Start here with my quest for alternatives to water as the solvent for speculative biochemistry, and here’s a brief side-step to talk about water vapor.
It might be clear at this point that my chemistry background isn’t quite solid (ha! “Solid!” Chemistry joke!) So I’ve needed a lot of help to get this far.
Here is a very nice paper on the benefits (and problems) with water in biochemistry. (One of the problems: C02 doesn’t dissolve well in water.) If you want something less dense (I sure did) this page presents some nice little summaries of biochemistries that could work on different planets (and moons) of our solar system. There’s also a slightly more involved look at Alternate Biochemistry here.
And if you’re curious about my aliens, here’s what I’m thinking so far:
Liquid ammonia biome:
Protein-equivalents are tin fluoride polymers suspended in liquid ammonia, contained in the interstices between crystals of sodium fluoride. In primitive lifeforms, the crystals move against each other to open channels for ammonia to flow through. In more advanced forms, tin fluoride polymers are laminated to sheets of crystal, which allows the whole structure to fold itself like origami. (I want to thank Alessandro Allievi, who found some stuff that isn’t soluble in liquid ammonia. You can also assume that anything in the subsequent paragraphs that isn’t wild hand-waving comes from Alessandro as well.)
Plumber biome:
Biochemistry is sulfur rings and phosphorus-nitrogen chains in SO2 (extracellular) and H2S (intracellular). Sulfur dioxide and hydrogen sulfide are only liquid between -75 and -60, so temperature regulation is very important. Perhaps life in this biome evolves a cooling system to keep its temperature around -70. Perhaps this biome has invaded a more Earthlike world, and is aggressively refrigerating it. 🙂
Space biome:
So you have a Jupiter-like gas giant. The gas giant is orbited by a moon similar to Io, with volcanic activity due to tidal forces squeezing its core. Volcanoes on the moon spew sulfur and other elements into space, which form a smoke ring around the gas giant. Life evolves in the gas giant’s atmosphere, making use of convection currents that exchange material and heat between the core and the outer atmosphere. There are many biogenic conveyor belts to cycle important elements. Eventually, one of these cycles extends into the smoke ring to access the sulfur from the moon, which is rare in the gas giant’s atmosphere. These organisms burn hydrogen with oxygen and propel themselves with the resulting rocket plume. From there, life evolves the means for full vacuum travel. (Thanks to Vladimir Nikolov for working out the beginning of this insanity)
Eventually, there’s a whole nest of transport cycles that use redirected comets to mine the gas giant for hydrogen, asteroids for iron, the moon for sulfur, and the upper atmosphere of the nearby earthlike world for oxygen.
The main energy source for autotrophes in the space biome is 4H+02->2H20, but there would be lots of free riders parasitizing that free hydrogen. A “liposhere biome” (polysilanes suspended in liquid methane) uses hydrogen to break C2H2 into CH4. There are iron-reducers too.
What do you think? Additions, subtractions, or critiques?