Could we terraform Mars, and make it habitable for humans?  Maybe so.  Excerpt:

Today, Mars has little atmosphere to speak of, sports an average temperature of -76 degrees Fahrenheit around the equator, and is pelted by ultraviolet radiation. It’s little more than a desert pockmarked by craters. And yet, there are some who think that Mars can live again.

“You don’t build Mars,” Chris McKay, a planetary scientist at NASA says. “You just warm it up and throw some seeds.”

It’s that simple.

Here are three easy steps to terraform Mars and make it habitable for humans.

Read the whole thing for an outline of the three necessary (and time-consuming – we’re talking thousands of years) steps.

Forgetting the astronomical cost (pun intended) and the time frame for a moment, and think about the implications of a population of humans living on a successfully terraformed Mars.  No, they aren’t likely to turn green, nor will they encounter thoats, exotic red princesses or any other boojums or boogers.  But they will change, as generations are born and grow on a planet with only a little over a third of Earth’s gravity.

The new Martians will be taller and thinner, most likely, as they adjust through growth on a low-gravity environment.  They will probably have to adjust to a colder planet, even after terraforming, but we can do that through technology as prosaic as coats; but gravity will have a more lasting impact.

Not least of which is this:  Native Martians may never be able to visit the home planet.  A 1G gravity field may kill them.

So, while this is interesting and may someday actually happen, any human population on Mars will probably have to be permanent.

Check out Kim Stanley Robinson’s Mars Trilogy for an interesting bit of speculation as to how this might actually work.