EUGENE, Oregon -- Martian biology is likely alive and well on the red planet, but tucked away in caves or dwelling underground, sustained by pockets of water.

That prospect has spurred scientists to look for exotic life forms here on Earth, far from the maddening crowd of topside biota that covers our planet.

This quizzical quarry for life is helping devise the strategies, the tools, and the procedures for unearthing the biological leftovers from an ancient Mars, or hardy microbes that might exist on that distant world today.

Experts on the search for underground Martian biology took part in the Sixth International Mars Society Conference, held here August 14-17.

For one group of investigators, the road to Mars starts at the Rio Tinto, a river in southwestern Spain.

Stoker said that below Mars surface, bacteria may dwell beneath the surface, eating minerals derived from subsurface rocks that contain iron and sulfur.

By studying the very acidic Rio Tinto, scientists hope to characterize the potential for a "chemical bioreactor" in the subsurface an underground microbial biosphere might well control the chemistry of the topside environment. These organisms live on chemical energy and they appear to do that without the presence of oxygen.

Making that discovery at Rio Tinto, Stoker said, would mean uncovering a new, previously uncharacterized metabolic strategy for living in the subsurface. "For that reason, the search for life in the Rio Tinto is a good analog for searching for life on Mars," she said.

The MARTE effort serves several purposes.

First of all is drilling - digging deep to explore for life in subsurface waters that are the source of the Rio Tinto. A second objective is to perform a simulation of a Mars drilling mission, to hone the technologies and mimic measures to be taken in a hunt for subsurface biology on Mars.

Scientists and engineers plan to explore the Rio Tinto using a drill and science gear designed for use in a Mars mission. In one phase of the work, the robotic drill is to be remotely operated, as will life detection instruments all from faraway control sites linked via satellite.

Stoker said that a key drilling challenge is not contaminating underground biology with life forms brought down from above, and not spoiling samples raised upwards by introducing surface biology.

At the drilling location in Spain, scientists will be conducting traditional core sample drilling and analysis to understand subsurface life forms at the site and to check the accuracy of the remote-control efforts to identify life forms, organic compounds and minerals.

This initial "ground truth" drilling is slated for mid-September. "Thats when the bit hits the ground," Stoker told SPACE.com. The month-long Mars simulation work is set for the spring of 2005, she said.

"Were starting with a clean sheet of paperinventing a whole bunch of new things. Also, we help train the next generation of Mars explorers," Stoker added.

When it comes to exploring the red planet, biologist Penelope Boston makes it know shed secretly liked to be called the "Empress of Mars".

Bostons day job, however, is director of the cave and karst studies program at New Mexico Institute of Mining and Technology, in Socorro, New Mexico.

On Mars, Boston advises, cruise that planets landscape for caves.

"A cave is simply a vehicleor if you are a small organism, its a little hole," Boston noted. Caves provide a rich environment, one that is removed from ultraviolet radiation that strikes the planets terrain, she said.

Caves offer surfaces, exposure of different kinds of rocks. You also have the possibility of a cave holding small, standing bodies of water, pools, as well as ices. Furthermore, caves come complete with micro-meteorological conditions that can protect biology from extreme swings in temperature. Sealed caves can trap gases, as well as water vapor, Boston said.

"You have three-dimensional complexityso the number of possible niches for life proliferates in caves," Boston told SPACE.com.

Caves and lava tubes are one in the same, and given the volcanic history of Mars, this feature is pervasive across the red planet, Boston said.

Boston said that her craving for caves here on Earth, and the exotic biology she has found underground, bolsters her confidence that Mars is likely rife with life.

"With all the evidence for subsurface water ice on Mars, Im thinking 70-percent chance of life. And thats the highest confidence Ive ever had," Boston said. "Im guessing that it is, essentially, ubiquitously distributed."

The more that is learned about Earths deep biosphere, the better the case for Mars life underground, Boston said. "My guess is that they are like the weeds of the subsurface on Earth."

A planet doesnt have to be dominated over its surface in order to have a living biosphere, Boston said. "Right now, what we have in our head is this oxygen-filled environment with Bambi the deer jumping around on the surface. That may not be the norm for biospheres."

Maybe there are a lot more subsurface biospheres that never made it on the surface, because the surface is much harder to live on, Boston said.

True, the surface of Mars is not the ideal locale for life. But the planet is a perfect environment for striking a balance of what both human and robotic talent have to offer.

That's the sense of Silvano Colombano, a computer scientist at the NASA Ames Research Center.

The red planet is far from being a hospitable world to easily explore, Colombano noted. Even in that stark environment, robots can perform decisive duties. "But the human mind, our impulsesthese are things that robots can't have. Using both is the ideal," Colombano told SPACE.com.

Trekking into perilous areas, far too dangerous for humans, is where androids can show the robotic right stuff, Colombano said. "Robots are the pioneers. Robots are going to be there first. We want to get as much information as we possibly can."

Colombano said that the robotic missions of today will likely pale when compared to what machines might offer in the future. "You don't just send a single mission and let it last a few weeks or months and then it dies. You want to create a robotic infrastructure that grows with every mission, and continues the exploration without stopping."

To create such an infrastructure means solving problems common to issues in sending humans. There is need to produce energy, provide shelter, and the ability to self-repair.

"By the time you solve all those robotic problems," Colombano said, "then you have paved the way for humans to go as well. As part of their tasks they can prepare shelter for humans, produce fuel, and complete other jobs. In doing so, now you've created an environment that humans can step into."

But there is a technical stumbling block. Machines break down.

"Biological systems have ways in which they can maintain themselves, such as self-repair and ultimately reproducing," Colombano explained. Efforts are now centered on self-maintaining robots. By acquiring some of the properties of biological systems, machines would self-repair, just like a human colony would propagate, he said.