Hunting for ET

It is an impressive fact, and one that would have astounded your grandparents, but astronomers now estimate that our home galaxy – the Milky Way – sports at least a trillion planets. That’s a number not easy to picture, a tally greater than the number of trees in the United States.

Most of those unseen worlds are undoubtedly like some of the loser locales of our own solar system – airless and dry worlds like Mercury, or fetid balls of gas like Jupiter. In other words, most of the trillion planets infesting our galactic home are likely to be sterile, and dead as stone.

But just as there are winners lurking in a trillion lottery tickets, so too is it likely that among the manifold orbs of the Milky Way are winning worlds – planetary cousins of Earth. There could be millions, perhaps billions of planets or moons sporting thick atmospheres and liquid, water-filled oceans. If a fraction of these has cooked up life – or better yet, intelligent life – we are surrounded by a great deal of cosmic company.

In other words, what most of the public already believes – that alien societies pepper the universe – now seems at least plausible on the basis of hard science.

How might we find these other civilizations? Despite the impression conveyed by movies and TV, we can’t go there. Our rockets aren’t nearly speedy enough to be practical for interstellar travel. Even the fastest NASA spacecraft would take more than 100 thousand years just to reach Alpha Centauri, the nearest star to us other than the Sun (and also, incidentally, the stellar neighborhood of the large moon Pandora, the setting of James Cameron’s latest film, Avatar.)

So we’re not going to discover the aliens by visiting them. And while one-third of the American public believes that extraterrestrials are visiting us, few scientists think that the evidence for planetary house guests is convincing.

But there’s another way to get in touch. Rather than count on a face-to-face hookup, we could hunt for evidence of extraterrestrial beings that reaches us on a light beam or a radio wave – proof of alien intelligence that travels to Earth at the speed of light. Just as our radar and TV transmitters loft kilowatts of signal into space, so too might distant civilizations make their presence known by a faint radio whine picked up from light-years away.

Attempting to eavesdrop on alien signals is an enterprise that’s exactly 50 years old this month. In April, 1960 astronomer Frank Drake used an 85 foot radio antenna in West Virginia in the first SETI experiment (SETI being the acronym for the Search for Extraterrestrial Intelligence). Drake examined two nearby star systems for radio emissions without hearing anything that was obviously extraterrestrial. And in the 50 years since his effort, we still haven’t picked up any radio chatter from galactic neighbors.

But that’s no reason to get discouraged. The march of technology (primarily improvements in the speed of digital electronics) has made today’s SETI experiments far speedier at checking out star systems over wide swaths of the radio dial than was possible during Drake’s pioneering search. SETI has been likened to searching for a needle in a haystack, but today’s equipment has upped the speed of hay reconnaissance by trillions of times.

The latest wrinkle in the SETI game is the construction of large radio antennas (usually called radio telescopes) that are designed from the get-go for signal searching. The SETI Institute, located in California’s Silicon Valley, has joined up with the University of California at Berkeley to construct such an instrument. It’s called the Allen Telescope Array, because the initial funding was provided by entrepreneur Paul Allen. At the moment, the ATA comprises 42 antennas, each large enough (20 feet in diameter) to thoroughly dismay your neighbors if set down in the backyard. The Array is located in California’s Cascade mountains, about 300 miles north of San Francisco – a rural, topographically rugged area which provides both shielding from the transmitters of the big cities, and freedom from all the electrical noise one finds in an urban setting. There are no cell phone towers for miles.

So what’s the future? In the next two dozen years, powerful instruments such as this new array will allow the scrutiny of a million nearby star systems or more, in a search for faint, deliberately broadcast signals. If there are tens of thousands of alien societies spread throughout the Milky Way, then sampling a million stars could produce a hit.

If that happens, if we find someone out there at least as clever as we are, would that cause panic or the disruption of our own civilization? Hardly. After all, these aliens would be hundreds or thousands of light-years distant – which means that neither conversation nor rendezvous would be practical.

But a SETI success would tell us something very interesting. Namely, that what’s happened here on Earth is not some sort of one-off event, but simply an example of a process that’s taken place on a myriad of worlds. It would tell us that life – even intelligent life – is not a cosmic miracle, but merely a cosmic infection.

About Author Seth Shostak, Ph.D. :

Seth is the Senior Astronomer at the SETI Institute in Mountain View, California, and the 2004 winner of the Klumpke-Roberts Award awarded by the Astronomical Society of the Pacific in recognition of his outstanding contributions to the public understanding and appreciation of astronomy.

He hosts the SETI Institute’s radio program Are We Alone? Each week, Shostak interviews guests about the latest scientific research on a variety of topics: cosmology, physics, genetics, paleontology, evolutionary biology and astrobiology, and once a month hosts “Skeptic Check”, a show focused on debunking pseudo-science, U.F.O.s and practices such as astrology and dowsing. Are We Alone? is available for download at the SETI Institute’s website ,and through podcasts.

Shostak has been an observer for Project Phoenix (SETI) as well as an active participant in various international forums for SETI research. He is also Chair of the International Academy of Astronautics SETI Permanent Study Group.