Elisnia is a small and remote ice moon within the Akodran Junction of the Palioxis Starfield. It orbits the gas giant known as Gaea at a relatively far distance, giving it its rock-hard icy shell which covers the entirety of the moon. Although Elisnia has not seen any colonization in the current era, complex research outposts situated in its equator indicate that it was a remote research post for a previous civilization many hundreds of millions of years ago.
Elisnia has a singular massive ecosystem located in the deepest parts of its subglacial ocean, particularly near thermal vents. These lifeforms evolved from simple microscopic organisms that fed off of thermal vents located on the seabed. Over a small course of time, more complex fish-like species started to evolve. During that period, a small group of organisms branched off from the evolutionary tree, becoming the invertebrate specie of Elisnia today.
Elisnia possesses an extensive ring system primarily composed of many rock and water-ice particles and meteoroids. These rings have a dense concentration of these particles, although there exist numerous gaps where particle density drops sharply.
With an estimated local thickness of as little as 10 m and as much as 1 km, these rings are composed of 99.8% pure water ice with a smattering of impurities that may include tholins or silicates. The main rings are primarily composed of particles ranging in size from 1 cm to 10 m.
Although the largest gaps in the rings can be seen from far away, closer examination of the rings has uncovered that the rings have an intricate structure of thousands of thin gaps and ringlets.
Elisnia's surface is exceptionally smooth, despite being covered by shallow furrows. The number of structures that rise above their surroundings by more than a few hundred meters is exiguous. Besides this, a large number of impact craters are seen on Elisnia, though they are oftentimes nearly as flat as the plains. The cratering rate is an indication that Elisnia's surface is geologically fairly old. Estimates of the impact frequency of comets and asteroids yield a maximum age of a billion years.
Elisnia contains a vast subglacial ocean deep below its rock-hard crust of water-ice. This ocean is located under a hundred kilometer thick crust, and is estimated to be five hundred kilometers in depth, although it could easily be double the depth. A vast array of thermal vents circle the subglacial ocean at the moon's relative equator. While fairly rarely found, a number of thermal vents can be found outside of the aforementioned array. The seabed of Elisnia is fairly flat at most region, though it experiences some limited elevation near the poles.
Biology & Ecology
Elisnia possesses an ecosystem filled with all sorts of alien creatures. These creatures are ninety percent similar to other catalogued deep- sea species. In place of eyes, Elisnia's animals have hyper-sensitive lobes which use echolocation as a means of sight rather than light waves. This allows for them to navigate the pitch-black waters of Elisnia far more efficiently than other forms of sight ever could.
Bones on Elisnia's animals are different in composition compared to most other organisms on terrestrial worlds. While most creatures on terrestrial worlds have primarily calcium-based bones, the seas of Elisnia mostly lack this metal, making them tend to have thinner and weaker bones than their terrestrial counterparts. Often, species will substitute bones for firm strips of cartilage, freeing calcium to be used in other processes.
Most life is concentrated near the deep sea vents, under the pressure of hundreds of kilometers of liquid water of top of them. The most common locations for the habitation of living organisms are hydrothermal vents, as most of the life on Elisnia still relies on them for nutrients. Only rarely do lifeforms stem far from these hydrothermal vents, as all the potential prey for the predators lies there.
Bioluminescence is a common sight within these deep waters, as it is used for numerous purposes. Some species use bioluminescence to confuse attackers. Many species of squid, for instance, flash to startle predators, such as fish. With the startled fish caught off guard, the squid tries to quickly escape. Bioluminescence is also used for searching for potential mating partners, or attracting prey. Bioluminescence is often created utilizing specialized organs and luciferin in a chemical reaction that produces light energy within an organism's body.
Elisnia formed during 2,600,000 ME, at the same time when its parent gas giant also formed. In the past, it only amassed a little mass and size, becoming a small oceanic planet closer to the star than now. Then on the planet got hit by a small planetary object around quarter of its size, redirecting its orbit around the gas giant of Gaea.
Due to the sheer temperature at that distance and the apparent lack of an atmosphere, it formed a thick sheet of water-ice after reaching orbit around Gaea. Nevertheless, the tidal forces emitted by Gaea and her moons prompted Elisnia to develop a subglacial sea, melting some of the ice from within.
Evolution of Life
Elisnia's first native species developed during 54,000 SE, from unicellular lifeforms in hibernation in the deep-sea hydrothermal vents, who likely first ventured to Elisnia through a hypothetical meteorite at the time when it still possessed liquid oceans. For hundreds of years, these species served as the cornerstone of the ecosystem. They began to evolve and prosper after seeking out numerous hydrothermal vents. Eventually, most lifeforms were concentrated around a vast field of thermal vents encircling the seas. Despite the early emergence of life on the moon, several species have been statistically restricted in their evolution.
The biosphere of the moon has remained essentially primitive, with single-celled creatures and a few complex multicellular species. Thanks to the protective layer of ice surrounding the oceans, mass extinction events were never experienced by the aquatic life. Another barrier to life's progress was a scarcity of resources. While the moon is abundant in oxygen and water, it is insufficient in base metals and carbon, limiting the size and prosperity of life on Elisnia. This would also seem to explain why most vertebral species rely on cartilage rather than bone to create their skeletons, as even small vertebrae use different mechanisms.