First Contact (6 page)

Doran and Stone's Lake Bonney robot logged 250 hours under the ice and traveled more than thirty-five miles to conduct the first sophisticated, 3-D exploration of a polar lake, one covered in about ten feet of ice. The Volkswagen-sized “Bot” was also a test of concept: Could a submersible robot be programmed to not only follow a preset path, but also to independently explore areas where something unusual appeared? During two
seasons under the ice the Bot, with the help of forty-five computers, performed as hoped.

But the real prize is hundreds of millions of miles away, on Jupiter's moon Europa. Beneath miles of ice, Europa is home to a giant ocean sixty miles deep and with twice as much water as the oceans of Earth—a prime target for astrobiologists. A joint NASA-ESA mission to Europa is now in the works for the 2020s, a scouting party preparing for the day when the moon's ice cover will be broken and a much smaller and more sophisticated bot than Lake Bonney's will be inserted into the waters below. A liquid ocean, even if it's kept dark by miles of ice, is the kind of place where life just might exist; in fact, we know it does exist right here on Earth.

Back in Baton Rouge, Christner might as well be in a different galaxy. He favors shorts and loud shirts—an azure Hawaiian shirt the day we met—and still puzzles about exactly how he became an ice man. His early great interest, what brought him into microbiology and then astrobiology, was thermophiles—the extreme organisms that live in and around hot springs, deep ocean vents, and the outer reaches of volcanoes. On schematics of the tree of life, many thermophiles can be found at the very bottom, leading some scientists to speculate they were the earliest or at least among the earliest life forms on Earth.

“Yes, I wanted to study thermophiles for my doctoral thesis,” Christner said, and laughed. But instead he went into the microbes-in-ice field, in part because his mentor at Ohio State University had a collaboration with another team that had a large collection of ice cores from around the world. “They had ice from the Andes, from Tibet, Greenland, and Antarctica; and it was a huge opportunity. But to tell the truth, I thought when I was done I would write up the findings and move on to something else. My assumption was based on the conventional wisdom of the time that any microbes in there were just hanging out in the ice, doing nothing. We could learn about the past from them, but nobody thought about anything beyond that. Bottom line, that's not at all what we found. We found things alive in the oldest ice, seven hundred and fifty thousand years old. Some
were spores, but some were not and seemed to be doing things, especially the ones near dust and sediment.”

His tentative hypothesis had been that glacial ice is generally not a reservoir for dead or hibernating microbes, but is instead an environment with a complex and extensive living ecology of its own. Five trips to Antarctica later, he is increasingly confident that this is true. In fact, based on what he acknowledges is very limited data collected from two drilling holes, he believes Antarctica—which contains about 70 percent of the fresh water in the world—may well sustain a world of microbial life that exceeds in mass all the life found in all the freshwater rivers and lakes of the world combined. In samples from the Vostok ice core, almost three miles down, Christner isolated a bacterium that produces a protein that may well help the organism to survive, in part by altering the freezing and recrystallizing of the nearby ice—directing the potentially destructive processes away from the organism. In other words, their survival advantage appears to have come from a molecular adaptation that allowed the microbes to change their frozen environment enough to make life possible.

That kind of remarkable ability to inhabit such a harsh environment, and to even seemingly transform it, is why Christner assumes microbes will one day be found on Mars and elsewhere. “Based on what we're learning on Earth, I can't see that microbes living on Mars would be such a big jump. I mean, the conditions they live in here are in some ways just as severe, yet they've adapted. Not only that, we believe that ice is a habitat for life—providing a liquid environment under otherwise frozen conditions. Waste from one microbe is food for another, so it is likely that microbes are interacting and cooperating to extract every usable bit of energy. Almost all the water we see in the solar system is in an ice form, and I don't see why some of that ice wouldn't have microbial life, too.”

It's that kind of leap of the imagination that has people like Christner looking deep inside the Earth to see life in the beyond. To enter, explore, and ultimately understand the world of microbial extremophiles, you need to be, inside your head, something of a human extremophile yourself.

What is life? Even though an answer has been passed on to generations of biology students, they weren't getting the full story. When scientists invented the modern field of astrobiology, they had to wrestle with a fundamental problem: There is no scientific consensus about precisely what makes something alive. Given that unsettling absence, did it really make sense for astrobiologists to apply to the rest of the universe the never-quite-exact definitions we had come up with on Earth? To make matters all the more confounding, what would be a sure signature of biology on our planet could be totally nonbiological on Mars, and vice versa. So how do you find life in the beyond if you can't agree on what life is on Earth?

Because it's in the business of trying to find “life” beyond Earth, NASA has probably done more to try to define it than any other organization. Here is an unofficial working definition: Life is “a self-sustaining chemical system with the capacity to evolve in a Darwinian manner.” The definition came out of a workshop of biologists, physicists, and chemists in 1994, and it does meet many of the basic criteria scientists and others are looking for. Broadly, it accounts for the known constants of life on Earth. All living organisms take in some form of energy, use and change it, and then release it as waste; all use the same twenty amino acids to construct the proteins that make that and all other activity possible; and all use RNA and DNA molecules to store genetic information and to construct proteins. The Darwinian
evolution comes directly and inevitably from the presence of DNA, since all DNA mutates.

But the definition has many critics, some of whom think it is not only incorrect but also misguided. The criticisms come from many directions: those who argue the definition would rule out viruses, prions (which cause “mad cow” disease), and other seemingly “living” organisms; those who want to base any definition on a specific capability such as metabolism or reproduction or the enclosing of a cell nucleus by a cell wall; those who think in the more abstract terms of a physicist and want a definition that takes their discipline (the Second Law of Thermodynamics, for one) into account. Relying on that law, the Austrian quantum physicist Erwin Schrödinger famously suggested that life—in its broadest terms—be defined as something that avoids immediate decay into “entropy,” the chaotic and then utterly uniform state the entire universe will someday revert to since all structure has in it the seeds of its own falling apart. Living things, Schrödinger proposed in his 1944 book,
What is Life?
, postpone this inevitable process by taking in nutrients and turning them into energy; at death the life forms eventually succumb to the force of entropy and break down so the atoms of the once-living body become evenly distributed again, recycled by the Earth.

Portland State University geobiologist Radu Popa, author of the 2004 book
Between Necessity and Probability: Searching for the Definition and Origin of Life
, said that he lost count of the proposed answers in the scientific literature after logging at least three hundred. And the definitions keep coming. Nilton Renno, a planetary and atmospheric scientist at the University of Michigan and a member of the Mars Phoenix lander science team, recently came up with this one in a paper on the likelihood that the heat from the spacecraft's landing created liquid water that remained visible for days: Life, he wrote, is a self-replicating heat engine with a capacity for mutation.

Perhaps the most subversive challenge to the proposed definitions of life comes not from those who think the NASA definition is incorrect, but
rather from those who think “life” is not a concept we can or should define. Philosophy professor Carol Cleland, from the University of Colorado, and Chris Chyba, an astronomy student of Carl Sagan's who now teaches at Princeton University, have argued for almost a decade that current definitions of “life” are little different from medieval definitions of “water,” which was seen then as a clear liquid with certain qualities such as wetness, transparency, tastelessness, odorlessness, and the property of being a very good solvent. We can now chuckle at the misunderstanding, since muddy water is certainly not transparent, salty water has a taste, and marshy water has a smell. Medieval alchemists classified nitric acid and some mixtures of hydrochloric acid as
aqua fortis
(strong water) and
aqua regia
(royal water) because they were such good solvents.

But water, as we now know, is H
₂
O—two hydrogen atoms bound to one oxygen atom. Those men and women trying over the centuries to define water knew nothing about the molecules and atoms that we now know make up all matter. That didn't come until the late eighteenth century, when Antoine Lavoisier came up with the convincing theory that matter is made up of molecules. Cleland, Chyba, and others have argued that the basic knowledge needed to make a definition of “life” is simply absent, rather like how the essential molecular nature of water was unknown during the Middle Ages. Based on her iconoclastic views—grounded in philosophy and at times a challenge to scientists—Cleland was included on a University of Colorado astrobiology team that was twice funded by NASA. Her thinking became more broadly known when she addressed a 2001 meeting called “The Nature of Life,” hosted by the American Association for the Advancement of Science. She told the audience of scientists that the search for a definition of life—something many were involved in—was a waste of time and, even worse, misleading.

“The logic of my argument was impeccable, but people just blew up at me,” recalls Cleland, an expert in the philosophy of science. It was a memorable evening. “They were yelling out their own definitions, saying this is the right definition or that is the right definition. It's as if they totally
missed my point that their approach was mistaken and there is no definition available now. I was kind of shocked and remember saying to myself, ‘These people just can't hear what I'm saying.' I've learned since then how to better talk with scientists, but I still think the whole definition project is hopeless.”

Ten years later, Cleland and Chyba's view is no longer outlandish. Addressing a NASA-NSF gathering of many of the nation's top practitioners of “synthetic biology” (the origins-of-life side of biotechnology), the evolutionary biologist Andrew Ellington, of the University of Texas at Austin, urged NASA to bring together a blue-ribbon panel to study and then throw out the agency's and all other definitions of life.

“It is my position that there is no such thing as life, and that the working statement in the NASA document does science a disservice by attempting to pretend the contrary,” he told the gathering of in 2008. “‘Life' is a term better suited for poets (or perhaps philosophers) than scientists, and the continuing attempts to determine whether a given system is alive or not harken back to quite ancient philosophers, with a similar level of resolution. I assert the following existence proof: if we haven't figured out what life is by now, there is little hope that we will figure out a definitive definition in the near term, and there is no research program that I can imagine, at any price, that will provide such a definition.”

Ellington then made clear why he felt as strongly as he did. As is so often the case in astrobiology, the purely scientific issues are surrounded by deeply felt and highly contentious social and even political issues. “I would further argue that the reason that what is nominally a rather pointless philosophical issue has become an important one for NASA is because of its near-term political ramifications,” he said. He believes defining “life” is a dangerous endeavor because the information collected will almost inevitably weigh down science. “I can imagine a day when the head of NASA would be brought before the Supreme Court in an abortion case and asked to define life,” he told me. “And I can imagine the long and uncomfortable silence that would follow.” Let the work progress on synthesizing molecules
that can do what living molecules do, and on determining if some unexpected substances have lifelike qualities, he says. But leave the definitions for later.

The controversy over a definition for “life” has actually been around for some time, even inside NASA, and it became a serious problem and even embarrassment in 1976 when the agency landed two Viking spacecrafts on Mars in a self-described search for life. To the initial delight of the Viking scientists, a key biology experiment on both Viking landers gave a strong signal that “life” had been found—meeting the painstakingly crafted criteria established before the spacecraft left Earth—and the control experiments seemed to confirm the finding. Yet the principal investigator of that experiment was held back from announcing what Viking had apparently discovered. The scientific community and NASA quickly formed a consensus that life had not been detected. The problem wasn't with the way the instruments performed or how the experiment was carried out, but rather with the definition of life that NASA itself had put together, one based on the way metabolism is known to work on Earth.

The story is best told through the life and times of Gilbert V. Levin, a pioneer of astrobiology who began his career as a sanitary engineer searching for microbes in drinking water. He first proposed a life-detection experiment for Mars in 1959 and had his idea embraced and tested time and again by NASA before the Viking launch in 1975. He got the results he had dreamed of within ten days of the first landing of Viking. It seemed like a scientific triumph of historic proportions, but it quickly slipped away and Levin has been fighting ever since to reclaim the victory. More than ever, he says, he is convinced that his Viking experiment did find something that indeed was—had to be—living. But the scientific verdict came down against him and, despite some converts, has not significantly changed.