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When the bacteria of a billion-year-old fossil was discovered on Mars, NASA called on the expertise of professors from both San Francisco and Israel to help determine whether life exists on the red planet.

But Professors James Orenberg of San Francisco State University and Amos Banin of Hebrew University in Jerusalem aren't looking for little green men.

"We're talking simple, primitive species on Mars," Orenberg said. "No one is walking around. We have no traces of that. It's more likely we might find evidence of the existence of primitive microbes and species like that covered up by the planet's light, fine soil."

Nonetheless, the possibility of life on Mars is rousing a good deal of interest. The National Aeronautics and Space Administration recently presented Orenberg, Banin and NASA's Ted Roush with an $125,000 grant to develop a prototype of the soil on Mars.

Because of the miles that separate them, the professors work via computer, phone and fax. In addition, Banin, professor of soil science at Hebrew University and adjunct professor of chemistry at SFSU, spends summers and sabbaticals as a senior research associate at NASA's Ames Research Center at Moffett Field in Mountain View.

While the cost of the research is considered relatively low, its results could have a big impact.

"The knowledge gained from studying the question of life, past or present, on Mars can tell us a good deal — not only about the formation of that planet but also about the emergence of life on our own planet and perhaps elsewhere in the solar system as well," Banin said via e-mail.

In order for astronauts or spacecraft to make contact with Mars or its potential inhabitants, scientists need to know more about the planet's environment. Developing a prototype of the soil is a critical step in gaining that knowledge.

"When we send up landers [space vehicles] or humans, we don't want to have any surprises in terms of an unfavorable environment or [find] that the soil has an oxidizing quality," Orenberg explained.

To date, Orenberg, Banin and Roush have established that Mars has a geological history similar to Earth's. The planet's origins are believed to be the same. And Mars is about as far as Earth from the sun.

In fact, Orenberg said, "one could propose these questions: Why did life develop in so complex a fashion on Earth? Did life begin on Mars or is it still there and we don't see it on the surface?

"This is why we want to mimic the soil composition: to see if the elements essential to life as we know it on Earth are present on Mars."

It appears they are.

In the late 1970s, NASA sent Viking spacecraft to Mars, programmed to conduct experiments on the planet's soil.

Data from those tests show that the soil on Mars is composed of salts and minerals similar to those making up the Earth's surface. Among them are palagonite (a weathering product typical of volcanic eruptions) as well as clay, hydrogen, carbon, nitrogen, oxygen and sulfur in the form of simple salts.

The trick now is refining the elements in this model to most closely represent the environment of Mars in order to do further exploration.

Until that time — and both Banin and Orenberg believe the possibility of Mars' present-day soil sustaining human life is a long way off — the research could significantly affect present-day living on Earth.

"If we can learn what caused life to cease on Mars, then we may be able to obtain some valuable lessons about what we should be doing to preserve our own planet," Banin said.