Clark said that the environmental conditions found by Opportunity are not incompatible with some bacteria we know about here on Earth. The robot, however, is not outfitted with the right science gear to measure organic materials, he said.
The Phoenix Mars lander in 2007 is equipped to dig down in the martian topside and probe for ice. "It will be very important to get down and see if ice is really there. Finding organic compounds in that ice would be another huge smoking gun for life," Clark said. The follow-on Mars Science Laboratory in 2009 could carry sophisticated drilling gear to help understand what lies beneath the martian landscape, he said.
Clark said the Opportunity landing site at Meridiani Planum is a great place for building up a human outpost.
New generation of instruments
The Opportunity findings show that the strategy of "follow the water" was the right direction to pursue, said Geoff Briggs, Scientific Director of the Center for Mars Exploration at the NASA Ames Research Center at Moffett Field, California.
Briggs said that the forthcoming Mars Science Laboratory mission will carry a new generation of instruments to help decipher "in the field" the history of the red planet.
The prospect of a returning to Earth soil and rock specimens from Mars next decade, while sure to be scientifically rewarding, would also flex the technology muscle to eventually send humans there, Briggs said.
Over the years, Briggs said, robotically returning samples from Mars has been inhibited by two things: high cost and high risk.
The NASA initiative that calls for humans to Mars in the foreseeable future, Briggs said, should give more programmatic support and the funds to make a robotic return sample effort happen before astronaut explorers set foot on the planet.
Briggs said that, ever since the Viking landers of the mid-1970s, robotic missions to Mars show the orders of magnitude difference between humans and automatons - in terms of speed and job performance.
"I've always been an advocate of sending human explorers to Mars because the science is very challenging and humans will do so much more in a fraction of the time," Briggs stated.
Nail in the coffin
Not to take anything away from the robots, Spirit and Opportunity also show their limitations when put up against flesh-and-bone investigators.
"I’ve maintained for some time now that Gusev was going to be a difficult story to untangle…and I think that was a correct prediction," said Ronald Greeley, planetary geologist from Arizona State University and a Mars Exploration Rover scientist.
The Athena science package carried on both Spirit and
Opportunity is well-suited to investigate Mars, Greeley said. "You have to take
all the pieces and put them together. No one of them is likely to be the nail in
the coffin," he told SPACE.com .
Greeley underscored the fact that the robots are doing an impressive job at Gusev Crater and Meridiani Planum. However, the robots also point out just how invaluable humans are in conducting on-the-spot science.
Slow-going science
One early message from Mars, Greeley said, is the slow-going nature of Spirit and Opportunity machinery. Even the easiest of tasks performed by a human, when attempted by the robots, turns into a painful process, he observed.
"The frustration does enter when you want to go from here to over there and do something. The rovers have got to go through an awful lot of machinations just to do the simplest of things," Greeley said.
Compared to robots taking a day or two on Mars to perform duties, human explorers could quicken the pace of work.
"The eye-brain is a marvelous combination of things that machines can’t begin to touch. The things Opportunity is doing at the outcrop, humans could do pretty quickly," Greeley said.
As example, a human standing where Opportunity is now exploring would not be fooled when eyeing the outcrop of rocks. For the robot, the viewing geometry and illumination it surveys are fixed, Greeley said. A flesh-and-bone geologist could instantly move about to rapidly consider whether or not a scientific interpretation was or wasn’t correct.
"With the rover, you’ve got a fixed perspective. You don’t have the luxury of doing a lot of finagling," Greeley added.
Mars underground
Similar in view is Penny Boston, Research Associate Professor of Cave and Karst Science at New Mexico Tech’s Department of Earth and Environmental Science in Socorro, New Mexico.
"Let any of us go up there with a geology hammer and a good microscope. We’d already have a lot of answers. But keeping us alive, that is really the sticky point," Boston said.
Boston said that the rover work on Mars has been impressive. But it’s clearly not the last word on the problems of underground Mars – where ground water and brines still could exist, along with martian biology that might be alive and well today.
"I’m excited about the surface water…but it’s pretty premature to draw any serious biology conclusions," Boston said.
Opportunity’s water find is vindicating, Boston said, and blows open the whole issue of looking for sedimentary rocks.
"There’s clearly a lot of sedimentary action that has gone on in the past. And where there are sedimentary rocks on Earth there are organisms. They are inextricably bound with that on this planet. It remains to be seen whether they are inextricably bound with the history of water and sedimentary rocks on Mars," she said.
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