LIFE ON MARS

The discovery of evidence that life may exist elsewhere in the universe raises that most profound of all human questions: Why does life exist at all? Is it simply that if enough cosmic elements slop together for enough eons, eventually a molecule will form somewhere, or many somewheres, that can replicate itself over and over until it evolves into a creature that can scratch its head? Or did an all-powerful God set in motion an unfathomable process in order to give warmth and meaning to a universe that would otherwise be cold and meaningless? The rock from Mars does not answer such questions. It does, however, make them feel all the more compelling.

Hurtling in from space some 16 million years ago, a giant asteroid slammed into the dusty surface of Mars and exploded with more power than a million hydrogen bombs, gouging a deep crater in the planet’s crust and lofting huge quantities of rock and soil into the thin Martian atmosphere. While most of the debris fell back to the surface, some of the rocks, fired upward by the blast at high velocities, escaped the weak tug of Martian gravity and entered into orbits of their own around the sun.

After drifting through interplanetary space for millions of years, one of these Martian rocks ventured close to Earth 13,000 years ago–when Stone Age humans were beginning to develop agriculture–and plunged into the atmosphere, blazing a meteoric path across the sky. It crashed into a sheet of blue ice in Antarctica and lay undisturbed until scientists discovered it in 1984 in a field of jagged ice called the Allan Hills.

Last week that rock–dubbed ALH84001–landed on the front pages of newspapers around the world and seized the imagination of all mankind. At a televised press conference in Washington, a team of NASA and university researchers revealed that this well-traveled, 4.2-lb. stone–about the size of a large Idaho potato–had brought with it the first tangible evidence that we are not alone in the universe. Tucked deep within the rock are what appear to be the chemical and fossil remains of microscopic organisms that lived on Mars 3.6 billion years ago.

If that evidence stands up to the intense scientific scrutiny that is certain to follow, it will confirm for the first time that life is not unique to Earth. That confirmation, in turn, would have staggering philosophical and religious repercussions. It would undermine any remaining vestiges of geocentrism–the idea that man and his planet are the center of the universe–and strongly support the growing conviction that life, possibly even intelligent life, is commonplace throughout the cosmos.

To a world long fascinated by legends and fantasies about the Red Planet, the news had an electrifying effect, inspiring awe, disbelief, excitement–and, from not a few experts, skeptically raised eyebrows. The importance of the putative discovery was underscored by an immediate response from the White House. “Today Rock 84001 speaks to us across all those billions of years and millions of miles,” proclaimed President Clinton as he set off for a three-day campaign swing through California. “It speaks of the possibility of life. If this discovery is confirmed, it will surely be one of the most stunning insights into our universe that science has ever uncovered.”

Cornell University astronomer Carl Sagan, perhaps the most prominent champion of the search for extraterrestrial life, was exultant. “If the results are verified,” he said, “it is a turning point in human history, suggesting that life exists not just on two planets in one paltry solar system but throughout this magnificent universe.”

At the Washington press conference, hastily convened after word of the discovery leaked to the journal Space News, NASA Administrator Daniel Goldin echoed the excitement. “It’s an unbelievable day,” he said. “It took my breath away.” But, he cautioned, “the scientists are not here to say they’ve found ultimate proof…We must investigate, evaluate and validate this discovery, and it is certain to create lively scientific controversy.”

Members of the NASA-led team arrived in Washington fully prepared to enter the fray. They distributed copies of their peer-reviewed report, which the prestigious journal Science accepted for publication in this week’s issue, and displayed some remarkable scanning electron-microscope images of the tiny structures found inside the meteorite.

The most striking image clearly showed a segmented, tubelike object, with a width about a hundredth that of a human hair, and to the untrained eye clearly resembling a life-form. Apparently to some trained eyes also. “When I took it home and put it on the kitchen table,” says Everett Gibson Jr., a geochemist at the Johnson Space Center, “my wife, who is a biologist, asked, ‘What are these bacteria?'”

Among other images, one revealed carbonate globules–circular features closely associated with fossils of ancient bacteria on Earth. Another showed what seemed to be colonies of sluglike creatures.

As startling as these images were, they constituted just one of several lines of evidence that team leader David McKay cites as “pointing toward biologic activity in early Mars.” In addition to the images, which McKay acknowledges are the weakest and most controversial parts of the evidence, the panel of scientists at the press conference cited complex chemicals found close by or inside the carbonate globules. These included polycyclic aromatic hydrocarbons (PAHS)–organic molecules that on Earth are formed when microorganisms die and decompose (but also when certain fossil fuels are burned)–and iron sulfides and magnetite, minerals that are often (but not necessarily) produced by living organisms.

That raised an obvious question. Could these compounds have resulted from earthly contamination of the meteorite during its long Antarctic layover? Not likely, says Richard Zare, a Stanford University chemist who developed and used the analyzer that detected the PAHS and other meteoric hydrocarbons. The researchers performed a “depth profile” on the meteorite, and although no pahs were found on its crust, they were found inside the rock. Had any of Earth’s abundant PAHS seeped in, says Zare, he would have expected to find more contamination on the outside than in the interior.

Moreover, the suspected fossils predated the meteorite’s arrival on Earth by many, many years. Scientists pegged the age of the carbonate globules at 3.6 billion years, strongly suggesting that they formed in crevices of the rock while it was still part of the Martian crust. That argument makes sense to Carl Sagan. “This is a time,” he says, “when Mars was warmer and wetter than it is today, with rivers, lakes and possibly even oceans. This is just the epoch in Martian history when you expect that life may have arisen.”

As to the origin of the meteorite, the researchers have little doubt that it was Martian. They base their conclusion largely on the composition of gases trapped in tiny pockets within the meteorite. The NASA team found a strikingly close match between the constituents of the rock gases and those in the current Martian atmosphere, which the unmanned Viking landers sampled in 1976, transmitting the data back to Earth. Summarizing the findings, NASA’s McKay concedes that “there are alternative explanations for each of the lines of evidence that we see.” But after 2 1/2 years of study, the team became convinced that the evidence, taken as a whole, points to the existence of early life on Mars.

UCLA paleobiologist William Schopf, best known for discovering the world’s oldest fossils, spoke for many who would urge caution. Invited by NASA to represent the natural (and healthy) skepticism of the scientific community, he repeated a familiar Sagan quotation: “Extraordinary claims require extraordinary evidence.” Said Schopf: “I happen to regard the claim of life on Mars, present or past, as an extraordinary claim. And I think it is right for us to require extraordinary evidence in support of the claim.” It was clear that to Schopf such evidence was not yet forthcoming. He noted that PAHS are routinely found in interstellar and interplanetary debris, as well as in other meteorites. “In none of those cases,” he said, “have they ever been interpreted as being biological.”

Turning to the putative fossils in the electron-microscope images, Schopf pointed out that they are a hundred times smaller than any found on Earth, too minuscule to be analyzed chemically or probed internally. Also, he noted, “there was no evidence of a cavity within them, a cell.” Nor was there any evidence of life cycles or cell division. This led him to believe that the structures NASA was touting as fossilized life-forms were probably made of a “mineralic material” like dried mud. “The biological explanation,” he concluded, “is unlikely.”

Schopf acknowledged that the NASA team had done first-rate scientific research, but he regarded it as only a “preliminary” report. “All I’m saying is that there’s additional work to be done.” On that point Goldin agreed. “We want these results investigated,” he said, “and we’re prepared to make samples of the rock available” to credible researchers with sound experimental proposals.

Whatever the outcome of these investigations, the Mars mystique will probably endure. Throughout history humans have been intrigued by the baleful glare of the Red Planet in the night sky. To ancient civilizations it was the god of war, dubbed Ares by the Greeks and Mars by the Romans. When the first telescopes revealed that the planets were neither specks of light nor gods, but worlds, perhaps like Earth, the notion grew that Mars might harbor life.

No scientist was more excited by this possibility than the wealthy American astronomer Percival Lowell. Inspired by what turned out to be false reports of carefully laid-out channels on the surface, he established an observatory in Arizona and dedicated it to the study of Mars. By 1908, influenced perhaps by optical illusions and wishful thinking, Lowell had charted and named hundreds of canals, which he believed were part of a large network conveying water from the polar ice caps to the parched cities of an arid and dying planet.

Lowell’s imaginative scenario, in turn, inspired English novelist H.G. Wells to write The War of the Worlds, a dramatic account of an invasion of Earth by octopus-like Martians. In 1938 a radio drama adapted from that novel by another man named Welles–Orson, that is–panicked many Americans who believed that a real Martian invasion was under way.

Even after the mighty 200-in. Mount Palomar telescope focused on Mars and found no evidence at all of networks of canals or other manifestations of intelligent life, the fascination continued, fueled by books, grade-B movies and TV sitcoms–all involving encounters with Red Planet denizens of various sizes, shapes and consistencies.

Mariner 9, placed in low orbit around Mars in 1971, cast a temporary pall on the fantasies when it transmitted pictures showing a desolate, crater-pocked landscape with no cities, bridges or other signs of intelligent life. But among the craters, canyons and volcanoes, Mariner discerned dry, meandering riverbeds and deltas, unmistakable evidence that water had once flowed freely on the surface in a warm, hospitable climate.

Could life have evolved during this balmy era? It was in part to answer that question that the Viking 1 and 2 spacecraft, each consisting of an orbiter and lander, reached Mars in 1976. Scooping up and analyzing Martian soil in an onboard chemistry lab, the landers found no signs of life, past or present. Still, says Stanford’s Zare, the failure in no way ruled out the possibility of existing Martian life. Since Mars lacks an ozone layer, he explains, solar ultraviolet light “will sterilize and break up any type of organics that might be on the surface.” For that reason, he says, when NASA gets to Mars again, “it should not just creep around the surface, but look deeper down.”

Despite Viking’s inability to find life, its orbiter seemed determined to keep the mystery of Mars alive. Among the images it sent back was an overview of a large surface feature resembling a human face. That stirred a frenzy among alien-life enthusiasts, eccentrics and mystics, who were soon insisting that the face–as well as another nearby formation that they described as a ruined city–were the works of an advanced but now extinct civilization.

That myth persists despite Administrator Goldin’s admonition last week. “I want everyone to understand that we are not talking about little green men,” he stressed. “There is no evidence or suggestion that any higher life-form ever existed on Mars.” Undaunted, tabloid editors promptly produced a flurry of new fantasy headlines and stories about aliens, some accompanied by pictures of the so-called Martian face.

NASA’s announcement also breathed new life into a worthy but largely unappreciated enterprise: the Search for Extraterrestrial Intelligence. SETI, as it is called, makes use of computer-monitored radio telescopes to scan the skies and frequency bands in the hope of picking up a message or signal from a distant civilization.

At SETI’s offices in Mountain View, California, the first signs of extraterrestrial life arrived last week not by radio but by fax. When they got the news from NASA, says astronomer Frank Drake, the organization’s president, workers abandoned their stations and gathered around a TV set to watch the press conference “hooting, hollering and cheering.” And for good reason. If the evidence is validated, explains Drake, who launched the first seti-like program in 1960, “it confirms what we’ve always believed–that life arises wherever the conditions are right.” And because the sun is just one star in a galaxy of 150 billion stars, in a universe of billions of galaxies, the universe may well be teeming with life, some of it intelligent. “We are just one iota among countless iotas in the universe,” Drake insists. Someday, he hopes, SETI’s radio telescopes will hear from the others.

At the Johnson Space Center, meanwhile, researchers are back at their instruments, gathering ammunition for what could be a long battle with their critics in the scientific community. “We feel we can already see a cell wall,” says NASA’s Gibson hopefully. NASA administrators were also busy, re-examining their scientific launch schedule, which includes two missions to Mars before the end of the year, and coyly suggesting that final confirmation may require sending rovers–and perhaps even people–to gather samples for closer analysis.

What remains largely unspoken is the lingering hope that such a mission might experience, somewhere beneath the desolate Martian surface, a close encounter with organisms that are alive today.

–Reported by Dan Cray/Los Angeles, S.C. Gwynne/Austin and Ainissa Ramirez/Washington, with other bureaus

For more information, see TIME ONLINE’s Life on Mars Website at time.com/mars