Why go to Mars?
The idea of a manned journey to Mars has animated science fiction for more than a century, and since the dawn of the space age, plans have been proposed for how it might be done. But for decades, any real momentum toward that dream seemed lost. In 1989, a plan advanced by President George H.W. Bush to send a manned mission to the Red Planet was shelved when its costs were estimated at more than $500 billion. In recent years, however, the prospects of a Martian voyage have been looking up. In 2010, the Obama administration called on NASA to set "far-reaching exploration milestones," including sending astronauts to Mars by the mid-2030s. But NASA still has no budget for a manned mission, let alone the technology to land humans there safely and then bring them back. Several commercial spaceflight companies are working on plans to send people to Mars in about a decade. Former astronaut Buzz Aldrin believes it's possible. "The challenge ahead is epic, but historic," he says. "We are on a pathway to homestead the Red Planet."

What would such a mission take?
Just getting humans to Mars would require new solutions to some stiff challenges. At the closest points of their orbits, Earth and Mars are 34 million miles apart, and astro-engineers figure it would take a manned spacecraft five to 10 months to reach Mars. That is a long time for astronauts to be in interplanetary space, where they'd need much tougher protection against cancer-inducing space radiation than they do in Earth's orbit. A trip to Mars would require vast quantities of equipment, food, and fuel. Some have suggested sending supplies separately to allow astronauts to travel in a lighter — and faster — vessel. But even if a manned mission reached Mars' orbit in good order, landing there safely poses other daunting problems. Mars' atmospheric pressure is less than 1 percent of Earth's, making it difficult to slow a spaceship hurtling toward the surface at an estimated speed of 13,000 miles per hour. Unmanned rovers have cushioned their descents with heat shields, parachutes, and rockets, but current technology is insufficient for landing a much larger manned spacecraft, even if supplies were sent separately. "We're talking about landing perhaps a two-story house, and then another two-story house with fuel and supplies right next to it," said former NASA technologist Bobby Braun. "That's a fantastic challenge."

How far have plans progressed?
NASA teams are working on experimental projects with an eye to a possible mission to Mars and back about 25 years hence. But some in the private sector don't want to wait that long. Multimillionaire space tourist Dennis Tito has hatched a low-budget, $128 million plan to send a 50-ish married couple on a 501-day flyby that would zoom past Mars in 2018 and then use the planet's gravity to slingshot the spacecraft back to Earth. More ambitiously, the Dutch nonprofit Mars One wants to start colonizing Mars within a decade, and has already collected more than 78,000 applications from civilians willing to take a one-way trip to Mars. The group plans to select six teams of four with the necessary "intelligence, resourcefulness, courage, determination, and skill, as well as psychological stability." They would then undergo seven years of training and testing, including time in mock Mars colonies — all to be chronicled in a revenue-yielding Survivor-style television series — to make the final cut.

Would living on Mars be dangerous?
Scientists have serious concerns about the health risks of long-term exposure to radiation, reduced gravity, longer days, and extraterrestrial atmospheric conditions. Astronauts are known to experience bone degradation, muscle loss, and swollen optic nerves from spending too much time in zero gravity. A Russian-sponsored experiment called Mars 500, in which six men were confined for 500 days under conditions meant to emulate a Mars mission, showed that Mars travelers could face severe sleep disturbances, lethargy, and depression. Scientists also worry about the Martian surface's ultra-fine dust, which contains highly chlorinated salts called perchlorates that can cause respiratory problems and thyroid damage. And there's a chance, however slim, that Mars harbors potentially virulent microbes.

What would daily life on Mars be like?
Martian colonists would need a base large enough to contain comfortable, long-term living quarters and a vast array of life-support systems and supplies. They would have to construct their pressurized, air-tight habitat in phases, much the way the International Space Station was built. A secure, long-term food supply would be crucial. One company is working on 3-D printers that would combine powders and concentrates to create foods that replicate the textures, flavors, and smells of natural foods. Eventually, Martian farmers could grow food in pressurized greenhouses, using genetically modified crops to compensate for the planet's high radiation and low sunlight. Volunteers for the commercial missions say that the trade-offs in quality of life would be worth it. "I've had a deep need to explore the universe since I was a kid," said Peter Greaves, a self-employed technologist. "I envision life on Mars to be stunning, frightening, lonely, quite cramped, and busy. But my experience would be so [different] from all 6 to 7 billion human beings. That, by itself, would make up for the factors I left behind."

An insurance policy for human survival
"Single-planet species don't survive," says former astronaut John Grunsfeld. He is among the researchers, astronauts, and space exploration firms who see establishing an outpost on the Red Planet not just as a scientific challenge, but as essential to mankind's survival. Cosmologist Stephen Hawking thinks so, too. "The human race shouldn't have all its eggs in one basket, or on one planet," he says. Should nuclear proliferation, shrinking resources, a growing population, climate change, or a visit by hostile aliens threaten humankind on Earth, a colony on Mars could serve as a lifeboat to keep the species going. "I believe that we will eventually establish self-sustaining colonies on Mars and other bodies in the solar system," Hawking says. But he figures it won't happen "within the next 100 years."