Twin NASA Rovers to Prospect for Water on Mars

Chad Cohen
National Geographic Today

May 29, 2003

Next month three missions to Mars are scheduled to lift off—two American and one European—in a rush to take advantage of a trajectory between Earth and the Red Planet that only happens every 26 months.

NASA's Mars Exploration Rovers (MER) A and B are twins, to be launched on June 5 and June 25, respectively, bound to land in January 2004 in different areas of Mars—the Gusev Crater and the Meridiani Planum.

The European Space Agency's Beagle II is due to land in Isidis Planitia, where it will stay put for its six-month mission. The compact Beagle II will look for traces of life.

Scientists have tested the rovers and other Mars instruments in what they call the sandbox—a large room at the Jet Propulsion Laboratory (JPL) in Pasadena, California, with volcanic rocks, dirt, and sand that simulate the Martian landscape.

The rovers are robo-geologists. Their goal is to search for water past and present.

"There is strong evidence from orbital missions that liquid water was once [on the Gusev Crater and Meridiani Planum]," says Steven Squyres, a planetary scientist at Cornell University in Ithaca, New York, and a team leader for the scientific instruments in the MER program.

"Mars today is cold, dry, and barren, not particularly friendly to life," says Squyres, "but data from orbiters [like Mars Global Surveyor and Mars Odyssey] suggest a very different history."

Hints of Water

Dramatic images of what appear to be river channels, lake beds, and mineral deposits suggest that Mars may once have been warmer, wetter, and more livable.

The Meridiani Planum contains gray hematite, a mineral that is a "powerful clue" to water's former presence, Squyres says.

In Michigan's upper peninsula, for example, gray hematite formed in deep water bodies millions of years ago. Deposits also appear in hot springs and in fine veins in underground rock where cold water trickles through.

The Gusev Crater is completely different from the Meridiani Planum, says Squyres. "It is a big hole in the ground with a water-carved channel, or dry river bed, running into it. If you know how to make these formations without water, tell me about it."

MER A and B differ significantly from the pioneering rover, Sojourner, which began exploring the Mars surface on July 4, 1997, during the Mars Pathfinder expedition. Sojourner carried a single scientific instrument and only roamed about 100 yards (91 meters) from the mother ship.

MER is a 400-pound (180-kilogram), 5-foot-square (1.5-meter-square) all-terrain vehicle with a platform rising about 3.5 feet (1.0 meters) above the ground. Each rover carries nine cameras, five scientific instruments, and a robotic arm with geological instruments.

Every Martian day (37 minutes longer than Earth's day), MER will travel about 44 yards (40 meters). The rover has the potential to cover about three-quarters of a mile (1.2 kilometers) during its estimated three-month life span on the Red Planet.

Robot Geologists

"It is going to drive around and do a lot autonomous things on Mars and at least twice a day it'll call home, tell us what it has done, what its seen, and we'll give it commands about what it's going to do next," says Randy Lindemann, lead engineer of the rover design team at JPL.

The rovers' tools can penetrate Martian rocks to get a closer look.

"Geologists on the Earth want to get inside the rocks because often times the outsides are coated or altered by interacting with the atmosphere and water," says Joy Crisp, a geologist and MER project scientist at JPL. "[If] you want to find out how the rock formed you crack them open with the rock hammer."

MER is equipped with a Rock Abrasion Tool, nicknamed RAT, that drills a two-inch (five-centimeter) diameter hole in a specific rock sample and allows the scientists to peer inside—from more than 120 million miles (200 million kilometers) away.

A microscopic imager at the end of the robotic arm acts like a geologist's hand lens, revealing the texture and particle structure of minerals. Three types of spectrometers can also analyze the chemical composition of a specimen.

"That may tell us that a rock was erupted by a volcano or was laid down by water or some other process," Crisp says.

First the rovers must safely touch down on Martian soil. They bounce on the surface in an air bag cocoon, and then emerge from the lander—one of the trickiest stages of the entire operation.

Large rocks or a steep slope could tip over the rover, derailing each U.S. $400 million mission.

That's why the scientists at JPL are rehearsing Martian maneuvers in the sandbox, which may come in handy again in January. Should the rover get stuck, the JPL scientists can troubleshoot a solution there.

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