Two remarkable vehicles are tooling around, remapping the history of Mars, and a geologist is in the driver's seat.
Bob Anderson of the Jet Propulsion Laboratory in Pasadena, Calif., is a planetary geologist helping steer the Mars Exploration Rovers (MER) -- two robot explorers designed to examine interesting geologic targets on the red planet.
Anderson's role on the MER science team is to work with both the geologic and operational aspects of the rovers, dubbed Opportunity and Spirit, deciding where they go, what targets they choose and how to analyze those targets.
Each machine is equipped with a wide array of instruments and cameras to collect data and beam it back to earth. The gear includes spectrometers, drills, rock hammers, lens and microscopes.
"The only thing we can't do is subsurface exploration," Anderson said. "For the top 10 centimeters or so we're doing pretty good."
Working with remote imagery has its challenges.
"When you can't go and grab a rock in your hand, it's almost like subsurface geology," he said.
"You have to respect the imagery and learn to understand the perspective," he continued. "When you look at some of the old Pathfinder photos from 1997, some rocks look very, very large. They're really not, because the rover was only the size of a microwave."
Anderson put together a desert field test using the "Fido" rover on earth to help scientists learn the machine's abilities and limits and how to interpret the imagery before the Mars rovers were launched.
The mission passed the "success" threshold long ago, Anderson said, adding that both rovers have exceeded their "warranties" in spectacular fashion.
The robots were designed with a goal of traveling at least 600 meters and relaying data for 90 "sols," or Martian day.
They have traveled about four kilometers and passed the one-year anniversary of the landings in January, still rolling and collecting data.
One major goal -- finding evidence of water in Mars' past -- was accomplished quickly.
"Spirit went looking for signs of water, and Opportunity was looking for hematite," Anderson said. "We found both at the Opportunity site. Spirit was all igneous, basalt and dust. But now in a hill it's found evidence of water, although it's not totally understood yet.
"We were looking for outcrops and layering," he said. "The odds of landing right next to an outcrop are slim, but we did it with Opportunity.
"A year ago we would have said the mission was a success," he commented. "Now we drive by an outcrop and go, 'Yeah, that's just an outcrop.'"
Much of the information coming back has been confirmative rather than surprising, but it will "probably rewrite the history books with respect to Mars," Anderson said.
No indications of life have been found.
Aeolian materials, basaltic rock, impact-dominated areas with shock type features were predictable, he said -- but still unexplained is what formed small spheres of hematite.
"MER has dominated my life for the last three years," he said, adding that he hopes to stay with the mission as long as he can.
Now that the scientists have taken the rovers' reins, Anderson concedes that "for the engineers, it's boring.
"We're sort of like the extra person during the development," he said. "If you want an instrument on board, there must be a trade off due to the size and power supply. The engineers give us what we can use ... that's the challenge.
"You have to walk in both worlds so engineering, operations or science doesn't scare you," he said.
Anderson is part of a team of about 100 scientists around the world analyzing MER data. The team, assembled by Steve Squyres of Cornell University, includes atmospheric scientists, engineers, igneous petrologists, geomorphologists, stratigraphy experts and astrobiologists, to name a few.
"We're bringing in more terrestrial geologists to look at the images," he said. "Once you've identified something, you can go out and field research it with the rover.
"Opportunity spotted some beautiful layers of sedimentary rocks," he added. "The only way to do that (research) is to get up close.
"We have demonstrated that you can do field geology with a rover."