CETI (Communication with ExtraTerrestrial Intelligence)

Unlike SETI, which is a passive, listening pursuit, CETI (Communication with ExtraTerrestrial Intelligence) attempts to initiate a dialogue with intelligent extraterrestrials. It does this by actively sending out coded signals at specific target stars, star clusters, or galaxies.

The earliest attempts at CETI were the various schemes dreamed up in the 19th and early 20th century for sending messages to supposed inhabitants of the Moon and Mars (see communication with the Moon and planets). More recently, the Arecibo Message was devised by Frank Drake and beamed toward the great globular cluster M13 in Hercules. In 1999, a far more elaborate message, known as the "Cosmic Call", was sent out from a radio telescope in the Ukraine as part of a CETI program sponsored by a Houston-based company, Encounter 2001, later known as Team Encounter. The "Cosmic Call" (see Encounter 2001 Message) was transmitted four times to four different stars from the Evpatoria Deep Space Center (EDSC); for further details, see the first of the external links listed below. A third interstellar message, known as the "Teenage Message to the Stars," was also transmitted from the EDSC in 2001. A fourth is planned for 5–6 July 2003. For details, again see the link below. The scientific head of these three Evpatoria messages is Alexander Zaitsev. Team Encounter also also plans to send hair samples, containing DNA, of sponsoring individuals, into space on a future mission.

Information affixed to the star-bound Pioneer (see Pioneer plaque) and Voyager (see Voyager interstellar record) spacecraft represent another form of attempted communication with alien intelligence. Over the years, a number of prominent scientists and other individuals have voiced their concern at the possible consequences of humans advertising their existence to civilizations of unknown disposition who may have technologies vastly superior to our own (see CETI, opposition).