Kinkajou : What is SETI?
Erasmus : SETI is a mnemonic word which stands for “Search for Extra Terrestrial Intelligence”. It has grown to become a worldwide corporation of astronomers, engineers, computer experts, scientists and even the general public. The first experiment was run by Prof Francis Drake in 1960 at a radio telescope facility in West Virginia. SETI is designed to answer the question “are we alone?” in the universe.
SETI predominantly listens to signals from space. The project looks for techno signatures arising from industrial civilisations. Possible sources of techno signatures include:
- spacecraft within and outside the solar system,
- asteroid mining within the solar system,
- optical light signals from planets arising from cities or from laser communications emissions or signalling,
- excess infrared radiation,
- chemical emission spectra,
- radio waves,
- All microwaves.
Kinkajou : I thought we were sending them a message?
Erasmus : Most SETI projects have not emitted signals into space.
ActiveSETI has however attempted messaging to extra-terrestrial intelligences by emitting radio signals into space.
However such activities have drawn some severe criticism.
- Stephen Hawking, a well-known physicist asserted in his book that alerting extra-terrestrial intelligences to our existence is foolhardy. He stated that human history has many examples of men treating civilisations of inferior technology very harshly. In his book “A Brief History of Time” he suggested that humanity should “lay low”.
- Science fiction author David Brin has expressed similar concerns. His novel “Startide Rising” is full of examples of hostile alien civilisations. (Big species with big fleets and even bigger guns).
- The International Academy astronautics SETI study group stated in a “Nature” magazine editorial in 2006 that “it is not obvious that all extra-terrestrials civilisations will be benign, or that contact with even a benign one would not have serious percussions”.
Drake Equation > Fermi Paradox
Kinkajou : So do they also look at UFOs here? Why look elsewhere for your aliens when they may just be visiting down the road?
Erasmus : SETI does not explore UFO phenomena.
Kinkajou : How likely is it that there are aliens out there?
Erasmus : Prof Drake pioneered the famous Drake equation, which is an estimate of how many planets in our Milky Way galaxy may be inhabited by intelligent life forms.
The Equation takes the number of stars in our galaxy, assigns a probability that those stars have planets, and a probability of a number of these planets that can support life, multiplies the probability that these planets may actually develop life at some stage, then multiplies the probability that these plants will develop “intelligent” life, again multiplies this by the fraction of civilisations that may develop a technology that can be detected in space by us, and finally multiplies this by the length of time which such civilisations release detectable signals into space.
Using this equation gives an answer of approximately 36 million planets able to support detectable intelligent life with in our galaxy alone.
Kinkajou : If there are that many of them out there, either we've got something wrong in our calculations or else there may be other factors preventing us from finding them.
Erasmus : Our experience leads us to believe that life is much more robust than we may have previously believed. Bacteria can live deep within the earth using rocks and minerals as energy sources.
Some bacteria can live at extremely high temperatures near ocean floor volcanic vents which emit sulphur, which oxidises to sulphuric acid. Recent experience in astronomy has revealed that many suns are orbited by large planets, detectable to us at distances of light years.
Kinkajou : So you know that planets exist and that life is possible in many different, even hostile places. Life should be common.
Erasmus : This statement is challenged by the Fermi Paradox. This asked the question of “why signals from extra-terrestrials have not been heard by us?” and “why we have not been contacted by extra-terrestrials?”
The Fermi paradox takes a Drake equation and makes the statement that “the size and age of the universe lead us to believe that many alien technologically advanced civilisations must exist within our galaxy”.
However, this belief is inconsistent with our observations. To date, humans as a civilisation do not believe that alien extra-terrestrial intelligences exist within our galaxy.
The Fermi paradox states that:
- Both our initial assumptions are incorrect and that technologically advanced intelligent life is much rarer than we believe or
- Our current observational methods are incomplete and we have not detected them yet or
- Our search methods are flawed or inappropriate, and we are not searching for the correct indicators for the presence of extra-terrestrial intelligences.
Looking for Aliens: "SETI"
Kinkajou : So what are we doing looking for these aliens?
Erasmus : Every SETI search tries to optimise four factors:
- percentage of sky to covered by detectors
- Spectrum coverage
- signal types analysis with background noise reduction
Kinkajou : Complicated. So we really are trying to do the best we can within the physical constraints of our search environment and search capacities. So what exactly are we doing?
Erasmus : The biggest Current SETI projects include:
- SERENDIP VI (one site based at the University of California, Berkeley; the other site based in Australia known as Southern SERENDIP).
Search for Extra-terrestrial Radio Emissions from Nearby Developed Intelligent Populations)
- Project Phoenix this project conducts observations at 64 meter parks radio telescope in Australia, at the 43 m radio telescope in Greenbank West Virginia and a 300 meter radio telescope in Puerto Rico. These telescopes monitored frequencies between 1200 MHz to 300 MHz and were sensitive enough to pick up high-intensity transmissions 200 light years away.
Berkeley SEI Search
Erasmus : Other projects include:
- SETI@Home This project coordinated several hundred thousand participants and their computers, developing a computational power of approximately 617 Teraflops. This allowed for accelerated analysis of data streams arising from the observational telescopes.
- Allen telescope array. Currently this project combines approximately 42 radio telescopes of approximately 6 m in diameter to form an array.
Between 2007 and 2015, the Allen telescope array has identified hundreds of millions of potentially technological signals. Further analysis of the signals suggested that Earth-based transmitters produced much of the “noise” detected.
However, a threshold time limit of one hour was assigned for the detection of signals. Signals under this time duration have been labelled as noise. The “WOW!” signal itself to not reach this threshold.
- setiLIVE: This project displays radio frequency signals LIVE from the SETI Institute's Allen Telescope Array (ATA) while it's pointed at stars that, based on Kepler exoplanet discoveries, have the best chances of being home to an alien civilization. If any possible signals are found, the ATTA will be retargeted for a follow up assessment.
The data observed covers frequencies where human made Radio Frequency Interference (RFI) exists. The working basis of this project is that the trained human eye may have a better probability of detecting significant signals than a computer algorithm, which may be programmed to look for not quite the right thing.
- Ohio State Big Ear: This project is based on of the former Ohio State University Radio Observatory (OSURO), also known as Big Ear. The Observatory was a Kraus-type radio telescope.
Big Ear covered an area larger than three football fields. The telescope was famous for discovering some of the most distant known objects in the universe, as well as for the "Wow!" Signal and the longest-running SETI (Search for Extra-terrestrial Intelligence) project entered into the Guinness Book of Records.
- The SETI League developed project Argus. The concept focused on coordinating a global network of small amateur built radio telescopes converted from backyard satellite TV dishes 3 to 5 m in diameter. These amateur radio telescopes have a sensitivity equivalent to the big ear telescope which detected the landmark “WOW! “signal.
- Columbus Optical SETI Observatory, Optical SETI at Berkeley, Optical SETI at Harvard.
This project uses optical monitoring for signs of extra-terrestrial intelligence.
Microwave Energy Strength
The premise of the project is that optical interstellar communication is possible. So the project hopes to detect a laser signal essentially downgalaxy (downwind) of the transmission target. A laser com signal fired at a distant star for communications purposes will spill over and perhaps hit a star down range, (us we hope).
The science on which it is based is that an infrared pulse or a light pulse from a laser focused into a narrow beam would appear thousands of times brighter than the sun to distance civilisations in the beam’s line of fire.
With current technology we can generate a directed laser pulse that outshines the broadband visible light of the sun by a factor of 10,000. We believe that we can detect a signal up to 60 light years away.
- One strategy for optical SETI is to look for narrow spectrum emissions consistent laser light in the high-resolution spectra of target solar systems.
- Another alternative is to look for short optical pulses. Currently monitoring as occurs uses the strategy looking for short optical pulses and the 300 to 600 nm band.
Diagram of the stars in the (20 light-years) Solar neighbourhood
Kinkajou : I think it needs to be more sensitive. There are lots of star systems within a 60 light year radius (statistically about 3000). But the issue is about what are the chances of accidentally overshooting onto a target downrange. I think that’s more likely to happen if we could detect signals at a 200-300 light year range.
Artist’s conception of the Milky Way with the Sun’s position. During the last decade it was clearly established that the Milky Way is a barred spiral galaxy
Also mis-shoots or misalignments may not last very long (I would guess minutes only), so you need to be monitoring everything almost all the time to increase success probability.
Problems with optical SETI revolve around the effects of wetness and cold causing photo -detector malfunctions. This means that the detected positive hits consist substantially of false positive detections due to partial detector failure. The current hit rate is approximately one good hit per night of observation.
So to be categorised as a possible pulse from extra-terrestrial civilisation signal would need to be composed of successive pulses from potential source, perhaps exhibiting some regularity in the transmissions.
City At Night
Kinkajou : So maybe we are actually detecting when aliens are having a hot steamy shower?
Erasmus : Maybe the aliens don’t wash. What happens if they are like reptiles and enjoy a good hot sand bath and maybe a bit of a sandblast as well?
Other SETI Projects
Erasmus: So let’s keep on going talking about other SETI projects.
- Project BAMBI (Design, construction, and initial observational results of a 4-GHz amateur radio telescope with circuit board layouts, software, and schematics.)
- Other SETI activities include some scientists searching the libration points in the vicinity of the Earth and the Moon. There are five Earth Moon Lagrangian positions/ stable solar synchronised positions. The purpose was to attempt to find possible orbiting extra-terrestrial interstellar probes.
Lagrange Points Our Solar System
BETA and Microwaves
Erasmus : I think the technology that best represents the SETI direction is the BETA project. BETA is mnemonic that stands for Billion channel Extra Terrestrial Assay.
The system is capable of monitoring 240 million channels through a 240 million channel Fourier spectrometer, capable of tracking 80 million channels each with a bandwidth of 0.5 Hz using three directional antennas. This gives a 40 MHz instantaneous bandwidth for each feed.
Programmable “feature recognisers sift through approximate 250 MB/sec of data looking for distinctive features in the signals that are consistent in the two sky antennas with the movement of the earth.
This observational cycle of 16 seconds repeats eight times at two seconds each time during the sidereal drift of a point source through the antennas 0.5° detection beam. The system scans the micro spectrum from 1.4 to 1.72 GHz in eight steps of two seconds each.
The spectrum of observation was chosen because there is a high detection band in the microwave frequencies, adjacent to the hydrogen spectral lines.
Erasmus : More about the science theory involved:
Calculations allow for the movement of the earth around the sun and through space as well is the rotation of the earth.) A third antenna faces the horizon and detects noise signals arising from the earth itself.
The interference signals are subtracted from the sky-based detection signals, using a computer-based adaptive RFI filtering. This scheme recognises that interference occurs consistently in time and frequency.
The algorithm states:
- If there is interference at a certain frequency of the certain time, it is probable that there will be interference at that frequency shortly before and shortly after that time.
- If there is interference at a specific frequency at a specific time there is likely to be interference at nearby frequencies at that time.
- The algorithm notches out small spectrum bands which show interference or noise. It enables the elimination of approximate 99% of the interference at the detector, while masking less than 1% of the available spectrum.
Kinkajou : Tell us about using microwaves for detecting the aliens!
Microwaves occur in the frequency range 300 MHz to 300 GHz.
Microwave wavelengths cover 1mm to 1000mm
Microwaves have a long wavelength, though not as long as radio waves.
Microwaves are a form of electromagnetic radiation. This broad definition includes both UHF and EHF (millimetre), and various sources use different boundaries.
In all cases, microwave includes the entire SHF band (3 to 30 GHz, or 10 to 1 cm) at minimum, with RF engineering often restricting the range effectively between 1 and 100 GHz (300 and 3 mm).
Air Water EMF Attenuation
The Earth's atmosphere is transparent to some wavelengths of microwave radiation, but not to others. The longer wavelengths (waves more similar to radio waves) pass through the Earth's atmosphere more easily than the shorter wavelength microwaves. Microwave telescopes need to be large, but not as large as radio telescopes.
Microwave Background Radiation (or Cosmic Background Radiation) is the primordial radiation field that fills the universe, having been created in the form of gamma rays at the time of the big bang. It has now cooled so that its temperature today is 2.73K and its peak wavelength is near 1.1mm (in the microwave portion of the EM spectrum)
The Microwave Anistrophy Probe (due to be launched in 2000) will study small fluctuations in the Microwave Background Radiation.
Erasmus : Not all microwaves can be detected on the surface of our planet.
The atmospheric attenuation of microwaves in dry air with a perceptible water vapour level of 0.001 mm. The downward spikes in the graph correspond to frequencies at which microwaves are absorbed more strongly. Some standards designate the right-hand side of the graph as within the range of infrared.
Radio Waves and SETI
Kinkajou : Tell us about how we are using radio waves to find alien civilisations!
Radio waves occur in the frequency range 3 Hz - 300 GHz.
Radio waves wavelengths cover 100 000km - 1mm.
Of all of the types of electromagnetic radiation, radio waves have the lowest frequency and the longest wavelength.
The atmosphere of the Earth is transparent to radio waves with wavelengths of a few millimetres to about twenty metres.
Due to the transparency of the atmosphere to radio waves Radio telescopes can be ground based. Radio telescopes consist of very large dishes constructed of metal plates which focus the radio waves to a point above the centre of the dish where the receiver is located. Radio telescopes have to be very large because the long wavelengths of the EM radiation result in poor resolution.
Today the majority of radio astronomy is done using interferometry which acts to improve the resolution obtained. The largest single radio telescope in the world in located in Arecibo, Puerto Rico. It is 300 metres in diameter and is constructed in a natural bowl shaped depression.
Numerous sources of radio waves have been detected such as radio galaxies and quasars as well as emissions from the centre of the Milky Way Galaxy.
The WOW Signal
Kinkajou : have we ever found anything:
Erasmus : Yes. The WOW! Signal is the main contender.
The WOW signal
On August 15, 1977 Jerry Ehman, a SETI project volunteer saw a printout containing a startlingly strong radio signal. The signal lasted the full 72 seconds of the observation window of the BIG EAR telescope.
Jerry Ehman circled the part of the printout containing the signal (the vertical column containing the sequence 6EQUJ5), and wrote “WOW!” in the margin of the page. The band with the signal is approximately 10 kHz. “6EQUJ5” describes intensity variation of the signal, each character representing approximately 12 seconds of detected transmission.
The signal appeared to arise in the sky in the region of the constellation Sagittarius. Tau Sagittarii is the closest and most easily visible staff. The band width at which the signal is detected is a band with reserved for astronomical purposes. Terrestrial transmitters are forbidden to transmit at this wavelength.
This signal is believed by some to be the best indication that extra-terrestrial intelligence exists. However repeated searches have not found any evidence of this signal again.
The SETI Institute does not officially recognise the WOW! Signal as being of extra-terrestrial origin as it was unable to be verified.
Telescope Array doing Long BaseLine Interferometry
Kinkajou : WOW!
So what can you see as the problems with SETI?
Erasmus : SETI has been plagued over a number of years by the need for private funding as well as intermittent and inadequate government funding. A number of projects have languished over the years as a result of this.
I think there are number of serious flaws with the SETI project. The most critical and basic observation is that a radio wave detection is focused within 200 MHz of the hydrogen line. This takes advantage of the transparency of the atmosphere to microwaves. However, I think that extra-terrestrial civilisations are likely to do the same things for the same reasons as we do.
We only use microwaves for point-to-point transmission at low signal intensities. Microwaves cook things. They are dangerous. They harm biological life forms.
I think the true Holy Grail of SETI observation will occur when we are able to undertake broad spectrum readings spanning from radio waves to light frequencies. This may mean that observational platforms may have to rest in orbit all be built on atmosphere free sites such as the dark side of the moon.
A claim was made that the detectors can detect a gigawatt of microwaves at 200 light years. However, it is much more likely that a megawatt of microwaves is emitted. Using inverse square law, this implies a detection range of approximate 6 light years. About the only place we can detect specific micro-outputs may be our closest star system, namely Alpha Centauri.
In fact, if alien civilisation use microwaves for communication, they may well be used to link from one star system to another adjacent star system. These emission beams would be focused, indeed most likely bypassing our solar system undetected.
Kinkajou : How safe do you think it will be to communicate with aliens?
Erasmus : I think there is a lot to be said for the danger of communicating to an alien civilisation. My own personal life experience is that a decision should be made when one has an understanding of the consequences of that decision. If one does not understand the likely response of one’s alien neighbours, perhaps drawing attention to oneself may be unwise.
There is no reason that other civilisations will not view us as competitors rather than compatriots.
Innovations in SETI
Kinkajou : What innovations do you think will help us find extra-terrestrial life?
Erasmus : A number of ideas suggest themselves.
- I think there is a need for the development of atmosphere free observational platforms. (i.e. platforms in space or one the dark side of the moon). These would need to cover optical as well as radio spectra. This will enhance our ability to study adjacent solar systems and improve our ability to detect extra- terrestrial civilisations.
- Alternatively, like in UFO the TV series, set up SID= Space Intruder Detector.
As a simple observation, when one looks into the night sky of a city there may only be several hundred stars visible due to light pollution and other chemical pollutants in the air. This would substantially degrade detection capability.
In country areas, there are millions of stars visible. The sky looks like there is white dust scattered across the band of the Milky Way. The effect of the atmosphere on the observations of the galaxy would mirror the effect of cities polluting the sky and hiding the stars.
- Lasers may well be used by alien civilisations. However they are most suited for point-to-point communication and it is likely that directed signals would bypass us and be unlikely to be detected.
High detection range / sensitivity is critical if you are trying to find downrange overshoots. (Scarily, to be a goer, this idea demands that the Aliens have a space based civilisation or empire, within which they need to communicate).
- Our search parameters are likely to be highly inappropriate. A probable detection scenario involves receiving a direct transmission from the planet to a spaceship.
If the spaceship is travelling to our solar system or into the region of our solar system, the transmission may well be detected. You’d have to wonder if this was inadvertently the basis of the WOW signal.
- Most stellar conversations will be one-way conversations for brief periods of time, sending bursts of information which may loop within the transmission segment but not repeat, due to the limitation of the speed of light affecting communications.
Erasmus :A substantial amount of information can be coded into high-frequency transmissions. So it is unlikely that two-way conversations will occur, due to limitations of the speed of light.
- Analysis of the nature of the signal is necessary to detect communications. For example, we use amplitude modulation (AM) and frequency modulation (FM) as signal modifiers to transmit information.
This information coding system becomes a lot more complicated if the aliens involved were trying hard not to be heard. Separation of a data stream into multiple carrier bands in a long term repetitive though seemingly random transmission sequence, especially with planned frequency drift would make signal detection hard.
I’m not sure our SETI signal analysis is up to the task of detecting these transmission methods. Could we record and put a signal back together again.
- Polarisation of signals also becomes important. Detectors with horizontal polarisation are unable to pick up vertically polarised emissions.
It becomes obvious that there are many complexities in detecting other extra-terrestrial civilisations. Atmospheric limitations on signal detection may well deny the ability to detect many transmission frequencies. It also becomes obvious we need to enhance our capacity to detect and process signals over a greater region of the sky.
We do have the technological capacity to put a substantial amount of observational equipment into space. It’s just not cost effective for us to seriously do this at this time. Other priorities suggest themselves as first choice to use space based resources. E.g. Military satellites, Weather satellites, Geological survey satellites, or Communications satellites suggest themselves.
Goo : Well here’s to the future.
As my mother told me, “Be careful what you ask for.
You may in fact get exactly what you ask for”.
Space Defence Platforms