Active SETI


Active SETI is the attempt to send messages to intelligent extraterrestrial life. Active SETI messages are usually 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. The term METI was coined by Russian scientist Alexander Zaitsev, who denoted the clear-cut distinction between Active SETI and METI:
In 2010, Douglas A. Vakoch of the 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 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". On 28 March 2015, an essay with a different point of view was written by Seth Shostak and published in The New York Times.

Rationale for METI

In the paper , 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, but at the same time are not against SETI searching. Such duality are called .

Radio message construction

The lack of an established communications protocol is a challenge for METI.
First of all, while trying to synthesize an Interstellar Radio Message, 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 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.
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.

Error correction

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
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
The 1999 Cosmic Call transmission was far from being optimal 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 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 message to reach its destination was the Altair Message, which likely reached its target in 1999.
Below is a table of messages sent and target/destination stars, ordered chronologically by date of sending:
NameDesignationConstellationDate sent
Arrival date
Message
Messier 13NGC 6205Hercules1974-11-161974-11-1627000~Arecibo Message
AltairAlpha AqlAquila1983-08-151983-08-152017Altair Message
LibraLibra1995NASDA Cosmic-College
1996NASDA Cosmic-College
SpicaAlpha VirVirgo1997-081997-082247NASDA Cosmic-College
1998NASDA Cosmic-College
16 Cyg AHD 186408Cygnus1999-05-241999-05-242069-112069-11Cosmic Call 1
15 SgeHD 190406Sagitta1999-06-301999-06-302057-022057-02Cosmic Call 1
HD 178428Sagitta1999-06-301999-06-302067-102067-10Cosmic Call 1
Gl 777HD 190360Cygnus1999-07-011999-07-012051-042051-04Cosmic Call 1
HD 197076Delphinus2000-08-292001-08-292070-022070-02Teen Age Message
47 UMaHD 95128Ursa Major2001-09-032001-09-032047-072047-07Teen Age Message
37 GemHD 50692Gemini2001-09-032001-09-032057-122057-12Teen Age Message
HD 126053Virgo2001-092001-092059-122059-01Teen Age Message
HD 76151Hydra2001-09-042001-09-042057-052057-05Teen Age Message
HD 193664Draco2001-09-042001-09-042059-012059-01Teen Age Message
HIP 4872Cassiopeia2003-07-062003-07-062036-042036-04Cosmic Call 2
HD 245409Orion2003-07-062003-07-062040-082040-08Cosmic Call 2
55 CncHD 75732Cancer2003-07-062003-07-062044-052044-05Cosmic Call 2
HD 10307Andromeda2003-07-062003-07-062044-092044-09Cosmic Call 2
47 UMaHD 95128Ursa Major2003-07-062003-07-062049-052049-05Cosmic Call 2
PolarisHIP 11767Ursa Minor2008-10-092008-02-0420292439Across the Universe
Gliese 581HIP 74995Libra2008-10-092008-10-0920292029A Message From Earth
Gliese 581HIP 74995Libra2008-10-092009-08-2820302030Hello From Earth
GJ 83.1GJ 83.1Aries2009-11-072009-11-072024RuBisCo Stars
Teegarden's StarSO J025300.5+165258Aries2009-11-072009-11-072022RuBisCo Stars
Kappa1 CetiGJ 137Cetus2009-11-072009-11-072039RuBisCo Stars
HIP 34511Gemini2012-08-152012-08-152163Wow! Reply
37 GemHD 50692Gemini2012-08-152012-08-152069Wow! Reply
55 CncHD 75732Cancer2012-08-152012-08-152053Wow! Reply
GJ 526HD 119850Boötes2013-07-102013-07-102031Lone Signal
55 CncHD 75732Cancer2013-09-222013-09-222053JAXA Space Camp
55 CncHD 75732Cancer2014-08-232014-08-232054JAXA Space Camp
PolarisHIP 11767Ursa Minor2016-10-102016-10-1024502450A Simple Response to an Elemental Message
GJ273bLuyten's StarCanis Major2017-10-162017-10-162030-11-03

Potential 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. Notable among its critics was Stephen Hawking, and scientist and science fiction author David Brin, particularly in his article "expose."
However, Russian and Soviet radio engineer and astronomer Alexander L. Zaitsev has argued against these fears. Indeed, Zaitsev argues that we should consider the risks of not attempting to contact extraterrestrial civilizations.
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 adopted in 2007 a new analytical tool, the San Marino Scale. Developed by Prof. Ivan Almar and Prof. H. Paul Shuch, 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.
In 2012, Jacob Haqq-Misra, Michael Busch, Sanjoy Som, and Seth Baum argued that while the benefits of radio communication on Earth likely outweigh the potential harms of detection by extraterrestrial watchers, the uncertainty regarding the outcome of contact with extraterrestrial beings creates difficulty in assessing whether or not to engage in long-term and large-scale METI.
In 2015, João Pedro de Magalhães proposed transmitting an invitation message to any extraterrestrial intelligences watching us already in the context of the Zoo Hypothesis and inviting them to respond. By using existing television and radio channels, de Magalhães argued this would not put us in any danger, "at least not in any more danger than we are already if much more advanced extraterrestrial civilizations are aware of us and can reach the solar system."
Douglas Vakoch, president of METI, argues that passive SETI itself is already an endorsement of active SETI, since "If we detect a signal from aliens through a SETI program, there’s no way to prevent a cacophony of responses from Earth."

Beacon proposals

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, such as humanity, on the Kardashev scale. 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 other's locations, the energy requirements for maintaining contact and exchanging information can be significantly reduced through the use of highly directional transmission technologies.
A 2018 study estimated a 1 to 2 megawatt infrared laser focused through a 30 to 45 meter telescope could be seen from about 20,000 light years away.