Aliens appear ad nauseam in film and television, most often pulverizing our cities and trying to kill us all. But despite their bad boy reputation – or maybe because of it – people are clearly intrigued by these hypothesized beings from afar.
Extraterrestrials also fascinate scientists. Alien life is an old idea and a modern activity, one pursued today by national space agencies as well as academics and non-profit institutions. So far, no one has convincingly proven the existence of anything biological beyond the bounds of our planet – not even a single bacterium. But just as everyone believes that a cure for the common cold could be around the corner, many scientists suspect that finding life beyond Earth is in the offing – and may occur before you finish paying off your mortgage.
The conviction that the universe could host a lot of pulsing protoplasm is based on the power of big numbers. In the last two dozen years, we’ve learned that planets are like roadside litter – they’re everywhere. In a typical galaxy, such as our own Milky Way, about a trillion planets serenely spin around their home stars. If only one percent of these is of the type that can support creative critters like ourselves, then we’re still talking 10 billion worlds.
While that implies a lot of cosmic company, it doesn’t prove its existence. But if no one’s there, then there’s something astoundingly remarkable about Earth and its history. Such special pleading for our home planet is always suspect.
Almost all the effort to find life in space is directed to searching for it nearby. There are at least a half-dozen habitable worlds close enough to be trawled for biology. These include Mars (the obvious candidate), which might have liquid water pooled beneath its ruddy crust, but also several of the moons of Jupiter and Saturn. The latter are known to have large liquid lakes or underground oceans, and it’s the presence of fluids that’s generally considered the sum and substance for life.
For anyone content with finding aliens that are microscopic, then searching the solar system is their best bet. A few years ago, NASA’s Chief Scientist, Ellen Stofan, said she expected the discovery of biology in our solar system within two decades. Admittedly, finding alien pond scum may not excite everyone, but it would enthuse scientists. It would imply that the universe is brimming with biology.
But forget the microbes. What about those soulless, big-eyed aliens we see every night on the telly? What are scientists doing to find them – creatures at least as clever as ourselves?
For the last 60 years, a very small group of researchers has dedicated their careers to ferreting out convincing evidence for such beings – the Search for Extraterrestrial Intelligence, or SETI. They’ve mostly used very large antennas – typically 80 to 1,000 feet in size – to scan the skies for radio signals that would be unmistakably generated by a transmitter on another world.
What qualifies as ‘unmistakable’? It’s not that we count on Klingons to send us prime numbers or the value of pi. Rather, any real alien signal will be constrained to a limited range of frequencies. This is unlike natural emitters, such as quasars, pulsars, and other members of the astronomical menagerie that generate static over wide swaths of the radio dial.
Today, only two groups in the United States are actively engaged in a radio search – at the SETI Institute in the Silicon Valley and at the University of California at Berkeley. There’s no funding for SETI in other countries, and frankly even the two California teams are largely dependent on the generosity of individual donors – people willing to commit some of their personal income to a search.
This limited financial backing for SETI may be puzzling, given that space agencies spend hundreds of millions of dollars a year or more in exploring Mars or the moons of the outer solar system. It’s not that these organizations find microbes more interesting than brainy biology. It may simply be a consequence of the fact that, unlike a robotic rover on the Red Planet, SETI experiments can’t conclusively say there’s no one home.
Sure, you can point a large antenna in the direction of another planetary system and hope to hear some alien-produced static, but if you don’t pick up anything, what does that prove?
Not terribly much, unfortunately. It’s possible that the apparent silence is simply because your setup doesn’t have enough sensitivity, or is tuned to the wrong frequency. Perhaps the aliens are on summer break – or maybe even a permanent break – simply because they don’t want to draw attention to themselves. For SETI, absence of evidence is not evidence of absence.
So, what are the prospects for finding E.T? Thanks to the indefatigable march of technology – and more specifically computer technology – the speed at which researchers are scanning the skies is accelerating. In the next two decades, more than a million star systems will be examined for signs of alien signals.
If, as some scientists guess, tens of thousands of such societies are scattered across the Milky Way, then a signal could be found soon. The foreseeable future could give us a major news story.
But of course, this scenario assumes that (a) the aliens are happy to transmit and have some beefy transmitters that can reach us across light-years of space, and (b) they’ve made a real commitment to this shout-out so that they’re always ‘on the air.’
It’s unclear whether these assumptions are reasonable or otherwise. But another approach could avoid such requirements altogether: We could search for alien artifacts.
Rather than betting on the presence of strong signals, we could look for massive engineering projects undertaken by truly advanced cultures. Perhaps someone has stuffed their solar system with swarms of solar panels to supply the energy needed for their active alien lifestyles. Maybe they’ve rearranged some nearby star systems to better suit their needs.
Obviously, we can only guess at the type of projects that sophisticated societies might tackle, but a search for artifacts is certainly worth considering. In addition to the advantage that no altruistic behavior by the extraterrestrials is required (they don’t have to transmit for our benefit), it’s also conceivable that we could discover their handiwork in the course of ordinary astronomical investigation. Structures are a ‘signal’ that’s always on.
If we find proof that someone is out there, what would be the consequence? In the long term, we might conceivably learn something from our galactic elders. But even if not, we’d be aware there are others out there. And that would be interesting to know.
Dr. Seth Shostak is the Senior Astronomer at the SETI Institute in Mountain View, California.
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