The term METI was coined by Russian scientist Alexander Zaitsev, who denoted the clear-cut distinction between Active SETI and METI:
The science known as SETI deals with searching for messages from aliens. METI science deals with the creation of messages to aliens. Thus, SETI and METI proponents have quite different perspectives. SETI scientists are in a position to address only the local question “does Active SETI make sense?” In other words, would it be reasonable, for SETI success, to transmit with the object of attracting ETI’s attention? In contrast to Active SETI, METI pursues not a local and lucrative impulse, but a more global and unselfish one – to overcome the Great Silence in the Universe, bringing to our extraterrestrial neighbors the long-expected annunciation “You are not alone!”
Also characteristics of the radio signal such as wavelength, type of polarization, and modulation have to be considered.
These projects have targeted stars between 32 and 69 light-years from the Earth. The exception is the Arecibo message, which targeted Glob cluster M13, approximately 24000 light-years away. The first message to reach its destination will be Cosmic Call 2, which should reach Hip 4872 of Cassiopeia in April 2036.
Stars to which messages were sent, are the following:
|Name||Designation||Constellation||Date sent||Arrival date||Message|
|Messier 13||NGC 6205||Hercules||November 16, 1974||approx. 25974||Arecibo Message|
|16 Cyg A||HD 186408||Cygnus||May 24, 1999||2069November||Cosmic Call 1|
|15 Sge||HD 190406||Sagitta||June 30, 1999||2057February||Cosmic Call 1|
|HD 178428||Sagitta||June 30, 1999||2067October||Cosmic Call 1|
|Gl 777||HD 190360||Cygnus||July 1, 1999||2051April||Cosmic Call 1|
|HD 197076||Delphinus||August 29, 2001||2070February||Teen Age Message|
|47 UMa||HD 95128||Ursa Major||September 3, 2001||2047July||Teen Age Message|
|37 Gem||HD 50692||Gemini||September 3, 2001||2057December||Teen Age Message|
|HD 126053||Virgo||September 3, 2001||2059January||Teen Age Message|
|HD 76151||Hydra||September 4, 2001||2057May||Teen Age Message|
|HD 193664||Draco||September 4, 2001||2059January||Teen Age Message|
|HIP 4872||Cassiopeia||July 6, 2003||2036April||Cosmic Call 2|
|HD 245409||Orion||July 6, 2003||2040August||Cosmic Call 2|
|55 Cnc||HD 75732||Cancer||July 6, 2003||2044May||Cosmic Call 2|
|HD 10307||Andromeda||July 6, 2003||2044September||Cosmic Call 2|
|47 UMa||HD 95128||Ursa Major||July 6, 2003||2049May||Cosmic Call 2|
To lend a quantitative basis to discussions of the risks of transmitting deliberate messages from Earth, the SETI Permanent Study Group of the International Academy of Astronautics adopted in 2007 a new analytical tool, the San Marino Scale Developed by Prof. Ivan Almar and Prof. H. Paul Shuch, the San Marino Scale evaluates the significance of transmissions from Earth as a function of signal intensity and information content. Its adoption suggests that not all such transmissions are created equal, thus each must be evaluated on a case-by-case basis before establishing blanket international policy regarding Active SETI.
Once civilizations have discovered each others' locations, the energy requirements for maintaining contact and exchanging information can be significantly reduced through the use of highly directional transmission technologies. In 1974, the Arecibo Observatory transmitted a message toward the M13 globular cluster about 25,000 light-years away, for example, and the use of larger antennas or shorter wavelengths would allow transmissions of the same energy to be focused on even more remote targets, such as those attempted by Active SETI.