Search for Extraterrestrial Intelligence

Search for Extraterrestrial Intelligence (English for ( the ) search for extraterrestrial intelligence, also called short SETI ) refers to the search for extraterrestrial civilizations. Since 1960, various scientific projects are operated to examine among other things the radio region of the electromagnetic spectrum for possible signs and signals of technical civilizations in space.

  • 2.1 Optical SETI
  • 2.2 SETA and SETV
  • 6.1 External Product

Fundamentals and estimates

The SETI research is based on the assumption that extraterrestrial civilizations exist in the universe and similar communication systems and message use technologies such as on Earth. So far it is not known whether extraterrestrial life exists, or whether there are other technical civilizations that are to transmit and receive signals interstellar able. An estimate has tried to with the Drake equation, the astronomer Frank Drake. In more optimistic assessment of the factors in this equation results in a possible number of over 300 such civilizations in the Milky Way. Stephen Dole in 1964 in a study for the RAND Corporation for the first time an estimate of the number of possible habit profitable worlds in the galaxy by. The Kardashev scale any technical possibilities of extraterrestrial civilizations be estimated. The galaxy in which is situated the earth, the Milky Way, has a diameter of about 100,000 light years and contains between 200 and 400 billion stars and findings to the effect that Kepler mission, 50 billion planets, of which an estimated 500 million planets in habitable zones.

Restrictions on the search area

The assumption that alien life forms majority could be based on carbon chemistry - like all forms of life on earth - is called in exobiology polemically as carbon chauvinism. Although a hypothetical alternative biochemistry as discussed, for example, silicon-based, carbon provides a greater diversity in the formation of semi-stable molecules.

Another assumption is that life requires liquid water. The water molecule is a simple molecule and an optimal environment for the development of complex carbon-based molecules that could lead to the development of life.

A third limitation is to focus on solar-type stars. Very big stars have relatively short lifetimes of only a few million years to a few ten thousand years, so that intelligent life would have very little time for the development on the surrounding planets. On the other hand, the energy released very small star is so small that only planet come to a close orbit as candidates for life in question. The lifetime of such a star is, however, up to 20 billion years. Due to the close orbit and the effect of the associated strong tidal forces, the self-rotation of such planets is usually passed very slowly, or in synchronous rotation. The result is an unfavorable, very strong temperature gradient as it can be observed in about the Mercury.

Properties of a hypothetical signal

To receive a radio transmission from an alien civilization, you have to scan the most common electromagnetic frequencies, since you do not know what frequency could use the aliens. Since the signal for easier detection should be stronger than the radiation from the home star, it is not advisable to transmit a strong signal over a wide range of wavelengths, and therefore it is likely that such a signal on a very narrow frequency band ( channel) is sent. This means that a large number of very narrow channels must be searched.

The modulation and coding of an extraterrestrial signal is also unknown. Interesting could be very narrow-band signals, which are stronger than the background noise and constant in their strength. A regular and complex pulse patterns would indicate that the signals are artificial. There have been studies on how to send a signal that can be easily found and decrypted. Nevertheless, of course, does not know whether the assumptions of these studies are actually valid.

Cosmic radiation and terrestrial radiation sources form a certain threshold for signals that we can still recognize it as such. To locate an extraterrestrial civilization that radiates its signals in all directions, it would have to use a very strong station. Its performance should be at least comparable to the total electric power, which today stands on the ground available. The beam of an alien civilization may be impeded: it could be blocked by interstellar nebula, or even superimposed interference and thus become unreadable. A very similar effect sometimes occurs even when the TV with terrestrial antenna reception: when the television signals are reflected from a mountain or a large object and thus reach the antenna in two different lengths of paths, so there is a time-shifted superposition.

In the same way, the bundled communication beam a distant civilization could be deflected or moved from interstellar clouds and thus come under the influence of interference, which could weaken the signal or make it unreadable. If interstellar messages are broadcast on bundled and transmitted beams encounter such problems, there is nothing we can do from our side to deal with these problems - except us to be aware of the problem and to anticipate potential problems. For the reception, and finding a mission of the cost is much greater. Searching of only one million receiving channels needs even when application is expected very fast programs and when only about one second for each channel without interesting information content, considerable time.

The modern SETI research began with the publication of "Searching for Interstellar Communications " of the two physicists Giuseppe Cocconi and Philip Morrison, which was published in September 1959 in Nature. Cocconi and Morrison came in to the conclusion that microwave frequencies between 1 and 10 gigahertz would be best suited for interstellar communication. Under a gigahertz called synchrotron radiation starts (caused by electrons that travel through galactic magnetic fields) to drown out other sources of radiation. About 10 gigahertz radiation from hydrogen and oxygen atoms in the Earth's atmosphere has a disturbing one for possible signals. Even if alien worlds have completely different atmosphere conditions, quantum effects make the construction of conventional ( electrical ) receivers for signals above 100 gigahertz difficult. In particular, the lower limit of this " microwave window " is well suited for communication: it is in principle easier to send signals with low frequencies and receive, than those with high. The low frequencies are more suitable because of the Doppler effect, which is caused by planetary movement. This effect leads to a change in signal frequency over the course of a transmission, and that the more serious, the higher the frequency of the radiated signal. Cocconi and Morrison came to the conclusion that the frequency of 1.42 gigahertz ( also called HI- line), the so-called 21- cm line, would be particularly interesting for an interstellar transmission: on that frequency radiates neutral hydrogen. Radio astronomers often search the universe for this frequency to locate large hydrogen clouds. If one were so close Send a Message to this " label frequency ", this would increase the chance of an accidental discovery. Since you are looking for spectrally narrow-band signals, one can exclude confusion with neutral hydrogen, because its radiation by the thermal motion a high Doppler broadening (see also spectral ) has. Another interesting frequency is 1.720 GHz (18 - cm line ). Is a frequency of OH, an oxygen -hydrogen molecule. The range from 1.420 to 1.720 GHz is designated by the radio astronomers as a cosmic water hole. The frequency range is protected by international treaties. The concept of the water hole was coined in this context in 1971 by Bernard M. Oliver. Two possible search strategies for signals would be targeted searches (English Targeted search) and search the entire sky (English all- sky survey ). Another method to detect signals from extraterrestrial civilizations may exist would be to examine the focused by the gravitational lensing effect of a star radio waves with space probes. This method is referred to as GL- SETI, which stands for gravitational lensing SETI and English mean for SETI with the help of gravity lenses. Stanisław Lem 1968 mentioned in his novel Glos Pana (Eng. The voice of the Lord) to use the opportunity neutrinos for SETI, even Isaac Asimov pursued this idea in extraterrestrial civilizations. The search for artificial neutrinos or antineutrinos has been repeatedly discussed by scientists.

Artificial terrestrial emission

Through the use of radio waves, TV signals, civil and military radar systems and other sources produced our civilization an artificial EM signature of the Earth (English Leakage radiation ) that of extraterrestrial technical civilizations with astronomical research interest within a distance of about 60 to 80 lj can possibly be detected. Estimates (as of 2009) go from about 3000 stars and an unknown number of planetary systems within a distance of 100 light years from. Some Seti scientists believe it is possible that military facilities, such as the long-range Phased Array Radar Don -2N, Cobra Dane, Sea -Based X - band Radar or HAARP due to the radiation power used could still be detected at distances of 500 light years and more.

History and Methods of Search

Early attempts to identify radio signals from aliens, took Guglielmo Marconi, who claimed in the early 1920s to have received signals, but what could not be confirmed. Much earlier also already dealt with alleged Nikola Tesla signals from Mars. The astronomer David Peck Todd suggested as early as 1909 before unsuccessfully to search with research balloon and receiving apparatus according to any extraterrestrial radio signals.

On April 21, 1960 marked the beginning Frank Drake of Cornell University, the first modern SETI experiment, called Project Ozma (named after the Queen of Oz from the fantasy books by Frank L. Baum ). Drake used a radio telescope at Green Bank Observatory with a diameter of 26 meters in order to investigate the two stars Tau Ceti and Epsilon Eridani near the 1.42 GHz band. He examined a 400 - kHz band around the marker frequency and saved the recording to tape in order to later search for suspicious signals. However, the investigation revealed no specific abnormalities. The total observation time was about 150 hours for the project were 2000 USD available.

In November 1961, the first SETI conference took place at the Green Bank Observatory. Participants were not limited to: Frank Drake, Otto Struve, Philip Morrison, Carl Sagan, Melvin Calvin, Bernard M. Oliver and John Lilly. The Soviet Union began in 1964 with a search program. 1964 and 1971 organized inter alia, Nikolai Kardashev and Joseph Shklovsky more SETI conferences, this time at the Byurakan Observatory. Carl Sagan and Joseph Shklovsky published in 1966 with Intelligent Life in the Universe a much-quoted book about SETI. 1971 NASA funded a study on a radio SETI project named Cyclops. There was an array with 1500 91.5 -meter telescopes proposed, but the costs were too high at about $ 10 billion.

In 1974 a one-time radio message of 1,679 bits in length into space in the direction of the globular cluster M13 has been sent (distance around 25,000 light years) from the Arecibo Observatory. The number 1679 has two prime factors, 23 and 73, and the message is to be understood as an image of 23 times 73 pixels. This message was sent by frequency modulation with 10 bits per second. The image is the Arecibo Observatory, a human figure, the DNA and the necessary for life on earth elements represent.

In contrast to passive eavesdropping sending signals known as Active SETI or METI (Messaging to Extra-Terrestrial Intelligence) and CETI (Communication with extraterrestrial intelligence ) was called. Researchers, such as the astrophysicist Stephen Hawking and David Brin speculate but that Active SETI could also be associated with significant risks. There are plans for a planetary defense. The risk assessment of a transmitted signal, the San Marino Scale was created. After the ten -point scale in 1974 sent Arecibo message, level would be 8

In 1979, the University of California at Berkeley (UC Berkeley ) SETI SERENDIP ( Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations ), with a frequency analyzer with 100 channels. There radio telescopes with mirror diameters of 25 to 65 meters were used. In the summer of 1979, funded NASA - Ames and other institutions, the project Oasis. The aim of Oasis was the design of a detector for instruments that had been designed in 1971 in the project Cyclops.

Carl Sagan, Bruce Murray and Louis Friedman founded The Planetary Society in 1980, which, among other various SETI projects financially supported.

Following proposals by Paul Horowitz 1981 new portable Radiofrequenzanalysatoren were developed. Compared to previous analog frequency analyzers they had the advantage that they had a lot more and narrower channels through their DSPs. From 1982 to 1985, a frequency analyzer with 131,000 channels was performed on a 25 - m radio telescope at Harvard University used (Project Sentinel ). In 1985 he was the project META (Mega Channel Extra-Terrestrial Array), conducted by Horowitz and supported by the Planetary Society and the director Steven Spielberg, with an analyzer with 8 million channels and a channel width of 0.5 Hz Another telescope, META II, looking from Argentina in the southern sky.

Also in 1985, launched the Ohio State University, a private SETI program, the project Big Ear, later received the financial support from the Planetary Society. In 1986, the UC Berkeley their second SETI program, SERENDIP II, with 65,536 channels. Mainly doing a 90 - m radio telescope at Green Bank Observatory has been used in West Virginia. The follow-up project SERENDIP III with about 4 million channels used the Arecibo Observatory. His successor SERENDIP IV also uses the Arecibo Observatory and works with around 168 million channels.

1992 decided NASA or the U.S. government to fund the SETI program MOP (Microwave Observing Program), which was later called the High Resolution Microwave Survey (HRMS ). HRMS included a targeted search at 800-1000 Sun-like stars within a distance of 100 light years. The frequency analyzers should have 15 million channels, each channel should be wide when retrieving a Hertz and 30 Hertz otherwise. As radio telescopes, the antennas of the Deep Space Network, a 43- m telescope in West Virginia and the Arecibo Observatory should be used. The program was, however, completed in 1993, one year after the launch, by the U.S. Congress.

In 1995 the privately financed project Phoenix. It was funded by the SETI Institute in Mountain View, California, and began the radio search with the 64 -m Parkes telescope in Australia. From September 1996 to April 1998 use the program, the Green Bank radio telescope and August 1998, the Arecibo Observatory. Phoenix was closed in 2004, 800 stars within a radius of 200 light-years were examined without result.

As the successor of the META project, the project BETA ( Billion -channel Extraterrestrial Array) of the Planetary Society is run now. Contrary to the name is less than a billion, that worked with only 250 million channels of 0.5 Hz width. The frequency range of 1400 to 1720 Megahertz is examined, this is two seconds ( shorter observation period would this high spectral resolution is not permit ) a range of 125 megahertz width (corresponding to the product of width and number of channels ) was investigated, and then, the area shifted, and it is again observed two seconds. After eight shifts, the original frequency range is reached again. Search methods such as the parasitic search behavior, or even piggyback (English: piggyback ), share the conventional radio astronomical observing programs, increase the efficiency of the search further.

In May 1999, the project SETI @ home was started by UC Berkeley, which uses the data from SERENDIP IV. This project uses the computing power of many computers on the Internet that is provided by users voluntarily. You can download the SETI @ home program that downloads data from the server at UC Berkeley, and these ( with the lowest priority) analyzed in the background when computing capacity is available on the computer. A special screen saver displays the progress of the work. After processing a data packet, the results are sent back. The SETI Institute is now working together with the University of California, Berkeley, in Northern California to a new radio telescope, which is to build the Allen Telescope Array. It will be devoted to both radio astronomy and the search for extraterrestrial intelligence. The telescope is supported by Microsoft co-founder Paul Allen and shall consist of approximately 350 6.1 - m telescopes exist. The observed frequency range is from 0.5 to 11.2 GHz. The individual telescopes are relatively cheap, the observatory is expected to cost a total of about 25 million U.S. dollars. Began in 2005 with the construction. The SETI Institute is especially money to build available, while UC Berkeley has designed the telescope and it will operate. It can simultaneously monitor at different frequencies and at the same time as the interferometer many objects within the field of view of the individual telescopes. In April 2011, the SETI Institute was forced for financial reasons to interrupt the research with the Allen Telescope Array.

Six months later, the provisional financing be guaranteed. With the help of private donors and the U.S. Air Force to continue operations could be resumed and to continue the search for extraterrestrial intelligence. Incidentally, the Telescope Array is now but also search space junk that could threaten satellites. In keeping with the discovery of the exoplanet Kepler 22b is to begin the search for extraterrestrial radio signals again. In the next few years, all normally silent frequencies will be scanned from 1-10 GHz systematically for signs of life on Kepler 22b. The ATA is this world the only device that is able to watch all 9 million channels (1 kHz per channel) at the same time. The evaluation of the data obtained here should continue to take place over the distributed computing project SETI @ home.

In Europe, the Nançay radio telescope was used in the 1980s for a SETI program and later the 32- m radio telescope in Medicina, Italy.

2009 was launched in Japan sazanka project. With 14 radio stations, 27 optical telescopes was performed a multi-site observing campaign.

In November 2010, the project began Dorothy. To mark the 50th anniversary of Project Ozma a Beobachtungskampage is carried out with the participation of researchers from 15 countries participate.

Optical SETI

Besides the search for radio signals to operate the search for signals in the visible and near- infrared range. This is known as Optical SETI referred (English Optical SETI ) or short OSETI. It starts from the assumption that extraterrestrial civilizations might use very strong technical laser for communication over interstellar distances. In visible light, the required mirror and lens size that you need, so that the emitted radiation a given divergence angle ( half angle of an imaginary radiation cone, within which is the bulk of the radiation) is having less than at the longer wavelength radio waves. While this reduces the probability of detecting a non- intentionally directed at the earth beam but the beam intensity increases near the center of a certain output power. The search for these optical signals is done with high-resolution spectrographs; trying to find very narrow spectral lines.

Published in 1961, Robert N. Schwartz and Charles H. Townes, a work about the possibility of interstellar and interplanetary communication by Maser. 1965 for the first time, an article on the use of lasers for interstellar communication has been published. In the 1970s, the first search was carried out by optical laser pulses at Selentschuk Observatory within the project MANIA ( Multichannel Analysis of Nanosecond Intensity Alterations ).

A working group led by Paul Horowitz has developed a detector in the 1990s and installed in a 1.55 - m telescope at the Oak Ridge Observatory, Harvard University. The detector worked parasitic, that is, parallel with other astronomical investigations. Between October 1998 and November 1999 about 2500 stars were observed with the detector. The researchers collaborated with the University of Princeton, at the 0.91 - m telescope of the observatory FitzRandolph also install a nanosecond detection system. Both telescopes observed then simultaneously in the same direction, so that the detection of a signal could be confirmed by the other telescope or rejected as false alarm. As of December 2000, built on a 1.8 - m telescope for a OSETI observatory, which is online since April 2006 and primarily for All- Sky ( total sky) scans, used for extraterrestrial laser pulses.

The UC Berkeley has two optical SETI programs. Geoffrey Marcy, an astronomer who studied mainly for exoplanets, led the Keck Observatory, by investigation of the spectra, but could not check for pulses, because the temporal resolution of the images was too low. The other program is using a 0.76 m telescope; there is a similar search performed as described by the group at Harvard University. Also at the Lick Observatory OSETI research was operated. In the southern hemisphere there was a OSETI program at Campbelltown Rotary Observatory of the University of Western Sydney in Australia, which was conducted from 2000 by the astronomer Ragbir Bhathal.


But evidence of extraterrestrial technological activities could provide not only electromagnetic signals. SETI researchers are also isolated for extraterrestrial artifacts, spacecraft, spacecraft in the solar system and their energy and drive signatures ( such as tritium or possibly annihilation of antimatter drives ), traces of mining activity on the Earth's Moon, Mars, asteroids, comets, etc. in the early 1980s search programs were carried out, among others, at Kitt peak National Observatory, where Lagrange points of the earth-Moon and sun-Earth system have been investigated for objects. 1980-1981 studied the radar astronomers Suchkin and Tokarev the Lagrange points L4 and L5 for artifacts in park orbits of the Earth and the Moon, the Earth-Sun system without success. It was also sought on several occasions by Dyson spheres, including with IRAS. In the future, could astronomical instruments, such as the Colossus still in the planning stages telescope are used to in space by infrared signatures possibly existing Mega constructs to look like Dyson spheres.

Also in the asteroid belt, the Kuiper Belt and the Oort cloud could relics of extraterrestrial technologies, such as inactive or be wrecked communications and intelligence probes or self-replicating spacecraft available. These methods are called SETA ( Search for Extraterrestrial Artifacts ) or as SETV ( Search for Extraterrestrial Visitation ) or also referred to as Xenoarchäologie or Exoarchäologie. The theories of Paleo-SETI, or ufology find dzt. no scientific reception.


Andrew G.Haley and Ernst pheasant, pioneers of space law, dealt early with possible legal issues of first contact with non- terrestrial species and developed a concept that is referred to as Metarecht.

Since 1999, the Institute for Astronomy of the University of California, Berkeley, the Watson and Marilyn Alberts Chair in the Search for Extraterrestrial Intelligence ( SETI ), an endowed chair, which was taken over in 2012 by Geoffrey Marcy.

The Exosoziologie tries possible sociological implications and hypothetical scenarios first contact between humans and intelligent extraterrestrial species to explore and different: Long-distance contact scenario ( such as by technical means by radio waves), artifact scenario and direct contact.

The effects of contact would be versatile for example, Natural sciences, philosophy, politics, religion, and are the subject of current interdisciplinary research and discussion. Some researchers, including Paul Davies, see the effects of a first contact for the established religious communities as potentially problematic right. NASA explored the possible consequences already in the 1960s and published it in the NASA Brookings Report ( Proposed Studies on the Implications of Peaceful Space Activities for Human Affairs ). The Global Risks Report 2013 of the World Economic Forum indicates a future discovery of extraterrestrial life as a possible X - Factor, which could have a profound impact.

As part of the IYA 2009, the Vatican held a study week of astrobiology at the approximately 30 specialist scientists from astronomy, physics, biology, geology, chemistry and Seti scientists as among other Jill Tarter and representatives of the Pontifical Academy of Sciences and the Vatican Observatory such as Guy Consolmagno and José Gabriel Funes, speakers and discussion.

2009, dealt the topic of the Scientific Services of the German Bundestag.

In October 2010, the SETI Permanent Committee of the International Academy of Astronautics adopted at a symposium in Prague a declaration ( Declaration of Principles Concerning the Conduct of the Search for Extraterrestrial Intelligence ) for the search and the discovery of a case of a signal. The SETI Research Group of the IAA has a history as a collection of behaviors, called SETI protocols proposed. The IAA operates various working groups dealing with various aspects of SETI, such as SETI Post- Detection and Communications with Extraterrestrial Intelligence deal.

To be able to classify and assess the importance and credibility of a possible discovery of an extraterrestrial signal or artifact was designed by the SETI researchers the Rio Scale. 2010 was presented at a meeting of the Royal Society London scale ( 0-10), which allows scientific importance to assess validity and potential consequences.