My first vision of Mars appeared in a 1950 book by a onetime German rocket scientist, Willy Ley, called The Conquest of Space. The book's art was by the brilliant Chesley Bonestell, who imagined needle-nosed rockets landing on the planet. Half a century before, the American astronomer Percival Lowell had argued that Martian engineers had built vast canals to irrigate the land with meltwater from the poles. Bonestell gave us a canal (though not much sense of the vegetation it supported).

In hindsight, it seems strange that Lowell, Ley, and a host of other pop-science writers hadn't thought things through: if Mars was so dry it needed irrigation, why canals instead of pipelines? And why grow crops in Mars's arid soil rather than in some more efficient medium?

For that matter, even Lowell could have done the math on a small planet far from the sun, and realized nothing would make Mars remotely habitable. When the first photos of the Martian surface came back in 1965, astronomers must have smacked their foreheads: of course the planet was pocked with craters -- it was too small to hold an atmosphere, so every incoming rock would leave its mark.

The planet certainly has its impressive features: Valles Marineris, an enormous canyon, and Olympus Mons, the largest single volcano in the solar system. But repeated landings have shown very little evidence of a planet that could sustain life.

In recent days, we've learned that liquid water actually does flow sometimes on this very cold, dry world. It flows only because it's so salty that it stays liquid in sub-zero temperatures. Along with the timely release of a big new movie, The Martian, the discovery has triggered another avalanche of interest in Mars.

This is fine, and I rejoice for Andy Weir, whose self-published novel has now made him very rich. But what interests me about his novel (and movie) is not its scientific accuracy but what it tells us about our continuing interest in a pretty boring little planet: a mirror for our own obsessive need to expand, explore and take control.

When H.G. Wells unleashed his Martians in The War of the Worlds, the satire must have seemed obvious. Imagine, Wells told his imperial British readers, what it might be like to be conquered -- to be overwhelmed as Britain and the other European empires had overwhelmed the rest of the world over the previous four centuries. It worked, giving readers an enjoyable scare before knocking off the Martians with bacteria they had no immunity against.

A-bombs against Martians

By the 1930s, the Germans were trying yet again to repeat the British and American successes in stealing empire from lesser peoples, and Orson Welles's radio adaptation of The War of the Worlds made its American audience understandably anxious: the last of the Indian Wars were in living memory, after all. Then Hollywood put the Martians on film in 1953, with a flying-wing bomber delivering an atomic bomb against the invaders' flying saucers -- to no effect.

Even earlier, in 1950, I'd been enthralled by Rocketship X-M, in which the first lunar expedition gets knocked off course and manages to land on Mars instead. This too was a post-Hiroshima Mars, a red-tinted desert populated by savage survivors of a nuclear war.

Never mind the scientific absurdity. Like most Mars fiction and films, Rocketship X-M was about us here on Earth, putting ourselves at terrible risk for a chance to conquer a new world. Ray Bradbury's The Martian Chronicles gave us the settlement, conquest and suburbanization of a second America, with the new colonists stupidly returning to Earth as soon as nuclear war breaks out there.

Ironically enough, our continued interest in such a war promoted the development of rockets that could reach Moscow and Mars with equal accuracy. So we went from a Martian flyby in 1965 to the Viking lander in 1976, and on to a string of successful robot landings. We now know some parts of Mars better than we know most of our own seabeds, and countless science fiction novels have described our eventual occupation of this planet just as the Americans occupied the Indian Territory and turned it into Oklahoma.

Mars as real estate

So we still think of Mars as real estate, and if it's not the home of potential enemies, it's there for the taking.

But why would hairless apes who evolved to survive on African savannahs even want to go to such a dismal place, let alone live in it?

The planet's gravity is only about 0.38 of ours. A beefy 100-kilo (220-pound) human would weigh only 38 kilos (83 pounds) on Mars. So anyone spending time on the surface would experience serious atrophy of bone and muscle. This would cause health problems for the first generation of colonists, and their children would be experimental animals with doubtful life expectancies. Good luck to anyone trying to return to Earth after an extended stay on Mars; they might suffer several broken bones just lifting off the surface.

Since the planet has no magnetic field or ozone layer, the surface is bombarded by relentless solar radiation. Life on Mars would really be life under Mars, shielded by several metres of rock from both radiation and surface temperatures averaging -63 C (-81 F). At best, colonists would enjoy brief ventures to the surface to glimpse a pale-pink sky.

Visitors and colonists would need elaborate solar-power systems to give them enough energy to keep warm and to run their life-support systems. Those systems would have to include desalination plants. The recent discovery of liquid water on Mars means that water must be saturated with salts. Perhaps some Martian organisms could thrive with such water, but we couldn't. Martian colonists would have to remove the salt, put it somewhere, and then store the clean water in usable form. Even a single failure of the energy supply or the desalination plant could finish off the colonists.

The economics of living on Mars

And let's assume that we overcome all these obstacles, and establish a working colony on Mars. What then?

At best, the colony would function like an Antarctic base, acquiring data about a very alien environment. It would have nothing to sell us but information: today's high temperature in Syrtis Major, what's on the menu for Saturday dinner, the air pressure and humidity in the colony garden. It would be entertaining, but only that -- a kind of reality TV show, amusing comfortable residents on Earth and helping a few faraway scientists.

It's hard to imagine a Martian colony with its own functioning economy, including rich and poor. What could a rich colonist do to earn his wealth, and how would he spend it? What would force other colonists into poverty, and why would they put up with it? For that matter, what country on Earth would be willing to keep shipping stuff to Mars in return for little or nothing beyond temperature readings and geological surveys?

What the colony could build for itself would depend on 3D printers. Virtually nothing made on Mars would have value on Earth except as a knick-knack or conversation piece.

Lots of science fiction novels have portrayed colonists breaking free of Earth's heavy hand, just like the American colonists, but more likely we'd ditch the colonists as soon as they showed any ability to survive on their own. If they kept sending scientific data, we might pay them with a couple of payloads of goodies every two years.

But by the 22nd century, the rest of us will have moved on from naive dreams of interplanetary empires. We'll likely be too busy struggling with life on an overheated Earth to care much about life on a frozen rustball called Mars.