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Alien call I.

© Rodolfo Astrada

For about a century now, the Earth has been broadcasting radio signals drifting outwards at the speed of light.
This was not on purpose, but the byproduct of long wave radio broadcasting emergence at first, and the rapid expansion all the way up to the microwave realm thereafter. Short wave radio, FM, low and high band VHF television, UHF television, point to point and mobile communications, radar, satellite telecomunications, space observatories and space probes data communications and so on.

With just a century of technology development - a blink in cosmological time scales - we have developed receivers capable of identifying radioed signals with the diversity and power levels of earthly emissions from several light years away. That is, were there a nearby planet inhabited with life forms capable of generating radio transmissions similar to ours, then we should be able to detect and identify them as non naturally occurring.

If on the other hand, there were intelligent civilizations sending powerful signals our way either on purpose, or as a consequence of radar scanning for meteorite menaces (or incoming warheads) as we do, then they could be detected and identified form tens to hundreds of light years away.

First try

This fact was recognized as early as 1960, when Dr. Frank Drake proposed a systematic search primarily targeted to nearby stars as likely candidates for the existence of planetary systems.
His was not simply an idea out of the blue, but founded in an statistical approach taking into account several parameters such as abundance of sun-like stars, probability for the existence of earth-like planets, of development of life and intelligent species and so on. Gloomily enough, one factor is the probable lifetime of a technological civilization before self destruction, or death of its parent star.
All these parameters are plugged in a formula, known as the Drake equation, which yields for example the likely number of communicating technological civilizations existing in the Milky Way.
Of course this is a statistical approach where starting values are subject to controversy and / or uncertainty, yet the Drake equation is still considered the best educated guess. Depending on initial assumptions, this number may fall anywhere from a few ones to several millions, for our galaxy alone.

Headed by Drake, Project Ozma started with a 26 m. microwave dish in Green Bank, West Virginia. As luck should have it, not even hours had elapsed when readings went crazy to the surprise and elation of all present. Disappointingly, the "alien" transmission was quickly identified as of an overflying aircraft.