Humans could be walking on Mars within the next couple decades, for only a fraction of the cost the United States has already budgeted for space exploration.
How? The answer is simple, say a pair of Mars researchers: Give the explorers a one-way ticket.
The most costly and tricky part of any manned space mission is providing life-support for its human crew: food, oxygen, and protection from radiation and other hazards of space travel. On a human mission to Mars, most of the cost – some 80 percent of it – would involve returning the crew to Earth, say Dirk Schulze-Makuch and Paul Davies in the October-November issue of the Journal of Cosmology. Rather than quintuple the cost, those funds could go toward building a permanent settlement, the two scientists argue.
They propose that, after several unmanned missions drop supplies at a base station on the Red Planet, two spacecraft carrying two humans each would be sent on the six- to eight-month voyage to Mars to begin the first human colony on another planet.
Further missions would continue to supply the first settlers, who would be older, beyond child-bearing age, and – of course – volunteers.
Eventually, as the colonists made more use of Mars' own resources, including water trapped as ice, they would be joined by more migrants from Earth.
"It's not a suicide mission at all," argues Dr. Schulze-Makuch, coauthor of the paper and an associate professor at the school of earth and environmental sciences at Washington State University in Pullman.
Mars, he admits, "will never be a second Earth, you know, our home planet. But it's feasible to have people staying for a long time, and people living there, actually."
Last spring, President Obama put forth a set of new goals for US space exploration, including sending astronauts into orbit around Mars by the mid-2030s and returning them to Earth. While Mars has a much weaker gravitational field than Earth's, the pull is significant, which would mean that ferrying astronauts to and from the Martian surface would be an additional challenge requiring more resources.
As Schulze-Makuch and Dr. Davies, a professor at Arizona State University, have promoted their idea, many people have stepped forward to volunteer for such a mission, they say.
One-way trips of colonization are common to human history, the authors argue. Most of the early settlers coming by ship to America had little hope of ever returning to Europe.
"They knew that they would never be coming back," Schulze-Makuch says.
Colonist-scientists living on Mars could produce a bonanza in basic research, the authors say. That would include a better understanding of the origin of Earth itself, and perhaps even the discovery of the first extraterrestrial life.
And in the long term, a Martian colony would be a huge first step toward humans moving away from Earth. Famed theoretical physicist Stephen Hawking has been among those arguing that because of the chance of a disaster on Earth, humans must start moving out into the solar system.
But these kinds of scientific and long-range concerns haven't really spurred the history of exploration here on Earth, points out Michael Robinson, a historian of science at the University of Hartford in Connecticut. Most explorers from Columbus to Lewis and Clark set forth with "mercenary and pragmatic goals," such as finding a new trading route to Asia.
The idea that humans have an innate urge "to boldly go where no one has gone before" is more myth than fact, Dr. Robinson says. Throughout most of history, humans have been "moving toward a more settled lifestyle," moving from a nomadic life into towns and cities. In general, "people don't want to die out in a wilderness," he says.
A fundamental debate over what is exploration lies beneath the discussion of human missions to Mars, Robinson says. Already, unmanned Mars rovers called Spirit and Opportunity have done amazing things. Another called Curiosity is set to land in 2012. "They're getting piles of data, really great data" for scientific study, Robinson says.
Yet for some in the space community, "robots don't really count" as true exploration, he says.
Exploration of Mars will require "very subtle forms of perception and on-the-spot intuition," argues Robert Zubrin, founder and president of the Mars Society, in another article in the Journal of Cosmology. "All of these skills are far beyond the abilities of robotic rovers.... Drilling to reach subsurface hydrothermal environments where extant Martian life may yet thrive will clearly require human explorers as well.
"Put simply," he says, "as far as the question of Martian life is concerned, if we don't go, we won't know."
Dr. Zubrin has set out his own plan to send humans to Mars – and return them. But he has no problem with a one-way expedition. "Life is a one-way trip," Zubrin says. "If you don't go to Mars, you're going to die on Earth. You're going to die somewhere."
He sees a one-way ticket to Mars as a Plymouth Colony scenario, in which more and more 17th-century English settlers slowly joined the original colonists in Massachusetts Bay.
Or, perhaps colonizing Mars is more akin to hitting the beach at Normandy, Zubrin says, referring to the invasion of Europe in World War II. The rationale would be "no matter what it takes, we'll take the beach," he says. "We may well run into problems, but we'll send more of everything. We're prepared to send more machines, more people, more supplies until the beach is taken."
But will the US and other nations offer that level of commitment? Is talk of scientific advances, national pride, or the need to someday abandon Earth enough to justify backing a colony on Mars in the near future?
Once humans arrive on Mars, support for them would have to continue uninterrupted for decades to come, despite changing economic or political conditions back on Earth.
A Mars colony could end up being like "your annoying crazy cousin in the basement" that you have to take care of, says Penelope Boston, an associate professor of earth and environmental sciences at the New Mexico Institute of Mining and Technology in Socorro, N.M., who for many years has studied the problems of supporting human life on Mars.
The practical issues of sustaining a long-term human colony on Mars are substantial. Just protecting the colonists from the much higher levels of radiation on the Martian surface would seem to be "a real showstopper," she says. (Schulze-Makuch and Davies argue that naturally occurring lava tube caves could provide ready-built shelters from radiation.)
All in all, "it's a stupefying task," Dr. Boston says. A Mars colony "is more likely to founder on human psychology and behavior and political considerations than any technical consideration."
If we're expecting the US, or even a coalition of countries to fund the colony, she asks, "What is the return? Why would they?"
Perhaps new options will present themselves. Robinson imagines a kind of "virtual" space exploration, where instruments send back data so complete and realistic that earthbound humans feel almost as though they've visited the Red Planet themselves.
But for some, nothing will replace making their own boot tracks in the Martian dust.
"I still have small kids I would like to see grow up, but otherwise, yes, I would go" on a one-way expedition to Mars, Schulze-Makuch says.
"I would be one of the first people on another planet and would experience seeing those canyons, those huge mountains. That would be just thrilling.... There would be so many things on the positive side for me as a scientist. It would be incredible."