Active SETI (Active Search for Extra-Terrestrial Intelligence) are attempts to send messages to intelligent extraterrestrial life. Active SETI messages are predominantly sent in the form of radio signals. 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). Whether humans should engage in Active SETI is controversial due to concerns about potential impacts of extraterrestrial contact, sparking a vigorous policy debate.
History 'Active SETI' was a term as early as 2005, though some decades after the term SETI. The term METI was coined in 2006 by Russian scientist Alexander Zaitsev, who proposed a subtle distinction between Active SETI and METI:
Concern over METI was raised by the science journal Nature in an editorial in October 2006, which commented on a recent meeting of the International Academy of Astronautics SETI study group. The editor said, "It is not obvious that all extraterrestrial civilizations will be benign, or that contact with even a benign one would not have serious repercussions". In the same year, astronomer and science fiction author David Brin expressed similar concerns. In 2013 Brin amended his initial article based on the recent developments in METI.Dabid Brin, Shouting At the Cosmos, 2013 addendum
In 2010, Douglas A. Vakoch from SETI Institute, addressed concerns about the validity of Active SETI alone as an experimental science by proposing the integration of Active SETI and Passive SETI programs to engage in a clearly articulated, ongoing, and evolving set of experiments to test various versions of the Zoo hypothesis, including specific dates at which a first response to messages sent to particular stars could be expected.
On 13 February 2015, scientists including Douglas Vakoch, David Grinspoon, Seth Shostak, and David Brin at an annual meeting of the American Association for the Advancement of Science discussed Active SETI, and whether transmitting a message to possible intelligent extraterrestrials in the Cosmos was a good idea. That same week, a statement was released, signed by many in the SETI community including Berkeley SETI Research Center director Andrew Siemion, advocating that a "worldwide scientific, political and humanitarian discussion must occur before any message is sent".
In July 2015, the Breakthrough Message program was announced. This was an open competition to design a digital message that could be transmitted from Earth to an extraterrestrial civilization, with a US$1,000,000 prize pool. The message was to be "representative of humanity and planet Earth". The program pledged "not to transmit any message until there has been a wide-ranging debate at high levels of science and politics on the risks and rewards of contacting advanced civilizations".
Rationale for METI In the paper Rationale for 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 is not agreed with by those who are against the transmission of interstellar radio messages, but at the same time are not against SETI searching. Such duality is called the SETI Paradox.
Radio message construction The lack of an established communications protocol is a challenge for METI. While trying to synthesize and project an Interstellar Radio Message (IRM), the receiving extraterrestrials (ETs) will first encounter a physical phenomenon and, only after that, perceive the information. Initially, a receiving system will detect the radio signal; then the issue of the 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 is termed anticryptography.
To this end, in 2010, Michael W. Busch created a general-purpose binary language, later used in the Lone Signal project to transmit crowdsourced messages to extraterrestrial intelligence. Busch developed the coding scheme and provided Rachel M. Reddick with a test message, in a blind test of decryption. Reddick decoded the entire message after approximately twelve hours of work. This was followed by an attempt to extend the syntax used in the Lone Signal hailing message to communicate in a way that, while neither mathematical nor strictly logical, was nonetheless understandable given the prior definition of terms and concepts in the hailing message.
In addition, characteristics of the radio signal, such as wavelength, type of polarization, and modulation are 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.
Error correction In METI research, 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 are spread on many lines. This increases its resistance against short bursts of noise like radio frequency interference or interstellar scintillation.
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 the Arecibo Observatory in 1974 did not have any feature to support mechanisms to cope with the inevitable noise degradation of the interstellar medium.
Error correction tolerance rates for previous METI messages are 9% (one page) for the 1974 Arecibo Message, 44% (23 separate pages) for the 1999 Evpatoria Message, and 46% (one page, estimated) for the 2003 Evpatoria Message.
Examples The 1999 Cosmic Call transmission was far from being optimal (from a terrestrial viewpoint) as it was essentially a monochromatic signal spiced with supplementary information. Additionally, the message had a very small modulation index overall, a condition not viewed as being optimal for interstellar communication. Over the 370,967 bits (46,371 bytes) sent, some 314,239 were "1" and 56,768 were "0"—5.54 times as many 1's as 0's. Since frequency-shift keying modulation scheme was used, most of the time the signal was on the "0" frequency. In addition, "0" tended to be sent in long stretches, which appeared as white lines in the message.
Realized projects
The below projects have targeted stars between 17 and 69 light-years from the Earth. The exception is the Arecibo message, which targeted globular cluster M13, approximately 24,000 light-years away. The first interstellar message to reach its destination was the Altair (Morimoto–Hirabayashi) Message, which likely reached its target in 1999.
The Morse Message (1962) Arecibo Message (1974) Cosmic Call 1 (1999) Teen Age Message (2001) Cosmic Call 2 (2003) Across the Universe (2008) Hello from Earth (2009) Wow! Reply (2012) Lone Signal (2013) A Simple Response to an Elemental Message (2016) The choice of targets, transmission rate, and encoding may effect how likely a message will be received and interpreted by extraterrestrial intelligence. "Across the Universe" and "A Simple Response to an Elemental Message" were sent to Polaris, which is 431 light years distant from us and whose planetary system, even if it exists, may not be suited for life, because it is a supergiant star, spectral type F7Ib which is only 70 million years old. In addition, both transmission rates were very high, about 128 kbit/s, for such moderate transmitter power (about 18 kW). The main defect of the "Hello From Earth" is an insufficient scientific and technical justification, since no famous SETI scientist made statements with validation of HFE's design. As it follows from : "After the final message was collected on Monday 24 August 2009, messages were exported as a text file and sent to NASA's Jet Propulsion Laboratory in California, where they were encoded into binary, packaged and tested before transmission", but nobody explained why he hopes that such encoded and packaged text will be understood and conceived by possible extraterrestrials.
Transmissions Below is a table of messages sent and target/destination stars, ordered chronologically by date of sending:[]
Name Designation Constellation Date sent Arrival date Message Messier 13 NGC 6205 Hercules 1974-11-161974-11-16 27000~ Arecibo Message Altair Alpha Aql Aquila 1983-08-151983-08-15 2017 CALL to the COSMOS'83 Libra Libra 1995 NASDA Cosmic-College 1996 NASDA Cosmic-College Spica Alpha Vir Virgo 1997-081997-08 2247 NASDA Cosmic-College 1998 NASDA Cosmic-College 16 Cyg A HD 186408 Cygnus 1999-05-241999-05-24 2069-112069-11 Cosmic Call 1 15 Sge HD 190406 Sagitta 1999-06-301999-06-30 2057-022057-02 HD 178428 2067-102067-10 Gl 777 HD 190360 Cygnus 1999-07-011999-07-01 2051-042051-04 HD 197076 Delphinus 2000-08-292001-08-29 2070-022070-02 Teen Age Message 47 UMa HD 95128 Ursa Major 2001-09-032001-09-03 2047-072047-07 37 Gem HD 50692 Gemini 2057-122057-12 HD 126053 Virgo 2001-092001-09 2059-122059-01 HD 76151 Hydra 2001-09-042001-09-04 2057-052057-05 HD 193664 Draco 2059-012059-01 HIP 4872 Cassiopeia 2003-07-062003-07-06 2036-042036-04 Cosmic Call 2 HD 245409 Orion 2040-082040-08 55 Cnc HD 75732 Cancer 2044-052044-05 HD 10307 Andromeda 2044-092044-09 47 UMa HD 95128 Ursa Major 2049-052049-05 Polaris HIP 11767 Ursa Minor 2008-10-092008-02-04 20292439Across the Universe Gliese 581 HIP 74995 Libra 2008-10-092008-10-09 20292029 A Message From Earth 2008-10-092009-08-28 20302030Hello From Earth GJ 83.1 GJ 83.1 Aries 2009-11-072009-11-07 2024 RuBisCo Stars Teegarden's Star SO J025300.5+165258 2022 Kappa1 Ceti GJ 137 Cetus 2039 HIP 34511 Gemini 2012-08-152012-08-15 2163 Wow! Reply 37 Gem HD 50692 2069 55 Cnc HD 75732 Cancer 2053 GJ 526 HD 119850 Boötes 2013-07-102013-07-10 2031Lone Signal 55 Cnc HD 75732 Cancer 2013-09-222013-09-22 2053JAXA Space Camp (UDSC-1) 55 Cnc HD 75732 Cancer 2014-08-232014-08-23 2054JAXA Space Camp (UDSC-2) Polaris HIP 11767 Ursa Minor 2016-10-102016-10-10 24502450A Simple Response to an Elemental Message Luyten's Star HIP 36208 Canis Major 2017-10-16 2030-03 Sónar Calling GJ273b
Controversy Whether or not to conduct Active SETI, as well as the tone of any message, is a highly controversial topic. Active SETI has primarily been criticized due to the perceived risk of revealing the location of the Earth to alien civilizations, without some process of prior international consultation. That is, Active SETI does not meet the criteria for informed consent in a mass experiment involving human subjects and, potentially, nonhuman sentient subjects.