Laurence Bergreen - The Quest for Mars - NASA scientists and Their Search for Life Beyond Earth

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.