I've already written about how Mars is great to explore, but NOT a great place to live. Nor is anywhere else. The best place to live and to shelter from cosmic or human created disasters is on Earth itself.
So, I think our focus should be on exploring the solar system. Let's set up colonies only when they are useful for exploration.
Our rovers are our "eyes" in the solar system. They can see much better than we can. The Mars landscape is dull and uninteresting to the unaided human eye. Everything is a dull dark brownish colour. Sometimes described as butterscotch but think of it as like a really dull day on the Earth - half the sunlight anyway - and then it is cut even more by the dust perpetually suspended in the Mars atmosphere which makes it a dim brownish red colour. Everything is tinted with this dull brownish red tinge.
Yet our rovers take great photographs, which look like a brightly illuminated Earth landscape. Often they have blue skies too. That's because the scientists adjust the white balance deliberately, to approximate an Earth landscape so that they can recognize rocks more easily.
Our rovers are our digitally enhanced eyes on the solar system. And there is great interest in their explorations of Mars, look at the interest in Curiosity, Opportunity, Spirit, Sojourner, Pathfinder, and the other rovers and landers on Mars. Mars is a great mystery and our rovers are trying to unravel this.
We don't need to send humans there. Indeed they would just get in the way and confuse the investigations on the surface. Our future rovers will search for tiny fragments of genetic material and amino acids, a single amino acid, and tiny signatures of chirality. Any humans in the vicinity will confuse the evidence, a bit like an investigator covering a crime scene with fingerprints.
The entire area around a human base on Mars would be contaminated by the flakes of skin, hair, soil, and then the microbes in dormant resting states scattered like dandruff over the surface of Mars. There is no way we can stop this, not with modern technology, our airlocks leak, our spacesuits leak all the time, and there is no way a human expedition on Mars can operate as a Biohazard laboratory sterilizing everything every time they go outside the habitat. And the habitat can never be totally closed at least with present day technology, there will be wastes that need to be vented onto Mars and it will be hard to make sure these are always contamination free. Then, if there is a crash landing on the surface of Mars or someone dies on Mars that's a huge immediate contamination.
We are looking for tiny traces of life on Mars both present day and past life. I think the general public probably don't quite appreciate the scale of what they hope to discover on Mars.
WHY OUR SOLAR SYSTEM IS OF SO MUCH INTEREST FOR EXOBIOLOGY
First, take a look around you - how much of modern civilization is based on wood, plastic, oil, and other plant products? What would be left if you took away all plant products - and all technology based on ideas from nature? I think not very much.
Also of course biology is of fundamental interest for medicine.
But life is not well understood. It might surprise you to know that as we look back into the past we can only see half way back to the beginning of evolution.
If you look at how life evolved from the first amino acids to present day life, then look at the informational complexity - measured in the number of non redundant nucleotides in our DNA, then we can only get back half way to the origins of life. There are as many steps of evolution between amino acids and the simplest known cells as there are between those cells and ourselves.
WHY NOWHERE ELSE IN THE SOLAR SYSTEM IS OF ANY VALUE AS A SECOND HOME FOR HUMANITY
Sometimes space advocates say we should colonize space as a second home for humanity in event of a great disaster. But what kind of disaster could make the Earth as inhospitable as Mars?
This disaster would have to remove 99% of our atmosphere, and remove not just 99% but all the oxygen from our atmosphere. It would have remove almost all of the water including the oceans, leaving a totally dessicated landscape. And it would have to cool down the planet to such an extent that the equator has average temperatures same as Antarctica is now.
Anything less than that and the best thing for any Mars colonists to do after the disaster is to return to Earth and try to rebuild Earth again - as Earth would continue to be far more habitable than Mars. And no foreseeable disaster could make Earth as uninhabitable as that.
Yes in the early solar system when there were embryo planets the size of Mars, some of these could collide with a planet and make the entire surface molten. This happened when the Moon formed, so we believe. But even those early impacts most of them, only created huge craters and made part of the surface molten.
There is a tiny chance of something like this happening in the far future a billion years from now. There is a tiny chance that Mercury could be perturbed from its orbit by resonances with Jupiter, and if this happens there is an even tinier chance that it could be deflected by the gravitational influence of Venus, and then hit the Earth (though it is more likely to hit Venus or be ejected from the solar system altogether).
So that is a disaster that would indeed make Earth uninhabitable and if that happens then our descendants a billion years from now might need to move to Mars. But we'll have plenty of warning of a disaster like that. We don't need to start worrying about it yet.
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