The Not-So-Big Dig

With the equivalent power of an electric can opener, engineers try to do more than scratch the Martian surface.

A prototype of NASA's Phoenix Mars Scout stretches its 6.6-foot-long arm to scoop soil at Death Valley National Park in California. On Mars, the probe will dig a trench up to 20 inches deep to analyze the history of surface ice. (NASA)
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Planetary geologist James Dohm doesn’t mean to disparage when he says Idaho Falls is a lot like Mars. A large, gentle man who has spent 19 years at the University of Arizona mapping the red planet, Dohm sees exceptional possibilities in this city of 50,000 people on the west side of the Teton Range.

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Idaho Falls straddles the Snake River headwaters a couple hours’ drive southwest of Yellowstone Park, where the Rockies smooth out into central Idaho’s sage-studded flatlands. But what makes it special, Dohm says, is what lies beneath—a layer of basalt that is similar to much of the crust of Mars. Basalt—a dark-colored, fine-grained igneous rock rich in iron and magnesium—is one of the barriers that planetary scientists will have to penetrate to get beneath the Martian surface. NASA is preparing now for drilling operations to better understand the planet’s evolution and perhaps answer one of its biggest mysteries: Did life ever exist there?
“Basalt is one of the hardest rocks on Earth,” Dohm says. “If we’re going to bore a hole in Mars, we need to get good at drilling into basalt.” Doing so with small but sturdy tools that haven’t quite been invented is the challenge.

As with the Earth, the surface of Mars is blanketed with regolith—loose sand, dust, rocks, and minerals deposited atop bedrock by meteors and spread by wind and erosion. Add to that eons of solar radiation bombarding the planet and you can be almost certain that no life remains on the surface. The logical step, for Dohm and other scientists, is to drill.

But deciding when, where, and how deep to drill will drive site selection discussions in the Mars exploration community for the next few years, just as such concerns kept Apollo-era scientists busy deciding where on the moon NASA astronauts should land and go prospecting.

On Mars, “there’s evidence of internal heat sources,” Dohm explains. In theory, that heat could sustain underground life. Data from orbiting spacecraft strongly suggest the presence of both hydrothermal and volcanic-driven heat flowing to the surface. “We are looking at a dynamic planet,” he says.

To go after the secrets beneath Mars, scientists can drill either into rock or ice. Drilling in rock may help them understand the geologic record of Mars, while drilling in ice could provide clues into the biological past. Since there won’t be astronauts along at first, making the drill autonomous is one of the biggest hurdles NASA faces.

So far, the space agency has had limited experience in extraterrestrial drilling. The Apollo astronauts hammered, raked, scooped, or drilled for the 842 pounds of moonrocks they brought home. The drilling, in particular, was difficult, as Apollo 15 astronauts David Scott and James Irwin, who landed on the moon in July 1971, can attest.

In boring a hole at Hadley Rille, Scott ran into trouble when the battery-powered drill jammed at about 5.5 feet. He gave up trying to wrestle it out of the lunar rock. The next day, he and Irwin manhandled the drill and its core sample out of the hole.

The problem was a key flaw in the drill’s design: Its threads were not carrying the cuttings to the surface. Instead, the cuttings were getting clogged in the hole, binding the drill stem. (Nevertheless, later X-ray analysis of the core showed 58 separate layers of regolith along with various pebbles and an increasing density down to the bottom of the core.) NASA fixed the problem on later flights. On Apollo 16, Charlie Duke drilled to the full eight feet in about one minute. On Apollo 17, Gene Cernan did it in just under three.

Robotic spacecraft also have used drills. The Soviets put drills on their Luna soil-sample return probe to the moon (capable of penetrating about 13 inches) and Venera spacecraft to Venus (just over an inch) in the 1960s and 1970s. The European Rosetta mission, which launched in 2004, is designed to land on a comet in 2014, drill down about eight inches and analyze the contents.

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