The Sands of Mars

Some information about the mechanical composition of the top meter or so of Martian soils could be gained by ground-penetrating radar or other sounding devices, Sture points out, but much deeper and you "probably need to take core samples." NASA's Phoenix Mars lander (landing 2008) will be able to dig trenches about a half-meter deep; the 2009 Mars Science Laboratory will be able to cut out rock cores. Both missions will provide valuable new data.

Credit: Stein Sture Mars-cranes might use vibrating buckets for excavation.

To go even deeper, Sture (in connection with the University of Colorado's Center for Space Construction) is developing innovative diggers whose business ends vibrate into soils. Agitation helps break cohesive bonds holding compacted soils together and can also help mitigate the risk of soils collapsing. Machines like these might one day go to Mars, too.

Another problem is "hoppers" - the funnels miners use to guide sand and gravel onto conveyor belts for processing. Knowledge of Martian soils would be vital in designing the most efficient and maintenance-free hoppers. "We don't understand why hoppers jam," Jenkins says. Jams are so frequent, in fact, that "on Earth, every hopper has a hammer close by." Banging on the hopper frees the jam. On Mars, where there would be only a few people around to tend equipment, you'd want hoppers to work better than that. Jenkins and colleagues are researching why granular flows jam.

And then there's transportation: The Mars rovers Spirit and Opportunity have had little trouble driving miles around their landing sites since 2004. But these rovers are only about the size of an average office desk and only about as massive as an adult. They're go-carts compared to the massive vehicles possibly needed for transporting tons of Martian sand and rock. Bigger vehicles are going to have a tougher time getting around.

Mars rover Spirit, an artist's rendition. Spirit and her twin Opportunity have been roaming Mars since January 2004.

Sture explains: As early as the 1960s when scientists were first studying possible solar-powered rovers for negotiating loose sands on the Moon and other planets, they calculated "that the maximum viable continuous pressure for rolling contact pressure over Martian soils is only 0.2 pounds per square inch (psi)," especially when traveling up or down slopes. This low figure has been confirmed by the behaviour of Spirit and Opportunity.