Active SETI

Active SETI (Active Search for Extra-Terrestrial Intelligence) is the attempt to send messages to intelligent aliens. Active SETI messages are usually in the form of radio signals, however, physical messages like that of the Pioneer plaque may also be considered an active SETI message. Active SETI is also known as METI (Messaging to Extra-Terrestrial Intelligence), or positive SETI. Active SETI is contrasted to passive SETI, which only searches for signals, without any attempt to send them.

The term METI was coined by Russian scientist Alexander Zaitsev. In [1] he 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, but a more global purpose – to overcome the Great Silence in the Universe, bringing to our extraterrestrial neighbors the long-expected annunciation “You are not alone!”

Message construction

The lack of an established communications protocol is a challenge for METI. Also characteristics of the radio signal such as wavelength, type of polarization, and modulation have to be considered.

Realized projects

• Arecibo Message (1979)
• Cosmic Call 1 (1999)
• Teen Age Message (2001)
• Cosmic Call 2 (2003)

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.

Perceived risk

Active SETI has been heavily criticized due to the perceived risk of revealing the location of the Earth to alien civilizations, without some process of prior international consultation.

But some consider this as panic and irrational superstition, see: Sending and Searching for Interstellar Messages

Beacon proposal

One proposal for a 10 billion watt interstellar SETI beacon was dismissed by Robert A. Freitas Jr to be infeasible for a pre-Type 1 civilization on the Kardashev scale.^[1] However, this argument, dated from 1980, assumes omni-directional beacons, which may not be the best way to proceed. As a result it has been suggested that civilizations must advance into Type I before the energy required for reliable contact with other civilizations. Advances in consumer electronics have made possible transmitters that can illuminate the stars only, and not the space between them.^[2] This can reduce the power and cost to levels that are reasonable with current (2007) earth technology. 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.

References

• Messaging to Extra-Terrestrial Intelligence, Alexander Zaitsev, IRE, Russia
• http://www.setileague.org/editor/actvseti.htm
• Making a Case for METI