The Rock From Mars (39 page)

David McKay could have played it safe and simply claimed to have found evidence that Mars was “habitable” in its youth, but he and his group had pressed on to suggest that there could be signs of Martian biology. Martin Brasier could have stopped with his challenge to the nature of Schopf’s fossil shapes, but he’d pressed further to suggest that the Australian formations held
no
signs of biology at all. The absence of biology in that case was as hard to prove as its presence.

In a funny way, Steele thought, Schopf had sealed his own fate when he’d set the bar so high for David McKay’s group. He had not met his own standard.

Steele believed that with the weight of the “Schopf doctrine” removed, that area of research was refreshed as if a window had been opened to let the breeze blow through. Young, energetic investigators could take up the hunt without being tromped on by the establishment regime. It might turn out that there had been oxygen-producing pond scum at an amazingly early point in Earth’s infancy, but acceptance of that notion would henceforth require more than a voice of one.

Even as researchers around the world—notably Japanese and Australian groups—took a fresh interest in the topic, Schopf would, with characteristic vigor, continue to defend his 1993 findings, and his way of presenting them. Meanwhile, he could take solace in the fact that he had accumulated a solid body of other work that he considered equally significant and that was widely admired by his colleagues. And, in an unwitting echo of Steele, he observed that he had always hoped his 1993 paper would “spur a lot of further work,” but for a long time it had not. “Now,” he noted somewhat dryly, “it has!”

On this spring day, as David McKay made his way out of the white tent after the debate, he still stood as Schopf’s rival in claiming the oldest known signs of life anywhere. But neither man could boast textbook certitude. And both were passionate about defending their claims.

Not surprisingly, McKay personally found Martin Brasier’s argument that Schopf’s little shapes were not true microfossils convincing. In his view, Schopf actually had less specific evidence of biology than the McKay team had put forth in 1996.

McKay remarked to a walking companion that his research team was more cautious in its published claims than Schopf had been. “He put down genus and species for eleven of these little forms [in the Australian rock]. We wouldn’t do that [for the fossil-like shapes in the Mars rock]. We were just more
conservative
than he was.”

McKay was reluctant to say more about the shocking assault on his nemesis.

But for many observers, the debate that afternoon had usefully outlined in neon two obstacles frustrating their collective enterprise: that nobody had yet found a reliable way to recognize the signature of life in the geochemical record on this planet, much less on any other; and, more fundamentally, that there was no consensus about the very definition of life.

CHAPTER FIFTEEN

DOWN THE RABBIT HOLE

O
NE AFTERNOON IN
early April 2004, McKay—pushing seventy now—was in his lab on the southern corridor of Building 31, staring at the monitor attached to his microscope. He was at 15,000 volts, in the dark and down the rabbit hole.

McKay happened to be lending Kathie Thomas-Keprta a hand with the preparation of selected bits from the Allan Hills meteorite. A facility in Austin had a new technique she wanted to try out on her magnetic crystals.

But much of the time, McKay was keeping an eye on events well over 100 million miles away, where the red planet was suddenly fairly
aswarm
with Earth robots that had managed to slide past the Martian devils.

In January, the twin U.S. surface rovers Spirit and Opportunity had bounced onto equatorial flatlands on opposite sides of Mars and quickly become the most prodigious excursionists on another world since the Apollo astronauts. They covered more alien acreage than their human predecessors. And they had better equipment. As they prowled their dusty way across crater and plain, the rovers deployed grinders and microscopes and other analytical tools, collected data, and sent back tens of thousands of images.

In detailed three-dimensional color imagery, the robot eyes translated the alien landscape into visual poetry and reminded Earth-bound citizens once again of the dreamy, savage beauty of interplanetary exploration.

At the Jet Propulsion Laboratory in Pasadena, the site of Mission Control, you could put on the special liquid crystal shutter glasses, stand in front of a freshly transmitted, wall-sized panorama of the rovers’ new habitat, scan the sci-fi pink sky and the play of light on gradations of browny-red in rock and dune—apricot, saffron, auburn, terra-cotta, russet, blood—and feel for a moment as if the ball of your foot had pressed into the cold sand, and you were poised to push off over that dune there toward the hills rising gently on the horizon. It was just a matter of stepping forward.

More important for the watching astrobiologists, Spirit and Opportunity were a species of water witch.

Decades of Mars observations had showed ancient riverbeds, valley networks, islands streamlined to the shape of teardrops, and other signs of flowing water from the period that ended some 3.5 billion years ago. There were even some hints of possible groundwater seepage onto the surface of modern-day Mars. Now the twin explorers were busy scraping up tantalizing signs of long-vanished water at both landing zones—the most definitive accumulation of water evidence ever pulled directly from Martian rocks themselves.

The rovers were cementing scientists’ recognition that the surface of early Mars might have been habitable.

In keeping with NASA’s “follow the water” mantra, scientists had recently shown that the Martian polar caps could contain a volume of frozen water equal to about 85 percent of the Greenland ice cap. In the northern hemisphere of Mars, the Odyssey orbiter had revealed concentrations of water ice filling up to 90 percent of the volume in the top meter of ground. In other words, the place was not a modern-day desert but frozen tundra—and a resource that could be used by future explorers.

(In early 2005, European scientists would report that their Mars Express orbiter had detected what could be vast bergs of frozen water only a few million years old buried beneath the surface at an unexpected location—quite close to the relatively balmy Martian equator. They would deem this “a place that might preserve evidence of primitive life.”)

At the same time, a particularly intriguing explanation for ancient (and to some extent continuing) radical global climate change on Mars was gaining currency with influential players such as Michael Meyer, the astrobiologist who had become head of NASA’s Mars program. The planet, it seems, has a habit of dipping like a dancer—though in very slow motion—on its sweeps around the sun. Though Earth and Mars are currently at about the same gentle tilt relative to the sun, advanced computer models (based on the accumulating data) indicate that the poles of Mars have bobbed to and fro dramatically over hundreds of thousands, or even millions, of years—sometimes making curtsies of as much as 60 degrees. (At a time of maximum tilt, for example, the summer polar cap would heat more as it pointed more directly at the sun. It could burn off the polar ice and contribute to a greenhouse effect.) As planetary investigators pondered the origins of the ancient branching channels, and the sources of the stunning, seemingly recent seepages from hidden aquifers, and wondered where all the Martian water had gone, they could point to growing evidence that the planet’s rocking provides a mechanism that might drastically alter the climate and move water on a global scale.

But were the signs of ancient water flows the result of flash floods from catastrophic events—comet impacts, volcano melts—which would have refrozen too fast for life to evolve? Or did Mars once have rain, oceans, lakes—waters that lingered long enough for chemistry to become biology? That question had vexed Mars investigators for years.

Key pieces of the water puzzle eluded the investigators. But near the Martian equator, they had detected a potential water beacon—a concentration of a reddish iron ore (hematite) known to form in the presence of water (although it could also form in other ways).

The mission team landed Opportunity at the site of the water beacon in an equatorial plain called Meridiani. The robot had the stunning good luck to hit a geological jackpot. It fetched up near the first rock outcrop ever found on Mars—“essentially a road cut, a piece of time-history” recorded in chronological layers, as Mars mission scientist Maria Zuber, of MIT, described it.

In its landing zone at Eagle Crater, a small impact hole in the vast, wind-rippled equatorial plain, Opportunity photographed legions of peppercorn-sized mineral orbs dubbed “blueberries” scattered across the surface. They contained the iron ore that had summoned the rover to this spot. On Earth, these mineral BBs form in standing water.

Opportunity also measured the highest concentration of sulfur ever seen on Mars. On Earth, rocks with this much sulfur in the form of sulfate salts would either have formed in water or been significantly altered by water after they formed. Scientists were most excited by the discovery of a hydrated iron sulfate salt (jarosite), which hinted that the rock might have rested in an acidic lake or hot spring.

Such highly acidic waters could solve another riddle: Why hadn’t the Martian explorers found the expected large deposits of carbonates, which (in addition to salts) should be left by any primordial seas or lakes? Because the acid could have dissolved them. The significance of the small deposits of carbonate globules in the Allan Hills meteorite, in terms of this bigger picture, remain unknown.

Once again, Mars was springing a surprise. Scientists had expected that the key to the Martian riddle would be carbon. Zuber said, “It turns out the real key is sulfur.”

The bad news for prospects of life: the water apparently came and went repeatedly in this locale. That unreliability plus the highly acid, salty conditions would have made living there difficult—though not impossible.

McKay watched with keen interest and no little frustration as the golf-cart-sized rovers went about their business. He was once again, as he had been that day in Apollo Mission Control thirty-five years earlier, dependent on the hands and eyes of a remote emissary to do the fieldwork on another world. And this time, he was even farther removed. He managed a few consultations with Mars team members by phone, to discuss details that interested him, but mainly, like much of the population, he had to watch on TV and the Internet.

Alternative approaches to the Martian mysteries also attracted McKay’s involvement. The acidic history exposed by the robot on the plain of Meridiani was mirrored in some ways at the highly acidic Rio Tinto (Red River) in Spain, where dissolved iron gives the waters the color of a Burgundy wine. McKay was detaching a young biotech engineer from his staff to work there with an international team of biologists and engineers as they tested deep drilling and other robotic techniques for Mars. They also hoped to find mineral-eating bacteria in a watery habitat deep beneath the surface—in conditions similar to those considered most likely for any microbial denizens of the other planet.

McKay was particularly interested in the Martian blueberries. He had joined a team led by a University of Utah scientist who was studying similar concretions in the desert Southwest, particularly Navajo sandstone in Utah. The researcher had found remarkably similar spheres—terrestrial blueberries—where groundwater had flowed through the sandstone and altered and dissolved the iron. Earlier published work convinced McKay that these things had precipitated from water at relatively low temperatures—mild enough for life.

Then there was an unusual patch of ground dubbed the “magic carpet,” where Spirit’s landing had disturbed the topsoil and left exposed crust that appeared to be “cakey” or matted, unusually cohesive and resilient. Rover team members speculated that there was some kind of electrostatic process at work or even possibly that sticky salt had been left when water had evaporated through the upper layer. But McKay thought the material looked like the mats formed by microbes on Earth. Had it been processed by Martian microbes? Of course, he knew, this was wild speculation, possibly even nutty. But he couldn’t get it out of his mind.

As always, the instruments on Mars were limited, some of the findings were subject to dispute, and the whole story remained unclear.

The twin explorers on Mars, in exceeding the fondest hopes of their human sponsors, incidentally provided the U.S. space agency the balm of good news after a year dominated by another
Challenger-
like calamity: the fiery February 1, 2003, disintegration of the shuttle
Columbia
over the southern United States, which killed seven more astronauts and crippled the human spaceflight program for years. (In January 2004, NASA had named Spirit’s landing site Columbia Memorial Station, in honor of the fallen crew.) In February 2004, President George W. Bush proposed to return people—working cooperatively rather than in competition with robots—to the moon and eventually on to Mars. (As one result, McKay found himself in demand once again because of his old specialty—moon dust.) This would not be a Kennedyesque all-out push but was billed as a long-term national commitment to proceed in manageable, affordable increments. The initiative quickly fell into the political gears, its fate uncertain.

But the Mars twins were a hit. The new plan called for NASA to keep sending new missions to the planet at every opportunity, and to continue the search for signs of life. The still-young field of astrobiology had grown fivefold in a decade. But the planners had learned the need for patience, and were devising small steps to be carried out before any direct attempt at life detection. Viking had proven the wisdom of this approach.

Besides, the Allan Hills rock had taught everybody about the tricky complexities of the enterprise. As a NASA committee reiterated ominously in a recent Mars exploration report, “completion of all the investigations will require decades of studying Mars. Many investigations may never be truly complete (even if they have a high priority).”

On August 12, 2005, the $500 million Mars Reconnaissance Orbiter lifted off from Cape Canaveral on course for arrival in March 2006. Spacecraft instruments were to tackle the question of whether—and in what places—Martian waters had persisted long enough for life to arise. They would search for minerals that form in such conditions and for shorelines of ancient seas or lakes, and they would study the character and depth of the recently detected subsurface ice deposits. The most powerful orbital “spy” camera ever sent to another planet would zoom in for close-ups. All of this would be plowed into landing-site selections for robots in the pipeline.

The labs in Building 31 were being remodeled, and McKay and his group were anticipating the arrival of two big new pieces of equipment: a $2 million ion microprobe and a new transmission electron microscope more advanced, and with more bells and whistles, than the one Thomas-Keprta had been using all these years.

Next door to McKay, Simon Clemett was trying to get his new laser lab up and running. But there had been setbacks, such as a power outage that had ruined an expensive pump. The lab door, with its combination lock, was almost completely covered up with warnings:
DANGER
:
CLASS IV LASER SYSTEMS
;
DANGER
:
INVISIBLE LASER RADIATION
;
DANGER
:
CARBON DIOXIDE LASER
;
DANGER
:
LASER RADIATION
,
AVOID DIRECT EYE EXPOSURE
;
DANGER
—
HIGH VOLTAGE
,
25
,
000 DC
.

Farther down the hall, Everett Gibson was in his office day and night this week, pushing hard to finish a proposal to study salts from evaporated waters in the dry valleys of Antarctica, to see if they were analogous to the salts the U.S. rover team was currently seeing on Mars. This was Gibson’s Plan B. He had hoped to be in London now, with his friend Colin Pillinger, working on data flowing from Pillinger’s Beagle 2 on the surface of Mars.

Just months earlier, on December 19, 2003, Gibson had returned to the Royal Geographic Society hall in London, to the podium where he had felt supremely honored to stand not long after the 1996 announcement. This time, he was part of a group that included Prince Andrew. The happy occasion was the arrival of the signal that Beagle 2 had separated from its mother ship, the European Space Agency’s Mars Express orbiter, and was on course for a Christmas Day landing near the Martian equator.

Gibson had been selected as an “interdisciplinary” scientist on the project. Beagle 2, named after Darwin’s ship, was to be the first such life-detection mission since the Vikings in the 1970s.

The key experiment, in Gibson’s view, was one designed to look for methane in the Martian atmosphere. Since this gas was destroyed by the sun’s ultraviolet radiation, its presence would suggest a source of recent renewal, such as outgassing by bacteria surviving beneath the lethal Martian surface. (On Earth, as fans of humorist Dave Barry well knew, methane is a major product of cow flatulence and other processes associated with single-celled organisms—but it can also come from nonbiological sources.)