Dr. Seth Shostak Answers Your Questions About SETI

by Fraser Cain on January 27, 2005

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Is there any other way a civilization can be detected other than by EM radiation (IR, UV, radiowave, microwave, etc) detection? What’s the probability of finding an intelligent lifeform in our lifetime? – Alfchemist

Well, sure, there are other possibilities for finding cosmic company. You could look for messages being transmitted by particle beams (even neutrinos), and this has been suggested. But the problem is that these require harder-to-build transmitters and receivers, and are also susceptible to absorption by interstellar gas. So they don’t seem to offer much advantage. The other possibility is to find some evidence of “alien engineering” — maybe sophisticated beings on other worlds have managed to rearrange the stars in their neighborhood, or build huge, starshine-collecting solar panels that we could somehow spot from afar. Some experiments have been done to locate such massive construction projects, but it’s hard to know how to look or even what to look for.

I think it’s likely that the new telescopes being built for SETI will trip across a signal by the year 2025.

The SETI Project and SETI@home have processed a bunch of data. Other than the search for intelligent signals, have you learned anything new about the universe from all this information? – corkft

In fact, not too much. This is rather surprising, because the history of astronomy suggests that whenever you build a new instrument, able to look at a previously unobserved bit of either space or the spectrum, you usually trip across some unexpected object or other. SETI projects have receivers with VERY narrow frequency channels. But there really doesn’t seem to be any natural phenomena that lend themselves to being discovered with such equipment. In a sense this justifies SETI’s assumption that any narrow-band signal would convincingly prove intelligence!

What is the maximum distance at which SETI can detect signals which are not deliberately beamed at us, such as normal radio telecommunications traffic? And are there plans to increase this range? – Steve t

Our best SETI experiments to date could detect Earth-like “leakage” signals at no more than 1 light-year’s distance. So not too far. But keep in mind that (1) our experiments do get more sensitive with time, so this distance will increase, and (2) we’ve only had radio for a century. Aliens, who may have invented this technology thousands or even millions of years ago, will undoubtedly have some transmitters and antenna systems capable of putting out signals far more powerful than what we manage with our erudite and always entertaining commercial television efforts!

To what degree does our SETI search make assumptions about the rate of information transfer? What transfer rates are we currently equipped to detect, and in what modulation modes? – wstevenbrown

We don’t worry at all about modulation, or schemes for encoding messages. That’s something to be considered after you’ve found that their transmitter is on! At the moment, all SETI experiments simply look for narrow-band (typically 1 Hz or narrower) components to a signal… somewhat akin to the “carrier” signal for earthly transmissions, but not limited to those. We also look for slowly pulsing signals, too. But the point is that at least some fraction of the aliens’ transmissions are assumed to put a lot of energy into a narrow bandwidth… making those signal components more easily detectable.

Assuming Big Bang origins, how soon would sufficient astronomical metallicity have occurred to produce a 0.8% or better probability of the formation of CHON-based life supporting planets? Is there any way to evaluate how “typical” is the time required for our evolutionary path to technical competence? – GOURDHEAD

Well this depends on where you are, as the metallicity varies across the Galaxy. I can’t speak to “0.8% or better probability,” as I don’t know where this number comes from and there’s no way to estimate it anyway. But put it this way: even in the oldest globular cluster star systems in our Galaxy — choked with stars that were born more than 10 billion years ago — there’s enough of the heavy elements (“metals”) to make earth-like worlds. I don’t think there was much “dead time” between the formation of galaxies and the growth of the heavy element abundance to the point where life was possible.

Do the recent conclusions that radio signals from advanced civilizations may be indistinguishable from the thermal radiation of their parent stars give you second thoughts on the likelihood of finding a positive signal? – Greg

Nope. It’s true that an optimally encoded signal would look like (white) noise, and I’m sure that advanced societies will be very good at encoding. But there are always applications for which you need some narrow-band signals. For example, you might have a solar-system-wide GPS network for interplanetary navigation. Or big radar sets for tracking incoming, long-period comets. Not to mention a deliberate broadcast to galactic brethren…!

How will the new Allen Telescope Array (ATA) be incorporated into SETI ? – 6EQUJ5

In the summer of 2005, there will be 32 antennas working at the ATA, and the SETI Institute will initiate a scan of the densest parts of the galactic plane. This is a straightforward SETI experiment that will scrutinize lots of stars, albeit stars that are (on average) thousands of light-years away. As the ATA gets built out to 350 antennas, it will switch over to targeting individual, relatively nearby (less than 1,000 light-years) star systems. By 2025, it should be able to check out as many as a million such systems.

Should an alien signal be identified, what would be the protocol for alerting the people of Earth? Would the news be limited to a few,or would be announced for all to listen? – Duane

Well, there’s no secrecy in SETI, and it’s been our experience that whenever we pick up an “interesting” signal, the media are on top of the story right away. So you can be sure you’ll be reading about any signal long before the SETI researchers themselves have fully checked it out to convince themselves that it isn’t interference or a software bug!


Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

Mark Chipman December 7, 2007 at 10:58 AM

Dr. Shostak–
I just read your “Aliens Apart” article on space.com. I concur with your assessment. However, the logical conclusion to be drawn from your article is that UFO sightings here on Earth are all bogus (i.e., not of ET origin). Personally, I am given over to the notion that some of these sightings are valid.
So, I am left in a quandary: take option (2) noted in your article [we haven't discovered the secret to star travel] or believe that UFOs don’t exist. I haven’t reached a conclusion yet, but I’m guessing you have: UFO’s don’t exist.
Forgive me for not having researched your other writings to ferret out the answer, but I felt a need to write.
Mark Chipman
San Diego, CA

Richard Celny July 19, 2008 at 8:08 PM

Seth, having listened to your responses on Larry King Live regarding the subject of UFOs as intelligently controlled non-terrestrial craft, I can only conclude that you have not visited the toilet for decades… You are so full of it, that your claims / interpretations are even more ludicrous than the possibility of ETs visiting this planet.

Can you say “blind denial”, Seth?

Frank Heynick October 11, 2008 at 4:37 AM


I tried sending you an e-mail with attachment (on a subject near and dear to your heart) at:


But it bounced.

So what’s your present e-mail address?


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