[abecedarius]

Yes, I was wondering why the focus on metals. (Admittedly they might be needed in trace amounts for catalysis, or convenient for conductors, etc., or for structural material if you're on a carbon-poor asteroid. Most metals are worse than carbon for the latter if you have reasonably high tech.)

[simiones]

The thing is, while the universe is full of metals, it's not that full of the materials needed to sustain life (as we know it, at least). You can find metals and other inorganic compounds on virtually every asteroid, moon, and planet, and many comets even. But water and nitrogen and carbon are significantly rarer.

Plus, life can't survive more than a few minutes in space without metal encasings and electronic life support; whereas metal alone only requires life at a much longer time scale. So, while it may be possible to build a fully inorganic self-replicating fleet, it's certainly impossible to build a fully-organic one with any technology or chemistry we know about today at least.

[abecedarius]

In the outer solar system organics and water are abundant (and in the inner there are plenty of carbonaceous chondrites, admittedly not the most generic inner-system bodies).

Agreed that metals should unlock wider opportunities in the inner system where solar energy is more abundant. I just don't think it matters much, you need a good place to plant your seed; once you've built up to scale you can then build wherever.

(False that life dies in minutes in space; plus the engineers can invest in even greater error correction than radiodurans.)

[simiones]

> (False that life dies in minutes in space; plus the engineers can invest in even greater error correction than radiodurans.)

What form of life can actually survive (that is, continue living, not just go into some dormant state from which it can later resurrect like a tardigrade) in space for more than a few minutes?

[torginus]

Actually the other way around:

https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elem...

There's tons of Carbon, Nitrogen and Oxygen in the universe, but very little metals. Heavier elements are much rarer.

[simiones]

Not in rocky bodies, except maybe for Oxygen (which is commonly found in the form of oxides, very rarely as a gas). Carbon and Nitrogen and Hydrogen and similar elements are mostly found in gas clouds and star that are not really conducive to any form of life or even really fit for extraction by a probe. Maybe some gas giants could be targets for a process of this kind?

[EA-3167]

Life as we know it relies on a complex and interdependent ecosystem, and complex life relies on countless other organisms to support us. Without plants we absolutely couldn’t survive, without microorganisms we can’t survive. Without ample supplies of food, water and oxygen we can’t function.

Generally speaking the pace of biological activity is a lot slower than industrial ones too. We might make up for the pace with scale, but then you’re back to the hard problem of dependencies and “fuel”.

I’m not sure that the problem of beneficiation changes because the system is biological rather than industrial. Edit: Without carrying whole ecosystems with the probe at least.

[abecedarius]

> complex and interdependent ecosystem

That's why my other comment pointed to the autotrophs with the simplest requirements, and the (unknown but complexity-bounded) origin of life.

> pace of biological activity is a lot slower than industrial ones

Bacterial replication times can be under an hour.

[EA-3167]

You’re absolutely right about how quickly some bacteria can replicate, but that depends on the proper substrate, ambient conditions, availability of nutrients, and any competition from contaminants.

What something like E. Coli can do in a well bioreactor is the ideal case, and even then most of what they produce is the bacteria themselves. On Earth this isn’t a problem at all, but as a means of husbanding every joule because you don’t know when or where the next one is coming from, I think it might matter.

It’s also probably a genuinely hard problem keeping your organisms viable without a constant supply of food, a means to get rid of mutants, or some hitherto unknown means of preservation that could handle the extreme time spans involved between “awakenings”.

[abecedarius]

Mainly my point there is that it doesn't seem reasonable to anchor advanced nanotechnology on the doubling times we're used to for industry. I don't want to guess just what to expect for early construction from a starseed arriving at e.g. an outer-solar-system carbon-rich moon -- but nothing like a human generation.

[scythe]

Carbon does not beat metal structurally. Some organic polymers are competitive in tensile strength. In flexural strength and fracture toughness, alloys continue to rule. And when carbon materials are competitive in strength and toughness, they tend to be highly temperature-sensitive and have sudden failure modes, which is not great for operating in space. Consider e.g. the Titan submarine that failed due to carbon fiber composite fatigue.

[abecedarius]

All our structural carbon is low tech by the relevant standards (civilization that can send star-seeds). https://dspace.mit.edu/entities/publication/49f95196-2ddf-48...