What might plausibly happen to Earth that'd make it less appealing than Mars, even temporarily? You've gotta practically melt the whole planet's surface or strip a bunch of its atmosphere or something wild like that to even maybe reach that point. Hell, all the oceans could simply vanish tomorrow and this place'd still be less awful than Mars (though obviously very, very bad—which just emphasizes how truly terrible a habitat Mars is, that we can go to such extremes and still not have made Earth as bad).

People and unpredictability.

In any worldwide disaster on earth, there are going to be a lot of people competing to survive. Building large fragile structures to, e.g., keep the now poisonous atmosphere out because people outside of those structures will have a tendency to destroy them. On mars, you don't have that, you have a relatively stable society where everyone is in one boat together.

If your on mars you also know exactly what you're going to face. The temperature, lack of significant atmosphere, and dust storms. That's pretty much it. You can prepare. On earth you don't know what's going to happen next. Significant die off of oxygen generating plants creating an unbreathable atmosphere? Lack of water? Too much water (flooding)? Hurricane? Nuclear war (or super volcano/asteroid, but those are less likely) throwing up dust and blocking out sun? Unmaintained dam breaking upstream? Unmaintained pipeline poisoning water supply? Earthquake? You can prepare for any one event, even in a post apocalyptic world, better on earth than on mars. But you can't necessarily prepare for them all as well. And even if you could, you won't be motivated to because you can cut corners.

>If your on mars you also know exactly what you're going to face. The temperature, lack of significant atmosphere, and dust storms. That's pretty much it. You can prepare. On earth you don't know what's going to happen next...

Is Mars somehow immune to volcanos and asteroids?

Man some people really want to get off this planet! Earth has given birth and sustained life for so long, and now earth is "unpredictable"!

No comments about your other "arguments".

Volcanoes, yes. There is no molten core.

Asteroids, no, but it is likely more immune to long term dust clouds in the atmosphere as a result (since the atmosphere is so thin). On the other hand dust storms are similar.

> Volcanoes, yes. There is no molten core.

Seems like we are not really sure about that...

https://www.newscientist.com/article/dn11962-lab-study-indic...

That's interesting. Still no volcanoes (or other seismic activity) has been observed on mars, so it's pretty safe to say it's not something to worry about.

> That's interesting. Still no volcanoes (or other seismic activity) has been observed on mars, so it's pretty safe to say it's not something to worry about.

I am not sure. Can you say how we have been looking for seismic/volcanic activity on mars.

Actually, there's at least one. There are essentially cosmic death rays that travel at the speed of light, undetectable until they reach us. I wish I could remember what they're called, but they're generated by black holes consuming stars, and they have far more energy than the asteroid that killed the dinosaurs.

It's implausible that one will hit us, but if you're looking for a scientific and logical motivation, it's a possibility.

Also, colonizing mars is a necessary step toward avoiding what happens when our star reaches the end of its life. May as well start while we have the opportunity.

Is it plausible that a cosmic death ray from afar could be so tightly focused that it didn't irradiate the entire inner solar system but only Earth?

I'm no astrophysicist, but I think I can answer this one.

No, it is not plausible.

Most bodies in the solar system easily fit into a hundred astronomical unit radius sphere. The nearest star is four light-years away, and a light year is eighty-six thousand astronomical units. The ratio between those distances is 2530[1]. It'd be like hitting a meter size target from more than two and a half kilometer. Pretty good shot, and we're talking about Proxima centaury (which, last time I checked, won't go supernova anytime soon) and the distance between say Sedna and the Sun. If we were talking about an accuracy more of an astronomical unit, more like the distance between Earth and mars, then we're talking about a centimeter sized target.

Thus a gamma-ray burst would have to be insanely narrow to hit Earth and not mars. Not to mention how ridiculously unlucky we would have to be then in order for it to be precisely aimed at us.

1. https://www.wolframalpha.com/input/?i=four+light-year+divide...

Mother Jupiter misses a catch and an asteroid hits the Earth, wiping out all life as we know it. Think world-ending events - as rare/far-fetched as they may be.

Some people don't want all of our eggs in one basket. The chances a planet gets destroyed is a bit higher than a solar system or multiple planets.

Also one counter-argument to this is "But then why not the Moon?" I don't have as strong of a counterargument for that other than without the Earth's gravitational pull keeping the Moon in orbit, maybe it will get knocked into the sun or something when Earth is destroyed. Also I'm pretty sure international treaties and such prevent colonization of the moon.

I'd think even a dinosaur-killer-stricken earth with all kinds of climate and other problems would still be a lot more pleasant to live on than Mars. I mean, if you imagine an Earth that's been totally ruined in every imaginable way you're basically describing Mars, but still better because at least there's 1G of gravity and a really good built-in radiation shield.

The actual answer to "why not the Moon?" is - AFAICT - because it's less likely to be able to sustain a human population. Notably, there's a significant shortage of water compared to even Mars (though recent discoveries seem to indicate that there might be more water than previously thought).

I think this is a case where Black Swans apply. You can't assume you know what the all the risks actually are, and in that case diversification is a good thing.

If we are capable to live on mars, we can live on Earth no matter what could plausibly happen to it.

Mars as a contingency plan is a weird idea. Whatever you plan on doing on mars to save mankind, you can do it much easier and for less money on Earth.

This sounds like an argument against backup plans in principal.

The idea of backups is to have another, "just in case". You can't always know, so have as many backups as you can afford.

But here are some concrete examples of threats that make earth a bad deal while leaving mars workable:

A nuclear war would like leave mars untouched and destroy civilization here. Even if earth is still "inhabitable" is doesn't matter if all the human on it are dead. Human Martians coming back a generation later and start anew or integrate with any meagre survivors.

A religious inspired genocide that works. If some group somehow got it in their heads that "technology is bad except for the purpose of destroying other technology" this would be bad. If this group goes to war with western democracy and wins it would be worse. This does sound a lot like one specific group that is currently not able to reach mars, and likely never will be able to no many how many western democracies the attack.

Any disaster that destroys then is done. Imagine a super-ebola that kills all humans. Because germs don't have a reliable space program mars is save and can wait 50 before sending scientists to check it out and trying to repopulate.

> You can't always know, so have as many backups as you can afford.

A backup on mars is basically the most ludicrously expensive backup you can imagine. It's as if when I make a backup for my hard-drive in Europe, I rent a safe in Japan to put it in. That would not make sense unless I think the whole European continent could be wiped out somehow. That's the thing : I don't think anything, not even the possibilities you mention, could make Earth worse a place to live than mars, not even a nuclear war. And I don't see a scenario that would wipe out all humans. Again, not even a nuclear war.

And even if one of these scenarios could indeed wipe out humans, chances are that in a world where interplanetary travel is cheap, mars would not be spared.

I think whatever is on your disk is less valuable than humanity as a species. I think the amount of backup you can "afford" should be relative to the value of the thing being backed up.

Backing up is also not the strongest reason to go to Mars. "Because its there" is easily the strongest, but its not understood by those who don't understand it... That seems tautological, but it is hard to label this thing, it is like a sense of adventure but less childish. It is the same thing started every other exploration into the unknown and left everyone who stayed behind alive and poorer for it. When it pays it pays off in vast sums, literal new worlds are the payoff.

"Because its there" is the argument of mountain-climbers[1]. That can be an argument for an Apollo-style mission, not for a colonization project.

1. Mallory is famously quoted as having replied to the question "Why did you want to climb Mount Everest?" with the retort "Because it's there", which has been called "the most famous three words in mountaineering". https://en.wikipedia.org/wiki/George_Mallory

I am well aware of the quote and its use in stopping analysis for a further reason, because it is the reason.

I don't see why there is a threshold between moonshot and mars colonization, it seems arbitrary to me. Could you explain to me the method for determining the threshold of validity in the reasoning behind "Because it's there"?