|How not to do it|
Science-fiction often contemplates beings like ourselves, but powered more efficiently by electricity or nano-nuclear-reactors. It seems curious, watching living things inefficiently stuffing themselves on seeds or carrion or cheesecake.
Yet life on Earth had to bootstrap itself from its primordial, inorganic environment. Through waves of autopoiesis, Earth's ecology got to where it is now. Imagine a conceptual, spherical membrane around the Earth, perhaps just beyond the Moon. Electromagnetic and cosmic radiation transiting this imagined membrane (plus the odd rock) is all that's necessary to drive the entire history of life on this planet.
Now consider a Mars colony. Earth's biosphere (through its human-technological component) may be up to creating a settlement on Mars. But insofar as the colony is not capable of autopoiesis, it's artificial. The Martian 'membrane' needs to be permeable to Earth-resupply for all those essential metals, solar cells, nuclear reactors, smart plastics and many, many other vital supplies.
So Elon Musk should be thinking sustainability .. does that mean Martian terraforming?
Not exactly: Mars couldn't merely replicate a Terran ecology. It needs a Martian ecology, based on what Mars could minimally be re-engineered to be. We need an engineering nudge to push Mars onto a new track, one capable of sustaining a stable, runaway process of biological autopoiesis. Ideally humans could be adapted to join that ecosystem.
How would you do that? Seems harder than launching an electric car into space. But creating a Martian magnetosphere does seem an early requirement - another Tesla business opportunity?
Here's a counter-argument. Put that imaginary membrane around London or the UK and permit only radiation to cross it? Could they survive in their current form? Obviously not.
Taking things further, if we couldn't rely on any technology beyond to-hand hunter-gatherer subsistence, the maximum carrying capacity of the UK is probably in the low thousands. Since we have a present GB population in excess of 61 million, we're plainly way above subsistence-equilibrium.
So it's not a slam-dunk argument against colonising Mars that its completely-isolated-from-Earth carrying capacity is zero for the foreseeable future.
This suggests that, like similar marginal propositions such as undersea cities or polar (or lunar) colonies, the two assessment dimensions are:
- business case (economic sustainability)
- existential fragility (environmental sustainability).