Tracks from NASA's Opportunity rover disappear toward the horizon on the Meridiani Plains of Mars. The rover has been on the planet since 2004.
"I don't know why you're on Mars, but whatever the reason for going to Mars is, I'm glad you're there and I wish I was with you."
That was a part of astrophysicist Carl Sagan's message, recorded a few months before he died in 1996, to the future human inhabitants of Mars.
Some of the earliest science fiction imagined voyages to the Red Planet. We now have the space-faring technology, and getting humans to Mars actually seems within reach. It would certainly involve massive resources and a lot of danger, but some believe the rewards would be massive.
Mission to Mars
A few years ago, President Obama set a more conventional goal for the mid-2030s.
"I believe we can send humans to orbit Mars and return them safely to Earth, and a landing on Mars will follow," Obama said. "And I expect to be around to see it."
Earthlings have actually been visiting Mars since the 1960s, at least our machines have. First there were fly-by missions and then orbiters. Primitive landing vehicles in the 1970s sent back the first pictures.
But the real triumphs began with the robotic rovers that started exploring the surface of Mars in the '90s. Ten years ago, NASA took a big leap forward when it landed the rovers Spirit and Opportunity on opposite sides of the planet.
Even John Grant, a planetary geologist at the Smithsonian National Air and Space Museum and part of NASA's rover mission team, thinks a manned mission is necessary.
Grant tells NPR's Arun Rath that even with the amount of information scientists have learned about Mars in recent years, there is still a lot of it left unexplored. He says what we've seen so far would be comparable to visiting a few national parks on Earth.
"Think if you had all of the continents on Earth to explore and you've only been to a handful of places," he says. "Would you say you really understand Earth?"
Grant says though the robots and rovers are critical to setting the stage for understanding Mars, it is a very slow process. In its 10 years on the planet, the Opportunity rover has traveled about 23 miles. He says humans would be more efficient.
"With the rovers, it's much more of a dragged-out process, simply because they can't do and think like we do," he says. "And because we have to tell them what to do, it just takes longer."
Practicing for Martian life
There are, of course, many concerns about sending people to Mars, and it is not the type of stuff you can sort out after launch. Once you're off, it's a long trip; the shortest round-trip ticket would take more than a year.
So here on Earth, scientists are conducting experiments at sites built to simulate these long-duration missions. University of Hawaii professor Kim Binsted is the principle investigator at one of these sites, located on one of Hawaii's volcanoes. The sites have no plant life or human activity visible.
"It's not the Hawaii you're used to thinking of and seeing ads for tourism," Binsted says. "It's very small."
In a small, 1,000-square-foot geodesic dome, six scientists live and work for months. That space includes their workspace, sleeping areas, kitchen and laboratories. And just like on Mars, the crew can only go outside in mock spacesuits. A recent mission finished in August was all about food, including cooking with the stable shelf food they will be traveling with.
"When you start talking about the surface of the moon or Mars, there's enough gravity there to keep the ingredients in the bowl," she says. "So that enables basic cooking."
The crew cooked everything from borscht to dumplings and even baking cakes, Binsted says. No fresh food though, so no salads on Mars.
Binsted says they have funding for subsequent missions that will look at growing food as well as the psychological concerns like crew cohesion and crew performance under the harsh conditions.
"Basically, how to support a crew and pick a crew so that they don't end up wanting to kill each other," she says.
There and back again
Getting to Mars is only half the problem. Getting back is another thing entirely.
Just think about all it takes just to get a simple satellite from the ground into Earth's orbit. Now imagine launching a trip home from Mars. How do you pack your own launch pad, rocket and the ridiculous quantity of fuel it takes to get home?
One group of Mars enthusiasts is getting around all of that by saying to simply forget going home.
Mars One is a Netherlands-based nonprofit that has a goal of establishing a permanent, sustainable human settlement on Mars by 2025. First, they'd send a set of robots to build a habitat and stockpile water. But their plan still faces serious problems, like potentially lethal levels of radiation on the surface of Mars and the extreme weather.
There's still a lot of money to be raised, and the company is looking to crowd-funding for some of it. John Logsdon, the former director the Space Policy Institute, says the idea is more fantasy that fact in his mind.
"[It's] not clear what they would do when they get there except be there," Logsdon says. "It's not impossible, but I think it's highly implausible."
That implausibility has not deterred more than 200,000 people across the world from applying to the program, willing to risk it all for that chance.
"Everything I have done academically and professionally has been for one reason: to leave this Earth and represent humanity on Mars," says 25-year-old Lt. Heidi Beemer. She and University of Hawaii's Binsted are among the more than 1,000 people who made it to the second round.
"I actually decided and told my parents when I was 8 years old that I was going to be an astronaut and go to Mars," Beemer says.
Beemer is an Army chemical defense officer with the Fort Campbell's 63rd Chemical Company in Kentucky. To most, the concept of a one-way trip to another planet seems daunting and disturbing, even crazy. Beemer's mind is made up.
"The thought of being afraid or having the fear of the fact that I'm going to die on a different planet doesn't really bother me," she says, "because this is something that will help out humanity for years and years to come."
Beemer's passion for the Red Planet goes back to an article she read in 1997 about the landing of NASA's Sojourner rover. She says that when she saw what a little rover was capable of, she knew we needed to send people there.
Buy the ticket, take the ride
Mars One plans to have the final round of astronauts selected in 2015 — about 40 or 50 applicants. They'll spend the next decade training at stations just like the one in Hawaii. Starting in 2024, the first set of four astronauts will set off on the one-way journey. Beemer says she's already connected with some of the other applicants on their Facebook group.
Beemer has a long way to go in the selection process, but even if her Mars One plan doesn't work out, she believes "it's just a matter of time" before there will be other opportunities.
"Regardless, my goal is to continue getting people excited about space," she says. "Getting the younger generations excited about the project is something I'm going to continue doing for the rest of my life, whether I'm on Earth or on Mars."