Rock May Bear Signs of Ancient Life on Mars

In what some scientists say may turn out to be one of the most spectacular scientific discoveries since humans first gazed skyward at other planets in our solar system, NASA and Stanford University scientists say they have found evidence that life may have existed on ancient Mars.

“This could be answering the question everyone’s been asking since they first saw the planet Mars,” said UCLA planetary scientist David Paige. “Could there be life there?”

NASA Tuesday confirmed that an ancient Martian rock found in Antarctica in 1984 contained fossils of one-celled organisms similar to ancient life forms on Earth. The 4.5-billion-year-old rock--dubbed ALH84001--was blasted off the Martian surface when an asteroid crashed into the planet about 15 million years ago; the rock landed in Antarctica about 13,000 years ago, scientists believe.

“NASA has made a startling discovery,” said NASA chief Daniel Goldin, who emphasized that these were not “little green men.” Instead, he described them as “extremely small, single-celled structures that somewhat resemble bacteria on Earth.”

Still, there are reasons to be skeptical, and even some scientists open to the idea of life on ancient Mars expressed reservations about the findings. “Spectacular findings demand spectacular proof,” said Paige, who had not yet seen the research results.

Stanford’s Richard Zare--one of the chief researchers on the finding--described the fossils as “egg shapes and tubular type things.” While it’s conceivable that inorganic processes created the structures, he said in an interview, other independent lines of investigation all converged on the conclusion that the most plausible explanation was some primitive form of life.

For example, materials commonly associated with bacteria, like magnetite, iron sulfide and globs of carbonate material, were found in the same place as the fossil-like structures. “Everything we see has other possible explanations,” Zare said. “But it’s the fact that everything is spatially together” that makes the evidence for life so compelling.

Zare and colleagues from Stanford, NASA’s Johnson Space Center in Houston, Lockheed Martin and other institutions subjected the rock to a series of tests to rule out the possibility that it had somehow gotten contaminated during its visit to the South Pole 13,000 years ago.

“We sliced it open,” said Zare, “then put it immediately into a high vacuum,” a process designed to keep the inside of the rock sterile. The researchers were also able to show that the globs of carbonate came from deep inside the rock, and were not picked up on the surface.

Few scientists had actually seen the research paper, which is to be published in the journal Science on Aug. 16. NASA was keeping the findings under wraps until a news conference planned for today, and the authors from the Johnson Space Flight Center were not available for comment. But rumors had been circulating within the planetary science community for weeks, and an article in the publication Space News forced NASA to release a statement Tuesday.

The possibility of life on ancient Mars has become tantalizingly real of late, and many researchers were ready to take the findings seriously.

“If you had asked me [about life on Mars] five years ago, I would have said, ‘No way,’ ” said UCLA geochemist Laurie Leshin. “Now, I think it’s more likely than not.”

Still, Leshin said it was highly unlikely that life would be found in the meteorite under study. “It’s the wrong kind of rock,” she said. “If you really want to go to look for life on Mars, you should go to ancient sea beds,” she said.

Carl Sagan, a leading authority on the search for extraterrestrial life, told Associated Press that the findings are “evocative and very exciting.” But he said the chemical compounds reported in the paper “are not evidence of life.”

ALH84001 is an igneous rock that crystallized out of molten rock at very high temperatures probably about 4.5 billion years ago. “Igneous rocks are typically dead,” Leshin said, whereas sedimentary rocks found in the bottom of Earth’s oceans, for example, contain ample evidence of extremely early life.

Still, scientific attitudes toward the possibility of life on Mars have undergone a revolution in recent years, she said. In part, scientists have changed their views on the climate of early Mars: Although the Red Planet is a parched desert today, researchers believe that it was wet and warm billions of years ago.

Moreover, scientists who study alternative scenarios for the evolution of life on Earth have come up with several plausible situations that would have worked on ancient Mars as well as on ancient Earth, said Leshin. Mars and Earth were both formed out of the primordial cloud of gas and dust that formed the sun and other planets some 5 billion years ago. Only recently have scientists discovered evidence of life forms on Earth dating back to more than 4 billion years--almost as soon as the Earth cooled down enough to support living things.

Some researchers believe that life could have originated on one planet and migrated to others, with comets and meteors acting like “seeds” to sprinkle DNA around the solar system. “It’s not a disprovable concept,” said Paige, who remains skeptical about the new findings until he sees the evidence for himself.

DNA is the master molecule that holds the blueprint for all life on Earth. One intriguing marker for life beyond our Earthly boundaries would be DNA that spiraled in a left-handed direction. For reasons unknown, all DNA on Earth spiral in the right-handed direction.

If samples from Mars spiraled all to the left, said Paige, that could be strong evidence for independent origin of life on other planets.

Other researchers wondered whether it was reasonable to think that a rock could be blasted off the Martian surface, and still arrive intact and undisturbed on Earth. Caltech’s Andrew Ingersoll, for example, said that would be “a pretty violent event,” although most researchers do agree that the rock found at the South Pole is from Mars.

“The Mars gases have a real distinctive signature,” he said, that is “unlike anything else in the solar system.”

However, Donna Shirley, who heads the Mars Program at NASA’s Jet Propulsion Laboratory in Pasadena, is taking a somewhat more cautious approach.

“We can’t be certain until we bring back a piece of Mars and compare it [to the rock],” she said.

The Viking missions to Mars in the 1970s found no signs of life. However, said Shirley, the problem may have been that Viking “looked for preconceived notions of life.”

Essentially, she said, the Viking experiments scooped up some Martian soil and plopped it in the equivalent of “chicken soup, to see if it grew and ate nutrients and produced waste.” Instead, Viking found that the surface of Mars was virtually sterile, and anything that might have lived there was long since destroyed by ultraviolet radiation.

This time around, NASA’s going back to Mars with a much more systematic approach. The Mars Global Surveyor, set to be launched in November, will make a complete map of the planet and will be able to resolve structures as small as a car. Mars Pathfinder will be launched in December and will send a rover to the surface to take pictures and chemically analyze samples on site.

Pathfinder is due to arrive at Mars on Independence Day, 1997.

Meanwhile, researchers give a great deal of credibility to the current findings, in part because of the reputations of the researchers involved. “I think it’s very reasonable,” said UC Berkeley geophysicist Raymond Jeanloz. “Zare is incredibly highly regarded.”

However, Paige pointed out that with science, you never know until all the research is in. “You can never be sure if you’ve got a glitch on your computer, or if you’ve got a Nobel Prize.”