byproduct, initiating the Great Oxygenation Event, lasting 600 million years, during which carbon dioxide in the atmosphere was converted to oxygen. This, combined with the outgassing and evaporation caused by the rise in surface temperature, eventually transformed Avalon’s atmosphere towards the composition and thickness it has today. Due to reactions between the oxygen and ammonia, this also had the effect of skewing the water and ammonia contents of the oceans until reaching an equilibrium near its modern-day ratio.
About 1.3 billion years ago, halfway through the Great Oxygenation Event, the first Eukaryotic cells developed and filled the oceans. The first multi-cellular life developed much later, about 900 million years ago, though didn’t develop complex organisms until the progression of the Great Oxygenation Event. The presence of oxygen was instrumental in powering the diversity explosion 300 million years ago, during which almost every animal phyla that would ever exist on Avalon came into existence within a relatively short span of time. The intervening time between 900 million and 300 million years ago is often named "The Boring 600" as not much biological or geological evolution occurred on Avalon during this time.
Immediately following the diversity explosion, the first photosynthetic lifeforms began to spread onto land, constrained to the coastal regions by harsh climates further inland. The same diversity explosion eventually gave rise to Invertebrates 150 million years ago, then Vertebrates shortly after.