Iron planets are planets which lack a significant mantle. These planets are essentially lone planetary cores. Since water and iron are unstable together iron pentacarbonyl and other exotic metal-based volatiles might form bodies of liquid on the surface of these worlds. An answer to an earlier question of mine suggested that such a planet might also have significant amounts of liquid ammonia under the right conditions. Here we'll assume that the planet only has a lot of gaseous ammonia in the atmosphere.

Could life plausibly arise in these iron pentacarbonyl oceans? What difficulties would it face biochemically speaking?

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    $\begingroup$ Life is complex. Take a look at even the simplest proteins, those are too complex for a person to make up on their own even though we know a lot about biochemistry. Now you want to make an entire biochemistry from scratch that would need completely different mechanisms. Here is the base line: Anything is possible with life. There could be life on the subatomic level. There could be creatures living in stars made out of plasma. We simply don't know and have no way to prove such things. Just do it. World building is about being believable, not about having an answer for everything $\endgroup$
    – Raditz_35
    Nov 16, 2019 at 15:47
  • $\begingroup$ If they lack a mantle they also lack light elements. How do they get the carbon, nitrogen and related? $\endgroup$
    – L.Dutch
    Nov 16, 2019 at 17:19
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    $\begingroup$ @L.Dutch-ReinstateMonica If they lack a mantle, they lack huge quantities of light elements. But huge quantities are not required--just a relatively thin film over the surface, such as could be held in crustal rocks, or outgassed from the metal core, or deposited by comet and asteroid impacts. $\endgroup$ Nov 16, 2019 at 17:27
  • $\begingroup$ Water and iron can be friends. Probably most friendly in a reducing environment but you can find iron as sulfides and oxides near the surface. $\endgroup$
    – Willk
    Nov 16, 2019 at 17:49
  • $\begingroup$ You know we don't have any idea how life can arise, how can this be science based? We've never seen it happen. You can start life on pentacarbonyl and no one can challenge it. The biochemical question entirely depends on how that life metabolizes nutrients. Find a high energy catalytic reaction common in that chemistry and call it good. $\endgroup$
    – Vogon Poet
    Nov 17, 2019 at 0:10

1 Answer 1


Well, Stephen L. Gillett thought so....

It's not really possible to give a definite yes-or-no answer to this, but it seems reasonably plausible. I haven't been able to find any data on the use of iron pentacarbonyl as a solvent itself, but it is soluble in most organic solvents (like ether and acetone) and slightly soluble in alcohols... so it seems reasonable that, conversely, nonpolar organic molecules would be easily soluble in it, while alcohols and other polar molecules would be slightly soluble. Thus, if you can form things like lipids with hydrophilic/hydrophobic ends, you could at least form bilayer membranes around cells (with an inside-out structure compared to our cells). And iron pentacarbonyl is a useful reagent for a lot of organic synthesis reactions, as well as acting as a precursor to a lot of more complex metallic compounds that have no analog in our own biochemistry, so it certainly seems plausible that you could in fact get lipid-like things, as well as plenty of more complicated macromolecules, forming in Fe(CO)5 solution.

DNA and proteins wouldn't work in iron carbonyl solution, but that's a common problem for all speculation about non-polar solvents. So, if you think life could exist in liquid methane, we're really on the same footing here. Meanwhile, PNA (peptide nucleic acid, which is actually simpler to form and more robust) should work just fine. And in the absence of more detailed speculation on replacements for amino acids and proteins, you could a page from ribosomes and I would find it plausible-enough-for-story at least that PNA serves as both a genetic material and a catalytic material (cf. the RNA world hypothesis).

  • $\begingroup$ Thanks for the book recommendation. $\endgroup$ Nov 16, 2019 at 18:07

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