The following article is from the Economist, February 25, 2006, at pp. 82 - 83 (in the "Science and technology" section):
"Waving at the neighbours
The search for extra-terrestrial life
Human beings are, on an astronomical timescale, recent arrivals - and when you first arrive in the neighbourhood, it is only polite to say hello to the neighbours. That, at least, is the attitude of the SETI Institute. SETI stands for the Seacrh for Extra-Terrestrial Intelligence, and that search has been going on, in various institutional guises, since 1960.
The SETI Institute's members reckon the best way to get in touch is by radio, so they have begged and borrowed time on the world's radio telescopes to listen either for signals deliberately being broadcast by other technological species who want to make themselves known, or for radio signals intended for domestic alien consumption that have simply leaked into space. So far, though, they have heard nothing.
Part of the problem is that intelligent aliens are thin on the ground and there are an awful lot of stars. With this in mind, Margaret Turnbull of the Carnegie Institution of Washington, D.C., has, as she explained at last week's meeting of the American Association for the Advancement of Science, been trying to refine the target list by going through the catalogue of the 120,000 stars closest to Earth and eliminating unsuitable ones to leave a subset of 'habstars' with more potential for life.
Dr. Turnbull starts from the premise that every star has a zone around it with the right temperature to support carbon-and-water-based life, the only sort so far known to exist. If there are suitable planets in this zone, they might contain life.
First to be tossed out, therefore, are stars lacking the metallic elements needed for planet formation. Astronomers have a rather odd definition of metal, so that any element heavier than helium counts. Carbon, oxygen, nitrogen, and silicon are all metals in the astronomical sense. Dr. Turnbull, though, uses iron, a real metal, for her assay. A star's light reveals how much iron it contains, and thus whether planets are likely to have formed around it.
After that, variable stars are thrown out, since they have moving habitable zones. Most binary stars go, too, because planets orbiting them would move in and out of the habzone. And stars that have ballooned into red giants or dwindled into white dwarfs are also rejected.
Finally, she throws out stars that are too young. Some of these are obvious, because they are burning so fast that they will never make their three billionth birthday, which is the minimum amount of time that Dr. Turnbull reckons is needed to go from uninhabited rock to technological civilisation. Other, slower-burning stars have their light analysed to see how much helium they contain, and thus how long they have been fusing hydrogen to helium to power themselves.
The result is a list of 17,000 habstars - still quite a lot, but far fewer than if the search were carried out exhaustively. If ET is out there, his hunters now have a better idea where to look."
Looking at her criteria, I think Dr. Turnbull has used a fairly conservative set of parameters, and has still come up with a list of just over 17,000 habstars in our "neighbourhood".
Let's assume that only 1/10th of one per cent of those habstars actually support planets that contain life.
That's 17 civilisations, give or take.
Let's assume - further - that half of those are as advanced or more advanced than we are (I'm probably being charitable here in assuming we're middle of the road). That's 8 civilisations that are at 21st century human technological levels, or beyond, with technology that we can only speculate about.
And if just one of them has figured out how to get from there to here, and back again?
Does any of this prove the ETH?
But it does mean that those debunkers who would dismiss it out of hand or, even worse, dismiss the concept of intelligent life somewhere other than here on Earth, are barking up the wrong tree.
Dr. Turnbull's work shows the possibilities that are out there (and perhaps are coming here) - including some that she, as a SETI proponent, probably doesn't agree with, but which are nevertheless impossible to ignore.
After all, if these civilisations that SETI are looking for can figure out radio, which means they are at least as advanced as we are, who knows what else they might have discovered?
For more information on Dr. Turnbull and her work, check out her homepage.
She may be a type II scientist, but her work clearly has Type III scientific implications.
Kudos to the Economist, which I think is the best news weekly magazine available, for taking this subject seriously. Now, if only they would run a serious article on the work of serious UFO researchers.
Maybe someone should mail them a copy of Dick Hall's UFO Evidence, Vol. II.