Like Still, Coal is a cool super-Earth. Unlike Still, Coal is a carbon world, formed from a protoplanetary disk with a higher proportion of carbon than oxygen. As a result, as on the iron-rich Cannonball, water is not geologically stable, as it reacts with carbon and nitrogen compounds to form carbon monoxide, methane, and urea.
The surface pressure is approximately 3 bars of 74% nitrogen, 16% hydrogen, 5% methane, and 5% ammonia, with ammonia clouds and precipitation, and traces of hydrogen cyanide, neon, argon, and xenon. Average global surface temperatures are around -40C. The oceans are anhydrous ammonia, with large quantities of dissolved salts, methylamide, formamide, hydrogen cyanide, urea, and nitro-silicon compounds. The large amount of methane produces a slight green tinge to the sky.
As on our own Solar system's Titan, photochemistry in the upper atmosphere produces a haze of complex hydrocarbons and carbon-nitrogen compounds (tholins). These compounds themselves and chemical energy obtained through hydrogenation are significant inputs to the surface ecosystem. Unlike Titan, however, ammonia rain regularly washes out the haze in the lower atmosphere, and native biology on Coal efficiently scavenges tholins reaching the surface, so large standing concentrations of hydrocarbons are rare.
In contrast to mixed ammonia-water worlds, life on Coal is able to optimize specifically for ammonia chemistry, and uses oxygen as a relatively rare heteroatom. Silane and it's reaction products with ammonia (the most common of which is silylamine), which is produced by volcanic activity along with its carbon-analog methane, also provides a source of bioavailable silicon which is also incorporated as an occasional heteroatom, as the Si-H bonds are considerably easier to break in favor of Si-C bonds than the Si-O bonds found in silica are--though it is not used to the same extent as on Blue Crystal or Vitrium, or even Opal, where silicon is a major structural element. The majority of crustal silicon on Coal is locked up in silicon carbide, rather silicates, which vastly reduces bioavailability compared to what might otherwise be predicted for a world with a strong alkaline solvent. In fact, it is the very same feature which permits the existence of the anhydrous ammonia solvent--namely, the high carbon fraction--which is also responsible for the unavailability of silicon!
In a strange parallel to nitrogen metabolism on Earth, the primary environmental source of oxygen for autotrophs, and disposal method of excess oxygen for heterotrophs, is urea. Fatty acids are substituted by carboxamidines (with ammonophilic -C=(NH2)-(NH) groups terminating hydrocarbon tails), with average tail lengths being shorter than those used in warm water biochemistries. Structural analogs of sugars and starches are fully nitrogenated, with =NH imidogen groups replacing nearly all uses of oxygen, and -NH2 amide groups replacing hydroxides, in water-based biochemistries. Amino-sugar synthesis and catabolism proceeds according to the large-scale equation
6 CH4 + 6 NH3 <=> C6N6H18 + 12 H2
However, the primary energy storage molecule in the Coal biosphere is not this glucose-analog, but acetylenamine, a more soluble derivative of acetylene which shares functions split between sugars and ATP in water-based biochemistries, and which can be hydrogenated to ethyleneamine (or further to methane and methylamine) to release large amounts of energy.
Although ammonia, like water, is a protonating solvent, proton pumps are a relatively rare energy-management mechanism on Coal. Instead, Coal lifeforms universally exploit ammonia's electron-solvating properties to store excited electrons directly and shuttle them across membranes and along electron-transport molecules to set up and exploit electrostatic gradients. This produces a consistent blue tinge (the color of low-density solvated electrons) to all native Coal cells.
As on Still, the most common respiratory pigments for complex heterotrophs are iridium-based, giving their circulatory fluids a bright yellow color, and facultative ammonia consumption is used to facilitate hydrogenation at depth or in other hydrogen-poor environments.
6 CH4 + 6 NH3 <=> C6N6H18 + 12 H2
However, the primary energy storage molecule in the Coal biosphere is not this glucose-analog, but acetylenamine, a more soluble derivative of acetylene which shares functions split between sugars and ATP in water-based biochemistries, and which can be hydrogenated to ethyleneamine (or further to methane and methylamine) to release large amounts of energy.
Although ammonia, like water, is a protonating solvent, proton pumps are a relatively rare energy-management mechanism on Coal. Instead, Coal lifeforms universally exploit ammonia's electron-solvating properties to store excited electrons directly and shuttle them across membranes and along electron-transport molecules to set up and exploit electrostatic gradients. This produces a consistent blue tinge (the color of low-density solvated electrons) to all native Coal cells.
As on Still, the most common respiratory pigments for complex heterotrophs are iridium-based, giving their circulatory fluids a bright yellow color, and facultative ammonia consumption is used to facilitate hydrogenation at depth or in other hydrogen-poor environments.
Human contact with Coal organisms is possible with the use of a drysuit and oxygen mask. Earthling and Coal 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 Coal lifeforms make off-world transport of specimens for further study relatively straightforward.
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