Life on Mars?
It was an evening in summer upon the placid and temperate planet Mars. Up and down green wine canals, boats as delicate as bronze flowers drifted .... In the amphitheatres of a hundred towns on the night side of Mars the brown Martian people with gold coin eyes were leisurely met to fix their attention upon stages where musicians made a serene music flow up like blossom scent on the still air. - Ray Bradbury, The Martian Chronicles
There is something about Mars that has long led Earthlings to wonder whether there might be life on the planet that glows bright red in the night sky. Writing in the 1940s, novelist Ray Bradbury imagined a wise and ancient race of Martians. But most sci-fi writers preferred to see them as little green men or as malign, tentacled monsters. The truth could turn out to be a lot less colorful - and far more exciting. A team of scientists, including a Canadian who specializes in producing images from advanced electron microscopes, last week presented evidence suggesting that primitive life forms may have once existed on Mars. Team members cautioned that the case for life on Mars had yet to be conclusively proved. "We are putting this evidence out to the scientific community for other investigators to verify, enhance, attack - disprove if they can," said Everett Gibson, a geochemist at the Lyndon B. Johnson Space Center in Houston. It was a challenge with phenomenal implications. As Toronto astronomer Karl Kamper observed, if the findings are substantiated, "for the first time we will have evidence that life can exist on other planets - that life isn't simply the result of a cosmic accident on our own planet."
The announcement in Washington by scientists from the National Aeronautics and Space Administration and three universities stunned the international scientific community, prompting criticism in some quarters that the claims were premature and exaggerated - and enthusiastic praise in others. President Bill Clinton was clearly impressed. "If this discovery is confirmed," Clinton said in Washington, "it will surely be one of the most stunning insights into our universe that science has ever uncovered." With two unmanned U.S. spacecraft already scheduled to embark later this year on flights aimed at gathering new information about Mars, Clinton said he had asked Vice-President Al Gore to convene a high-level meeting to look at ways of pursuing the question of whether life may have existed on Mars.
The cause of all the excitement: an unimposing lump of dark-colored rock weighing just over four pounds and known as ALH84001. According to the researchers, whose findings are being published this week in the Washington-based journal Science, the rock had an eventful life: formed on Mars about 4 ½ billion years ago when the planet was young and perhaps warmer than it is today, it was torn from that planet's surface around 15 million years ago by the impact of a comet or asteroid. Hurled into space, the rock became a meteorite that orbited the Solar System until it was sucked into the Earth's gravitational field about 13,000 years ago. Scientists found it in Antarctica in 1984. They subsequently identified it as Martian in origin after finding that gases trapped inside were similar to samples taken from the surface of Mars by unmanned Viking spaceships in 1976.
But what made ALH84001 really interesting were traces of material in its interior that hinted of the presence long ago of a primitive microbial life form. Last year, scientists from California's Stanford University studying the rock detected polycyclic aromatic hydrocarbons (PAHs), a type of molecule that is usually organic in origin. Other team members focused on iron-bearing particles in the meteorite that appeared similar to those produced by some bacteria on Earth.
To help study another intriguing aspect of the meteorite, Dr. David McKay, the NASA geochemist in charge of the research project, decided last January to call on a Canadian expert - Dr. Hojatollah Vali, a senior scientist in McGill University's department of earth and planetary sciences in Montreal. The Iranian-born Vali, who came to Canada in 1989, is an internationally recognized expert on transmission electron microscopy - an advanced technology that can achieve such a high degree of magnification that the molecular structure of objects becomes visible. Besides his technical skills, Vali's own scientific interests made him an ideal choice to study the meteorite. "I have a passion," Vali told Maclean's, "for trying to understand the origins of life."
Vali's assignment at the Johnson Space Center was to study microscopic squiggles in the meteorite to determine whether they could be the fossilized remnants of microbes. His high-resolution images, which showed tube-like structures similar to microbial fossils on Earth, convinced team members that they probably were. "There is not any one finding that leads us to believe that this is evidence of past life on Mars," declared McKay. "Rather, it is a combination of many things" - PAHs, iron-bearing substances and possible fossil remains - "that is the most compelling evidence."
Some scientists are not so easily convinced. Dr. Paul Benoit, a specialist in cosmological chemistry at the University of Arkansas in Fayetteville, argues that the presence of PAHs and other organic compounds in the meteorite is not convincing proof. Such substances, he says, are often found in meteorites "that we know did not come from other planets." Other scientists pointed out that the team's theory rests on a number of unproven assumptions - including the idea that Mars, now a largely frigid and arid planet, once had a warmer climate with flowing water and conditions favorable to life. And critics noted that even though scientists have persuasive reasons for believing that the meteorite is Martian in origin, that claim has not been proved.
At the same time, if the dramatic new theory about life on Mars is substantiated, that will only serve to raise more questions about the origins of life. Many scientists believe that life on Earth may have emerged from a chance mixing of just the right elements in a "primordial soup" that existed billions of years ago - perhaps with a bolt of lightning acting as catalyst. If living organisms came into being that way on both Earth and Mars, that, some scientists reason, could be an extraordinary coincidence; or it could mean that life arises relatively easily and therefore is probably widespread throughout the universe.
There are other possibilities as well. Life may have begun far beyond the Solar System - and reached Earth and Mars as spores travelling through interstellar space. Alternatively, since science has confirmed that chunks of planets often reach other planets as meteorites - life might have originated on either Earth or Mars, and travelled to the other planet aboard a meteorite. "It's all very fanciful stuff," says Hal Levison, a planetary scientist at the Southwest Research Institute in Boulder, Colo., "but if either of those things happened, it's much more likely, because of Earth's stronger gravitational field, that life originally came to Earth from Mars."
Further study of the meteorite, as well as journeys that NASA's Mars Global Surveyor and Pathfinder spacecraft are scheduled to begin in November and December, could shed more light on whether Mars ever supported primitive forms of life - and perhaps still does. (Some scientists speculate that microbial life might exist in warmer conditions far below Mars's surface.) Meanwhile, Vali says the expressions of doubt that greeted the announcement in Washington are fully justified. "I agree with the skeptics," Vali says. "We have to do much more to prove the claims that have been made. The important thing is that we have made a start in looking at this thing." It could be some time before Earthlings know for certain whether life ever flourished on Mars - or anywhere else in the endless expanses of the universe.
Maclean's August 19, 1996