Ready to live on Mars? It won't be as easy as you think.

When the Mars One organization based in the Netherlands asked for volunteers to make a reality-show backed trip to Mars, more than 200,000 people volunteered as tributes, despite knowing they'd never be coming home.

Something about our red neighbor fires up the human imagination and exploration instinct, because the overly optimistic Mars One isn't the only one aiming to worlds beyond our atmosphere. High-profile scientists including Stephen Hawking and SpaceX chief executive Elon Musk have gone as far as calling a Martian colony essential to the survival of the species, an existential back-up in case things go too wrong on humanity's home planet.

But substantial obstacles stand in the way of long-term Mars habitation. Would it be worth the cost, and the risk? At least one NASA astronaut thinks our priorities may be out of whack, telling Quartz the idea people might someday abandon Earth to live on Mars is "utter nonsense."

To be clear, there's a world of difference between NASA visiting Mars and an organization like SpaceX trying to build a million-strong city. NASA has ambitions of sending a crew to the red planet in the 2030s, but like Apollo, it will be a relatively short visit. A largely bring-your-own habitat mission, they'll travel, explore, and return, all within two to three years. A successful colony, on the other hand, would require heavy on-the-ground construction, as well as the ability to harvest resources from the planet itself to make up for anything less than 100 percent perfect recycling systems.

From that point of view, it's easy to see why Mars is a popular target. From dirt, to ice, to clay, useful raw materials abound, as long as we can develop the technologies to access them. But what about the environment?

In addition to the obvious stuff like air, the Earth envelopes us with a protective magnetic field that shields us from carcinogenic cosmic and solar radiation. Recent measurements from the NASA rover Curiosity suggest that a trip to Mars would come along with an increase in radiation on par with a career in a nuclear power plant. Some astronauts might find that level of risk acceptable for a quick jaunt through the solar system, but it might be a tough sell for long-term colonists.

But like resource recycling and collection, radiation problems can conceivably be solved with technology, such as advanced shielding or even a big pile of Martian dirt. A bigger problem is Mars's weak gravity, a little over one-third as strong as Earth's.

Spending our entire lives under the pull of gravity, our bodies are finely tuned to its effects, down to the microscopic level. Without gravity to fight against, astronauts quickly lose bone mass, which crew members on the International Space Station ward off by exercising two-and-a-half hours every day. No matter how far habitat technology advances, or how much we re-shape the Martian environment to resemble Earth's, we'll never be able to change its mass and gravity.

Almost nothing is known about how the human body will react to a lifetime in low gravity, as the record for longest time spent in space doesn't crack the year-and-a-half mark. Al Globus, a NASA software developer and member of the National Space Society board of directors, says that the complete lack of human data at Martian gravity levels means that “everything is speculation.”

Some speculations assert that children born on Mars could well adapt to Martian gravity, but would have weaker bones and muscles than average Earth-born babies. This fragility may not be a deal breaker in the low-gravity environment, but it would mean that no native Martian would ever be able to return to Earth.

“One-way settlement is a lot less desirable than settlement that people can reverse if they choose. Also, if your kid is a world-class violinist you’d like them to play Carnegie Hall, or an athlete to compete in the Olympics,” Mr. Globus tells The Christian Science Monitor.

Rather, Globus favors a less drastic approach, starting from settlements in Low Earth Orbit: “I prefer settlement plans that gradually expand from Earth with short logistical trails and incremental development close to help when needed rather than a gigantic leap tens of millions of kilometers away where you can’t go home in case you turn out to hate it. The chances of success with incremental development and short logistics are much, much higher.”

Ron Garan, a former NASA astronaut, is also skeptical of humanity’s Martian future. He has suggested the focus of space exploration should be to improve conditions on our home planet, rather than escape it.

“Space is our future; we need to devote resources and time and effort toward further exploration of our solar system, including human exploration. The primary reason for doing this is not so that we can have a plan B, via having another planet we can go live on, but instead so that we can use the technology that’s developed through those efforts to help us here on Earth,” he said in an interview with Quartz magazine.

To Lieutenant Garan, the idea of escaping to Mars rather than fixing Earth is illogical, considering the monumental scale of the undertaking. “It’s a lot easier to control our own atmosphere and our own oceans than it is to create an entirely new atmosphere,” he told reporter Georgia Frances King.

Instead, he advocates a more gradual expansion into space, similar to Globus, with the first permanent human presence on the moon, which could eventually serve as a "transportation hub to the rest of the solar system."

With all the recent talk of becoming a multi-planet species, Garan urges people not to get ahead of themselves. A Mars mission may hover on the horizon, but if settlement is in our future, that future is a long, long way off. He referenced Carl Sagan’s take on the problem, as relevant now as it was more than two decades ago:

“The Earth is the only world known, so far, to harbor life. There is nowhere else, at least in the near future, to which our species could migrate.”

“Visit, yes. Settle, not yet. Like it or not, for the moment, the Earth is where we make our stand.”