The SETI League, Inc., a membership-supported, non-profit {501(c)(3)}, educational and scientific organization Searching for Extra-Terrestrial Intelligence

Ask Dr. SETI ®

Chapter 1: Astrophysics

Detection of Extra-Terrestrial Lightning

Dear Dr. SETI:
I believe that we must have some fundamental problems with our perceptions of what we should be able to detect. In my opinion, the calculations relavent to our detection equipment's ability is only a minor consideration in the likelyhood of detecting ET radio waves. There may be 1 or even a 101 technical reasons, that we don't yet understand, as to why the radio waves we are looking for aren't getting here.

I suggest that we look for other radio waves nearby in our galaxy that have about the same power as our most powerful common transmissions, namely radio waves generated by lightning. Lightning generated radio waves should be studied to learn if their frequency composition is unique in any way. If it does have any unique properties, we may be able to sort them out from the rf din of this galaxy. If we can not detect or identify such equally weak waves that we "know" are out there, it would safe to say that ET waves aren't going to punch through either.

JP, Ludington, MI

The Doctor Responds:
Your basic premise may of course be true. On the other hand, there is no clear evidence that these radio waves aren't getting here! All we can say for sure is that we have not yet received them in a verifiable, repeatable, conclusive way.

Analysis of the lightning spectrum has been done, extensively, by an electrical engineering professor named Paul Ryan. His work was done twenty years ago while developing a device called a Storm Scope, used by pilots to detect and avoid thunderstorms. Lightning does indeed have a unique and unmistakable electromagnetic signature, at least on Earth. Unfortunately, its energy peaks near a frequency of 50 kHz, a portion of the spectrum which will not penetrate our ionosphere. Certainly space-based searches for extra-terrestrial lightning are feasible, but far beyond our budget. This is my personal opinion, which not everybody in the SETI community shares. For an alternative viewpoint, see this article.

You do bring up an important point. One good way to verify that our equipment is doing what is expected of it is to use it to detect known natural electromagnetic phenomena. We do this with our SETI receivers, when we point them at known extra-solar radio sources and measure signal strength. By using SETI receivers for conventional radioastronomy (the detection of those "equally weak waves that we 'know' are out there"), we have indeed determined that their ultimate sensitivity is adequate to the task at hand.

Incidentally, we also use known artificial signals to verify the operation of our equipment. When Project Phoenix went on the air two years ago from the Parkes observatory in Australia, scientists calculated that they should be able to receive the 10 watt beacon from the Pioneer 10 spacecraft, beyond the edge of the solar system. They received not only the carrier, but also the modulation sidebands, verifying the sensitivity of their equipment. More recently, SETI League members have received the 1.3 Watt omnidirectional beacon from the Mars Global Surveyor satellite at 5 Million km from Earth, at levels consistent with what our calculations predicted.

It is often assumed that our failure to verify SETI hits to date is somehow due to their being unreceivable here on Earth. In fact, all our studies and computations indicate that they should be quite easily detectable, with the equipment at hand, if we only look on the right frequency, in the right direction, at the right time. But all the world's SETI searches to date have logged just a few thousand hours of observation, over a tiny fraction of the sky, on precious few plausable frequencies. Not only have we not yet scratched the surface, we haven't even yet felt the itch.

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