Some forty years ago, a bacterium that usually cowers in the moist comfort of the mouth appeared to have hitched a ride to the moon and back, unscathed, though not in Neil Armstrong's throat or Buzz Aldrin's root canals. Rather, it seemed to have survived in the foam insulation of a TV camera that Surveyor 3 dropped on the moon in 1967 and Apollo 12 brought back to Earth, two years later. Or so the story goes.

How Streptococcus mitis, the surprisingly resilient space hobo, snuck into that camera is still debated. But the anecdote illustrates the kind of "accident" that space-explorers seek to avoid: unwittingly spreading Earth microbes into space, or bringing back alien microbes and setting them loose on Earth.

Preventing these mishaps is the purpose of a branch of NASA that eschews acronyms for the reassuring name of Planetary Protection Office. The concept of clean space exploration predates the Apollo missions. But its strict implementation has become more urgent with the renewed belief that Mars and other worlds could harbor some life forms. Robots that visit these worlds must be clean of Earth microbes, to avoid confusing life-detecting sensors. Moreover, a mission that brings back Mars samples need satisfy severe quarantine requirements to avoid a potentially catastrophic infection of our world.

"We don’t know if there is life on Mars, and we don’t know whether Earth life would survive there," says Margaret Race, of the SETI (Search for Extra-Terrestrial Intelligence) Institute in Mountain View, California. "But we can’t be arrogant. Life and science keep surprising us."

Space exploration has entered a new age. We no longer just gaze from afar, but probe, poke, harvest samples and prepare for future manned explorations. This past year, while the robots Spirit and Opportunity roamed the surface of Mars and bored into its rocks, the Huygens probe landed on Saturn’s moon Titan. Genesis crashed its solar wind samples in the Utah desert, and Stardust began its return trip to Earth with a precious dust load it snatched from the tail of comet Wild 2. Next summer Deep Impact will slam into comet Tempel 1. Ambitious and ever more intrusive Mars missions–including drilling and bringing back samples of martian soil and gas--are planned for the next decades.

NASA’s planetary protection office sees to it that spacecraft and landers are launched clean. The costs are surprising: 5% to 10% of a mission’s budget can go towards cleaning and sterilization efforts, depending on the mission’s purpose. The gold standard is Viking, the 1976 mission that pioneered efforts to find life on Mars. The two Viking landers were cleaned and completely baked–30 hours in a 250°F oven–at the whopping current equivalent of $200 million. But Viking’s life detection experiments were inconclusive. No longer looking for organisms, NASA relaxed its cleanliness requirements: Sojourner, the 1996 rover prototype, and the current Mars rovers were cleaned but spared the bake.

Meanwhile, other missions have charted the ice caps at Mars’s poles and detected signs of frozen water underneath the planet’s surface. Deep gullies and trenches cut through the martian landscape, evoking past rivers or glaciers. On Earth, wherever there is water there is life: Life thrives in liquid water and sleeps in ice for hundreds of thousands of years. NASA can no longer ignore the possibility that there was, or is, life on Mars. If Mars can host life, hitchhiking Earth microbes could grow there and perhaps even displace indigenous life forms. Reciprocally, Mars microbes could threaten our health or our environment if we bring them back to Earth. Consequently, NASA is stepping up its planetary protection standards.

But perhaps it is too late. Scientists estimate that Spirit and Opportunity each brought 100,000 Earth microbes to Mars. "One might wonder if that was clean enough," SETI’s Race muses. At the very least, others maintain, future more sensitive missions cannot afford to be sloppy.

Preparing for the unknown.

Race is a communicator. She draws her experience from many sources: her graduate training in ecology, her professional experience at the Environmental Protection Agency, a stint in radio journalism, and her lifelong fascination for space exploration. And she explains tirelessly--to engineers, the precautions they will have to take when handling a sample from Mars or when sending humans there; and to the public, the purpose and methods of planetary protection.

She turns her knowledge of biology, engineering and policy into recommendations for future space missions and essays on the ethical implications of finding life beyond Earth. Her biggest fear is that the public won’t understand, hence won’t support, a mission that would bring a sample back from Mars.

"We can take risks, we do it all the time," she says with conviction. If there is life on Mars, it will be microbial, she explains. We know how to handle that: The Centers for Disease Control, the Environmental Protection Agency, and the Department of Agriculture all have designed protocols to handle microbial risks safely. We just need to adapt these protocols to the particular needs of Mars exploration, Race maintains.

NASA plans to build a special laboratory to analyze the pound of Mars soil the return mission will bring back in a decade or so. The new lab will be modeled after the ones where scientists study the most virulent pathogens on Earth–SARS, anthrax and others. "One problem," Race says, "is that biologists want to prevent anything from leaking out, but the planetary scientists want to prevent anything from leaking in." The solution was to design a room with successive air locks holding different pressures.

Though the topic seems dry, Race grows animated as she describes containment measures. She slips her hands into an imaginary glove box she just drew in the air, to illustrate how scientists will preserve sterility barriers while handling samples. The return mission poses other challenges, such as keeping the returning spacecraft and sample container free of martian contamination. Then there is avoiding a crash landing on Earth–what specialists refer to as an "unplanned Earth impact." Should the returning trip be doomed, the vessel will be diverted or destroyed, rather than allowed to spill its potentially live payload on Earth. "Planning for sample return will take eight to ten years," Race concludes.

Race is quite confident that we can handle a small piece of Mars on Earth, but whether Mars can handle Earth visitors is harder to assess. "We know that when we move a species from one place to another on Earth, it might compete with native species," Race warns. As a graduate student, she studied an invasive mud snail that was taking over the habitats of resident mud snails in the San Francisco Bay, a century after seafood businesses dumped East Coast oyster shells laden with the invader’s eggs. We know that this happens on Earth, but could it happen on Mars? "We don’t know," she says.

Her colleague John Rummel, who heads the planetary protection office at NASA, likes to remind audiences that a few months after Viking failed to detect life on Mars, scientists discovered hydrothermal vents at the bottom of the ocean. These hot vents harbor thriving ecosystems at a depth and pressure that seemed incompatible with life. His prediction is that there is still much that we do not know about Earth or Mars.

Planetary protection is all about preparing for the unknown.

Life, the unavoidable?

Finding life on Mars would be exciting. It might not quell the anguish of our cosmic solitude, for Mars microbial inhabitants are unlikely to join in our metaphysical banter. But it would bring us closer to solving the riddle of life’s origin on Earth. If the microbes of Mars and Earth closely resemble each other, they probably share a common ancestor that arose once long time ago and spread its seeds to both planets. If they are radically different, then they probably hark back from two separate lineages that arose independently on each planet. And if life arose twice, it probably arose a few more times as well. Life–at least microbial–might be banal, rather than wondrous; the rule, rather than the exception.

The problem is that detecting life on Mars is nowhere as easy as rubbing dirt on a clean Petri dish and watching bacterial colonies grow. Nobody expects Mars to teem with life: Viking would have seen that. And even if it did, we might not know how to grow its organisms. We can barely grow one percent of all known Earth microbes. Life-detecting robots look for subtler–and more universal–clues: gas exchanges, transformation of organic matter, signature organic molecules. These robots would be fooled easily by Earth contaminants. Therefore, they need to be squeaky clean.

That, in many scientists’ minds, is the main purpose of planetary protection. "We want to preserve the ability to do good science," says Rummel. "We are as conservative as we can be."

Viking was clean enough not to contaminate its own experiments. But baking a spacecraft is no longer an option because materials used in modern electronics and hardware cannot withstand the heat. Planetary protection has launched research into new cleaning methods. No longer satisfied with alcohol or detergent washes, scientists puff hydrogen peroxide on the pesky astronaut wannabes that hide inside hard drives or stick to metallic surfaces, or zap them with ultraviolet light or gamma rays. Engineers who assemble spacecraft are themselves clad head-to-toe in sterile clothing. Barely an eyebrow or an ear sticks out from under their masks and goggles.

Still they worry about microbes that might resist their extermination attempts. The dry and bare clean rooms in which they assemble spacecraft might in fact appeal to hardy microbes that will resist almost any extreme of radiation, drought, cold or heat, and hence a trip to Mars. So research is going into new detection methods, and in a thorough inventory of the clean room microbial flora. "If we send microbes into space, it would be nice to know who they are," Rummel says with a chuckle.

NASA certainly needs to take cleanliness seriously. The cost of its missions and the wide publicity they receive leave very little room for failure. And the space shuttle accidents and loss of previous Mars missions have called its performance into question.

"We are always concerned about the prospect that we are going to do a bad job and find Earth microbes all over Mars," Rummel says. Revisiting the Streptococcus mitis enigma recently, he concluded that the microbe had not spent two years on the moon after all. The contamination, he now believes, occurred at the very last step, at the hands of the scientists who examined the camera’s contents after its return. A dirty pair of tweezers might be all that it took, he says.

It would be a great embarrassment for NASA scientists to claim they found life in a Mars sample and discover later it was an Earth microbe.

Life, the hardy.

Whether any of the microbes remaining on a spacecraft could survive a trip to Mars and an extended stay there is still an open question. Many microbes can enter a spore state that allows them to survive extremely dry and cold conditions. But the thin Mars atmosphere provides little protection from the Sun’s ultraviolet radiation, which should quickly destroy DNA and proteins. Rocco Mancinelli, a SETI researcher who specializes in organisms that survive extreme conditions (extremophiles), has studied this problem. He and his colleagues found that Bacillus subtilis, known dwellers in clean rooms, would dwindle to a thousandth of their original number after just one minute of sunbathing on Mars. By now, radiation has probably dispatched most of Spirit and Opportunity’s passengers, unless they traveled in the shade and hid in martian dust at landing. "But they won’t grow, they’ll have nothing to eat, it will be too cold for them to do anything," Mancinelli says.

Seen from the clean room, microbial life is not so much a wonder of adaptability as a resourceful nuisance that interferes with our ability to detect extraterrestrial life. And yet it is exactly the stubborn resilience of microbial life on Earth that makes us believe microbes might also live on Mars.

The best place to find life on Mars, scientists now think, is in the permafrost--the mix of dirt and ice that lies below the surface. On Earth, permafrost holds life forms that are mostly dormant. They awaken during seasonal thawing or thrive in small pockets of liquid salt water. Another possible niche for martian life is under the ice cap of Mars’s South pole, where high pressure might keep water liquid. On Earth, bacterial and algal beds cover the bottom of Arctic lakes that freeze over most of the year. The evaporites that Spirit and Opportunity uncovered are another candidate. These layers of salty minerals suggest the transient presence of liquid water and may hold fossils, if not current life. On Earth, bacteria are known to survive in the high salt concentrations of salt ponds or dry lakebeds.

Most probably, detecting life on Mars will require drilling. This presents the risk of burying Earth microbes stuck to the drill in areas they might find hospitable and eventually colonize. "This means we can’t be sloppy. We can’t contaminate these sites with life or organic matter," Mancinelli says.

Chris McKay, an extremophile specialist from NASA Ames, concurs. He is currently preparing a proposal for life detection by the Phoenix scout near the South pole of Mars, a mission planned for 2008. The plan is to drill through the ice, and look for life–most likely dormant--in the oldest ice layers. "The drill has to be rigorously sterile," he says. Just clean is not enough.

It can be difficult to get a scientist to explain why Mars exploration should be clean, except for the protection of their current experiments. "It’s responsible, " Race says. "It’s a matter of general aesthetics," Mancinelli says. But McKay looks further ahead.

"If there is a biosphere on Mars and it is different from Earth, we might decide to encourage that biosphere and warm it up, make Mars a biological planet," he says. "But that is impossible if Earth life is already there."

So far, and yet so close.

Though Mars seems far from Earth, the two planets may not be biologically isolated. Meteorites from Mars land on Earth often, at a rate of perhaps one per month, though none have yet harbored convincing signs of life. Rocks ejected by large meteor impacts might also have made the more difficult trip between Earth and Mars–especially three or four billions of years ago, a time when life was just starting on Earth. Calculations and experiments suggest that bacteria inside large rocks might not suffer much damage from the impact or heat inherent in such violent transportation.

Perhaps we will find that Mars, a mere stone’s throw away, is indeed part of the Earth family. If so, boundaries will fall, quarantines will become obsolete, and we will think no more of colonizing Mars than we do of making a desert bloom on Earth. Perhaps we will instead find Mars to be foreign. Then we might grant it its own right to be left undisturbed, or we might try to tame it, and eventually domesticate it. Perhaps we will find that life started on Mars but quickly faltered, succumbing to the double insult of vanishing water and plunging temperatures.

For now, in any event, we might just tread lightly on its mysterious salt flats and ice caps and, unlike Columbus or the East Coast oysters, keep our germs to ourselves.


Lake Vostok

Below the ice: Life, the hypothetical

Deep, dark, cold, and lost to the world for some 15 million years, Lake Vostok lies two miles below the Russian research station in Antarctica. It may be a frigid and deserted abyss–or it may yet harbor life. The only way to know is to drill through its thick seal of ice. But, there’s the rub: A drill could "pollute" the lake with life, rather than just sampling whatever life might already be there.

The problem came to light when traces of bacteria were found in the ice cores that Russian scientists, drilling for records of ancient climates, brought back to the surface in 1998. Some thought the bacteria were proof of life in the lake. But others blamed dirty drilling or sloppy storage of samples. "It’s very difficult to rule out contamination," says biologist Chris McKay of NASA Ames. The Russian team stopped drilling a few hundred meters before reaching liquid water, for fear of contaminating the lake with drilling fluid and surface organisms.

Now the Russians want to resume drilling with their original technology. They argue that no life could take hold in the lake, which they think contains toxic levels of oxygen leaching in from the ice layer. McKay, for his part, wonders whether there is any energy source to sustain life in the utterly dark lake. Still, he and SETI collaborators are working on a tiny robotic explorer, the "cryobot," which could melt its way through the ice with minimal risk of contamination.

To many scientists, Lake Vostok is the Earth equivalent of Jupiter’s moon Europa. Pictures gathered by NASA’s Galileo spacecraft showed that Europa is covered with ice. Salt water may flow underneath, making Europa a favorite destination for future missions to search for alien life. The sterile techniques developed to explore Lake Vostok could eventually be used on Europa, decades from now.

In 2003, after 14 years exploring Jupiter and its moons, Galileo crashed into Jupiter’s gaseous atmosphere. The plunge was intentional: NASA engineers did not want the aging radioactive spacecraft to drift toward Europa and risk contaminating the ice queen, whose biological potential it had helped uncover.

"It’s the first time we have ever terminated a spacecraft for the purpose of protecting one of its discoveries," says John Rummel, who led the decision as NASA’s planetary protection officer.

Will it be the last? The answer may depend on what secrets loom in the glacial depths of Lake Vostok.


ABOUT THE WRITER

Françoise Chanut
B.S. (cell biology) & M.S. (plant physiology), Université Pierre et Marie Curie, Paris
Ph.D. (biology), University of Utah

ABOUT THE ILLUSTRATORS

Anne Kaferle hails from New England, where she grew up wandering the woods of her small hometown in Connecticut. She received her B.A. in 2003 from Colby College (Waterville, Maine), where she majored in art and minored in geology. Anne spent several seasons taking on a variety of environmental education-oriented jobs before making her way out to Santa Cruz, Calif. to join the ranks of Science Illustration Program graduate students. Comfortable working in a wide variety of different media, Anne is particularly interested in executing illustrations that may help to foster both an appreciation of the natural world and a feeling of environmental responsibility in the viewer.

Ann Altstatt attended the University of California, Santa Cruz, receiving a B.S. in earth science and a B.A. in studio art in 2001. Her lifelong interests in the natural sciences and in art-making were further brought together this past year in the Science Illustration graduate certificate program at UCSC. She interned as an illustrator at the Channel Island National Marine Sanctuary in Santa Barbara. Ann has not yet traveled to Antarctica.