WASHINGTON — Researchers on both sides of the Atlantic are eagerly searching for clues to determine whether primitive life could exist in the harsh environment of Mars, just as it does in some very harsh environments on Earth. One focus of that search is the presence of methane on Mars.

At a private gathering of space enthusiasts in Northern Virginia Feb. 13, two NASA researchers, Carol Stoker and Larry Lemke of NASA’s Ames Research Center in Silicon Valley, generated considerable excitement within the group as they discussed their research examining harsh environments on Earth and the implications it might have for the search for life on Mars.

What Stoker and Lemke are studying, according to people who attended the private meeting, is not direct proof of life on Mars, but methane signatures and other signs that could possibly be the result of biological activity similar to that recently discovered in caves here on Earth.

In response to Space News’ original article about Stoker and Lemke’s presentation to the private gathering, posted Feb. 16 on spacenews.com and picked up by space.com and other Web outlets, NASA issued a statement calling the reports incorrect. “NASA does not have any observational data from any current Mars missions that supports this claim. The work by the scientists mentioned in the reports cannot be used to directly infer anything about life on Mars, but may help formulate the strategy for how to search for martian life. Their research concerns extreme environments on Earth as analogs of possible environments on Mars.”

NASA spokeswoman Dolores Beasley said Feb. 18 that Stoker and Lemke were not available for interviews. Stoker did not respond to messages left Feb. 15 on her voice mail at Ames.

Space News interviewed a half-dozen space officials who attended the Feb. 13 event at a private home in Northern Virginia. All requested that they not be identified in print because the discussion was considered off the record.

Stoker and other researchers have long theorized that the Martian subsurface could harbor biological organisms that have developed unusual strategies for existing in extreme environments. That suspicion led Stoker and a team of U.S. and Spanish researchers in 2003 to southwestern Spain to search for subsurface life near the Rio Tinto river, so-called because of its reddish tint, the product of iron being dissolved in its highly acidic water.

Stoker told Space.com in 2003, weeks before leading the expedition to southwestern Spain, that by studying the very acidic Rio Tinto, she and other scientists hoped to characterize the potential for a “chemical bioreactor” in the subsurface — an underground microbial ecosystem of sorts that might well control the chemistry of the surface environment.

Making such a discovery at Rio Tinto, Stoker said in 2003, 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.

Stoker told the private audience Feb. 13 that by comparing discoveries made at Rio Tinto with data that is being collected by ground-based telescopes and orbiting spacecraft, including the European Space Agency’s Mars Express, there is a strong case to be made that life could exist below Mars’ surface.

The two scientists, according to sources who attended the Feb. 13 event, said Mars’ fluctuating methane signatures and nearby surface concentrations of the sulfate jarosite, a mineral salt found on Earth in hot springs and other acidic bodies of water like Rio Tinto that have been found to harbor life despite their inhospitable environments, could be a sign of an active underground biosphere.

Methane findings also have been the focus of some researchers examining data from the European Space Agency’s Mars Express satellite.

The British magazine New Scientist reported Feb. 16 that an Italian scientist, Vittorio Formissano of the Institute of Physics and Interplanetary Science in Rome, would be speaking at a Mars Express conference in Noordwijk, the Netherlands the week of Feb. 21 about methane findings that he said can only be explained by the presence of life. But as other scientists have pointed out, and the same New Scientist article noted, methane in the concentrations that have been observed on Mars could also be explained by non-biological processes such as volcanic activity.

Stoker is slated to present a paper she authored with Lemke and several others about the Rio Tinto research and its implications for present life on Mars at the Lunar and Planetary Institute’s annual conference in League City, Texas, March 14-18.

The abstract of that paper, “Characterization of a Subsurface Biosphere in a Massive Sulfide Deposits [sic] at Rio Tinto, Spain: Implications for Extant Life on Mars,” is posted on the Lunar and Planetary Institute’s Web site at www.lpi.usra.edu/meetings/lpsc2005/.

Stoker and Lemke’s research, attendees of the Feb. 13 gathering said, could lead the search for martian biology underground, where a living ecosystem might account for the curious methane signatures the two have been analyzing.

“They are desperate to find out what could be producing the methane,” one attendee told Space News. “Their answer is drill, drill, drill.”

NASA has no firm plans for sending a drill-equipped lander to Mars, but the agency is planning to launch a powerful new rover in 2009 that could help shed additional light on the search for possible life on Mars. Dubbed the Mars Science Laboratory, the nuclear-powered rover will range farther than any of its predecessors and will be carrying an advanced mass spectrometer to sniff out methane with greater sensitivity than any instrument flown to date.

Brian Berger is editor in chief of SpaceNews.com and the SpaceNews magazine. He joined SpaceNews.com in 1998, spending his first decade with the publication covering NASA. His reporting on the 2003 Space Shuttle Columbia accident was...