Two of NASA's finest are being readied for far-off duties on Mars.

Dispatched to different regions of the red planet, the pair of wheeled robots are expected to explore and analyze the world like never before.

Last month, after an exhaustive appraisal of some 185 potential landing sites, Mars officials whittled away at candidate locales. They finally came down to two spots of prime, equatorial martian real estate.

The target zones selected fulfill two crucial requirements: they will allow for high-quality science and assuage engineers "not too" worries. That is, the sites are not too dangerous. Not too steep. Not too rocky. Not too hot or cold. And not too dusty.

If all goes well early next year, dual Mars Exploration Rovers will settle in for science at Meridiani Planum and Gusev crater. Both places show intriguing evidence for past liquid water and may reveal telltale signs of ancient, perhaps even present-day life on Mars.

To say that Mars scientists are eager and ready for action is to state the obvious.

Athena team members gathered last week at JPL, practicing two days of MER surface operations.

The simulations helped hone the skills of the science teams in their use of software to analyze science data. Also, the teams ran through ways to keep tabs on the health of Athena instruments, as well as train themselves to set up day-to-day commands for gathering science at Mars.

"Give them a pair of working rovers and they will read the rocks and tell us all the 'water story'," said James Garvin, Mars Exploration Program Scientist at NASA Headquarters in Washington, D.C. "Rocks are Mother Nature's artifacts and they never lie. All we have to do is decipher their messages. Our MERs are outfitted to do so," he told SPACE.com .

Combining the agility to saunter over to rocks recognized as interesting after "on-the-ground" reconnaissance from a rover -- given a mix of tools all geologists would like to have -- is a "breakthrough step," Garvin noted.

"We have never flown a real mineralogy sensor to the surface of any planet before, so this is another breakthrough. Add to these major advances, the RAT allows us to get through the ubiquitous dust and other weathering rinds that appear to have affected most rocks. The MER science capabilities are literally 'light years' beyond those we had on the Pathfinder/Sojourner rover," Garvin said.

Garvin salutes the Mars Global Surveyor and the Mars Odyssey - both still busily at work as they orbit the red planet.

"We have reached new milestones thanks to those spacecraft. Indeed, the new Mars that is emerging is far more interesting, complex, and with all sorts of potential," Garvin said.

MER will allow scientists to understand one possible path that Mars may have taken- namely, that of preserving its record of a former wet time in which liquid water existed at the surface in a persistent way," Garvin said. "MER will make breakthroughsbut we just cannot predict how so," he explained.

"I think we have a great match of instruments to test different scientific hypotheses at Gusev and Meridiani," said Catherine Weitz, MER Program Scientist at NASA Headquarters. "We intend to use the

Athena science instrument suite on each rover to decipher the past water activity at both sites," she said.

In the case of Gusev, Weitz explained, the hope is to identify evidence of a lake within the crater, and sediments that were deposited in that possible lake. MER instruments could show diagnostic minerals and

layering that would support deposition of material within a standing body of water.

At the Meridiani site, snooping out the mineral hematite is a major MER undertaking.

"We know that on Earth hematite generally forms in association with liquid water, but this isn't always the case," Weitz said. "So we will use the instruments on MER to identify landforms and other minerals that could have formed in association with the hematite to determine which process most likely deposited the hematite and if it involved liquid water," she said.

Nathalie Cabrol is a planetary scientist with the SETI Institute and works at NASA Ames Research Center at Moffett Field, California. Along with husband and physicist, Edmond Grin, the two have been giving Gusev birds-eye looks for some 13 years through the sensors of various spacecraft.

Matching their talents, they have studied where the lakes could have been in the crater, trying to pin down their variations in extent and depth through time.

"Now we will have the privilege to see this site from the ground," said Cabrol. "Although space missions are more numerous today, they are still rare events and this is a chance of a lifetime," she explained.

"As a geologist, this is as close as it could get from being in the field...unless I am able to go to Mars in person one day, which I am still hoping for," Cabrol told SPACE.com .

Safely landing MER inside the crater allows for an on-the-spot assessment. To see whether or not a river and lake system at Gusev truly exists.

Is Cabrol afraid of a little "ground-truth"?

"Not one minute. This is where all the excitement is. If we are right, fine. Let's celebrate because we will have found a most interesting and promising site to explore, telling the tale of long gone lakes and shores now silent," Cabrol responded.

"If we are wrongwell, we better rethink seriously what we believe about water and channels on Mars. Finding out what could have caused us to possibly misinterpret the site will be scientifically extremely important for our understanding of the history of Mars," Cabrol said. MER is heading toward a wonderful mission of exploration and discoveries, she added.

The Mars robots are outfitted with geologic instruments rather than biologic life-detection instruments. It is unlikely then, Cabrol said, that the rovers will find direct evidence of past or present martian life.

But the rover missions will likely be successful in determining whether the past environments when the rocks formed were favorable for life, and in determining the likelihood of preservation of fossil life in those rocks, she added.

"We have only a tiny window in the history of these sites that we will be able to explore and only limited

ground we can cover. Still, this is our chance and we will take it," Cabrol said.

"If Gusev was the lake we believe it was, its potential to shed some light on life on Mars could be

significant. Lakes are favorable environments for life, for its inception, development, and for its preservation as fossils," Cabrol concluded.

Halfway around the planet from Gusev is Meridiani Planum. It is this area that features deposits of an iron oxide mineral called hematite.

"It is literally a God-given site. It's scientifically compelling. It is at the equator, and at low altitude. Also it is flat, rock free, and the temperatures are just right," said Philip Christensen, a leading Mars planetary geologist at Arizona State University in Tempe. He is a strong advocate for Meridiani having a chemical signature of past water. Gray hematite is usually, but not always, produced in an environment where there is liquid water.

There are several ways hematite results from water-related activity: Standing bodies of water; ground water systems; an atmospheric water coating on rocks; as well as rainfall. But it can also be created as a by-product of volcanic processes, having nothing to do with water.

"Even if it doesn't turn out to be as water-related a process as I think it will besomething unique happened there," Christensen told SPACE.com. "I think it is a high probability that water was involved in that process. In my mind, you can't get closer to 'follow the water' than some place where there are minerals that formed in water."

"Whatever the case, Meridiani is an interesting place to go look," Christensen said. "You go. You land. And you look," he said.

When the rover gets up and running at Meridiani, Christensen said, the first images and data relayed to Earth should be immediate and telling about hematite status.

One possibility is spotting finely layered lake sediments.

"I don't expect this, but if those are seen, any type of organism that lived in that lake, even bacterial mats, might be found as a real thin layer. The most interesting data may come out of Athena's Microscopic Imager," Christensen said. "I'm going to look really hard at the details of those layers."

The findings at Meridiani may be so compelling, Christensen added, that a future return sample mission to the site could be warranted. "Or the MER could land and find a volcanic lava flow. That would say don't bother to come back."

Given the first images relayed from the rover, seeing flat, sedimentary rocks would be fantastic, Christensen said. "I'm going to vote for flat rocks."

Christensen said his eye is quickly going to gravitate to two things at Meridiani. "One is to look for rocks that are layered. Also, to look at the horizon and find a buttea little hill somewhere that we can drive to and see exposed layers."

"If the site turns out to be a parking lot and way off in the distance is a hill, then it's easy driving to get there. If the site is really rocky and you can't go very far, you probably don't want to because there's so much to explore. So those are two very reasonable options," Christensen stated.

What if hematite is nowhere to be seen? Would the geologist feel bamboozled by something akin to Fool's Gold on Mars?

"I'll sleep just fine," Christensen said. "But the funny thing is right now, you go to meetings and you think there's 40 people who had all came up with the idea of hematite. But I've got this feeling I know what will happen if we land and it turns out not to be hematite. I'll be looking around for those 40 people. They won't be anywhere near me. They'll be saying, what the hell are we doing at this place?"

"But that's part of exploration. Life is full of risks. And I'm willing to take the chance of being wrong," Christensen said.