Extraterrestrial Civilizations - Isaac Asimov [138]
If the search for messages from extraterrestrial civilizations is to be carried through with some reasonable hope of success, however, far more time must be spent than was the case in Project Ozma; far more stars must be studied, far more elaborate equipment must be used. In short, a very expensive project must be set up.
WHERE?
In 1971, a NASA group under Bernard Oliver suggested what has come to be called Project Cyclops.
This would be a large array of radio telescopes,* each 100 meters (109 yards) in diameter, and each adjusted for reception of microwaves in the waterhole region.
The array would consist of 1,026 such radio telescopes in rank and file, all of them steered in unison by a computerized electronic system. The entire array working together would be equivalent to a single radio telescope some 10 kilometers (6.2 miles) across.
The array would be capable of detecting something as weak as Earth’s inadvertent leakage of microwaves even from a distance of 100 light-years, while the deliberately emitted message beacon of another civilization could be detected at a distance of at least 1,000 light-years.
Earth’s surface may not be the best place for it. If it could be built in space, or, better yet, on the far side of the Moon, it would be insulated from most or all of the background of Earth’s own microwave noise.
Project Cyclops would not be easy to construct and certainly not cheap. Estimates are that the construction and maintenance of the array and the search itself would cost anywhere from $10 to $50 billion, even allowing for the fact that eventually the listening will be completely computerized and will not take much in the way of people-hours.
Anything that could be done to make the search simpler and quicker would be helpful, therefore. There might be places in the sky, for instance, where it would pay us to search first because they are more likely sources of messages than other places are.
Where might these places be?
First, the best place to search is in the neighborhood of some star where a planetary civilization with copious energy at its disposal might exist. (There might be, to be sure, signals being sent out by free-worlds or automatic probes that are closer to us than any star, but we have no way of knowing where such objects are and therefore no particular target to aim at.)
Second, the objective should be a nearby star rather than a distant star, since, all things being equal, the microwave beam will be more intense and easier to detect the closer the planetary system from which it starts.
Third, the objective should be a Sunlike star, since it is there we expect habitable planets might exist.
Fourth, the first objectives should be single stars, since, even though it seems that binary stars may still have habitable planets circling them, the chances are perhaps greater in the case of single stars.
As it happens, there are just seven Sunlike single stars within 2 dozen light-years of us, and they are:
STAR DISTANCE MASS
(light-years) (Sun = 1)
Epsilon Eridani 10.8 0.80
Tau Ceti 12.2 0.82
Sigma Draconis 18.2 0.82
Delta Pavonis 19.2 0.98
82 Eridani 20.9 0.91
Beta Hydri 21.3 1.23
Zeta Tucanae 23.3 0.90
None of these stars has a familiar name, for those that do are generally the brightest, which are too large and short lived to be suitable for civilizations.
Stars that are visible to the unaided eye, even if they are not outstandingly bright, are generally named for the constellation in which they are found. Sometimes they are listed in order of brightness, or position, by the use of Greek letters (alpha, beta, gamma, delta, epsilon, zeta, and so on) or by Arabic numerals.
The stars in the table above are from the constellations Eridanus (the River), Cetus (the Whale), Draco (the Dragon),