# Non-carbon based life forms on hot planets

I am writing a story with people made of elements other than carbon. A couple of planets in this series are really hot, so I need compounds with high melting points.

For example, there is a lone girl who lives on Venus, which is hot enough to melt lead. I decided to use tungsten carbide for her house.

But on another planet, there are humanoids made of silicon who survive at higher temperatures than humans on earth.

Is this scientifically possible?

If you're interested in my book and don't mind a bit of self-promotion, watch for the next few years and keep an eye out for:

The New Worlds Series #1: Into the Flames
The New Worlds Series #2: Call of the Cybans
Milky Fight #1: The Authority Gains Strength.

• Google for Refractory metals, Superalloy,Ultra-high-temperature ceramics etc – Eka Mar 5 '16 at 5:54
• I don't want to sound mean, but this is borderline self-promotional. We're happy to delve in chemical aspects of a story's background, but I don't see the relevance of your books' names prior to having written them, nor the current title of the question. – Nicolau Saker Neto Mar 5 '16 at 6:52
• Welcome to Chemistry.SE! I like to see writers coming here to get some scientific background for their works. Nevertheless, I took the liberty to (heavily) change your question and make the self-promotion criticized by Nicolau (for good reason) a bit less obvious. If you think that it contradicts your intentions, please feel free to roll back. – Klaus-Dieter Warzecha Mar 5 '16 at 7:36
• If you come here more often, which I hope, because I like the scifi and crime story questions, please consider to register your account and make it permanent. Otherwise, it's just based on cookies and might get lost. – Klaus-Dieter Warzecha Mar 5 '16 at 7:42
• Related chemistry.stackexchange.com/questions/18843/…. Not a dupe though I think. – bon Mar 5 '16 at 11:17

Given that a $\ce{C-C}$ bond dissociation energy is $83\ \mathrm{kcal\ mol^{-1}}$, and $\ce{Si-Si}$ bond dissociation energy is $52\ \mathrm{kcal\ mol^{-1}}$, a silicon based life form is much worse off on a high temperature planet. It's actually for this very reason that there aren't nearly as many silicon based compounds as there are carbon based compounds. Thats not to say they don't exist, however. There are silicon hydrides that in the form of silicon chains, analagous to alkanes, existing up to about 8 silicon long. They are all readily hydrolyzed and are thermally unstable, especially the longer chains.

Silicon is also not quite as versatile as carbon in terms of the types of bonds it can form. Carbon is capable of forming single, double, and triple bonds due to its ability to hybridize its $\mathrm{s}$ and $\mathrm{p}$ orbitals. Silicon is a larger atom than carbon, and as a result it is much more difficult for its $\mathrm{p}$-orbitals to overlap with the $\mathrm{p}$-oribatls of adjacent atoms. Again, this is of course not to say that this doesn't happen, as it does in the case of diselenes and disilynes, but again, these are (very) unstable.

Most often silicon is found combined with oxygen, as in the very stable $\ce{SiO2}$, or as you might know it: glass, sand, or quartz; not exactly ideal for a moving, living creature. Just an idea, but if you're trying to make scientifically feasible life forms on a hot planet, you might just be better off having carbon based life forms in an inert atmosphere. In other words, an atmosphere that doesn't lend to them bursting into flames.

I'm not sure how set you were on making these different races out of other elements, but no element by itself really matches the chemical variability that carbon offers.

EDIT: After doing a little more research, I thought it might be beneficial to include polysiloxanes, or silicone, which consist of $\ce{C-(Si-O)_{n}-Si-C}$ bonds. These actually are actually very interesting because they are extremely elastic, functional over a wide range of temperatures ($-100^\circ \mathrm{C}-300^\circ \mathrm{C}$), resistant to ozone and UV radiation, do not promote bacterial growth (but who knows about extraterrestrial bacteria), have a low chemical reactivity, high electrical resistivity, and most interestingly, have self-healing properties.

I would now change my tune and say that maybe a race of silicon-carbon based life forms isn't too far fetched at all! At least for sci-fi writing purposes.

• Polysiloxanes seem pretty heat resistant, fluid and versatile. Maybe mixing silicon, oxygen and carbon could be a way to go? Kind of locks you in a system, but I could see some biological ability. Carbon definitely could do variability better, though, since it wouldn't be locked in that pattern. – SendersReagent Mar 5 '16 at 18:28
• @DGS I definitely kept thinking about the possibility of carbon-silicon compounds even after I posted the answer... Maybe I'll make an additional section about them. – ringo Mar 5 '16 at 18:36
• Only one can evolve, And you should know which of the two can thrive in the environment suggested. – user5434678 Mar 5 '16 at 23:46