Mars has several advantages, you can pretty much google this and get better arguments then I'm able to make here. But here are a few key points.

- Earth like day period, 39 minutes longer versus almost a month longer than earth.

- More stable day-night temperature

- More gravity

- A weak atmosphere (versus none), and the capability to retain a earth like atmosphere.

- Easy access to Water, and CO2. Important for growing plants and making rocket fuel amongst other things.

We aren't really looking for liquid water [0], as you say that evaporates pretty much instantaneously. Rather we are looking for ice, the pheonix lander confirmed the that this exists naturally on mars [1]. In the worst case water bound to the soil that can be baked out [2].

As for the atmosphere being stripped away, that's not really a concern on time scales humans care about. Though I've heard people talk about setting up a artificial magnet field to reduce the amount of radiation you receive, which should also prevent this.

[0] Well we are, but as a scientific curiosity not as a way to sustain a colony.

[1] http://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080...

[2] http://www.space.com/22949-mars-water-discovery-curiosity-ro...

In the long term, mars lost its previous atmosphere over billions of years. If you have the technology to rebuild an atmosphere in human timescales (few hundred or thousand years) the atmospheric loss is small enough that it almost becomes a rounding error. Maintaining it should be easy.

As far as minerals, I really doubt there are any which would be cheaper to mine on mars, load on a rocket and transport back to earth, than to mine directly on earth. Even if you build a space elevator on Mars (which is much easier than building one on earth).

Maybe you could setup a 3 way trade. Even without the space elevator, it's cheaper to ship things from Mars' surface to basically anywhere in the solar system than it is from earth's surface.

So Mars could ship oxygen, water, CO2 filters, building materials, maybe even food to an asteroid station (whatever they can't source locally) and the asteroid station could ship whatever they mine from the asteroid to earth.

Yes, it's a hugely ambitious goal.

- mining industry

- chemical industry with thousands of end products.

- biochemical industry (medicines, plastics etc.)

- microprocessor fab and IC fabrication

- indefinitely sustained biosphere

- manufacturing industry for different high-end products, including rockets, instruments etc. and ability to maintain them.

I think you need large city with maybe 500,000 people at minimum with current technology.

Now imagine that you're on a different planet, and there are only a few firms that CAN resupply, and they'll only do it if you can compensate them sufficiently.

Better hope the colony is built on a platinum and rhodium mine!

Not a problem in a shielded, climate-controlled shelter, e.g. one partly underground or in a cave.

> more radiation than you can reasonably survive on the way to Mars.

Putting food and water between space and interplanetary astronauts is a popularly-discussed option.

I think you may have been down-voted on your tone. This is an optimistic, bleeding-edge project. Unless you are an expert, it is more appropriate to ask why something isn't a problem than to prematurely declare it as unsolved or unsolvable.

If you want optimism for the sake of optimism, Facebook has some lovely mother's groups.

- Mars has a (thin) atmosphere, mostly made up of CO2 -> good for plant growth. The Moon has none.

- Mars has gravity closer to Earth than the Moon.

- Mars has lots of water, while the moon has possibly just a little?

EDIT: found http://www.mars-one.com/faq/mission-to-mars/why-mars-and-not..., which cites similar and more reasons (although Mars One seems to be pretty much a scam).

Has anyone got numbers for this?

> Musk has said a fully loaded Dragon could even be sent to make a touchdown on the moon or Mars

or https://www.nasaspaceflight.com/2016/04/spacex-debut-red-dra... :

> “With Dragon launched on a Falcon Heavy, it can go pretty much anywhere in the solar system, because that’s a heck of a big rocket,” he continued.

> “Dragon, with the heat shield, parachutes and propulsive landing capability, is able to land on a planet that has higher entry heating, like Mars. It can also land on the Moon, or potentially conduct a Europa mission.”

How does that fit with the statement "Dragon doesn't have enough delta-V to land on the moon"?

Depends on what you mean by close. 0.38 is closer to 16.7 than 1, but any improvement on that is important

So if we could do humans on Mars, it would mean that we had learned far more than we used to know. It's like the difference between climbing a hill in your city, and climbing Mt Everest.

And if the aim is to just try to do the hardest possible thing we can think of, why Mars and not, say Venus?

I think difficulty is a red herring. The other suggested reasons (atmosphere, gravity, water) seem much better reasons.

As I said, the other answers seemed to give credible suggestions.