Nicar is a carbon world, like Coal, formed from a protoplanetary disk with more carbon than oxygen; as on Coal and Cannonball, water is geologically unstable and the chemical environment is strongly reducing. The atmosphere is approximately 2 bars of nitrogen, with traces of ethane and more complex hydrocarbons as well as smaller amounts of methane and ammonia. The average global temperature is approximately -40C.
Unlike Coal, Nicar is not a super-Earth. It could be considered a carbonaceous analog of Mars--small enough that it loses hydrogen to space easily, and ammonia is easily photolyzed. Life originated on Nicar in ammonia seas under a methane/ammonia atmosphere and developed an initially hydrogen-breathing ecology, like on Coal--but, the accelerated release of hydrogen by photosynthetic life also accelerated the loss of hydrogen to space and the steady destruction of Nicar's primordial atmosphere and seas.
If it were an oxygen world, like Mars, Nicar would have inevitably become sterile like Mars as its oceans evaporated. However, while the ammonia ocean was shrinking, dissociation of methane simultaneously produced a growing layer of hydrocarbons--principally ethane, propane, butane, and pentane--with propane and butane condensing under a growing atmosphere of nitrogen to form a hydrocarbon cap over the remaining liquid ammonia, protecting it from further evaporation. Nicar thus has two oceanic layers of entirely dissimilar materials, with a colloidal mixing zone in between.
Life in the lower ocean continues to use essentially the same biochemical pathways as on Coal, although ammonia-consuming respiration is nearly universal due to extremely low hydrogen concentrations, which limits organisms' size dependent on pressure at depth. Near the surface, photosynthesizers still rely on hydrogenic pathways, although access to more complex feedstocks like butane and methylamine result in reduced bulk hydrogen output compared to a true hydrogen-breathing worlds. Nearly all released hydrogen, however, is quickly recaptured in either the upper ammonia layers or the lower hydrocarbon layers and used to hydrogenate unsaturated hydrocarbons, crack long-chain hydrocarbons, or regenerate dissolve nitrogen gas into new ammonia, all of which are energy-releasing reactions.
When these hydrogen-consuming reactions are accounted for, the net chemical equilibrium between producers and consumers in the Nicar biosphere is a mixture of the following three major equations:
6 C3H8 (propane) + 2 NH3 + 8 N2 <=> 3 C6H18N6
8 C4H10 (butane) + 4 NH3 + 16 N2 <=> 6 C6H18N6
6 CH3NH2 (methylamine) + 2 N2 <=> C6H18N6 + 4 NH3
along with several other more minor synthesis pathways.
When summarized this way, we can see that the energy metabolism on Nicar is not, in fact, ultimately centered around hydrogen; hydrogen is shuffled between hydrocarbons and ammonia and amine groups during the process, but fundamentally, energy is stored and structure built by incorporating nitrogen into the biosphere, and energy is released by freeing nitrogen. This is the exact reverse of oxygen metabolism, and serves as an excellent example of why "nitrogen breathers" do not exist.
The colloidal and hydrocarbon zones provide an additional source of interest for xenobiologists. Life in the hydrocarbon zone still uses ammonia as its intracellular solvent, but has adapted to the external environment by abandoning bilayer cell membranes, which are dissolved in the hydrocarbon phase, and instead developing single-layer inverse micelles. Multicellular colonies in this region appear to have only a single double-layer membrane separating intracellular environments, as the lipophilic tails of their membrane exteriors interlock with each other.
The lack of ammonia evaporation from the capped oceans also complicates life on land. While there is weather, with hydrocarbon clouds and hydrocarbon rain, the liquid that rains down on land is not directly usable as biosolvent. Thus, for all practical purposes, land biomes on Nicar are all deserts, similar to Rust and Cannonball, in which all available biosolvent must be manufactured by the biosphere itself. (Nevertheless, Nicar as a whole is not formally classified as a desert world, as it still has ammonia seas which support a large fraction of the biosphere.) Terrestrial ammonosynthesis is done by photosynthetic autotrophs which capture light hydrocarbon compounds and free nitrogen from the air, split hydrogen from hydrocarbons to form longer hydrocarbon chains (some of which are incorporated as components of fatty carboxamidines, and some of which are released into the environment, ultimately flowing into the upper ocean), and use the liberated hydrogen to fix nitrogen into ammonia. This fluid can then be eaten or drunk by heterotrophs, who again exclusively use ammonia respiration to produce energy and return nitrogen to the air. Nicar is thus one of very few worlds, like Rust, to have produced animal-analogs which have no need to breathe!
Human contact with Nicar organisms is possible with the use of a drysuit and oxygen mask. Earthling and Nicar biologies are, however, mutually corrosive to each other, so chemical isolation procedures must be strictly observed. The relative safety of human interaction, along with the relatively low pressures and clement temperature ranges suited to Nicar lifeforms make off-world transport of specimens for further study relatively straightforward.
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