'The Martian' just scratches surface of danger on Mars

Martians are not the villains. Mars is. At least, that's the message in the new big-screen space thriller "The Martian."

After an astronaut is stranded alone at a Martian research base, the planet does its best to starve, suffocate, and freeze the puny human. Yet the perils in the movie are just a taste of the challenges that Mars will throw at humans who try to keep themselves alive on the surface.

Space experts say the film, which opens nationwide Friday, paints a plausible vision of Mars exploration – "the best space movie since '2001,' " says Robert Braun, NASA's former chief technologist for NASA – but glosses over some of the worst character traits of by the planet next door.

Some of the dangers brushed off in the movie could ensure that "The Martian" remains solidly in the camp of science fiction for a long time to come. Among the possible hazards:

- Dust. Moon dust made the Apollo astronauts sneeze and gummed up their spacesuits. Mars dust could be even worse. On the moon, dust settles quickly, but on Mars, the winds keep dust aloft, says Braun, now at the Georgia Institute of Technology. Even worse, the Martian soil is full of a toxic salt called perchlorate, which causes thyroid malfunction.

"If the amount of perchlorate that's in the soil of Mars were in your backyard, the EPA would turn your yard into a Superfund site," says Chris McKay of NASA's Ames Research Center. The perchlorate level on Mars "is thousands of times higher than the highest limit that's acceptable for human exposure." NASA plans to keep dust at bay by having astronauts leave their spacesuits outside, which would mean a lot less dusting for the crew.

- Radiation. Unlike Earth, Mars has only a wispy atmosphere and no protective magnetic shield. As a result, galactic radiation bombards the planet's surface. The best protection would be a thick layer of water or Martian soil. That glass-walled residence that shelters Matt Damon in "The Martian"? "I wouldn't use it. I'd want a big, deep hole," says planetary Ray Arvidson of Washington University in St. Louis.

A Mars expedition would expose a crew to more radiation than NASA guidelines permit and would lead to a slightly higher cancer risk, says Jim Green, NASA's director of planetary science. The trip to and from the planet, rather than the surface sojourn, is the more dangerous phase. But a big solar storm that unleashed a cascade of radioactive particles into space could be lethal to humans on the planet's surface unless they took shelter.

- Reduced gravity. Martian gravity is roughly one-third the gravity on Earth. Experiments on the International Space Station show that plants, animals and humans all suffer in weightlessness, but no one knows how living creatures will fare in reduced gravity.

"Maybe plants will be happy, maybe animals will be happy, maybe humans will be happy," McKay says. "Or maybe not." The effect of reduced gravity isn't easily tested ahead of time and though probably not a huge problem, it could be a "showstopper," McKay says.

Mars madness. On Mars, astronauts will cope with long delays in their communication with Earth and the knowledge that if they get into trouble, no one can help them. The sense of isolation will be heightened by what's known as the "Earth-out-of-view" phenomenon: Mars crews will see Earth as a tiny star in the sky, and it's not clear how humans will respond to such a bizarre and unprecedented sight.

Studies of polar explorers and other groups show that isolation and confinement can lead to depression, sleep problems and loneliness, which can in turn sap crew members' energy and judgment. In "The Martian," Matt Damon's character maintains a wisecracking good cheer for the duration. Just such a sense of humor will be crucial for humans making a genuine trip to the planet, says human-performance expert Jason Kring of Embry Riddle Aeronautical University.

Despite the long list of threats posed by Mars, it also boasts soil that could be tilled and, as scientists revealed earlier this week, liquid water. There's plenty of carbon dioxide to supply plants and to be processed to make oxygen.

"We will discover more issues that we need to address, but they're also unlikely to change the basic story," McKay says, "that this is indeed a place where humans can live and work."