is the attempt to send messages to intelligent aliens. Active SETI messages are usually in the form of radio signals. Physical messages like that of the
may also be considered an active SETI message. Active SETI is also known as
), or positive SETI. Active SETI is contrasted to passive
The term METI was coined by Russian scientist Alexander Zaitsev, who denoted the clear-cut distinction between Active SETI and METI:
transmission of the information into the Cosmos is treated as one of the pressing needs of an advanced civilization. This view is not universally accepted, and it does not agree to those who are against the transmission of interstellar radio messages.
First of all, while trying to synthesize an Interstellar Radio Message (IRM), we should bear in mind that Extraterrestrials will first deal with a physical phenomenon and, only after that, perceive the information. At first, ET's receiving system will detect the radio signal; then, the issue of extraction of the received information and comprehension of the obtained message will arise. Therefore, above all, the Constructor of an IRM should be concerned about the ease of signal determination. In other words,
the signal should have maximum openness, which is understood here as an antonym of the term security. This branch of signal synthesis can be named
Also characteristics of the radio signal such as wavelength, type of polarization, and modulation have to be considered.
Over galactic distances, the interstellar medium induces some scintillation effects and artificial modulation of electromagnetic signals. This modulation is higher at lower frequencies and is a function of the sky direction. Over large distances, the depth of the modulation can exceed 100%, making any METI signal very difficult to decode.
In METI research it is implied that any message must have some redundancy, although the exact amount of redundancy and message formats are still in great dispute.
Using ideograms instead of binary sequence already offers some improvement against noise resistance. In faxlike transmissions ideograms will be spread on many lines. This increases its resistance against short bursts of noise like radio frequency interference or
One format approach proposed for interstellar messages was to use the product of two prime numbers to construct an image. Unfortunately, this method works only if all the bits are present. As an example, the message sent by Frank Drake from Arecibo in 1974 did not have any feature to support mechanisms to cope with the inevitable noise degradation of the interstellar medium.
transmission was far from being optimal (from our Terrestrial point of view) as it was essentially a monochromatic signal spiced with a supplementary information. Additionally, the message had a very small modulation index overall, a condition not viewed as being optimal for interstellar communication.
These projects have targeted stars between 20 and 69 light-years from the Earth. The exception is the
| Name |
Designation |
Constellation |
Date sent |
Arrival date |
Message |
Messier 13Messier 13 or M13 is a globular cluster of about 300,000 stars in the constellation of Hercules....
|
NGC 6205 |
HerculesHercules is a constellation named after Hercules, the Roman mythological hero adapted from the Greek hero Heracles. Hercules was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations today...
|
1974-11-16November 16, 1974 |
approx. 27000 |
Arecibo Message The Arecibo message was broadcast into space a single time via frequency modulated radio waves at a ceremony to mark the remodeling of the Arecibo radio telescope on 16 November 1974. It was aimed at the globular star cluster M13 some 25,000 light years away because M13 was a large and close...
|
| Altair |
Alpha Aql |
AquilaAquila is a stellar constellation. Its name is Latin for 'eagle' and it is commonly represented as such. In mythology, Aquila was owned by the Roman god Jupiter and performed many tasks for him....
|
1983-8-15 August 15 1983 |
1999 |
Altair (Morimoto - Hirabayashi) Message |
SpicaSpica is the brightest star in the constellation Virgo, and the 15th brightest star in the nighttime sky. It is 260 light years distant from Earth...
|
Alpha Vir |
VirgoAquila is a stellar constellation. Its name is Latin for 'eagle' and it is commonly represented as such. In mythology, Aquila was owned by the Roman god Jupiter and performed many tasks for him....
|
1997-8 August 1997 |
2247 |
NASDA Cosmic-College |
| 16 Cyg A 16 Cygni or 16 Cyg is a triple star system approximately 70 light-years away from Earth in the constellation of Cygnus. It consists of two Sun-like yellow dwarf stars, 16 Cygni A and 16 Cygni B, together with a red dwarf, 16 Cygni C...
|
HD The Henry Draper Catalogue is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension , published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the...
186408 |
CygnusCygnus is a northern constellation lying on the plane of the Milky Way. Its name is the Latinized Hellenic word for swan. One of the most recognizable constellations of the northern summer and autumn, it features a prominent asterism known as the Northern Cross...
|
1999-05-24May 24, 1999 |
2069-11November 2069 |
Cosmic Call Cosmic Call was the name of two interstellar radio messages that were sent from RT-70 in Yevpatoria in 1999 and 2003 to various nearby stars. The messages were designed with noise resistant format and characters....
1 |
| 15 Sge 15 Sagittae is a 6th magnitude star in the constellation Sagitta. In 2002, a brown dwarf, 15 Sge b, was discovered around 15 Sge.-15 Sagittae B:...
|
HD The Henry Draper Catalogue is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension , published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the...
190406 |
Sagitta Sagitta is a constellation. Its name is Latin for "arrow", and it should not be confused with the larger constellation Sagittarius, the archer. Although ancient, it is insignificant, for it has no star brighter than the 4th magnitude and is the third smallest of all constellations...
|
1999-06-30June 30, 1999 |
2057-02February 2057 |
Cosmic Call Cosmic Call was the name of two interstellar radio messages that were sent from RT-70 in Yevpatoria in 1999 and 2003 to various nearby stars. The messages were designed with noise resistant format and characters....
1 |
| |
HD The Henry Draper Catalogue is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension , published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the...
178428 |
Sagitta Sagitta is a constellation. Its name is Latin for "arrow", and it should not be confused with the larger constellation Sagittarius, the archer. Although ancient, it is insignificant, for it has no star brighter than the 4th magnitude and is the third smallest of all constellations...
|
1999-06-30June 30, 1999 |
2067-10October 2067 |
Cosmic Call Cosmic Call was the name of two interstellar radio messages that were sent from RT-70 in Yevpatoria in 1999 and 2003 to various nearby stars. The messages were designed with noise resistant format and characters....
1 |
| Gl 777 Gliese 777, often abbreviated as Gl 777 or GJ 777, is a yellow subgiant approximately 52 light-years away in the constellation of Cygnus. The system is also a binary star system made up of two stars and possibly a third...
|
HD The Henry Draper Catalogue is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension , published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the...
190360 |
CygnusCygnus is a northern constellation lying on the plane of the Milky Way. Its name is the Latinized Hellenic word for swan. One of the most recognizable constellations of the northern summer and autumn, it features a prominent asterism known as the Northern Cross...
|
1999-07-01July 1, 1999 |
2051-04April 2051 |
Cosmic Call Cosmic Call was the name of two interstellar radio messages that were sent from RT-70 in Yevpatoria in 1999 and 2003 to various nearby stars. The messages were designed with noise resistant format and characters....
1 |
| |
HD The Henry Draper Catalogue is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension , published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the...
197076 |
Delphinus Delphinus is a constellation in the northern sky, close to the celestial equator. Its name is Latin for dolphin. Delphinus was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains among the 88 modern constellations recognized by the International Astronomical...
|
2000-08-29August 29, 2001 |
2070-02February 2070 |
Teen Age Message The Teen Age Message was a METI message, transmitted from the Yevpatoria Planetary Radar to 6 nearby Sun-like stars during August–September 2001. Unlike the previous digital-only Messages, Arecibo-1974 and Cosmic Call 1, the TAM has complex, three-section structure with different forms of...
|
| 47 UMa 47 Ursae Majoris is a solar analog, yellow dwarf star approximately 46 light-years away from Earth in the constellation of Ursa Major. , it has been confirmed that three Jupiter-like extrasolar planets orbit the star...
|
HD The Henry Draper Catalogue is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension , published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the...
95128 |
Ursa MajorUrsa Major , also known as the Great Bear, is a constellation visible throughout the year in most of the northern hemisphere. It can best be seen in April...
|
2001-09-03September 3, 2001 |
2047-07July 2047 |
Teen Age Message The Teen Age Message was a METI message, transmitted from the Yevpatoria Planetary Radar to 6 nearby Sun-like stars during August–September 2001. Unlike the previous digital-only Messages, Arecibo-1974 and Cosmic Call 1, the TAM has complex, three-section structure with different forms of...
|
| 37 Gem |
HD The Henry Draper Catalogue is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension , published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the...
50692 |
GeminiGemini is one of the constellations of the zodiac. It was one of the 48 constellations described by the 2nd century astronomer Ptolemy and it remains one of the 88 modern constellations today. Its name is Latin for "twins", and it is associated with the twins Castor and Pollux in Greek mythology...
|
2001-09-03September 3, 2001 |
2057-12December 2057 |
Teen Age Message The Teen Age Message was a METI message, transmitted from the Yevpatoria Planetary Radar to 6 nearby Sun-like stars during August–September 2001. Unlike the previous digital-only Messages, Arecibo-1974 and Cosmic Call 1, the TAM has complex, three-section structure with different forms of...
|
| |
HD The Henry Draper Catalogue is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension , published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the...
126053 |
VirgoVirgo is one of the constellations of the zodiac. Its name is Latin for virgin, and its symbol is . Lying between Leo to the west and Libra to the east, it is the second largest constellation in the sky...
|
2001-09-03September 3, 2001 |
2059-12January 2059 |
Teen Age Message The Teen Age Message was a METI message, transmitted from the Yevpatoria Planetary Radar to 6 nearby Sun-like stars during August–September 2001. Unlike the previous digital-only Messages, Arecibo-1974 and Cosmic Call 1, the TAM has complex, three-section structure with different forms of...
|
| |
HD The Henry Draper Catalogue is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension , published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the...
76151 |
Hydra Hydra is the largest of the 88 modern constellations, measuring 1303 square degrees. It has a long history, having been included among the 48 constellations listed by the 2nd century astronomer Ptolemy. It is commonly represented as a water snake...
|
2001-09-04September 4, 2001 |
2057-05May 2057 |
Teen Age Message The Teen Age Message was a METI message, transmitted from the Yevpatoria Planetary Radar to 6 nearby Sun-like stars during August–September 2001. Unlike the previous digital-only Messages, Arecibo-1974 and Cosmic Call 1, the TAM has complex, three-section structure with different forms of...
|
| |
HD The Henry Draper Catalogue is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension , published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the...
193664 |
DracoDraco is a constellation in the far northern sky. Its name is Latin for dragon. Draco is circumpolar for many observers in the northern hemisphere...
|
2001-09-04September 4, 2001 |
2059-01January 2059 |
Teen Age Message The Teen Age Message was a METI message, transmitted from the Yevpatoria Planetary Radar to 6 nearby Sun-like stars during August–September 2001. Unlike the previous digital-only Messages, Arecibo-1974 and Cosmic Call 1, the TAM has complex, three-section structure with different forms of...
|
| |
HIP 4872 |
CassiopeiaCassiopeia is a constellation in the northern sky, named after the vain queen Cassiopeia in Greek mythology, who boasted about her unrivalled beauty. Cassiopea was one of the 48 constellations listed by the 2nd century Greek astronomer Ptolemy, and it remains one of the 88 modern constellations today...
|
2003-07-06July 6, 2003 |
2036-04April 2036 |
Cosmic Call Cosmic Call was the name of two interstellar radio messages that were sent from RT-70 in Yevpatoria in 1999 and 2003 to various nearby stars. The messages were designed with noise resistant format and characters....
2 |
| |
HD The Henry Draper Catalogue is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension , published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the...
245409 |
OrionOrion, often referred to as The Hunter, is a prominent constellation located on the celestial equator and visible throughout the world. It is one of the most conspicuous, and most recognizable constellations in the night sky...
|
2003-07-06July 6, 2003 |
2040-08August 2040 |
Cosmic Call Cosmic Call was the name of two interstellar radio messages that were sent from RT-70 in Yevpatoria in 1999 and 2003 to various nearby stars. The messages were designed with noise resistant format and characters....
2 |
| 55 Cnc 55 Cancri , also cataloged Rho1 Cancri or abbreviated 55 Cnc, is a binary star approximately 41 light-years away from Earth in the constellation of Cancer...
|
HD The Henry Draper Catalogue is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension , published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the...
75732 |
Cancer Cancer is one of the twelve constellations of the zodiac. Its name is Latin for crab and it is commonly represented as such. Its symbol is . Cancer is small and its stars are faint...
|
2003-07-06July 6, 2003 |
2044-05May 2044 |
Cosmic Call Cosmic Call was the name of two interstellar radio messages that were sent from RT-70 in Yevpatoria in 1999 and 2003 to various nearby stars. The messages were designed with noise resistant format and characters....
2 |
| |
HD 10307 HD 10307 is a star similar to the sun in mass, temperature and metal content, situated about 41 light-years from Earth in the constellation Andromeda...
|
AndromedaAndromeda is a constellation in the northern sky. It is named after Andromeda, the princess in the Greek legend of Perseus who was chained to a rock to be eaten by the sea monster Cetus...
|
2003-07-06July 6, 2003 |
2044-09September 2044 |
Cosmic Call Cosmic Call was the name of two interstellar radio messages that were sent from RT-70 in Yevpatoria in 1999 and 2003 to various nearby stars. The messages were designed with noise resistant format and characters....
2 |
| 47 UMa 47 Ursae Majoris is a solar analog, yellow dwarf star approximately 46 light-years away from Earth in the constellation of Ursa Major. , it has been confirmed that three Jupiter-like extrasolar planets orbit the star...
|
HD The Henry Draper Catalogue is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension , published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the...
95128 |
Ursa MajorUrsa Major , also known as the Great Bear, is a constellation visible throughout the year in most of the northern hemisphere. It can best be seen in April...
|
2003-07-06July 6, 2003 |
2049-05May 2049 |
Cosmic Call Cosmic Call was the name of two interstellar radio messages that were sent from RT-70 in Yevpatoria in 1999 and 2003 to various nearby stars. The messages were designed with noise resistant format and characters....
2 |
PolarisPolaris |Alpha]] Ursae Minoris, commonly North Star or Pole Star, also Lodestar) is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole, making it the current northern pole star....
|
HIP 11767 |
Ursa MinorUrsa Minor , also known as the Little Bear, is a constellation in the northern sky. Like the Great Bear, the tail of the Little Bear may also be seen as the handle of a ladle, whence the name Little Dipper...
|
2008-10-09February 4, 2008 |
20292439 |
Across the Universe Across the Universe is an interstellar radio message consisting of the song "Across the Universe" by The Beatles that was transmitted on 4 February 2008, at 00:00 UTC by NASA in the direction of the star Polaris...
|
Gliese 581Gliese 581 is a red dwarf star with spectral type M3V, located 20.3 light years away from Earth in the constellation Libra. Its estimated mass is about a third of that of the Sun, and it is the 89th closest known star system to the Sun. Observations suggest that the star has at least six planets:...
|
HIP 74995 |
LibraLibra is a constellation of the zodiac. Its name is Latin for weighing scales, and its symbol is . It is fairly faint, with no first magnitude stars, and lies between Virgo to the west and Scorpius to the east.-Notable features:]...
|
2008-10-09October 9, 2008 |
20292029 |
A Message From Earth A Message from Earth is a high-powered digital radio signal that was sent on 9 October 2008 towards Gliese 581 c, a large terrestrial extrasolar planet orbiting the red dwarf star Gliese 581. The signal is a digital time capsule containing 501 messages that were selected through a competition on...
|
Gliese 581Gliese 581 is a red dwarf star with spectral type M3V, located 20.3 light years away from Earth in the constellation Libra. Its estimated mass is about a third of that of the Sun, and it is the 89th closest known star system to the Sun. Observations suggest that the star has at least six planets:...
|
HIP 74995 |
LibraLibra is a constellation of the zodiac. Its name is Latin for weighing scales, and its symbol is . It is fairly faint, with no first magnitude stars, and lies between Virgo to the west and Scorpius to the east.-Notable features:]...
|
2008-10-09August 28, 2009 |
20302030 |
Hello From Earth HELLO FROM EARTH is an Interstellar Radio Message . It was sent from the 70-meter dish at NASA Deep Space Station 43 , at midday on Friday 28 August 2009...
|
| GJ 83.1 TZ Arietis is a red dwarf star in the constellation Aries. It is too faint to be seen by the naked eye, although it lies relatively close to our Sun at a distance of about 14.5 light years. It is a flare star, which means it can suddenly increase in brightness for short periods of time.-External...
|
GJ 83.1 |
AriesAries is one of the constellations of the zodiac, located between Pisces to the west and Taurus to the east. Its name is Latin for ram, and its symbol is , representing a ram's horns...
|
2009-11-07November 7, 2009 |
2024 |
RuBisCo Stars RuBisCo Stars is an interstellar radio message sent from the Arecibo radio telescope on November 7, 2009. The message contained the genetic code for the RuBisCO protein used by terrestrial plants to perform photosynthesis. It was sent to three nearby stars .-External links:* * *...
|
| Teegarden's Star Teegarden's Star, also known as SO J025300.5+165258, is an M-type red dwarf star or brown dwarf in the constellation Aries, located about 12 light years from the Solar System. Despite its proximity to Earth it is a dim magnitude 15 and can only be seen through large telescopes. This star was found...
|
SO J025300.5+165258 |
AriesAries is one of the constellations of the zodiac, located between Pisces to the west and Taurus to the east. Its name is Latin for ram, and its symbol is , representing a ram's horns...
|
2009-11-07November 7, 2009 |
2022 |
RuBisCo Stars RuBisCo Stars is an interstellar radio message sent from the Arecibo radio telescope on November 7, 2009. The message contained the genetic code for the RuBisCO protein used by terrestrial plants to perform photosynthesis. It was sent to three nearby stars .-External links:* * *...
|
| Kappa1 Ceti Kappa1 Ceti is a yellow dwarf star approximately 30 light-years away in the constellation of Cetus. The star was discovered to have a rapid rotation, roughly once every nine days. Though there are no extrasolar planets confirmed to be orbiting the star, Kappa1 Ceti is considered a good candidate...
|
GJ 137 |
Cetus |
2009-11-07November 7, 2009 |
2039 |
RuBisCo Stars RuBisCo Stars is an interstellar radio message sent from the Arecibo radio telescope on November 7, 2009. The message contained the genetic code for the RuBisCO protein used by terrestrial plants to perform photosynthesis. It was sent to three nearby stars .-External links:* * *...
|
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. Notable among its critics is scientist and science fiction author
However, Russian and Soviet radio engineer and astronomer Alexander L. Zaitsev has argued against these fears: see
. Indeed, Zaitsev argues that we should consider the risks of NOT reaching out to extraterrestrial civilizations: see
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
. Developed by Prof. Ivan Almar and Prof.
, 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.
One proposal for a 10 billion watt interstellar SETI beacon was dismissed by Robert A. Freitas Jr. to be infeasible for a pre-Type I civilization on the
. As a result it has been suggested that civilizations must advance into Type I before mustering the energy required for reliable contact with other civilizations.
However, this 1980s technical argument assumes omni-directional beacons which may not be the best way to proceed on many technical grounds. Advances in consumer electronics have made possible transmitters that simultaneously transmit many narrow beams, covering the million or so nearest stars but not the spaces between. This multibeam approach can reduce the power and cost to levels that are reasonable with current mid-2000s 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.
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.