The Sands of Mars

Driving, digging, mining: these are things astronauts will be doing one day in the sands of Mars. It's not as simple as it sounds.

Imagine this scenario. The year is 2030 or thereabouts. After voyaging six months from Earth, you and several other astronauts are the first humans on Mars. You're standing on an alien world, dusty red dirt beneath your feet, looking around at a bunch of mining equipment deposited by previous robotic landers.

Echoing in your ears are the final words from mission control: "Your mission, should you care to accept it, is to return to Earth - if possible using fuel and oxygen you mine from the sands of Mars. Good luck!"

It sounds simple enough, mining raw materials from a rocky, sandy planet. We do it here on Earth, why not on Mars, too? But it's not as simple as it sounds. Nothing about granular physics ever is.

Granular physics is the science of grains, everything from kernels of corn to grains of sand to grounds of coffee. These are common everyday substances, but they can be vexingly difficult to predict. One moment they behave like solids, the next like liquids. Consider a dump truck full of gravel. When the truck begins to tilt, the gravel remains in a solid pile, until at a certain angle it suddenly becomes a thundering river of rock.

Understanding granular physics is essential for designing industrial machinery to handle vast quantities of small solids - like fine Martian sand.

The problem is, even here on Earth "industrial plants don't work very well because we don't understand equations for granular materials as well as we understand the equations for liquids and gases," says James T. Jenkins, professor of theoretical and applied mechanics at Cornell University in Ithaca, N.Y. "That's why coal-fired power plants operate at low efficiencies and have higher failure rates compared to liquid-fuel or gas-fired power plants."

Mars soil in 3D, photographed by the Spirit rover in 2004. Put on your red-blue glasses and take a look.

So "do we understand granular processing well enough to do it on Mars?" he asks.

Let's start with excavation: "If you dig a trench on Mars, how steep can the sides be and remain stable without caving in?" wonders Stein Sture, professor of civil, environmental, and architectural engineering and associate dean at the University of Colorado in Boulder. There's no definite answer, not yet. The layering of dusty soils and rock on Mars isn't well enough known.