Martian Message - There Was Once Ancient Life Here

Article excerpt

Life on Mars? After decades of speculation, a team of scientists has found "compelling" evidence of ancient life on the Red Planet. The stunning discovery moves mankind closer to solving one of the great riddles of human history: Does organic life exist elsewhere in the universe?

The proof was microscopic, and circumstantial. While examining a 16-million-year-old meteorite from Mars, researchers discovered residues of organic chemicals indicative of primitive life. They also found structures similar to fossils of ancient bacteria that may have existed billions of years ago.

The findings, reported yesterday by a team led by scientists at the National Aeronautics and Space Administration (NASA), shook astronomers, but also brought out its share of skeptics.

If confirmed by other investigators, this would be "a major first discovery" in NASA's efforts to find signs of life on other worlds, says Arden Albee, a leading Mars expert at the California Institute of Technology.

In announcing the discovery, NASA administrator Daniel Goldin acknowledged that while "the evidence is exciting, even compelling ... {it is} not conclusive." David McKay of the Johnson Space Center in Houston, one of the team leaders, explained: "There is not any one finding that leads us to believe that this is evidence of past life on Mars. Rather, it is a combination of many things...."

He added that it is the relationship of these chemical residues and microscopic forms to each other that "is the most compelling evidence." Now, he said, it is up to others to confirm or overturn his team's findings.

Those findings will be detailed in the Aug. 16 issue of Science magazine, in a paper written by nine scientists from seven NASA and university research centers. But the news was leaked this week, forcing NASA to release the information early.

The rock in question

The meteorite under study is a 4.2-pound potato-size object. It is some 4.5 billion years old, dating from the time when Mars and Earth were formed.

Scientists believe that 16 million years ago an asteroid knocked the rock out of its location beneath the Martian surface. It then traveled through interplanetary space until falling to Earth in Antarctica 13,000 years ago. There it was found in the Allan Hills ice field in 1984 - hence its name, ALH84001. It is the oldest of 12 Antarctic meteorites whose composition differs from that of other meteorites but matches the composition of Martian material analyzed by the Viking lander spacecraft.

Mars today is cold, arid, and generally inhospitable for life. But during its first billion or so years it appears to have had a more accommodating climate. At that time, primitive life could have evolved in ponds or subsurface water and in fissures in rock formations. This appears to be the habitat of the presumed meteorite fossils.

Carbon dioxide from the CO2-rich Martian atmosphere would have permeated such fissures. There, primitive life forms would transform the CO2 into carbonates. The scientific teams have found carbonate globules within the meteorite. They are associated with chemicals called polycylic aromatic hydrocarbons or PAHs for short. …