Through SpaceX, Elon Musk has done more than perhaps anyone to rekindle interest in space travel. And he hasn't been shy about his ambitions for the company, stating that he hasn't taken SpaceX public because of his unwavering commitment to its central mission: making humans an interplanetary species.

Needless to say, there's nothing easy about that. In fact, the Mars One program, whose proponents think it can be done within a decade, recently had their plan savaged as untenable by researchers at MIT, namely because a colony wouldn't survive long, and would likely die of starvation.

But as Ross Anderson, who interviewed Musk for Aeon, points out, one particular obstacle towers over the rest when building a Mars colony: "no one knows how to manufacture an entire atmosphere." We barely know enough about how our own atmosphere works to keep from destroying it.

"On Mars, the best we can expect is a crude habitat, erected by robots," Anderson writes. Those first pioneers will face a unique set of problems, including carrying out medical and equipment repair procedures they know nothing about. What works for them definitely won't scale to house 1 million people comfortably enough for them to want to spend the rest of their lives there.

Earth's atmosphere is unique and difficult to come by; the other atmospheres found in our solar system would be a lot less friendly to Earthlings like us. NASA / Goddard / Arizona State University

Underpressured

It's not that Mars doesn't have an atmosphere, exactly — it's actually one of four terrestrial bodies in the solar system that does, a short list that also includes Venus and Saturn's moon Titan. The problem is that the atmosphere of Mars differs radically from our own.

For one thing, atmosphere of Mars is 100 times lighter than that of Earth, making the air too thin to breathe. The low atmospheric pressure is also partially responsible for Mars' frigid average surface temperature of -81 degrees Fahrenheit (compared to 57 degrees on Earth). And even if we could breathe the Martian atmosphere, it's composed almost completely of carbon dioxide.

But for a true Martian metropolis to exist, in which humans and other earthly life would not merely survive but thrive, we would need to somehow replace Mars's inhospitable atmosphere with one that mirrors our own.

Here's how the atmospheric composition of the two planets compare, according to NASA, at a glance:

Reinventing the Earth

Some people are convinced Mars can be made to have an Earth-like atmosphere via "terraforming." The idea of terraforming has been proposed for our own moon, as well as for Mars, though bringing it from the realm of science fiction into reality will take time — as well as some serious technological breakthroughs, such as mastering the ability to efficiently transport masses of raw material across the solar system.

As Robert Zubrin, president of the Mars Society, a nonprofit dedicated to Martian exploration, told Popular Science, "We know how to warm planets; we're doing it right now," albeit to our own planet, by emitting greenhouse gases into the atmosphere.

Zubrin suggests that adding flourocarbons to the Martian atmosphere would increase the greenhouse effect, in particular tetrafluoromethane, a refrigerant that, unlike the notorious chloroflourocarbons that have contributed to the destruction of Earth's ozone layer, would not backfire and destroy the very atmosphere we are trying to create.

Inflatable habitats, such as this one imagined for a lunar colony, could sustain human life on Mars before we're able to establish an atmosphere. NASA/Wikimedia Commons From there, Zubrin speculates:

As Mars warms, its frozen soil would thaw enough to release carbon dioxide, and more carbon in the atmosphere would further accelerate the greenhouse effect, bringing the average temperature up to 32°. Mars's frozen underground water supply would melt and flow back into ancient riverbeds. And when the water reaches Martian soil, it would break down latent peroxides, releasing oxygen into the atmosphere—not yet enough to sustain human life, but enough to grow plants—which would further increase the supply.

Once the plants took root, we could just wait for oxygen to accumulate. At this point, Mars colonizers, who Zubrin imagines would work out of a research base camp and wear something akin to scuba gear to supplement their oxygen intake, would also grow algae and seaweed in ponds, which could anchor a growing food chain. "You could have fish farms on Mars," he says. "Water would become the first environment that would be habitable by higher animals without any kind of artificial assistance."

And once aquatic creatures could live happily, we could move onto insects, mammals, and of course, humans. With an atmosphere established, we'd have breathable air and comfortable temperatures, and could move freely, sans bulky suits and supplemental oxygen.

After all, no one wants to carry an oxygen tank for a night on the town.