Life Beyond Earth
(Excerpts from the January 2000 NATIONAL GEOGRAPHIC)

By Joel Achenbach

Something astonishing has happened in the universe. There has arisen a thing called life—a flamboyant, rambunctious, gregarious form of matter, qualitatively different from rocks, gas, and dust, yet made of the same stuff, the same humdrum elements lying around everywhere.

Life has a way of being obvious—it literally scampers by, or growls, or curls up on the windowsill—and yet it’s notoriously difficult to define in absolute terms. We say that life replicates. Life uses energy. Life adapts. Some forms of life have developed large central processing networks. In at least one instance, life has become profoundly self-aware.

And that kind of life has a big question: What else is alive out there?

There may be no scientific mystery so tantalizing at the brink of the new millennium and yet so resistant to an answer. Extraterrestrial life represents an enormous gap in our knowledge of nature. With instruments such as the Hubble Space Telescope, scientists have discovered a bewildering amount of cosmic turf, and yet they still know of only a single inhabited world.

We all have our suppositions, our scenarios. The late astronomer Carl Sagan estimated that there are a million technological civilizations in our galaxy alone. His more conservative colleague Frank Drake offers the number 10,000. John Oro, a prominent comet researcher, calculates that the Milky Way is sprinkled with a hundred civilizations. And finally there are skeptics like Ben Zuckerman, an astronomer at UCLA, who thinks we may well be alone in this galaxy if not in the universe.

All estimates are highly speculative. The fact is that there is no conclusive evidence of any life beyond Earth. Absence of evidence is not evidence of absence, as various pundits have wisely noted. But we still don’t have any solid knowledge about a single alien microbe, a solitary spore, much less the hubcap from a passing alien starship.

Our ideas about extraterrestrial life are what Sagan called “plausibility arguments,” usually shot through with unknowns, hunches, ideologies, and random ought-to-bes. Even if we convince ourselves that there must be life out there, we confront a second problem, which is that we don’t anything about that life. We don’t know how truly alien it is. We don’t know if it’s built on a foundation of carbon atoms. We don’t know if it requires a liquid-water medium, if it swims or flies or burrows.

Despite the enveloping nebula of uncertainties, extraterrestrial life has become an increasingly exciting area of scientific inquiry. The field is called exobiology or astrobiology—every few years it seems as though the name has been changed to protect the ignorant.

Whatever it’s called, this is a science infused with optimism. We know that the universe may be aswarm with planets. Since 1995 astronomers have detected close to 30 planets orbiting other stars. NASA hopes to build a telescope called the Terrestrial Planet Finder to search for Earth-like planets, examining them for the atmospheric signatures of a living world. In the past decade organisms have been found thriving on our own planet in bizarre, hostile environments. If microbes can live in the pores of rock deep beneath the earth or at the rim of a scalding Yellowstone spring, then they might find a place like Mars not so shabby.

Mars is in the midst of a full-scale invasion from Earth, from polar landers to global surveyors to rovers looking for fossils. A canister of Mars rocks will be rocketed back to Earth in the year 2008, parachuting into the Utah desert for scrutiny by scientists in a carefully sealed lab. In the coming years probes will also go around and, at some point, into Jupiter’s moon Europa. That icy world shows numerous signs of having a subsurface ocean—and could conceivably harbor a dark, cold, biosphere.

The quest for an alien microbe is supplemented by a continuing effort to find something large, intelligent, and communicative. SETI—the Search for Extraterrestrial Intelligence—has not yielded a confirmed signal from an alien civilization in 40 years of experiments, but the signal-processing technology grows more sophisticated each year. The optimists figure it’s only a matter of time before we tune in the right channel.

No one knows when—or if—one of these investigations might make a breakthrough. There’s a fair bit of boosterism surrounding the entire field, but I’d bet the breakthrough is many years, if not decades, away. The simple truth: Extraterrestrial life, by definition, is not conveniently located.

But there are other truths that sustain the search for alien organisms. One is that, roughly speaking, the universe looks habitable. Another is that life radiates information about itself—that, if nothing else, it usually leaves a residue, an imprint, an echo. If the universe contains an abundance of life, that life is not likely to remain forever in the realm of the unknown.

Contact with an alien civilization would be an epochal and culturally challenging event, but exobiologists would settle gladly for the discovery of a tiny fossil, a mere remnant of extraterrestrial biochemistry. One example. One data point to add to the one we have—Earth life. That’s what we need to begin the long process of putting human existence in its true cosmic context.

* * *

Exobiologists go to the worst places on Earth, or at least the most extreme—the driest, coldest, most Mars-like or Europa-like environments they can find.

The place to find Penny Boston is in the nastiest cave imaginable. I tagged along with Boston on one of her trips to a wet, bat-ridden cave in southern Mexico called Villa Luz. Boston has been studying the microbes that thrive there—in environments where a human being not wearing a gas mask would perish.

“All my life I’ve wanted to cross the cosmos, go to other planets,” says Boston. “This is probably as close as I’ll get at my age.”

The cave floor was covered with water of varying depths and no transparency, and we walked gingerly so as to avoid discovering unmapped deep water. By caving standards, though, this was a walk in the park—no ropes required, just some crawling and scrambling through low-ceilinged passages.

Eventually we reached the deepest, largest chamber, known as the Great Hall. Midges flitted, spiders spun webs, bats zagged and zigged just over our heads, emitting their high-pitched sonar. Red rock walls were covered with green slime, black muck, gooey white gypsum paste, and limestone in the process of being dissolved by sulfuric acid.

Just as I was thinking how much this cave resembled the human nasal cavity, we came to the snottites (Boston is lobbying to have the word recognized as a scientific term). Snottites are gelatinous structures formed by microbial wastes. They dangle from the ceiling. Boston and her team have been measuring their growth, trying to understand the metabolism of the microbes and their long-term effect on the geology of the cave. Dry weather since her last visit seemed to have inhibited the growth of the structures.

Mike Spilde, another member of the team, splashed over to where I’d been inspecting a water bug whose shell was covered with eggs. He reached into a spring burbling from under a rock and pulled out some gray wads the consistency of cooked cabbage. These are known, in keeping with the theme of the place, as phlegm balls. They are vibrant microbial communities, not clinging to life in a narrow niche but proliferating in it, replicating up a storm.

Taking a break back on the surface, Boston placed some of her cave work in context. “We have discovered”—she means scientists in general—“organisms thriving in environments harsh to us but essential to them. It broadens your perspective. We all suffer to some extent from ‘expertitis’ in science. It’s good for your soul, and good for your intellect, and good for your work to have your imagination stretched, to be open to the possibilities.”

The most tantalizing possibility is that the universe hums with life and that in the coming centuries we will find it. An exobiologist’s abiding optimism is fired by the knowledge that living things are primarily constructed of hydrogen, nitrogen, carbon, and oxygen—the four most common chemically active elements in the universe. And life is inextricably interwoven with nonlife; not even the sharpest razor can perfectly slice them apart.

We also know that a functioning ecosystem does not require sunlight or photosynthesis. In the early 1990s researchers found that the basaltic rock deep beneath Washington State contains an abundance of microbes totally cut off from the photosynthetic world. Even more complex life can adapt to hostile places. When scientists in the deep-sea submersible Alvin went tooling around the mid-ocean ridges, they found hot vents covered with shrimp and mouthless tube worms.

What remains unknown is whether life can survive over time in narrow ecological niches on largely barren worlds. Could life survive in aquifers far below the harsh surface of Mars? What could endure the cold, dark environment of Europa’s hypothesized ocean? Can an alien world have just a little bit of life, or are biospheres an all-or-nothing proposition?

The cave at Villa Luz, as remote as it is, does not exist in isolation. It is a small, connected piece of a world that riots with life.

* * *

As scientists struggle to find a trace of life somewhere else in the universe, there exists for many people a more dramatic situation, one in which extraterrestrial life isn’t microbial and slimy but rather intelligent, technological, and lurking in our midst. The believers in these aliens are not likely to be convinced that ETs are a bogus phenomenon. An ability to elude detection and confirmation, particularly by mainstream thinkers, is a presumed characteristic of the Visitors.

Having dropped in on a couple of UFO conventions and visited Roswell, New Mexico, and its UFO museum, I’ve come to the conclusion that it’s not possible to win an argument about space aliens. True believers and skeptics rarely go over to the other side. I think it’s fair to say, however, that flying-saucer aliens lack scientific stature. If they insist on being so jumpy, if they insist on abducting people in the middle of the night when no one else can verify their presence, then they have no right to enter a reputable natural history museum.

But neither are people who believe in the UFO narrative—which generally is dated to the 1947 sighting of some flying “disks” near Mount Rainier in Washington State—necessarily irrational, much less crazy, as they are sometimes depicted. Most people operate from the same instinct, which is to know the truth about the universe. That so many people would adopt a theory of aliens utterly contrary to that of mainstream science (and that of, among agencies, the U.S. Air Force, which spent 22 years investigating UFO reports) is a reminder of the special attraction of the idea of extraterrestrial life.

As many writers have noted, aliens are, for some people, the secular equivalent of angels and demons and ghostly spirits. The aliens are an extrapolation of modern astronomy and engineering (big universe, fast rocket ships), but they also possess some ancient urge to come to Earth and mess with human beings. What makes them so intriguing is that even scientists will concede that alien beings could very well be out there somewhere. Therefore the scenario in which they come to Earth requires only some imagination about transportation.

Many scientists don’t wonder why aliens are buzzing the Earth in flying saucers—they wonder why they aren’t. In 1950 Enrico Fermi, a physicist, asked some of his colleagues a question that would become famous: Where is everybody? Humans could theoretically colonize the galaxy in a million years or so, and if they could, astronauts from older civilizations could do the same. So why haven’t they come to Earth? This is known as the Fermi paradox.

Could it be that they’re observing us but not interfering? (The zoo hypothesis.) Did they come and leave artifacts and get bored and go away? (This is the “ancient astronauts” idea that posits the aliens as builders of pyramids and so forth.) Or could it be that for all intelligent species, interstellar travel is too expensive and time-consuming? (It’s just less than 25 trillion miles [40 trillion kilometers] from Earth to the nearest star beyond the sun.)

Or could it be possible that, at least in our part of the galaxy, the most technologically advanced species is the one right here on Earth?

* * *

Every three years a bioastronomy meeting gathers many of the leading thinkers in the field. I went to the 1999 assemblage in August on the Big Island of Hawaii, and at the opening reception around a hotel pool a University of Toronto sociologist named Allen Tough offered a provocative theory:

“I think a probe is already here. It’s probably been here a long time.”

He didn’t mean flying saucers. His alien probes would be much smaller—“nanoprobes,” tiny robotic exploratory craft sent to Earth from advanced civilizations. The alien probes may, at some point, let themselves be known to human civilization. How? Where? “I think it will happen on the World Wide Web,” said Tough.

Tough and about a dozen other visionaries had a pre-conference meeting to discuss what to do if human civilization receives a “high-content” message from extraterrestrials. There was much uncertainty about how well prepared humankind is for such an event. We might have trouble crafting a response. Should we be forthcoming about the flaws of our species? If we acknowledge our history of wars and slavery, could that be misinterpreted as a threat? What if, even as an international committee of well-meaning thinkers tried to put together a message, some guerrilla radio broadcaster or “shock jock” beat everyone to it?

Bioastronomy also has its more down-to-Earth side. The meeting reminded me how much there is still to learn about our own little solar system. Exobiologist Jack Farmer made a simple yet stunning point one morning when he noted that neither the Viking landers in 1976 nor the Pathfinder spacecraft in 1997 carried to Mars the tool so vital to a geologist: a magnifying lens. Nor would the polar lander scheduled for a December 1999 landing carry such an instrument. Farmer’s comment remained in my mind when Cindy Lee Van Dover, an oceanographer, noted that no one has ever made a dive in a deep-sea submersible to an active hot vent in the Indian Ocean to see what might be alive down there.

So before we worry about our dealings with the Galactic Empire, we have some serious fieldwork to do closer to home.

Freeman Dyson, a physicist, has argued that humans may engineer new forms of life that will be adapted to living in the vacuum of space or on the surface of frozen moons and comets and asteroids. In Dyson’s universe, life is mobile, and planets are gravitational traps inhibiting free movement.

“Perhaps our destiny is to be the midwives, to help the living universe to be born,” he said recently. “Once life escapes from this little planet, there’ll be no stopping it.”

But life must first survive this planet. Humans in their modern anatomy have been around only 125,000 years or so. It is not clear yet that a brain like ours is necessarily a long-term advantage. We make mistakes. We build bombs. We ravage our world, poison its water, foul its air. Our first order of business, as a species, is to [survive].

I would hope that anyone who investigates this issue will come away with a renewed appreciation of what and who we are. In a universe of empty space and stellar furnaces and ice worlds, it is good to be alive. And we should remember that even if we find intelligent life beyond Earth, it may not be what we expect or even what we were searching for.

The alien may not speak to that part of our consciousness that we deem most important—our spirit, if you will. It may have little to teach us. The great moment of contact may simply remind us that what we most want is to find a better version of ourselves—a creature we will probably have to make, from our own raw elements, here on Earth.

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