The Quest for Mars: NASA scientists and Their Search for Life Beyond Earth

The Best Guess Scenario assumes that some kind of simple life did exist on Mars a few billion years ago, as Steve described. And it assumes that asteroids have bombarded Mars ever since, pockmarking its surface with craters. Sixteen million years ago, according to the scenario, a refugee from a disorganized asteroid belt struck the surface of Mars with tremendous force. Since Mars has only 38 per cent of Earth’s gravity, the impact was sufficient to drive pieces of rock buried beneath the surface high into the Martian sky and beyond. The pieces shot into space five times faster than a bullet – fast enough to escape the Red Planet’s gravity. Until a few years ago, it was thought the shock of impact would vaporize or severely deform the ejected material – the ejecta – along with everything in it, including any signs of life, but recent computer modeling has shown that the physics involved would allow the ejecta to remain intact. In the model, the asteroid comes in at an angle, strikes, and creates a vapor cloud that sweeps across the surface at an extremely high speed and carries material off Mars into solar orbit. The whole process might take five or ten seconds, long enough for some fragments of Mars to remain intact. “That’s a fairly gentle way to get stuff off the surface,” says Mark Cintala, who studies craters at NASA’s Johnson Space Center – gentle enough to launch a fossil-bearing meteor on a trajectory to Earth.

There’s a variation in the Best Guess Scenario that incorporates another method of ejecting material safely from the surface of Mars: spallation. Much of the work on the spallation model was done by Jay Melosh at the University of Arizona, and it’s extremely simple, in theory. You put a quarter on a tabletop, rap the underside of the table, and bump the quarter into the air; that’s spallation. “You’re sending a stress wave through the table, and that stress wave is transmitted to the quarter. Imagine that happening on Mars,” Mark Cintala says. In that case, the asteroid’s impact would create a compressional wave, as if it were a depth charge below the surface. The resulting shock wave would bounce a rock fast enough to escape the relatively weak Martian gravity and send it on its way. “At least, the calculations say it can.”

In the Best Guess Scenario, one of these dislodged pieces of Martian rock sped off in the direction of Earth, a cosmic message in a bottle floating through an ocean of outer space. The journey lasted millions of years, and the ancient chunk of Mars crashed to the surface of Earth a mere 13,000 years ago. The size and shape of a potato, it buried itself in the Allan Hills of Antarctica. The meteor had become a meteorite.

Meteorites have held a special fascination as relics from the heavens, mute messengers from parts unknown. In the Middle Ages, meteors falling to Earth generated superstition and concern. Where did they come from? What did they mean? The faithful brought them to the authorities, and in time, the Catholic Church acquired a large repository of these curiosities. In 1969, the study of meteorites underwent a quiet revolution when Japanese researchers found high concentrations of them preserved in arctic ice. Since 1977, NASA, a technological Vatican, has been collecting meteorites from Antarctica and housing them at the Johnson Space Center in Houston. Each year, there are hundreds of new arrivals, and when there’s a promising delivery, scientists clamor to get a piece to study. There are now nearly 10,000 rocks under lock and key in Building 31 at Johnson, many of them preserved in nitrogen. By measuring the radiation absorbed by the meteor during its space travels, scientists can determine approximately when the rock arrived on the Earth, and even how long it spent in space before it arrived on our planet.

In December 1984, Roberta Score was hunting for meteorites in Antarctica. At the time, she was employed by Lockheed Martin and working at the Johnson Space Center. Around Johnson, a meteorite collecting mission is not exactly choice duty; join one, and you were said to have become part of the “Houston weight loss program.” Walking across an apparently endless sheet of ice, Robbie Score came across a greenish stone about the size of a potato. Once she removed her sunglasses, she saw the meteorite was not greenish, after all; it was gray and brown, but she knew it looked different from the ordinary meteorites she found in the field. Along with other samples, it was kept in a freezer aboard the ship that brought it from Antarctica to Point Magu, California, where it was packed in dry ice and sent to Johnson, where it was stored in cabinets that once held moon rocks. The meteor curators, including Robbie Score, designated it ALH 84001 – their way of saying this was the most interesting meteorite collected in 1984 in the Allan Hills of Antarctica. But after being delivered to Johnson, ALH 84001 was misidentified as an asteroid fragment, a diogenite, rather than a piece of Mars, and stored in Building 31. It was not ignored, however; small sections were allocated to the scientific community for further study over the years; in all, almost a hundred “investigators” examined it, and everyone continued to misclassify it as a diogenite – with one exception.

In late 1993, David Mittlefehldt, a veteran Lockheed Martin scientist also working at Johnson, reexamined ALH 84001. Mittlefehldt was an expert on diogenites, and this particular rock didn’t look like one to him. It seemed to have more oxidized minerals in it than your normal diogenite, for one thing. Using new technology in the form of high-resolution laser spectrometry, two other scientists, Donald Bogard and Pratt Johnson, extracted gases trapped inside the strange meteorite and discovered that their very idiosyncratic characteristics exactly matched gases on Mars as measured by the Viking spacecraft in 1976. Mittlefehldt published his findings in 1994 in a scientific journal, and attracted the notice of the science community. Although this wasn’t the first meteorite from Mars to have been discovered, the reclassification created a stir. Of the thousands of meteorites that have been cataloged, only fourteen are believed to have come from Mars; the overwhelming majority come from asteroids, and a few from the moon. Meteorites are named for the places where they have fallen to Earth, so the Martian meteorites have some fairly exotic names – Shergotty (India), Nakhla (Egypt), and Chassigny (France), among them – and are known collectively as SNC or “snick” meteorites. “SNC meteorites” is an elaborate way of saying “meteorites from Mars.”

Carefully considering his find, Mittlefehldt noticed minuscule reddish-brownish areas deep within ALH 84001; they looked a lot like carbonates, and on Earth, carbonates such as limestone tend to form close to water. What made this all so curious was that no one had detected carbonates – and their suggestion of water – in the other Martian meteorites. They were billions of years newer; they probably came from a more recent era in the geologic history of Mars, after the water that once flowed freely across its surface had disappeared. This one, however, apparently harkened back to that warm and wet golden age on Mars. Dating confirmed that the meteorite was indeed very old: 4.5 billion years old, much older than other known Martian meteorites, and it contained carbonates that were 3.9 billion years old. Mittlefehldt wanted to get some idea of the temperature range in which the carbonates had formed billions of years ago, so he went to yet another NASA scientist, Everett Gibson, who examined the very curious meteorite with Chris Romanek; they published a paper in the December issue of Nature in which they said the carbonates had formed at temperatures below 100° C, in other words, at moderate, Earthlike temperatures – “well in the range for life processes to operate,” as Gibson puts it.

By now a line of reasoning was beginning to take shape. The team had their meteorite; it was from Mars. Almost no one disputed that singular fact. And it was very old, when water was thought to exist on the Red Planet. And it had carbonates, suggestive of water, formed at moderate, Earthlike temperatures. With each new discovery, the stakes became exponentially higher. ALH 84001 had gone from being a curiosity to an interesting and instructive case study to a potential harbinger of a scientific revolution. Each new link had been more difficult to fashion than those that had preceded it, and the final link – to life on Mars – would be the most difficult of all to fashion.

Other scientists soon began angling for a piece of the curious, potato-shaped Martian meteorite, among them David McKay. Over the years at Johnson, he’d become known as a solid and reliable scientist, not the type to go out on a limb. Carl Sagan he was not. If you asked around about McKay, you often heard words like “cautious” and “self-effacing,” yet he had a distinct air of authority; he’d published hundreds of scientific papers, and he knew his way around Johnson and around NASA. Over the decades, he’d learned about science and about maneuvering in the world of scientists. He knew about the pitfalls, how quick others were to leap on “discoveries” and tear them to bits. Yet with all his experience, he seemed destined to retire in honorable obscurity, until ALH 84001 came to his attention.

“I’m going to get a piece of that meteorite and look for signs of life in it,” he told his wife.

“Sure you are,” she said.

McKay had a vast storehouse of information and impressions about rocks on which to draw. In his long career, he had looked at perhaps 50,000 of them, and he spent many hours studying the most intriguing he’d ever seen, ALH 84001, with a scanning electron microscope capable of magnifying objects 30,000 times. With this instrument, McKay identified a bunch of – well, they looked a little like miniature subterranean carrots, or worms, or tubes. Whatever they were, they didn’t look like something you’d expect to find in a meteorite.

Again, he turned to another scientist for assistance. Kathie Thomas-Keprta was a biologist who had spent almost a decade studying extraterrestrial particles – space dust – before she focused her attention on the meteorite from Mars. She was accustomed to making do with very little. A specially modified B-57, flying at high altitude for an hour, might collect just one extraterrestrial particle from an asteroid, a particle too small to see but big enough for her to examine under a powerful microscope. When McKay invited her to study a Martian meteorite, she was delighted to have something as big as one millimeter by one millimeter to work on after all those years of studying specks. Even better, she was an expert with a new type of electron microscope that could reveal the mineral composition of the carbonates locked in the meteorite. McKay and Gibson showed her the photos taken by the scanning electron microscope, and they proposed that she examine those peculiar, worm-like structures to see if they were fossils. She listened respectfully to their proposal, and when she got home that night, Kathie told her husband, “These guys are nuts!”

A team of researchers based at Stanford subjected chips of the meteorite to further laser tests, which yielded polycylic aromatic hydrocarbons – PAHs, for short – which are often associated with life. That finding raised more questions than it answered, for PAHs are also associated with inorganic material such as pollution and exhaust. If that were the case, the carbon in the meteorite could be the result of very recent contamination on Earth, not evidence of ancient life on Mars. Additional tests showed that the PAHs were buried inside the meteorite and probably quite old, lessening the likelihood that they were the result of exhaust. It looked like the PAHs came from Mars, after all.

The team felt confident enough to announce some initial findings at the 1995 Lunar and Planetary Science Conference, held at the Johnson Space Center. In the planetary science community, the LPSC is a very big deal, a sort of scientific Super Bowl. If you don’t show up for this event, scientists say, everyone assumes you’ve died, and when you do show up, you come to make news, if you can. On behalf of the meteorite team, Kathie Thomas-Keprta presented a paper about the unusual and provocative features of ALH 84001 observed by the team. The paper stopped short of declaring they had found evidence of life on Mars, even very ancient, very tiny life. In fact, she adamantly denied it to a reporter from the Houston Chronicle who suspected she was hinting at it.

She knew other scientists would soon challenge her findings, no matter how cautiously expressed. Faulty science or clumsy handling of the situation could mar several carefully-tended careers. So McKay and his colleagues ran still more tests on the meteorite with an even more powerful scanning electron microscope designed to inspect rockets for minuscule fissures; this instrument was capable of magnifying objects up to 150,000 times. McKay put a four billion year-old piece of Mars under the microscope, and on his monitor there appeared a bunch of worm-like forms. He printed an image, and gave it to his teenage daughter.

“What does it look like to you?” she asked her father.

“Bacteria,” he answered.

Kathie Thomas-Keprta eventually decided the guys on her team weren’t nuts, after all. Her conversion occurred in Building 31 at the Johnson Space Center one night when she was working late. As she examined the shapes of the nano-fossils in the meteorite, she knew from experience they were of biological origin. “It was gregite, an iron sulfite present in the carbonate. It had a certain morphology known to be produced by bacteria. It was actually a biomarker, a thumbprint left by biological activity. I thought, ‘That’s it. There’s life on Mars.’

“I walked out the door to the parking lot, half-expecting to see flags waving and bands playing, but there was nothing at all out there, just a dark, empty parking lot at night.”

The chain of reasoning was more or less complete. The meteorite was old enough to contain of a record of Mars’ early days, when water was plentiful. It had carbonaceous material; it probably had Martian rather than terrestrial PAHs; and it had gregite, a universally accepted sign of biological activity. Although each distinct link could not be taken as proof, they all added up to a fairly strong argument for ancient life on Mars.

The team, now grown to nine, approached Science magazine. They realized that getting the prestigious journal to accept their paper would be difficult and delicate; they might have to withstand as many as four or five anonymous critiques of their work. Science was tempted by the paper but reluctant to support invalid conclusions, so the publication sent out the manuscript to nine readers. The resulting article relied solely on sober observations and rigorous science, and its title reeked of compromise: “Search for Past Life on Mars: Possible Relic of Biogenic Activity in Martian Meteorite ALH 84001.” The most important sentence was the summary: “Although there are alternative explanations for each of these phenomena when taken individually, when they are considered collectively … we conclude that they are evidence of primitive life on Mars.” In other words, the meteorite offered the first scientific evidence that ours is not the only planet in the Solar System where life emerged. Publication of the issue of Science containing the article was set for August 16, 1996.

When Jim Garvin heard about the impending Science paper, he felt the skin on the back of his neck prickle. “I was dumbstruck,” he said. In 1990, he had looked at another meteorite, Shergotty. At the time, no one realized that particular rock had come from Mars. He borrowed a piece of it from the Smithsonian, where it is stored. “I took it up to our lab and made the measurements I’d wanted to make for impact metamorphism” – looking for evidence of shock waves, that is. “This was a passive measurement, by the way, like bouncing a laser pointer off a rock; we weren’t destroying it.” There he was, examining a piece of Mars without realizing it.

The force of the new paradigm – that life on other planets was probably tiny – spun Jim’s thinking in a new direction. “We were still a few months before the launch of Pathfinder and Mars Global Surveyor, and the question was asked, ‘What could be done with these ready-to-go spacecraft to look for more signs of life?’ ” Suddenly, Jim’s Mars mission had a new reason for being. He had always believed it presumptuous to assume that life existed only on Earth, and he was sympathetic to the meteorite team’s conclusions about ALH 84001. Their research science was rigorous, it was cautious, and it was consistent with the latest findings concerning extremophile life. There was something in that meteorite that could not be explained away by conventional arguments. Jim agreed with the team that the burden of proof had now shifted to those who insisted there was no life on Mars. If that was the case, he said, “an interesting explanation as to why life failed to make at least a tenuous foothold would have to be crafted.”

The midsummer Martian madness started in earnest a couple of weeks before publication of the article, when Dan Goldin, the mercurial, publicity-loving head of NASA, heard that Science had accepted the article for publication. Next, the White House wanted to make a grand occasion out of the discovery of possible life on Mars. In preparation for the announcement, Goldin summoned David McKay and Everett Gibson to Washington. “We had thirty minutes scheduled with Dan to talk about the meteorite,” Everett told me. “After an hour and a half, Dan said, ‘You guys take a break, I’ve got some things to do, and then we’ll continue.’ During the break, he dictated a commencement address he was going to deliver at UCLA and handled a few other things, and then we continued for another hour and a half. I felt like I was giving an oral defense of a Ph.D. thesis. I mean, Dan went back to first principles, and he took twenty-eight pages of notes.” At the end of the ordeal, Dan Goldin had one last question for the two scientists: “Can I give you a hug?” The gesture was pure Goldin. In general, NASA is not a touchy-feely place – but Goldin is a man of enthusiasms.

After that, the story began to leak everywhere. Space News, a weekly trade journal, hinted at the forthcoming Science paper about ALH 84001, and the buzz preceding an important Washington story started; then things suddenly went awry. At the stylish Jefferson Hotel in Washington, Dick Morris, an advisor to President Clinton, told a prostitute named Sherry Rowlands about the discovery, in the vain hope of impressing her. “Is it a bean?” she asked. Well, no, not really, he replied. It was, uh, more like … a “vegetable in a rock.” When Rowlands got home and opened her diary to write about her day with Dick, she noted, “He said they found proof of life on Pluto.” Scientists dread being misunderstood by the public, but who could have imagined the magnitude of misunderstanding generated by this discovery? The situation deteriorated even further when the befuddled hooker tried to peddle the story to the tabloids, which turned out to be more interested in extraterrestrial life in the form of little green men than vegetables in rocks, thank you. And her inability to recall just what planet Dick said they’d found life on – Saturn, maybe? – didn’t help her credibility, either. There was no sale.

The life-on-Mars story quickly took on a life of its own. The CBS Evening News was making disturbing noises that it might break the news even before confirmation, according to an account that appeared in Texas Monthly. Other networks sensed news in the making and assigned reporters. Science tried to halt misunderstandings by posting the article on the Internet shortly before publication. On the first day alone, the website received over a million hits. Giving substance to an age-old dream, and terror, the article’s findings excited worldwide attention. The announcement gave new impetus to America’s expensive, beleaguered space program, especially its investigations of Mars. Goldin was delighted to confront a challenge of this magnitude, and the mood surrounding it recalled the great days of the space race, when Americans had an emotional investment in NASA and the nation’s fortunes seemed to rise and fall with the agency. But the issue of life on Mars was more complicated to explain to the public and sell to Congress than sending people to the moon had been. There was no life-on-Mars race for politicians to exploit. National security and national pride were not at stake. Only the science really mattered. The discovery involved concepts difficult for most people, even scientists, to understand, including a meteor of unimaginable age that had traveled to Earth from an unimaginable distance, containing evidence of life that was unimaginably tiny.

NASA finally made the announcement at a flashy press conference, at which an exuberant Dan Goldin proclaimed, “What a time to be alive!” (And the head of NASA, he might have added.) Bill Clinton, campaigning for reelection, appeared on the South Lawn of the White House to hail the discovery as if it were another triumph for his administration, but he actually sounded a note of caution that went largely ignored: “If this discovery is confirmed, it will surely be one of the most stunning insights into our universe that science has ever uncovered.” That was still a big if. And his declaration that the American space program would now “put its full intellectual power and technological prowess behind the search for further evidence of life on Mars” did not necessarily mean additional money for a beleaguered NASA. His words amounted to a mere presidential pat on the back.

The summer of Mars was underway. For a while, the names of the several NASA scientists on the meteorite team – McKay, in particular – were known to journalists and the general public. The sudden popularity threw the scientists for a loop. They naturally desired professional recognition, but not celebrity. In their line of work, being famous meant being considered suspect, a semi-charlatan, a talking head rather than a working research scientist. None of them aspired to become the next Carl Sagan, bridging the gaps among the media, the scientific community, and the public. Although their thinking was revolutionary, they weren’t visionaries; they just wanted their funding, and they wanted to pursue their scientific interests. The announcement concerning ALH 84001 made it harder for them do that, as publicity insinuated itself into the normally orderly process of disseminating scientific information. Instead of addressing specialists at conferences and publishing in specialized journals, science teams proclaimed their findings in press releases, in advance of publication. Freed of the constraints imposed in a refereed publication such as Science, the releases tended to make larger claims than the articles that inspired them. Conducting science by press release troubled many, including those engaged in the practice.

The announcement concerning ALH 84001 transformed NASA. For the first time, many people realized that NASA supports scientists, not just astronauts and engineers and the crews that send them into space. In its youth, NASA had accomplished one spectacular engineering feat after another: putting an astronaut in orbit, sending astronauts to the moon, keeping astronauts in orbit for months on end. These missions included science, but science was rarely the point. Flags and footprints on the moon were the point. Astronauts did collect a few hundred pounds of moon rocks for scientists to analyze, but the public had scant interest in lunar geology. Now, with the announcement of possible nanofossils in ALH 84001, NASA scientists were no longer overlooked. And with the end of the cold war, they could participate in missions that were primarily scientific rather than political, missions that might become more significant than sending people to the moon. They suddenly had an opportunity to devise experiments exploring fundamental questions about the nature of the universe and the origins of life. Their results of their search, a NASA report concluded, “may become a turning point in the history of civilization.”