Re: Why Bother with Planets?
So from where does the energy to drive a large object with thick rock walls into interstellar space come?
Without the sudden discovery or gift (neither very likely IMHO) of a new technique to get immense spatial displacement for little cost in energy. it has to be incremental, until people can at least work out how to run a viable and largely non-dependent outpost under the relatively known and benign conditions of Mars.
Meanwhile, thanks to a large and irresponsible arc from Afghanistan, throgh Bangladesh to South Africa, and, including India, the exponential population growth continues apace, as does the profligate waste by the privileged everywhere (stand up Al Gore, the Google management, and UAE high-ups on this point, just as three choice examples, the reader's own wealthier neighbours might do just as well).
Population of 8,000 million is not far off.
There will be a breaking point, when it is clearly visible and how much remains possible after that is impossible to predict, to paraphrase Lovelock, if this situation collapses, no sites will have oil bubbling to the surface, no readily extractable bodies of metal will remain.
Sure and all, garbage mining will have its day.
Good luck with getting out into the solar system after the human population hits say, 10 or 11 thousand million, neither too distant if present trends continue, and there's nary a hint that they won't.