Of course, despite our best efforts, we may never know how accurate our guesses are. Yes, there’s hope that instruments to be built in the coming two decades, including the Terrestrial Planet Finder, will show that other worlds have life. But these telescopes won’t be able to take us down onto those worlds to give us detailed pictures of what’s on the ground. For that we either have to travel to the stars, or hope for an alien bestiary that might be transmitted by intelligent beings for our edification. Neither eventuality is a sure thing.

But even though we might never know the details, this much seems probable. While you go about today’s business, strutting and fretting through all the things that seem important in your life, it’s worth pausing to consider the likelihood that right now – on many billions of worlds – there are other creatures doing the same, unknown to you and to each other. Life may not be just a bit of fluff, decorating the occasional, odd cosmic habitat, but a widespread and commonplace occurrence. Life may be plentiful beyond what is easy to imagine.

However, and somewhat coincidentally, within that same time frame, two other kinds of searches for extraterrestrial life will also shift into a higher gear. Within a decade, NASA will launch its orbiting Terrestrial Planet Finder (the Europeans will launch a similar telescope, called Darwin). This scope will be able to capture the light from planets the size of Earth, unknown worlds orbiting stars many dozens of light-years away. The TPF and Darwin will not only be capable of seeing these planets, but will make a crude spectral analysis of the light reflected back from their atmospheres. If they find gasses such as methane, oxygen, or water vapor in the right quantities, that will provide some fairly convincing evidence that these planets are veneered with life.

The third salient in the multifaceted attempt to discover living things elsewhere is the improved technology that will be deployed for SETI, the search for extraterrestrial intelligence. As a prime example, the
Allen Telescope Array, being constructed in northern California, will be able to check out a million star systems or more in the coming two decades, listening for the type of radio signals that only transmitters can make. That’s a thousand times as many stellar targets as have been carefully examined so far.

So the race is on. It could be that all contenders will be scratched, and we will fail to find life of any kind with these efforts. On the other hand, I’m betting that at least one of the horses will cross the finish line in the next 20 years. Which one? Wait and see.

There are several reasons why we haven’t mounted a massive transmitting project. Part of it is money. All SETI experiments in the United States are funded with private donations, and there’s barely enough to undertake a state-of-the-art listening effort. Since any transmitting scheme would take many years to pay off (perhaps a millennium or more if the nearest extraterrestrials are many hundreds of light-years away), there’s a greater incentive to spend the money on experiments that might succeed this week, or at least within a few decades. Then there’s the fact that it really doesn’t make much sense to transmit only for a few minutes, hours, or days. There are occasional commercial “demo” projects that do this (“send photos of your pet ferret into space! Only $3.99 a minute). But the chance that any alien has pointed his antenna in the right direction at the right time to hear them is smaller than a bacterium’s backpack. If you’re going to transmit, you have to do it for a long time, maybe thousands of years. We’ve only had radio technology for a century or so, and making reliable equipment that could manage long-term broadcasting is still too much of a challenge for us. Leave this kind of heavy-lifting project to advanced aliens, many scientists will argue.

Also, some people worry that broadcasting might be dangerous, as it would alert unknown societies to our existence and coordinates. “Who knows what’s out there,” these folks declaim. However, this argument ignores the fact that continuous, high-powered broadcasts have been leaking off Earth for more than a half-century. Our FM radio, television, and radar transmissions have already flooded the nearest several thousand star systems, and there’s no retrieving these unintentional transmissions. The Arecibo radar, used for research, produces a signal that could be easily detected on the far side of the galaxy (although it will take 80 thousand years to get there). But paranoia aside, some researchers have argued that a carefully thought out broadcasting effort might be valuable – and only partly because it might put us in touch with cosmic pen-pals. Designing a transmitting system effective enough to reach an unknown audience light-years away could give us valuable insights into how we might better shape our SETI listening efforts.

Other aspects of this poll have also surprised me. Most of the respondents think that ET, if he exists, would be more advanced than us. Well, of course, any extraterrestrial signals we might detect are very likely to come from societies that are, indeed, more technically advanced than our own. We won't hear from the alien equivalent of Neanderthals. So this does, indeed, make sense. But perhaps most surprising of all is the fact that 90% of those who anticipate life on other planets think that if we pick up an extraterrestrial signal, we should respond. Rather than being fearful of contact with other beings, we seem to want to encourage it. Once again, this indicates that, despite all of the nasty aliens that populate pop culture, most folk have a far sunnier view of what our cosmic brethren might be like.

I would love to hear what you think of the poll... let me know!

Thanks.

-Seth

That was then, and this is now. Theoreticians, armed with fast computers, have calculated what happens to planets in multiple-star systems. It turns out they’re not all condemned to eventual exile. There are two cases in which planets will just hang around and hang around.

1) Close-in double star systems, where the suns dance about one another in hours or days. Planets that orbit, say, a hundred million miles from this tightly pirouetting pair will experience its gravitational tug as one large star, and their orbits will remain stable for long periods of time.

2) Widely-separated doubles offer a similar opportunity. If the stars are separated by more than five times the distance at which a planet orbits one or the other of them, those planets, too, will be around for the long haul.

You might think this is all much ado about nothing. But roughly half of all stars are in multiple-star systems (doubles, mostly, but also triples and even larger litters). By including the right kind of doubles in our searches, we have doubled the amount of cosmic real estate that is worth checking out for life.

But the TPF, unlike your 1987 Yugo, will go farther. The first telescope to be launched will be a single-mirror instrument, with a device to block out the light from stars—kind of like a mechanical thumb— in order to see the much dimmer planets that might be in orbit around them. The second TPF, scheduled for lift-off in 2020, will operate at infrared wavelengths where stars are somewhat dimmer and planets aren’t. It will use multiple mirrors, flying in formation like UFOs in attack mode, to simulate the visual acuity of a telescope that’s hundreds of feet across. It will be a true hawk’s eye in space, sharp enough to see Earth-size worlds -- not just infer their presence, but actually see them. Planets will appear as small dots buzzing around their sun. This means that all sorts of information can be directly measured as these dots move over the course of weeks or months: orbit size and shape, the length of the year, etc.

A second function of the TPF is to follow up on these planetary discoveries by taking apart the light from a newfound planet. On-board spectroscopes will accomplish this spectral slice-and-dice, allowing astronomers back on Earth to hunt for absorption features that can be used to fingerprint gasses in the planet’s atmosphere. They’ll be looking for the tell-tale signs of large-scale biota. For example ozone, which is just oxygen, would signal the presence of photosynthesis (or something like it). Methane is another gas that’s common in our own atmosphere because of pigs, cows, and bacteria (not necessarily in that order). Finding it in the atmosphere of another world might be big news -- not just because of the dining possibilities. The TPF is coming and so are big discoveries, so mark your calendars.

In fact, as a tour of any zoo will convince you, there’s a breathtakingly wide variety of creature designs that work on our planet – and presumably on theirs, too. So why would intelligent extraterrestrial life look anything like us? Probably it wouldn’t, although there’s a mechanism known to biologists as “convergent evolution” that argues for at least a bit of a resemblance. Convergent evolution is the idea that as nature works its way down a Darwinian path, selection favors good designs that enhance survivability.

A "stinger fan forest," one
of many life forms imagined
in Extraterrestrial on the
National Geographic Channel.These designs can be arrived at via different evolutionary routes. For instance, predators in the ocean will have a survival advantage if they can swim fast. Consequently many of them have a torpedo shape, simply because this streamlined form gives them a better chance at snagging a dinner. Dolphins and barracudas look similar in silhouette, even though they evolved from very different forebears. Their shapes are the result of convergent evolution. Some biologists have suggested that the same may be true of humans and extraterrestrial life -- that the human body plan is a good design for an intelligent creature. We have free appendages (these are known by the technical term: “arms”) terminated by graspy little hands useful for writing, wielding tools, or ferrying snacks to our mouths. We also have two eyes with overlapping vision, providing 3-D views of the world that facilitate tool use. The eyes are located high up, permitting us to peer over grass and brush to find a mate or a meal. And the list goes on. Humans, in many ways, are a reasonably functional design for a technically sophisticated creature.

But it’s a bit extreme to maintain that we are the best design, and therefore convergent evolution will ensure that an intelligent alien looks like your brother-in-law. After all, an extra set of arms might be useful, as would an eye in the back of our heads. A double spine might allow faster and easier walking, and a few extra digits on each hand could make for better tool use or piano playing. The bottom line is that any biological creature we find that’s at least as clever as we are might have, some features in common with us (two eyes, instead of one, for instance). But there’s little reason to think our own design is so wonderfully optimal that all thinking beings will have converged on it. Intelligent extraterrestrials may look vaguely humanoid, but no more than vaguely.

What is the basis for this point of view? A lot of it has to do with recent discoveries made with telescopes and space probes. In the last decade, we’ve finally been able to uncover planets around other stars. We thought planets might be common, but our telescopes have replaced speculation with hard data, and we now have good reason to think the number of planets in the universe is greater than the number of stars. Our exploration of our own solar system with space probes also revealed something rather surprising: Worlds that even a dozen years ago were thought to be as barren as the Gobi on a dry day might actually have niches sporting moderate temperatures and liquid water – and possibly also life. Mars could be laced with underground aquifers where microbes strut their miniscule stuff. Several of the moons of Jupiter might have vast, hidden oceans of salty water, possibly infested with life. Even cold, sticky Titan might conceivably have spawned biology. What we’ve learned is that a duplicate of Earth is not essential to give life a chance. Various kinds of worlds might host living things.

Then there’s the numbers argument. If there really are hundreds of billions of planets in our galaxy, as seems probable, then the observable universe is stuffed with more than ten thousand billion such worlds. It requires a truly jumbo-size helping of hubris to think that, among this vast quantity of planetary real estate, our world is the only one to witness life.