In general, I take a non-committal stance on the question of extraterrestrial life. Like nearly every other question entangled in religion and metaphysics, the question of humanity's role in the universe is inevitably muddied by pop culture, mass ignorance of science and ulterior motive. It's fine if UFO enthusiasts and little green men supporters want to believe that carbon-based biogenetics also happened to evolve metazoa capable of traveling to Earth in mechanical craft ala Newtonian means, but don't say the facts of astronomy, physics or statistics support it!
I just spent about fifteen minutes looking for legitimate survey results to get a feel for the current level of belief in extraterrestrials. Nothing persuasive popped up, and the top results all mentioned the rather unconvincing 2002 Roper poll, funded by the SciFi Channel. One blogger claimed a Gallup poll had in fact been conducted, but this link to the Gallup web site says the page is unavailable. Most sites and figures I observed seemed to hover around two-thirds of Americans believing in extraterrestrial life. Other interpretations report one-third of Americans believe the government is hiding information about the UFO phenomenon. More liberal interpretations claim "most" Americans are psychologically and spiritually ready for an extraterrestrial encounter. All reports I observed revealed majority belief. I feel this is largely due to the proliferation of ET and paranormal themes in popular culture over the last decade in conjunction with the staggering scientific advancements of the last century.
Identified in the Star catalog by German astronomer Wilhelm Gliese (1915-1993), Gliese 581 (Wolf 562, HO Librae) is a red dwarf star just over twenty light years from Earth. The star hosts a series of planets, and its April 2007 discovery was the first time astronomers confirmed the existence of a low mass extrasolar planet relatively situated in its habitable zone. Although the current scientific consensus is that Gliese 581 C would suffer from a runaway greenhouse effect and not be amenable to life, discoveries like these lend themselves to bolstered claims of probability. Our Milky Way contains an approximated 200 billion stars; per the law of probability, it certainly appears plausible that a situation similar to Earth may exist, but the extent to which we develop our belief systems on this plausibility is another issue entirely.
Pop culture and even legitimate journalism can produce loose science writing, typified by misleading, unfairly-emphasized or undisputed statements. When a study is released to major media, there is a natural and inescapable level of anxiety on behalf of journalists to cover the story. Although fitting for the ambitious journalist, ulterior motives such as wanting to be the first or most controversial reporter to cover a story often have negative repercussions for the truth. Sure, headlines of "Life In A Test Tube?" or "Aliens In Government Bases" are virtually guaranteed to increase readership and newspaper sales, but are they ethically, socially or scientifically responsible?
Heard time and again in print, over the radio and on presumably educational TV programs, one popular line of reasoning goes something like this: In a universe full of billions upon billions of stars, galaxies and planets, is it not probable that there is life beyond Earth? However, especially in the absence of even a shred of non-anecdotal evidence, are these types of common statements ethically, socially or scientifically responsible?
Part of our belief in aliens and extraterrestrials that does not stem from Hollywood might stem from liberal interpretations of evolutionary theory. The twentieth century's unprecedented progress in the hard sciences has certainly illuminated and arguably trivialized our view of life, and there's been a common misconception for the past half-century or so that all you need for complex life is a handful of the right chemicals placed upon a rocky planet with water situated about yeah far from a local host star, best expressed by the common phrase, "If life could get started here, couldn't it get started somewhere else?
The idea is not too repulsive philosophically, but scientifically, we still have no clue how life got started on Earth. If you'll allow me to break another cardinal rule of accurate reporting (avoiding all-inclusives), I'm fairly confident there is still no theory that can credibly account for the huge leap from inorganic matter to the first replicator, or the sudden and mass proliferation of biological forms in the Cambrian. As much as we think we know, our knowledge is dwarfed by our ignorance, and the imminent success of scientists creating life in a laboratory asks as many questions as it answers, just like any other valid scientific success story.
Evolution can explain how pre-existing biological organisms evolve, but at least in our solar system, biological organisms are apparently the newcomers on the universal scene, and who can say from whence they came? If we don't know how it happened here, what qualifies us to say conclusively whether it happened, is happening or can happen elsewhere? How do we know what to look for? If these beings travel from other galaxies, how much fuel do their craft use? If we posit antigravity as the means, how do the craft avoid asteroids and planetesimals? Assuming the speed limit of light is still the universal speed limit, how fast do these antigravity craft travel? It is both obvious and expected that unanswered questions about these craft persist, and the difficulty in identifying a set of biochemical conditions in exoplanets we can't even yet see or sample from should be apparent.
Like religious dogmatists, UFO enthusiasts rarely address such questions or attempt to frame their arguments in a scientific backdrop. In most of our UFO stories, basic facts and questions like these remain unanswered, and we are often told unilaterally that aliens exist. For every UFO or extraterrestrial enthusiast receiving national airtime with their speculations, we have millions of scientific laypeople completely unfamiliar with the extremely rare conditions that must be met to support life.
What do we need to get life going anyways? The full answer is beyond the scope of this piece, and although I'll refrain from asking you to accept some statistical figure I pulled off the internet, suffice it to say that the odds against the development of complex life appear to be astronomical.
Central to the development of carbon-based life are the good old-fashioned planet and host star, and not just any planet and star, either. First we need the right type of star. Aged or variable stars (white dwarfs, red giants, Cepheid variables) won't work. Further consensus states that life could only develop on a planet with a circular orbit around a metal-rich central host star. Two-thirds of the stars in the universe belong to binary or multiple systems, precluding such systems from the development of life. Of the remaining one-third, we would need a star about .8 - 1.25 solar masses to support life. If the star were smaller, its planet would orbit too close causing devastating tidal forces that would slow the planet's rotation causing it to cook on one side, like Mercury. If the star were larger, it would burn out long before intelligent civilization could arise. The star must be appropriately sized, otherwise a runaway greenhouse effect or permanent ice-age results, and that's if the planet even has water.
The planet also has precise requirements, and water appears to be primary. The planet has to
be large enough to support an atmosphere and small enough to maintain
correct gravity. To support the development of carbon-based life, the
host planet must be about .8 - 1.25 the size of Earth's mass or
temperature variations would presumably halt the development of life within about
2 billion years. The planet must also have some mechanism for the
preservation of carbon-dioxide, or else chain reactions resulting from
the presence of water would deplete carbon-dioxide from the atmosphere.
On Earth this occurs via plate tectonics and volcanic activity.
The solar system in which the planet and host star exist also has a set of prerequisites. Much of our universe and galaxy contains dead zones completely unhospitable to the development of complex life, and the positioning of the solar system relative to its galactic center is key. A galactic habitable zone also exists, as solar systems also orbit the center of barred spiral galaxies like ours. Just as the rocky planet must be within correct range from its host star, the host star must also be within correct range from its galactic center. The ability of a star to produce the metals necessary for complex life decreases with distance from the galactic center, and the prevalence of life threatening X and gamma ray radiation increases as we near the black hole at the center of our galaxy. If the solar system is too far out, not enough metal; if the solar system is too close, too much radiation. Also, within the solar system there cannot be large planets with elliptical orbits, because their perturbations would either eject or annihilate smaller planets. Conversely, it is thought that the solar system must contain large planets with circular orbits to act as buffers for asteroids and meteors that would otherwise strike with regularity causing mass extinctions much more often, but current evidence also suggests that gas giants like Jupiter may emit as much debris as they sweep.
These requirements could be extended ad nauseum, and I don't expect you to take my word on any of it. For the serious student, I suggest review of the Rare Earth hypothesis and the Drake Equation as starting points. I include the above summary only to dispel with the mythical, unscientific wishful thinking so prevalent in pop culture. All our science to date suggests that the universe is not literally teeming with planets capable of supporting life. You'll rarely ever hear questions or facts like these from UFO enthusiasts, but I feel fair and balanced reporting still has merit in science.
I think the general public has some deep-rooted misconceptions about space. Largely due to the enormous size of our universe, many people seem to view space with an "anything's possible" attitude, but our universe is more than just emptiness interrupted by an occasional star here and there, and unyielding natural law doesn't stop at the outer edge of Earth's atmosphere. Of 287 known exoplanets to date, zero appear capable of supporting complex life.
Don't get me wrong. I don't have a problem with the idea that our universe might be populated with higher intelligences. I don't have a problem from a religious or philosophical standpoint with the idea of God creating other life forms elsewhere in the universe. However, I often tell friends and acquaintances I don't believe the UFO phenomena represents carbon-based life forms visiting Earth from other galaxies, and I'm far less convinced that unguided, carbon-based biogenetics also happened to evolve metazoa capable of traveling to Earth in mechanical craft ala Newtonian means. Quantum manipulation or time travel are far more appealing to me, and this wild speculation supports another wild speculation of mine which posits that these beings and craft are electromagnetic in origin, capable of metamorphisis or otherwise able to temporarily embody a physical form.
Science usually dispels myth; sometimes it takes longer than others, some myths survive longer than others, and sometimes science even introduces myths of its own, but by and large if we want to know the truth of some physical phenomenon we turn to hard scientific results. On the other hand, hard scientific results inevitably lend themselves to charlatans and by their very nature require human interpretation.
That's where the room for error is, and I'd like to close this rambling abstract with a simple cautionary warning: When the question at hand involves science, always be skeptical of those who advance arguments in the absence of hard data.
*Milky Way rendering by CalTech's R. Hurt, all other photos courtesy NASA
