The Rana Bioring was an inhabited planetary ring system which sported a complex ecology. It was discovered by humanity in the 23rd century in the Delta Eridani system (formerly known as Rana), 29 light years from Sol. While it was not uncommon to find microbial spores in planetary rings, this marked the only known ring system to have become a trap for various domains of complex life which had migrated from elsewhere, adapted to the vacuum of space. It was one of the largest known self-contained ecosystems and is under protection of the Milky Way Cooperative.

Environment Edit

Rana is a Jupiter-mass gas giant that orbits about 6 AU from Delta Eridani, an orange subgiant that will soon join the red giant branch. The discovery of life in this system was unexpected to humanity, found by smugglers who had chanced upon the rings in an attempt to hide from authorities.
Rana formed in a much earlier time, behind the 'snowline' where icy bodies can coalesce. The ring system formed less than 60 million years ago from a moon that strayed too close to Rana's Roche limit, and so was pulled apart by the planet's gravity well. It is a relatively young ring system that is still over a 1000 metres thick in places, and has only recently (in geological terms) settled into a flat disc of divided rings. The material of the inner ring has an orbital velocity of 32 km/s. It almost entirely composed of water ice, the rest being carbon dioxide, methane (CH4), ammonia and a trace of tholins and silicates. The ice is laden with volatiles which are converted to tholins by ultraviolet radiation. Solar heating from Rana's old star causes the ice to sublimate, producing a thin atmosphere of water vapour and CO2. UV further breaks some of this down into molecular oxygen and hydrogen. The greenhouse gases and increased luminosity of the star conspire heat the dayside of the atmosphere into gases and at night (in Rana's shadow) they eventually freeze. Compression in the bigger ice fragments maintains liquid solvents of water-ammonia solutions.
Between gaps in the rings there are shepherd moons which clear the material in their orbits. Some of the moons sculpt waves and even mountains of ice particles that cast long shadows across the disc. There are also more significant satellites; Rana C orbits elliptically because it is in a 2:1 orbital resonance between Rana D. It constantly ejects plumes of water vapour that feed the rings, and might be a source for at least one domain of life in the ring system (see below).

Ring material composition

H2O (99.0%) CH4, CO2, N2 (0.7%) Tholins (0.2%) SiO2, FeO (0.1%)

System Edit

Rana's most significant neighbour is Rana D, with a diameter of 9834.34 km. It has an atmosphere rich in CO2 and CH4, similar to Archean Earth. Thought to former Titan-like world, the host star's evolution has warmed the atmosphere to the point that most of moon's surface is now covered by a deep ocean of liquid water except for the subequatorial extremes.

In the next few million years, Delta Eridani will have entered the red giant phase, where it is predicted to last a few hundred million years. It is unknown what effect this phase will have have on the Rana ecology, which is no longer in the snowline. The increase in heat received from the star will warm the rings even more, causing more ice sublimation and a denser atmosphere. The increased radiation pressure may also decrease the overall lifespan of the rings, by blowing away the atmosphere and icy particulates, although this may be offset for a time by the gas giant Rana's magnetosphere. It is possible life will migrate to the outer star system or beyond during this process.

Ecology Edit

The Rana ring system is host to a rich variety of flora and fauna, many belonging to completely unrelated domains of life.

Biochemistry Edit

There are two known forms biochemistry native to the rings (although with various subgroups): CHON and silane-based life. The former primarily use the basis of carbon-oxygen bonds and use water as a solvent. The latter consist of silicon-silicon polymers and use ethane and methane as a solvent.

The ring boasts ecology with both chemotrophs and phototrophs. They are all slow metabolisers; the extreme cold in particular is a huge problem for CHON life because large molecules won't dissolve in water at extremely low temperatures. They must rely on exothermic reactions and solar energy for heat. Many use the violence of ultraviolet radiation to help them liberate useful compounds from tholins. CHON organisms synthesise ATP to conserve the energy they release from oxidising food. They pump protons across a membrane to catalyse ATP, and use a range of metabolic pathways. Methanogens react carbon dioxide with molecular hydrogen to form methane and water. The sulphate reducers react hydrogen sulphide with carbon dioxide, creating formaldehyde, water and sulphur byproducts. There are also some rare organisms that capture molecular oxygen to metabolise ammonia and carbohydrates. Rarer still is the so-called ammono life which are based on carbon-nitrogen bonds (another type of CHON) and use ammonia as a solvent. These organisms compete for resources with the nitrifying metabolisers.

Not all interactions between the various domains are competitive. Some silane-based animals have evolved symbiotic relationships with methanogenic microbes, exchanging methane for hydrogen and carbon dioxide. The compounds are contained in special membranes that allow methane in and keep oxygen and water out, which would otherwise destroy their silicon polymer structure. Silane life uses a different energy-conserving principle by pumping electrons instead of protons. They do this by exciting electrons across their membranes using the light from their star, making them partially phototrophic. For silane life, the low-pressure environment of Rana's rings rules out liquid methane. Fortunately methane volatiles under pressure can be suspended in liquid ammonia, and at low temperatures ammonia does not react with it or silane-based compounds. Large numbers of biochemical reactions occur more efficiently in liquid; allowing silanes to exist in regimes of low pressure. This had lead to some further symbiotic and parasitic interactions between the two domains, with silane life relying on ammono life to extract the ammonia-methane liquid. These organisms line their internal membranes with siloxane, a silicon-oxygen bond which is strong enough to resist water and ammonia, preventing them from being dissolved by their own bodily fluids.

Diversification Edit

The scientific consensus was that complex life would have migrated to the rings rather than originating there, due to the very young estimated age of the rings. It would have made use of microbes already adapted for survival. The CHON domains arrived from plumes ejected by Rana C and had already evolved complexity in its subterranean oceans. Silane polymers are destroyed by water, so life based on it could not share this common origin. It possibly migrated from Rana D while it was cold enough to have retained a hydrosphere of ethane and methane, the world is now too hot and poisonous for its existence. However, it is possible that the silane-based life originated elsewhere further back in time and had been transported to Rana D before it transformed.

It was reasoned that the diversification of complex life must have been a geologically recent affair and probably happened within a few million years, akin to the Cambrian Explosion on Earth. Once organisms adapted to survival in the vacuum, the explosion was brought about by the competition and cooperation of organisms for scarce resources.

Researchers identified unique lineages of life in the various rings, distantly related to each other (making an analogy to plate tectonics causing continent drift). As the rings stabilised, the material started to differentiate with densest materials sinking to the innermost rings. Moons and moonlets opened up gaps in the rings. Life found it much harder (though not impossible) to migrate between gaps in the ring, largely stranding them in their rings where they specialised on the local chemical abundances. The innermost rings have the highest concentration of silicon and metal oxides, and so have the biggest population of silane life. Ethane is the most abundant solvent, which they use. The innermost rings are inhabited by contain CHON life, which metabolise hydrogen sulphide. Methanogen and nitrogen metabolisers inhabit the middle and outer-most rings. Some silane-based life inhabits the middle-portions of the ring where they became stranded by a gap-forming shepherd moon. These silanes adapted to take in methane and evolved symbiotic relationships with the CHON ecology that is present. The silane life here has evolved to rely on ammono life to extract liquid ammonia which contain methane gas that was compressed in it (or the silanes extract methane from another source e.g. methanogens and force it through ammonia). In turn, the CHON-based life hitches a ride on migratory silane creatures that help it spread throughout the rings.

Notable organisms Edit

Creator Spluff5 Wormulon
Organism Gelatoa Kingdom Rotatoa
Biochemistry CHON CHON
Energy Phototrophic Chemoheterotroph
Region Icy/Rocky Moonlets Icy particulates, atmospheric drifter

Super-domain: CHON-oxybiota Edit

Domain: Oxy-prokaryota Edit

Domain: Oxy-eukaryota Edit

Kingdom: Gelatoa Edit

Gelatoa are a kingdom of single celled organisms that evolved on some of the larger sub-moon sized ice/rock bodies in the rings. Individual Gelatoans will aggregate together to form a gel with the cells cooperatively exchanging nutrients and signals. The cells in these gels are only loosely associated and can be seprated into multiple fully functional smaller gels. Thus, each gel is not a multicellular organism.

A gel will often secrete rigid scaffolds of a keratin-like protein called frangin which will form hard structures. These structures are dead and so do not require nutrients from the gel, but are constantly replaced to repair damage. Fragin structures may be used to support terrestrial gel spheres above the surface of a body, or act as a physical defense against predation. Augurin is a transparent protein secreted by almost all species. This forms a transparent, hard shell around the gel that prevents water loss in the dehydrating thin ring atmosphere, maintains internal fluid pressure to prevent evaporation, and usually molds the gel into a spherical shape. This shape minimizes the surface area of the gel, decreasing the area that can be damaged by cosmic radiation.

Cyclic Photosynthesis

The general scheme for cyclic photosynthesis. Electrons are energized by absorbed light energy and used to pump protons (H⁺) across a membrane. The protons create an electrochemical gradient, allowing the protons to flow back through the purple protein complex, turning it like a turbine. The rotational motion activates catalytic sites that convert ADP to ATP. The low-energy electrons released by the pump protein are re-energized by more light.

All Gelatoans are phototrophic, producing energy from the the weak Delta Eradanian sunlight. The augurin shell lets only certain wavelengths through which accounts for the often distinct coloration of the gel. The radiation that is allowed in penetrates the whole sphere so cells even near the center can subsist on it. At the very core, little light is present, so cells here are specialized to be carry out other metabolic processes and are fed by carbohydrates excreted by the outer cells. Photosynthesis is cyclical, not requiring an input of water or CO₂. This helps with the unimaginably scarce resources in the ring.

Kingdom: Animalia Edit

Phylum: Rotatoa Edit

Rotatoa are multicellular organisms that may have originated from Rana C's vents. To obtain food they rely on symbiotic relationships with bacteria.

They are capable of drifting through the thin envelope of gas until they find a solid surface to grip with their prehensile holdfasts. The animal then extends a beak into ice and slowly bores its entire body by turning its graspers until it encounters a liquid, typically water, which it draws up. To tackle fluid uptake in microgravity, rotators use capillary action to first fill the beak, before they use muscles to pump it out, allowing the beak to refill by adhesion alone. It will take up any bacterial chemotrophs and phototrophs present (typically sulphate reducers in the inner rings, and methanogens and nitrogen metabolisers in the outer rings). In turn the rotators aid the bacteria in colonising new icy bodies. The prehensile holdfasts also double as a primitive gills; fractal morphology maximises the surface area, increasing the capability of absorbing CO2 and O2 gas present in the rings, which rotators use to feed the symbiotic bacteria they store. They may also occasionally capture spores of symbiotic bacteria.

While they mostly live attached to ice, rotatoa are not helpless drifters. They have evolved a simple reaction-control system based on bladders and valves using the gas released by the bacteria. To orient themselves, rotatoa can sense light gradients and Rana's magnetic field.

Rotatoa have silvery-white bodies like most macroscopic creatures, to help protect them from overheating in Delta Eridani's full glare.

Super-domain: CHON-ammonobiota Edit

Domain: Ammono-prokaryota Edit

Domain: Ammono-eukaryota Edit

Super-domain: Silanebiota Edit

Trivia Edit

  • This is work was born out of discussion by Wormulon and Drom, with feedback provided for subsequent revisions by Spluff5. Comments, suggestions and feedback is welcome. If you want to create species for this ecology, please contact us.
  • Sources of the planetary images is Space engine 0.980, created by Vladimir Romanyuk for non-commercial worldbuilding purposes.
  • Templates for figures inspired by Drom.
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