On Mars, these volcanic hot spots have stilled, leaving behind surface formations like weathered basalt as a frozen testament to the tumultuous ancient past. Did life exist in those ancient fumaroles and vents? On Earth, before photosynthesis appeared, microbes harnessed sulfur chemistry for the energy to drive their metabolism. It's plausible that the same strategy evolved among the volcanic features on early Mars.

But would such life forms have left evidence of ancient microbial activity? It's hard to tell. Without a clear understanding of how those basalts formed and were sculpted by their acidic environment, it's difficult to identify features that might signify past biological activity.

It's also difficult to know if the conditions were hospitable to life. In lieu of traveling to Mars, researchers look for terrestrial analogs to study and understand, but fresh volcanic basalt with a Mars-like chemistry is difficult to find.

At a recent geology meeting in Idaho, Brian Hynek, a research scientist at the Laboratory for Atmospheric and Space Physics at the University of Colorado, described martian basalt formations to some volcanologists. "They said 'you've got go to this place in Nicaragua, it's exactly what you're describing,'" Hynek recalls. The place was Cerro Negro, a volcano that first erupted in 1850.

Hynek traveled there to see for himself and found just what he was looking for. "The formations have a lot of the same minerals that we're seeing with the Mars rovers. There is a transition [occurring] from pristine basalts into these chemically altered products.

On Mars we see the fresh stuff and we see the weathered material, but we don't really understand how it got from point A to point B. [At Cerro Negro] it's happening before our eyes, so we can understand the role of water and biology in these types of environments," Hynek says.

In the volcano's crater, martian-like basalts are exposed to volcanic steam vents that emit sulfur gases and water vapor, producing sulfuric acid that is causing rapid weathering of the basalt. The volcano's youth has produced pristine basalt formations with perfectly known chronology - new basalt has formed in the past eight years from lava oozing out of fissures.

Those formations allow Hynek to study the chemical weathering of basalts as well as the microorganisms that exploit the chemical weathering reactions to harness energy.

Temperatures at Cerro Negro range from 50 to 288 Celsius (122-550 F). The environment is also highly acidic, with high concentrations of salt and low levels of nutrients. Hynek aims to determine which organisms are scratching out a living there.

Hynek and his co-investigators Tom McCollom at the University of Colorado and Karyn Rogers at the University of Missouri plan to analyze the microbial community that survives in this harsh environment, to determine the varieties of microbes and the metabolic functions that dominate. They will also search for novel organisms and attempt to culture them in the laboratory.

Those results should inform models that shed light on the energy sources that are available to microorganisms in such environments and how they might be metabolized. This information in turn can help guide future space missions as they survey for life in areas on Mars that had similar conditions in the past.

They also plan to introduce microbes into controlled laboratory experiments that mimic conditions at Cerro Negro, to see how their presence might influence the rate of weathering, since they consume reduced forms of sulfur as part of their metabolism.

Those metabolic processes might speed up or change the pathway of chemical weathering, and perhaps leave behind a fingerprint that could be detected during future missions, Hynek says. "We're trying to replicate the conditions at Cerro Negro and what we think early Mars, and parts of Earth, might have been like."

His team is also working with freshly formed basalt in the lab, subjecting it to artificial weathering using sulfuric acid at different concentrations to try to reproduce what is observed in the field. The studies have already produced some surprising results.

The weathering "can happen pretty quickly," Hynek says. "That means you didn't have to have water around a long time or to have [strong] heat sources for a long time to get pretty significant alterations." Co-investigator McCollom is conducting computer simulations to replicate the processes and geochemical pathways.

Hynek and his team just returned from a trip to Cerro Negro in July to develop sampling techniques and determine the best sampling locations. They will return in the fall to refine their methods and do more extensive studies. Hynek expects to collect samples with microbes that can be brought back to his and Rogers' labs and analyzed.

DNA sequences will be used to identify the microbes and he and his team will then try to culture them in the lab. If he can get them to grow, he can alter their environment to see how they respond to various extremes of temperature, acidity, radiation, and other factors.

"We can see how well they do, and apply that to what we think early Mars was like and what that says about its chance of being habitable," Hynek says.

On the fall trip, he also hopes to bring an X-ray diffraction instrument that is slated for the Mars Science Laboratory rover that will be launched in 2009.

NASA Ames researcher David Blake led the team to develop the instrument, which will use an X-ray beam to determine the chemical composition of martian rocks and soils. Measurements from the Cerro Negro materials will help Blake and his team interpret data from the Mars mission.

Unfortunately, Hynek isn't yet certain that he will have access to the instrument. He reports that Blake is enthusiastic, but there are logistical problems yet to be overcome. It may prove more challenging to move the instrument to Central America than part way across the solar system. "There is no customs checkpoint on Mars," Hynek points out.

Terrestrial analogs like Cerro Negro are critical to understanding and interpreting the data from past and current Mars missions, as well as to planning future expeditions, says Jennifer Heldmann, a research scientist in the division of space sciences and astrobiology at NASA Ames Research Center.

Researchers can test computer models by comparing simulations to the actual processes in places like Cerro Negro, and use those observations to refine and improve them. "Physics doesn't change, whether it's happening on Mars or on Earth," says Heldmann.

Hynek's research is support by a grant from NASA's Exobiology and Evolutionary Biology research program.

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