First Contact (16 page)

Mahaffy brought several off-the-shelf versions of SAM instruments with him to Svalbard, but the real SAM remained in a locked clean room at Goddard Space Flight Center. That's where I had seen it earlier, and it was quite a technological and aesthetic marvel.

In my short time with SAM, I was startled time and again by what it can do. It has, for instance, little heat chambers where rocks and sediments are baked into gases, and these can reach 1,000 degrees Celsius using but forty watts of electricity. Although it's tucked into the larger rover, SAM will be exposed to temperatures ranging from –40 to +40 degrees Celsius, sometimes in a matter of hours. It carries a “tunable laser spectrometer” that bounces received laser light some fifty times between two mirrors before it measures how the light is absorbed for gases like methane. The instrument can detect methane to a level of parts per billion. The maze of pipes and circuits and wires needed to run SAM so it can learn whether a particular piece of Martian rock has biologically produced molecules, or precursor molecules, or the extreme long shot of living molecules, is almost laughably complex. But the overall effect is of elegance, in part because the SAM containment box is plated in gold. Mahaffy said it's essential for controlling “thermal response.”

Do scientists really think they'll find something—some sign of past or
present Martian life? Probably nobody knows more about that question now than Steve Squyres, the Cornell University astronomer and planetary scientist who has led NASA's rover missions Spirit and Opportunity since they landed, packed into two large bouncing balls, on Mars in early 2004. These are the little rovers that could, the ones that were expected to pass out some ninety days into their mission, but instead were still going more than six years later. As they've wandered their little patches of Mars, they've collected more data about the planet than any other mission, and Squyres has been in the driver's seat the whole time. He's also now a Svalbard regular.

Results from the rovers, he said, “show more convincingly that Mars at some point in its past was a habitable world. You have to be careful, and I'm always reminded of the parable of the blind man and the elephant: We have two little, tiny spots on Mars we're looking at and we have to be careful about what we conclude. But the rovers are in very different places, and both show compelling evidence of near surface water, of interaction of that water with rocks and minerals, and in the case of Spirit site, you have hydrothermal activity—hot water and steam. These are the features that on Earth lead to local habitable niches.”

It was quite definitive, and Squyres is hardly a starry-eyed newcomer. I met him at an astrobiology conference where he discussed and sought feedback about NASA's planetary sciences road map for the next ten years, an effort that he leads. I wanted to make sure I understood what he was saying, so I asked if the rovers have nailed that habitability question.

“I feel that they have,” he replied, with a glint in his eye. “Yes.”

You would think that a science that has fought so hard to be taken seriously would nourish a culture of dissent. But perhaps because of its urge for legitimacy, or because the discipline itself so often enters terra incognita, astrobiology has shown a consistent need to enforce a consensus. That is evident in the way it can treat those who diverge from the general view of what constitutes life on Mars and other celestial bodies.

Three reputable, diligent, and veteran researchers, for instance, are convinced that they have detected or even seen remains of life from Mars and from other celestial bodies. But not a single one can fill a hotel meeting room with their argument. Two are career NASA scientists who now carry the title of astrobiologist, and one was the creator and principal investigator for the main life-detection experiment sent to the surface of Mars for the two 1976 Viking missions. Together they have some seven decades of experience researching and analyzing experiments about extreme and extraterrestrial life, and two have been at center stage for some of the most important moments in NASA history.

Yet when the three took their places with others on a small side room dais at the Marriott Hotel in San Diego to address the topic of “Life in the Cosmos,” few of the five thousand scientists attending the conference they were part of—hosted by the optics and imaging organization SPIE—were anywhere to be found. The Marriott's Marina Ballroom, Salon F, has seats for about 130 people, but on that summer night in 2009 only a quarter were filled. So it goes when the scientific community has concluded you're off base on a subject as charged as extraterrestrial life.

The first to unspool his findings was David McKay, the NASA researcher who introduced the world to the softball-sized meteorite from Mars that, for a short time in the mid-1990s, was hailed as containing strong evidence that life once existed on that planet. He and his team at the Johnson Space Center never claimed they had
proven
the rock, found in 1984 in the remote and meteorite-rich section of Antarctica called Allan Hills (and named ALH 84001), had been home to living microbes. Rather, they reported finding five distinctive characteristics of the rock, determined through various chemical analyses to be Martian and about 4.2 billion years old. Those characteristics are generally associated on Earth with microbial activity. McKay did report the possibility that the meteorite contained a Martian “microfossil”—the minute remains of the outer sheath of a bacterium—but his strongest results involved the presence of minerals and rock alternations that are considered signs that bacteria and other microbes were once at work eating the rock, transforming the rock, and depositing waste in the rock.

Not surprisingly, “proof of life on Mars” is the way the story played when it came out with a bang in 1996, and the “microfossil” was the star of the show. The discovery was featured in a major article in the journal
Science
, a full NASA press conference with two hundred reporters and cameramen present, and these words from President Bill Clinton: “Today Rock 84001 speaks to us across all those billions of years and millions of miles. 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.” But in a foreshadowing of the bizarreness to come, the article was rushed into print because news about “life on Mars” was beginning to leak out. The source: a prostitute who was in the hire of Clinton political consultant Dick Morris. The president had apparently told Morris about the breakthrough, and Morris had told his companion, who then took the news to the tabloids.

Still, for a while McKay and his colleagues were on top of the scientific world, invited and feted everywhere. But like a pitcher whose nohitter
is spoiled in the ninth inning and who then loses the game, McKay quickly went from hero to goat. His team and their findings were subject to a fierce and wounding attack by other specialists in meteorites, geology, microbiology, and the study of ancient life-forms in rocks. That the Martian meteorite paper would inspire other scientists to study and criticize its methodologies and findings is hardly surprising—that's how science works. But that doesn't mean emotions and human defensiveness, offensiveness, and grandstanding weren't also at play. Attacking and defending the paper soon became a blood sport, an often brass-knuckled and highly personal struggle over the true contents and meaning of the meteorite. Suffice it to say that fourteen years after the paper was published, much of the scientific community has dismissed it, or at least concluded that it didn't offer the “proof” that it actually never purported to offer. McKay, who needed quadruple heart bypass surgery a year after the controversy exploded, has spent much of the intervening time responding to his critics, doing the experiments and reexamining the data in the hope that he can convince the world that the Allan Hills meteorite really did once house living Martian organisms.

Given this history, it was no surprise that McKay took shots that day at the Marriott at both his scientific critics and at a press corps that he said jumped on all the doubts raised about his work but seldom was interested when those critiques were found to be wanting. “What I would like to do today, if I can, is convince you that the Martian meteorite studies are very much alive, and furthermore that the evidence is becoming stronger all the time that Mars meteorites contain evidence for life on Mars,” he began. “Now that sounds like an opinion, but I hope to reinforce that with some facts.” What followed was a detailed and emphatic recounting of where things stood regarding both the original Mars meteorite and several others that McKay and his team have examined.

McKay's story goes like this, and is quite persuasive: His initial research led him to conclude that rock from Mars contained slightly magnetic grains or crystals that, on Earth, are often produced by bacteria that use
and leave behind when they die signatures of the planet's magnetic field. The McKay team's original assertion that the meteorite held these magnetites was attacked as near ridiculous, since nobody had ever detected the presence or remnants of a magnetic field on or around Mars, either now or in the past. In addition, magnetites, like so many possible microscopic signs that living organisms once were present, can also be formed through nonbiological processes, and at least eight substantial papers have been written arguing for a range of origins that had nothing to do with life. The most common counterargument has been that the magnetites were formed when asteroids, perhaps the one that ejected the meteorite, hit Mars about fifteen million years ago and formed magnetites in the resulting shock and enormous heat.

But the McKay case was substantially strengthened in the late 1990s when the Mars Surveyor orbiter did detect remnant signs of an ancient magnetic field on the planet. It was a huge coup: McKay's prediction based on his early research—in this case, that Mars once had a magnetic field—was actually confirmed with observed data and measurements. Making predictions which are ultimately proved correct greatly strengthens any hypothesis. McKay then followed up with another rebuttal to his critics: His team published years of lab work that found the ALH 84001 magnetites were too pure and their concentration was too great to be explained by the contending “thermal shock” hypothesis—that they were formed in the scalding heat of a meteorite impact. In addition, a mineral needed to form magnetites nonbiologically was not present in the meteorite. Their conclusion: The magnetites were the mineral remains left by bacteria on Mars that, like some bacteria on Earth, contain magnetic crystals.

But McKay and colleagues Kathie Thomas-Keprta and Everett Gibson didn't get the rehabilitation they craved. Their foes kept insisting the original research was botched. For instance, Allan Treiman, a senior scientist at the Lunar and Planetary Institute, located in Houston, wrote in a 2009 paper that it was hard to disentangle the origins of ALH 84001 in part because the clues present have been “muddied by now-discredited claims for
biological activity.” Treiman later told me: “Would any reasonable person conclude that there was life on Mars based on the proportion of magnesium in submicron grains of magnetite?”

But McKay kept at it. His initial research had shown that the meteorites contained carbonates, which are minerals formed only in the presence of the liquid water needed for life. That finding faced the same hurdles as the finding of magnetites did: no confirmation of liquid water on or near the surface of Mars and the contention that the carbonates were formed in a superhot environment, where no life could possibly exist. But McKay's team was again helped by new discoveries on Mars, this time a fast-growing body of evidence that water had indeed once flowed on the Martian surface and that ice can still be found in substantial amounts just beneath the surface. McKay's colleagues had dated the carbonate globules at about 3.6 billion years old—when Mars was still potentially habitable—and subsequent tests have tended to support that conclusion. Considerable evidence now exists that Mars was much wetter and had a thicker atmosphere at that time. Lakes and even oceans likely existed. The idea that the carbonates were formed in a Martian cauldron is not heard much today.

McKay's microfossil was also controversial because no bacteria or other life-forms so small had ever been detected. McKay no longer argues as strenuously that the tiny microfossil is an important part of his case, because he is finding what he believes are much larger Martian microbes in other meteorites. Nonetheless, in the time since the paper first came out to such acclaim and criticism, many living organisms as small as the reported Allan Hills microfossil have been identified and categorized on Earth.

McKay's firm conclusion: The original meteorite did, indeed, show signs of ancient life. But—and potentially far more important—several other Martian meteorites he has since studied contain larger and more readily identified bacterial microfossils, and many are embedded deep in what he considers to be the undeniably Martian core of the rocks. McKay looks back on his time in the scientific trenches and wishes things had been different. “If we knew then what we know now, we would have had a
stronger story that was much more resistant to criticism,” he says. “Every bit of new Mars data is ‘pro-life' in the sense of supporting the hypothesis that life has occurred on Mars. Every bit.”

Where McKay and other students of meteorites are most vulnerable is in defending the rocks from the charge of Earthly contamination. The ALH 84001 and all other meteorites, many scientists argue, are corrupted with bacteria that move in as soon as they hit the planet and possibly even as they pass through the atmosphere. While some meteorites are collected soon after they fall, others remain undiscovered for eons; in the case of the ALH 84001 meteorite, the wait was about thirteen thousand years. That rock fell in the relative cleanliness of Antarctica, but other important samples fall in areas teeming with microbes, which can quickly penetrate the outer crust of the extraterrestrial rocks. Some pieces of the Murchison meteorite—the one that Glavin and Dworkin have used to explore chirality—landed on or near Australian farmland, other samples in the brush. Adding further to the threat of contamination, the Mars meteorites come filled with carbon compounds, which the microbes especially like.