> several should survive even a Chicxulub-class event
That's an interesting proposal. I'd love to read a study on that.
> But I suspect you mean something different than independent biospheres. If so, what risks are you thinking of?
Well there are degrees of independence. Perhaps "isolation" in the systems engineering sense is a better term. There are a lot of high-risk probabilities that arise as technology advances - and the Fermi paradox isn't encouraging about our chances. For some example risks, let's say grey goo, cybernetically enforced self-destructive tyranny and unexpected stable artificial black hole. In some case, the light-minutes of separation may make the difference.
It might make more sense to build an artificial orbital habitat at L5 or the like, but these seem so fragile compared to biospheres that could be constructed on Mars. Being out of the gravity well is a huge advantage, but the gravity on Mars is low enough that space elevators become a real possibility. Perhaps Ceres is a good compromise - lots of water, metal rich asteroids all around.
The Chicxulub impact had global consequences, but far enough from the crater would have been survivable in any bomb shelter. http://users.tpg.com.au/users/tps-seti/climate.htm gives an estimate of the damage radius, with 1 psi overpressure to 4000 km. While it says there was a global firestorm, the most recent analysis believes that that wasn't the case, see http://www.exeter.ac.uk/news/featurednews/title_430274_en.ht... . It does says that being on the other side of the planet would have been worse than North America, in terms of heat flash, so the Canadian Shield would be survivable, as would most nuclear bomb shelters in the world.
It's very hard to model those risks. A non-terrestrial habitat will certainly be more fragile than one on Earth, and easier to fall prey to a malicious computer attack by rogue AIs. A gamma ray burster would be more survivable in a shelter 1,400 m underground[1] than anything we are likely to build soon on another planet, or Ceres. A "Dark Star" scenario as in Fritz Leiber's "A Pail of Air" feels more likely than an unexpected stable artificial black, and in that story, access to nuclear fuels, along with a stockpile of liquid atmosphere and frozen materials, helped keep civilization going. Or perhaps the Free Peoples of Ceres will send an asteroid killer our way, to keep the solar system from being infested by flatlanders.
So while there are scenarios where separation is important, there are also scenarios where separation won't help, and might end up taking funding away from something which would have helped. With probabilities that low, and with such high error estimates, it's hard to tell which approach is best. The cheapest is self-sufficient here on Earth. If that works, then there's the base knowledge for how to set that up off-planet.
([1] I refer to the Laboratori Nazionali del Gran Sasso, which is a neutrino lab. While not the deepest lab, it's one with an access road instead of an elevator. Very handy if you want to supply your colony.)
That's an interesting proposal. I'd love to read a study on that.
> But I suspect you mean something different than independent biospheres. If so, what risks are you thinking of?
Well there are degrees of independence. Perhaps "isolation" in the systems engineering sense is a better term. There are a lot of high-risk probabilities that arise as technology advances - and the Fermi paradox isn't encouraging about our chances. For some example risks, let's say grey goo, cybernetically enforced self-destructive tyranny and unexpected stable artificial black hole. In some case, the light-minutes of separation may make the difference.
It might make more sense to build an artificial orbital habitat at L5 or the like, but these seem so fragile compared to biospheres that could be constructed on Mars. Being out of the gravity well is a huge advantage, but the gravity on Mars is low enough that space elevators become a real possibility. Perhaps Ceres is a good compromise - lots of water, metal rich asteroids all around.