At the driest spot in the driest part of the driest desert in the world, NASA is getting ready to invade the Red Planet.
A saddleback ridge and two gentle peaks the color of rust rise from a rough, rock-strewn plain. The soil is a powder dotted with gray and salmon pebbles. Every footfall raises tiny puffs of dust and leaves a sharp-edged track. The piercing blue sky extends in an unbroken arc; the wind howls and tastes of salt. Everywhere I look is utter desolation, without a trace of any living thing – just stone, sand, and sky. It could be a picture from Spirit, Pathfinder, or Viking. It could be Mars.
Indeed, that's why a couple dozen scientists are now scattered across the hillside. One group sets up an array of sensors on the ridge to monitor ultraviolet radiation. Other groups scout for the best location to station a weather monitor. Fred Rainey, a microbiologist from Louisiana State University, is cursing softly but colorfully in his Northern Irish brogue. With a small group of graduate students, he struggles to dig a pit. He wants it for soil sampling, but he keeps hitting layers of rock-hard sediment. The students look worried.
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Photo by Patrick Zachmann/Magnum Bioengineer Elizabeth Lester hunts for microbes.
Chris McKay, a lanky guy with a Lincolnesque profile, wearing jeans and a floppy green hat, comes by to check Rainey's progress. The pit is barely a meter deep; they'd hoped for two or three. McKay is the leader of the expedition, one of the world's foremost experts on Mars, and Rainey's apparent lack of progress doesn't bother him a bit. "This is great," he says. "This will do just fine." Rainey goes back to his shovel, and McKay continues showing a group of first-time visitors the absolute desert.
The ridge and hills are near the geographic center of the Atacama, 40,000 square miles of brutal wasteland in northern Chile. It is the driest spot in the driest part of the driest desert on the planet. "There are lots of places that look as dry as this," McKay says, gesturing across the barren expanse. "But the stories people there tell, 'This is a place where it never rains,' are hyperbolic. People exaggerate."
Except when it comes to this part of the Atacama. It is the only place on Earth that is, as far as anyone has been able to tell, devoid of life. The most inhospitable environments – boiling undersea thermal vents, acidic hot springs, superbriny seas, even pools of nuclear waste – all, amazingly, harbor some living thing. But not here. No one knows why. That's why McKay's team has come: This killing turf, this parched soil, is Earth's best proxy for Mars.
McKay has spent his career at the most Mars-like places on Earth. In pursuit of the toughest organisms known, called extremophiles, he has scuba dived in the ice-crusted lakes of Antarctica's dry valleys, climbed in Mexico to the world's highest tree line, and searched the wastes of Ellesmere Island, the planet's northernmost landmass. He once spent seven days driving through roadless Mongolian desert; the chief of the village Ehin Gol welcomed the team with a banquet. The scientists spent the next few days vomiting.
But of all the places McKay has been only the Atacama matches the utter desolation of Mars. Even the soil chemistry is, so far, indistinguishable. Like many scientists, he suspects that Mars may have harbored life once. Then it fell over a climatic cliff to extinction – just as it did here, in the former mining outpost of Yungay. "We don't know what the limiting factor is," McKay explains. "Is it a lack of one or more nutrients? Or water? Or is it something in the soil that kills off anything that tries to grow there? We don't know."
What scientists do know, or suspect, about Mars is that the air is thinner than at Earth's highest mountaintops. The temperatures are colder than Antarctica, and water in liquid form is nonexistent. But signs of long-ago riverbeds and shorelines suggest that the planet may once have been more habitable, with lakes and streams and rainfall. The air must have been thicker and the climate warmer. It may have been nearly Earth-like.
So finding what's left of life, if anything, in the Atacama may help scientists to know what to look for, and how to look for it, on Mars. It costs hundreds of millions of dollars to light the candle under missions like Spirit, Opportunity, and others to come; tens of billions, probably, if human beings are sitting at the top of the rocket, as President Bush has promised they will. So the Atacama is a kind of proving ground – not for astronauts, but for the experiments Mars-bound missions will carry. Every bit of science McKay's team does has to be simple, reliable, and durable, because it's all a dress rehearsal.
And the stage is Yungay base camp, an abandoned research station left over from a desert agriculture experiment that ran out of funding. The simple cinderblock-and-wood buildings house a spartan but effective biology lab, concrete-floored rooms where some of the team beds down – others sleep in tents, or under the stars – and a bathroom with a cold-water shower. The lab is a tiny bastion of high technology, packed with centrifuges, DNA analysis machines, racks of petri dishes and chemical reagents, and a wide assortment of beakers, flasks, vials, and test tubes. Laptops are everywhere. There's also a kitchen, one of the rare luxuries of this site, with a gas stove, a couple of plastic coolers, a sink, a table, and a single light bulb hanging from the ceiling. A generator outside hums constantly.
A few years ago, McKay, who works out of NASA's Ames Research Center in Mountain View, California, set up an ultrasensitive weather station here. After 24 months, the gauge for rainfall showed an absolute flat line. "My first inclination was, 'Well, we've got a broken sensor, we've got to go out and fix it,'" he says. So on his next trip he measured a liter of water into a bottle, carried it out to the sensor, and poured it over the detector – his own little artificial rain experiment. "I looked at the data, and there it was, a liter of water recorded, all sensors working fine. The conductivity shot up, the soil humidity shot up. Then it began to sink in for me: It really did go two years here without rain."
In four years of data collection (ending in 1999 when someone stole the $2,000 weather station, probably for scrap), it rained once. "A whopping 2 millimeters," McKay says. "But I was ecstatic, because finally there was enough rain that the ground got wet." It's a basic precept of biology that where there's water, there's life. With that bit of moisture, McKay knew that if there were any cyanobacteria – aka blue-green algae – lying dormant in the dirt, they would spring back to life. But it didn't happen. Even blue-green algae, among the hardiest and most primitive organisms, don't live here.
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Photo by Patrick Zachmann/Magnum Astrobiologist and team leader Chris McKay.
On this trip, McKay has been joined by his colleague and mentor, Imre Friedmann. An 82-year-old Hungarian microbiologist and Holocaust survivor, Friedmann retired from Florida State University in 2001, but he's still an avid field researcher. Eight years ago, he brought a few little pieces of flint from Israel's Negev Desert and set them on the ground at Yungay. Like translucent stones gathered from any desert on Earth, they harbored within them hundreds of thousands of cyanobacteria. These creatures have existed since the dawn of life. Friedmann has found that they can survive on just the scarcest rainfall, or even on fog that collects on rocks in the morning and filters inward a few millimeters, or drips underneath, where it's protected from evaporation. Because the rocks allow enough light through for photosynthesis, the blue-green algae make a living: good light and free drinks.
Not here, though. After eight years, Friedmann picks up the flint pieces, one by one, and brings them close, turning them over slowly. McKay, standing nearby, watches closely. Nothing there, Friedmann murmurs. No, nothing on that one. Nothing there either. No, no. The verdict is clear: Life can't make it here even when you give it a head start.
So the soil is inhospitable, but what about the air? Fred Rainey decides to check it out. He figures he'll need data from four different times of day in three locations, using six different kinds of nutrient growth media. To capture his airborne samples, he attaches a testing device – in essence a fan that blows a controlled volume of air over a petri dish – to a weather balloon. If there are floating microbes here, then something in the soil must be killing them off as soon as they land. So maybe the same is true on parts of Mars; just because we haven't found anything alive doesn't mean there aren't any bugs over the next hill.
While others pump helium into what looks like an 8-foot-high, Kermit-green beach ball, Rainey carefully unseals the first sampling dish and loads it into the device while holding the balloon's neck under his arm in a kind of half nelson. The wind starts to pick up, nearly dragging the balloon – and Rainey – away. He has to work fast to avoid contaminating the dish with ground-level dust. The balloon rises; the first sampling goes well. Seventeen more to go.
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Photo by Patrick Zachmann/Magnum (From left) Rafael Navarro-Gonz�lez, Fred Rainey, McKay, and engineer Joe Jordan prep an air-sampling weather balloon.
By the fourth sample, the wind has picked up, and the balloon is whipping dangerously close to the rocks that surround us on all sides. We're beginning to wonder if it will survive this first run, never mind three or four days. Amid gusts and dust, two team members run around, making volleyball-like digs as the balloon swoops downward. At one point, the steel-clad sampling device hits the ground; one sample contaminated, but no real damage done.
It takes three hours to get 18 samples. Then there's a three-hour break for dinner and a bit of rest back at the station while McKay splices a broken control wire in preparation for the next set. Three hours sampling, three hours rest, and so on. Eventually, it's time to drive the fully inflated balloon, along with the helium tank and other gear, 90 miles to the south. They work for 24 hours, then get back on the truck for a 150-mile haul. The team won't be getting much sleep on this trip. And all that work will be just one part of a larger journal article – just a few points on a graph. Of course, it'll also teach them something about unmanned aerial vehicle sampling on Mars.
In McKay's earlier work at Yungay, he studied topsoil only, to a depth of about an inch. Now he has a new theory. Maybe there's something toxic in that top layer – some chemical produced by the sun's intense ultraviolet rays – that destroys organic molecules. If he's right, that means bugs might exist deeper down. That's why Mars thinkers send probes that can drill and dig.
This site, Yungay, was originally mined for nitrates – chemicals used for everything from food preservatives to explosives. So the terrain is pockmarked with holes and craters. After a conference in the kitchen, the team decides to take soil samples in a 20-foot-deep pit a few hundred feet from the base camp. This is arduous fieldwork – they spend three days rappelling, hammering, drilling, and scooping. But they bring back the dirt. Rafael Navarro-Gonz�lez, an astrobiologist at the National Autonomous University of Mexico, and his student Jos� de la Rosa hustle the bags of sandy soil into the lab.
Another member of the team is Lauren Fletcher, a Lockheed-Martin engineer who designs biological equipment for the International Space Station. He is trying to build an automated version of the polymerase chain reaction. Using a near-alchemical concoction of enzymes and heat, PCR takes vanishingly small amounts of DNA and copies them over and over, building quantities sufficient to analyze. (When the guys on CSI want to test a suspect's DNA, they use PCR.) It's another way to look for life; Fletcher's combing the dirt for DNA as he tries to package the test for an automated Mars visit. So far he has found nothing in the Atacama.
But Navarro-Gonz�lez, looking for different kinds of organic molecules, announces that he may be on to something. Everyone gathers in the kitchen, pulling chairs up to his laptop in a hushed circle. The dots appear in luminous blue and red on the graph: Just a few feet below the surface, there's a very sharp rise in the level of organics – and of water. Everyone looks in silence at the startling results.
McKay gets it first. He frowns. "It's us!" he says. There's no place else all that water could be coming from except runoff from the station itself. Three days of dangling precariously from ropes under the baking sun and all they've done is detect the contamination from a decade of work at this research station.
Science is about bracketing the problem. Rainey tested for microbes in the air, with results to come. McKay fruitlessly looked for cyanobacteria and organic molecules in the topsoil and underground. Fletcher searched for DNA and didn't find any. There's one last thing to try. When bacteria have been pushed past their limits, they switch to an alternate survival mode, turning into shriveled, small versions of themselves called spores that can spring back to life if conditions improve, like when a rain shower suddenly ends a drought. Spores are amazingly persistent, and some tests, though controversial, suggest that they can revive after many millions of years. In nearly every place on Earth, a gram of dirt contains hundreds of such spores; they might persist on Mars, too.
But finding spores in the Atacama will involve some seriously fastidious sample collecting. Teaming up to do it are Elizabeth Lester, a Caltech graduate student in bioengineering, and her professor, Adrian Ponce, a chemist from the Jet Propulsion Laboratory. Before dawn, they stow their gear in the back of a pickup for a long ride over bare dirt and rock. They need places upon which no human has ever trod. They find one: a flat, red expanse interrupted by rocks the size of basketballs.
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Photo by Patrick Zachmann/Magnum A rock sample from Aguas Calientes; the translucent quartzite will be tested for extremely hardy photosynthesizing bacteria.
Lester carefully opens a sterile plastic wrapper containing a white Tyvek clean room jumpsuit. She slips into it, gingerly avoiding contact with its outer surface. She laces similarly sterile booties over her sneakers, and dons goggles and a surgical mask. Cocooned, Lester walks out into the rolling wasteland of sand and rock. Ponce pulls on his gear partway and follows a few dozen paces back and downwind, so as not to contaminate the site. The morning air is cool; if they had waited any longer they'd be sweating in the harsh sun. Lester crouches on the rough ground and slowly pulls sterile trowels from a sterile wrapper, filling sterile amber jars with desert soil.
Watching her, I see an astronaut. Mars mission spacesuits will be light like that Tyvek, nowhere near as bulky as the ones used on the moon or at the space station. But Lester has never worked this way before. "I couldn't really feel the ground," she tells me later. "It did feel pretty much like a spacesuit. Usually out in nature, you're there, but with the suit there's this serious barrier."
There has to be. Ponce and Lester are dealing with the same problem a life-hunter on Mars will. At the limits of detectability, you've got to be darn careful not to contaminate samples with traces of yourself. If you're going to go all the way to Mars, the last thing you want to find is a spore that hitched a ride from Cape Canaveral. "You can't ever be certain you haven't contaminated the sample," Ponce says, "but you can certainly minimize the possibility."
The researchers plan to take the soil back to Caltech for analysis. They've been working on a new technique, sensitive enough to pick up a single spore. Regardless of species, all bacterial spores produce a metabolite called dipicolinic acid, or DPA. Lester and Ponce plan to burst the spores open with microwaves and mix in a solution containing the element terbium, which DPA turns a bright green. Preliminary results in the base camp lab came up negative, but like Fletcher's PCR package, the dipicolinic acid test has a good chance of going to Mars, where spores might be the last remnants of an ancient ecosystem.
About a week later, at the Antofagasta International Airport, one of McKay's students is freaking out. A security guard wants to open every baggie and jar of Chilean soil and run her rubber-gloved fingers through it. The student speaks no Spanish; the guard, pleasant but firm, speaks no English.
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Photo by Patrick Zachmann/Magnum Biologist Charlie Cockell lays out ultraviolet radiation sensors made from a thin film of bacterial spores.
"No," the student says, trying sign language and brandishing a piece of paper. "NASA." But the guard has the lids off the huge plastic tubs that hold the samples, and inspectors really don't like soil. Finally the student calls McKay.
He speaks only a little Spanish, but he does have letters from NASA and official US Customs soil permits. After more sign language, paperwaving, and mutually incomprehensible conversation, the guard relents.
A few hours later, the whole team does it again at Dallas/Fort Worth International, only in English. It's a little ironic, of course, since what the customs officials are most concerned about is the spread of dangerous microbes from one country to another. Yet these containers are filled with the only soil on Earth that has been exhaustively tested and found to be utterly, surgically sterile.
Someday, there's going to be a much more interesting version of this border crossing. When and if soil samples are brought back from Mars, the question that's being discussed here at the airport is going to come up again. Is it safe?
A few weeks after the trip I call Ponce. He doesn't want to discuss the results of the DPA test, the one-spore-sensitivity analysis, because he says they're still preliminary. But there's a certain excitement in his voice.
"We found something, which is interesting," he says. "But it remains to be verified." Typical scientists' caution. Maybe there are spores in the Atacama after all.
That doesn't mean that we'll find them on Mars. But it sure does suggest that we might want to look.
