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Way Cool Scientist! Robert Sullivan

The rovers can learn a lot by cruising across the martian landscape, but in order to unlock mysteries lurking just below the surface, they must break ground. Now, there's one problem with this scenario: the rovers are not equipped with shovels. That's why Rob Sullivan, our latest Way Cool Scientist, along with his MER science team colleagues, have been developing strategies to penetrate the Martian exterior. The technique that they have developed is called "trenching."

Rob testing the rover wheel action.
Trenching involves using one wheel of the six that are available on each rover. Five of the six wheels are immobilized while the sixth rotates. As the sixth wheel spins, it plunges into the surface instead of rolling forward. Wherever soil is deposited in layers, a small trench can expose those layers, revealing the geological story of the site.

Each wheel is made out of a single piece of cast aluminum, and it's almost completely hollow to save weight. The spokes are fashioned with spiral patterns as opposed to straight lines, and they're filled with foam--this gives the wheel shock absorption. Most importantly, the wheel is big enough to take a rover just about anywhere the scientists want it to go. Now, common sense tells us that the bigger the wheel diameter, the easier it is to navigate rugged and irregular terrain, but that's not the only benefit of having a big wheel. It also helps to dig trenches.

Martian soil is derived from weathering processes affecting Martian rocks. These processes may or may not have included water. Recent results from the Mars Odyssey spacecraft suggests that there is an abundance of water ice near the surface in regions where the Rovers have landed.. By digging a trench, it's possible a rover could expose some of that ice or at least measure the release of water vapor from freshly dug soil.

Rob and the Rover in the lab.

Before the mission began, Rob spent most of his time in the lab, experimenting with exotic soils from around the world. In one type of experiment, colored sand was poured into a sandbox so that the scientists could keep track of the different layers as the rover penetrated the surface. Rob conducted a series of rotations to gradually dig into prepared targets. The product and effect of each rotation was photographed and documented. By observing this process, scientists were able to estimate how well the wheel could excavate soil at different levels below the surface. Once a trench was created, the scientists could examine the patterns that were left by the color-coded soils--the patterns tell the story of how different types of soil are distributed under the surface. For Rob, digging trenches is an intrinsically fun activity. "To do my science, I have to make the rover move," says Rob. "The rover is my Tonka and Mars is my sandbox."

During the mission, scientists receive data from the rovers and decide when and where to dig a trench. The experimentation and rehearsal in the "sandbox" has provided the science team with the skills to summon the rovers to dig trenches in diverse conditions. "We have to make sure that these trenching sequences are in the bag, so that it's not such a difficult thing to do under pressure of operations," says Rob.

Rob is a Senior Research Associate in the Department of Astronomy at Cornell University in Ithaca, New York. He is a full-time researcher, and occasional guest lecturer. Since receiving his Ph.D., he has participated in several NASA flight projects: Galileo, Mars Global Surveyor, Mars Pathfinder, and now the Mars Exploration Rover mission. For MER, he's a member of the science team, but he's also been trained as a Payload Downlink Lead for the Pancam and the Microscopic Imager instruments, as well as Payload Uplink Lead for Pancam. Whether he's working in one of the instrument back rooms or in the Science Assessment area, his primary job is to keep the rover busy with the highest priority observations and commands.

For Rob, Mars is a whole new world, all it's own. "When Mars seems alien compared to what we know about Earth, that's fascinating," says Rob, "and when Mars turns out to be earth-like in one way or another, that can be even more fascinating." As a member of the MER science team, Rob has played a key role in developing innovative strategies to unearth new clues about the Red Planet's past.