What else is involved in "silicon based" life?
Silicon is often brought up in science fiction as being very similar to carbon, just below it on the periodic table. The silicon-based "organic" molecules are more tightly bound and thus would find a higher temperature to be appropriate.
Being too hot for liquid water, what would it use as a solvent? That is, what would the Horta drink?
Hal Clement wrote a novel where the aliens found Earth to be extremely cold, so much so that their base on Mercury's (thought at the time to be tidally locked) day side was further heated another hundred degrees with reflected sunlight. They breathed sulfur (an analog of oxygen) as a gas. I don't recall if he went into the chemistry in more detail.
Given a toolkit of a few kinds of atoms with different numbers of binding sites, the heavier ones in the same period might substitute for what we are familiar with, to a first approximation.
So once you switch Silicon for Carbon, what other changes might be useful to make a workable toolkit-for-life? What solvents are available/possible in different temperature and pressure regimes?
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The term I've seen used to describe the necessary solvents for silicon-based life is cryosolvent. In Planets and Life: The Emerging Science of Astrobiology, by Sullivan & Ross (relevant excerpt here), the authors cite the work of Bains (2004) on various alternate solvents to form the basis for various alien biochemistries. Ethane, methane, and liquid dinitrogen are all considered as possibilities, with liquid dinitrogen showing the most promise for silicon-based life.
At low temperatures, silicon-silicon chains can exist, containing up to 30 silicon atoms and mimicking the structure of certain carbon polymers1. As noted here, these chains aren't as stable as carbon chains, and less stable in many liquids. However, this becomes less of a problem at low temperatures. Furthermore, as Bains' website says, silicon may be the only option for liquid dinitrogen.
Almost paradoxically, silicon-based life has advantages over carbon at high temperatures, as the Center for Astrophysics discusses! Silicon-oxygen and silicon-aluminum bonds can withstand temperatures hundreds of kelvin above temperatures on Earth. However, the lack of a good solvent that is compatible with silicon at these temperatures is a stumbling block. Sulfuric acid has been considered as a solvent, but not, as far as I know, with silicon.
As mentioned here, silicon photosynthesis is also possible. However, be careful before drawing a direct analogy between silicon-based life and carbon-based life in terms of respiration. As shown here, SiO2 produced from respiration (the analogue to CO2) would be solid, which would make it very difficult for an organism to breathe.
Bains writes on his website that you could create a system analogous to the Krebs Cycle using ethylene, acetylene, and water, which would generate CO2 and methane, but he doesn't discuss if and how fast this could happen at low temperatures. You still have the problem of instability of silicon-silicon chains when faced with water.
1 As this report concluded, "hybrid" chains of the form SinC2nH2n+1On+1 are also possible. They would look like this:
I'm not aware of the temperature regimes in which they could remain stable, though.
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