Space Chronicles: Facing the Ultimate Frontier (6 page)

If the aliens decide that Earth’s chemical features are strong evidence for life, maybe they’ll wonder if the life is intelligent. Presumably the aliens communicate with one another, and perhaps they’ll presume that other intelligent life-forms communicate too. Maybe that’s when they’ll decide to eavesdrop on Earth with their radio telescopes to see what part of the electromagnetic spectrum its inhabitants have mastered. So, whether the aliens explore with chemistry or with radio waves, they might come to the same conclusion: a planet where there’s advanced technology must be populated with intelligent life-forms, who may occupy themselves discovering how the universe works and how to apply its laws for personal or public gain.

O
ur catalogue of exoplanets is growing apace. After all, the known universe harbors a hundred billion galaxies, each with hundreds of billions of stars.

The search for life drives the search for exoplanets, some of which probably look like Earth—not in detail, of course, but in overall properties. Those are the planets our descendants might want to visit someday, by choice or by necessity. So far, though, nearly all the exoplanets detected by the planet hunters are much larger than Earth. Most are at least as massive as Jupiter, which is more than three hundred times Earth’s mass. Nevertheless, as astrophysicists design hardware that can detect smaller and smaller jiggles of a host star, the ability to find punier and punier planets will grow.

In spite of our impressive tally, planet hunting by earthlings is still in its horse-and-buggy stage, and only the most basic questions can be answered: Is the thing a planet? How massive is it? How long does it take to orbit its host star? No one knows for sure what all those exoplanets are made of, and only a few of them eclipse their host stars, permitting cosmochemists to peek at their atmospheres.

But abstract measurements of chemical properties do not feed the imagination of either poets or scientists. Only through images that capture surface detail do our minds transform exoplanets into “worlds.” Those orbs must occupy more than just a few pixels in the family portrait to qualify, and a Web surfer should not need a caption to find the planet in the photo. We have to do better than the pale blue dot.

Only then will we be able to conjure what a faraway planet looks like when seen from the edge of its own star system—or perhaps from the planet’s surface itself. For that, we will need spaceborne telescopes with stupendous light-gathering power.

Nope. We’re not there yet. But perhaps the aliens are.

• • •
CHAPTER THREE

EXTRATERRESTRIAL LIFE
^*

T
he first half-dozen or so confirmed discoveries of planets around stars other than the Sun—dating to the late 1980s and early 1990s—triggered tremendous public interest. Attention was generated not so much by the discovery of exoplanets but by the prospect of their hosting intelligent life. In any case, the media frenzy that followed was somewhat out of proportion to the events.

Why? Because planets cannot be all that rare in the universe if the Sun happens to have eight of them. Also, the first round of newly discovered planets were all oversize gas giants that resemble Jupiter, which means they have no convenient surface upon which life as we know it could exist. And even if the planets were teeming with buoyant aliens, the odds against these life-forms being intelligent are astronomical.

Ordinarily, there is no riskier step that a scientist (or anyone) can take than to make a sweeping generalization from just one example. At the moment, life on Earth is the only known life in the universe, but compelling arguments suggest that we are not alone. Indeed, nearly all astrophysicists accept the high probability of life elsewhere. The reasoning is easy: if our solar system is not unusual, then the number of planets in the universe would, for example, outnumber the sum of all sounds and words ever uttered by every human who has ever lived. To declare that Earth must be the only planet in the universe with life would be inexcusably big-headed of us.

Many generations of thinkers, both religious and scientific, have been led astray by anthropocentric assumptions and simple ignorance. In the absence of dogma and data, it is safer to be guided by the notion that we are not special, which is generally known as the Copernican principle. It was the Polish astronomer Nicolaus Copernicus who, in the mid-1500s, put the Sun back in the middle of our solar system where it belongs. In spite of a third-century
B.C.
account of a Sun-centered universe (proposed by the Greek philosopher Aristarchus), the Earth-centered universe has been by far the most popular view for most of the past two thousand years. In the West, it was codified by the teachings of Aristotle and Ptolemy and later by the preachings of the Roman Catholic Church. That Earth was the center of all motion was self-evident: it not only looked that way, but God surely made it so.

The Copernican principle comes with no guarantees that it will guide us correctly for all scientific discoveries yet to come. But it has revealed itself in our humble realization that Earth is not in the center of the solar system, the solar system is not in the center of the Milky Way galaxy, and the Milky Way galaxy is not in the center of the universe. And in case you are one of those people who think that the edge may be a special place, we are not at the edge of anything either.

A wise contemporary posture would be to assume that life on Earth is not immune to the Copernican principle. How, then, can the appearance or the chemistry of life on Earth provide clues to what life might be like elsewhere in the universe?

I do not know whether biologists walk around every day awestruck by the diversity of life. I certainly do. On our planet, there coexist (among countless other life-forms) algae, beetles, sponges, jellyfish, snakes, condors, and giant sequoias. Imagine these seven living organisms lined up next to one another in size-place. If you didn’t know better, you would be hard pressed to believe that they all came from the same universe, much less the same planet. And by the way, try describing a snake to somebody who has never seen one: “You gotta believe me! There’s this animal on Earth that (1) can stalk its prey with infrared detectors, (2) can swallow whole, live animals several times bigger than its head, (3) has no arms or legs or any other appendage, and yet (4) can travel along the ground at a speed of two feet per second!”

N
early every Hollywood space movie includes some encounter between humans and alien life-forms, whether from Mars or an unknown planet in a faraway galaxy. The astrophysics in these films serves as the ladder to what people really care about: whether we are alone in the universe. If the person seated next to me on a long airplane flight finds out I’m an astrophysicist, nine times out of ten she’ll query me about life in the universe. I know of no other discipline that triggers such consistent enthusiasm from the public.

Given the diversity of life on Earth, one might expect diversity among Hollywood aliens. But I am consistently amazed by the film industry’s lack of creativity. With a few notable exceptions—such as the life-forms in
The Blob
(1958) and
2001: A Space Odyssey
(1968)—Hollywood’s aliens look remarkably humanoid. No matter how ugly (or cute) they are, nearly all of them have two eyes, a nose, a mouth, two ears, a neck, shoulders, arms, hands, fingers, a torso, two legs, two feet—and they can walk. Anatomically, these creatures are practically indistinguishable from humans, yet they are supposed to have come from another planet. If anything is certain, it is that life elsewhere in the universe, intelligent or otherwise, will look at least as exotic to us as some of Earth’s own life-forms do.

The chemical composition of Earth-based life is primarily derived from a select few ingredients. The elements hydrogen, oxygen, and carbon account for more than 95 percent of the atoms in the human body and in all other known life. Of the three, it is carbon whose chemical structure allows it to bond most readily and strongly with itself and with many other elements in many different ways—which is why we say life on Earth is carbon-based, and why the study of molecules that contain carbon is generally known as “organic” chemistry. Curiously, the study of life elsewhere in the universe is known as exobiology, one of the few disciplines that attempt to function, at least for now, in the complete absence of firsthand data.

Is life chemically special? The Copernican principle suggests that it probably isn’t. Aliens need not look like us to resemble us in more fundamental ways. Consider that the four most common elements in the universe are hydrogen, helium, carbon, and oxygen. Helium is inert. So the three most abundant, chemically active ingredients in the cosmos are also the top three ingredients of life on Earth. For this reason, you can bet that if life is found on another planet, it will be made of a similar mix of elements. Conversely, if life on Earth were composed primarily of manganese and molybdenum, then we would have excellent reason to suspect we’re something special in the universe.

Appealing once again to the Copernican principle, we can assume that an alien organism is not likely to be ridiculously large compared with life as we know it. There are cogent structural reasons why you would not expect to find a life-form the size of the Empire State Building strutting around a planet. Even if we ignore the engineering limitations of biological matter, we approach another, more fundamental limit. If we assume that an alien has control of its own appendages, or more generally, if we assume the organism functions coherently as a system, then its size would ultimately be constrained by its ability to send signals within itself at the speed of light—the fastest allowable speed in the universe. For an admittedly extreme example, if an organism were as big as the orbit of Neptune (about ten light-hours across), and if it wanted to scratch its head, then this simple act would take no less than ten hours to accomplish. Subslothlike behavior such as this would be evolutionarily self-limiting, because the time since the beginning of the universe might well be insufficient for the creature to have evolved from smaller forms.

How about intelligence? When Hollywood aliens manage to visit Earth, one might expect them to be remarkably smart. But I know of some that should have been embarrassed by their stupidity. Surfing the FM dial during a car trip from Boston to New York City some years ago, I came upon a radio play in progress that, as best as I could determine, was about evil aliens that were terrorizing earthlings. Apparently, they needed hydrogen atoms to survive, so they kept swooping down to Earth to suck up its oceans and extract the hydrogen from all the H
₂
O molecules. Now those were some dumb aliens. They must not have been looking at other planets en route to Earth, because Jupiter, for example, contains more than two hundred times the entire mass of Earth in pure hydrogen. I guess nobody told them that more than 90 percent of all atoms in the universe are hydrogen.

And what about aliens that manage to traverse thousands of light-years through interstellar space yet bungle their arrival by crash-landing on Earth?

Then there are the aliens in the 1977 film
Close Encounters of the Third Kind,
who, in advance of their arrival, beam to Earth a mysterious sequence of numbers that is eventually decoded by earthlings to be the latitude and longitude of their upcoming landing site. But Earth’s longitude has a completely arbitrary starting point—the prime meridian—which passes through Greenwich, England, by international agreement. And both longitude and latitude are measured in unnatural units we call degrees, 360 of which are in a circle. It seems to me that, armed with this much knowledge of human culture, the aliens could have just learned English and beamed the message “We’re going to land a little bit to the side of Devil’s Tower National Monument in Wyoming. And because we’re arriving in a flying saucer, we won’t need runway lights.”

The award for dumbest movie alien of all time must go to the entity that called itself V’ger, from the 1983 film
Star Trek: The Motion Picture
. An ancient mechanical space probe, V’ger had been rescued by a civilization of mechanical aliens and reconfigured so that it could accomplish its mission of discovery across the entire cosmos. The thing grew and grew, acquiring all knowledge of the universe and eventually achieving consciousness. In the film, the crew of the starship Enterprise come upon this now-immense heap of cosmic information and artifacts at a time when V’ger has been searching for its creator. Clued in by the badly tarnished letters “oya” on the original probe, Captain Kirk realizes that V’ger is actually Voyager 6, launched by earthlings in the late twentieth century. Okay. What irks me is how V’ger acquired total knowledge of the cosmos yet remained clueless that its real name was Voyager.