Why would biological systems be a counterargument? Smelting metals and sustaining life both require an enormous amount of water and about ~1ATM of atmosphere, as far as we know, and there's no plausible known mechanism for sidestepping this requirement. So "magical synthetic biology that can self-replicate in space" is actually a worse solution to the problem than "magical metallurgy that can be done in space" since humans at least have smelted metals, but we've never built synthetic forms of life. (Not counting CRISPR)

Somewhat famously with life, you aren't necessarily replicating the same thing at the end as you are at the beginning, which is an awkward property for an engineered system.

> Wouldn't a counter this argument be biological systems? These are reasonable points as long as we are talking about current methods, but I assume if we were to get to the point of self replicating probes it would be done by something like nanotechnology, synthetic biology like systems.

Biological systems require extremely specific environments that aren't space.

Yeah, you can self-replicate (well, not exactly self-replicate), but just think of all the "infrastructure" you need to do that: massive volumes of air and water, all kinds of weird chemicals not found in minerals, a whole biosphere of other stuff, a literal star, etc. And none of that infrastructure is really space-worthy on any reasonable scale for a probe.

If you broke it all down, I bet you'd need a mass/volume at least as big as a more technological probe. And you still need the technological infrastructure to build a vessel to hold it all together.

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.)

Biology ignored some of the most abundant elements because they can't be worked with under the constrained temperature and pressure conditions where biological systems operate. Biology barely uses any silicon, even though it is the second-most common element in the biosphere. Biology does not use aluminum, the third-most common element, at all. Biology does use iron but cannot reduce it to the pure metal. In fact, biological systems produce no metals. Structurally, biology relies on weak minerals like calcium carbonate and calcium phosphate, rather than much stronger ones like quartz and alumina, because of the difficulty of biochemical processing.

This isn't insurmountable for a probe. Biology can get stuck in local optima. Humans have the Periodic Table and quantum mechanics. But it means we are on untrodden ground. Refining titanium, today, uses a massive molybdenum-lined reactor operating at 1600 C (2900 F). The alternative processes (FFC and Chinuka) use liquid calcium chloride, mp 773 C. The square-cube law points to enormous energy losses trying to scale these processes down. And that's just one element.

We are selfreplicating bots - can eat anything, self healing minor damage, very agile, autonomous. When we stop growing numbers the harvest will begin