x-risk is existential risk, as in humans get wiped out. Some big ones are meteor impact, nuclear war and disease. The risk of those things ending all of humanity are greatly reduced with a second planet. They're not reduced with a desert colony.

> The risk of those things ending all of humanity are greatly reduced with a second planet.

I can imagine a situation where that's true. But right now, for almost any situation, a series of super-bunkers is orders of magnitude cheaper and more effective. A lot of ridiculously destructive things can happen to Earth and it will still be a better place to live than Mars.

our earth has had impact events that no bunker would save us from. like the one that created the moon or the much smaller impact that created the Borealis Basin on mars would boil the oceans and melt the surface.

It would be massively cheaper and faster to robotically colonize near-Earth space and get really, really good at killer asteroid detection and redirection.

Ok but redirection capability must be abundant enough that outright sabotage and terrorism can be fixed by another nation or else you will have an increase in extinction risk.

Th early solar system was very different with way more debris including large planetismals. The planetismals caused the big impacts you mentioned, and the smaller stuff caused the impacts can see on other bodies.

The solar system is much cleaner place now. All the planetismals and most of the asteroids have impacted or been kicked out. Big things are in stable orbits. There are a lot of dangerous asteroids but we track most of the large ones. There is a risk that something big will be kicked out of orbit but it is rare enough we don’t know how unlikely.

Large impacts, 5km or bigger, are every 20 million years.

Yeah you can come to different conclusions than colonizing Mars being a good strategy for human survival. I'm just answering the "why not the desert?" question.

None of those things would make Earth less hospitable than Mars. A desert colony would still be better off than trying to survive on Mars, particularly once Earth's resources are cutoff. Mars is far more hostile than anything likely to happen to Earth over the next hundred million years.

It's not about hospitable. It's about survivable. There are large enough meteor strikes where you'd be better off on a self-sustaining Mars colony than anywhere on Earth.

Unless you're personally in the strike zone, that's not true.

And one should also bear in mind that Mars is at no less risk of meteor impacts than Earth.

It’s not about Mars being lower risk but independent risk. Someone could decide to keep copies of important documents in their vacation home not because it’s less likely to have a fire, but because it’s less likely for both houses to have a fire.

I used the wrong word when I said meteor. They’re too small. A comet or asteroid of 100km diameter would raise the temperature of the surface of the Earth by hundreds of degrees and then there’d be decades of darkness. https://www.sciencedirect.com/science/article/pii/S001632872...

Presumably because the goal is to survive something bad that happens to Earth. If you're on Mars (and self-sustaining...), that's no big deal. If you're in the Gobi Desert, you're going to be the first people to get wiped out by whatever happens to Earth.