Radio Astronomy Points to Extraterrestrial Life

Radio Astronomy Points to Extraterrestrial Life

In a 1960 broadcast, a Voice of America reporter interviews Dr. Campbell Wade of the National Radio Astronomical Observatory about his discoveries analyzing radio waves to see 1 billion light years into space and about the possibility of life on other planets.

Massive Hunt for Extraterrestrial Life Completed: What Astronomers Found in Search of 10 Million Star Systems for Alien Technology

The Murchison Widefield Array radio telescope, a portion of which is pictured here, was used to explore hundreds of times more broadly than any previous search for extraterrestrial life. Credit: Goldsmith/MWA Collaboration/Curtin University

A radio telescope in outback Western Australia has completed the deepest and broadest search at low frequencies for alien technologies, scanning a patch of sky known to include at least 10 million stars.

Astronomers used the Murchison Widefield Array (MWA) telescope to explore hundreds of times more broadly than any previous search for extraterrestrial life.

The study, published this month in Publications of the Astronomical Society of Australia, observed the sky around the Vela constellation. But in this part of the Universe at least, it appears other civilizations are elusive, if they exist.

The research was conducted by CSIRO astronomer Dr. Chenoa Tremblay and Professor Steven Tingay, from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR).

Dipole antennas of the Murchison Widefield Array (MWA) radio telescope in Mid West Western Australia. Credit: Dragonfly Media

Dr. Tremblay said the telescope was searching for powerful radio emissions at frequencies similar to FM radio frequencies, which could indicate the presence of an intelligent source.

These possible emissions are known as ‘technosignatures.’

“The MWA is a unique telescope, with an extraordinarily wide field-of-view that allows us to observe millions of stars simultaneously,” she said.

“We observed the sky around the constellation of Vela for 17 hours, looking more than 100 times broader and deeper than ever before.

“With this dataset, we found no technosignatures—no sign of intelligent life.”

Tile 107, or “the Outlier” as it is known, is one of 256 tiles of the MWA, located 1.5km from the core of the telescope. Lighting the tile and the ancient landscape is the Moon. Credit: Pete Wheeler, ICRAR

Professor Tingay said even though this was the broadest search yet, he was not shocked by the result.

“As Douglas Adams noted in The Hitchhikers Guide to the Galaxy, ‘space is big, really big’.”

“And even though this was a really big study, the amount of space we looked at was the equivalent of trying to find something in the Earth’s oceans but only searching a volume of water equivalent to a large backyard swimming pool.

“Since we can’t really assume how possible alien civilizations might utilize technology, we need to search in many different ways. Using radio telescopes, we can explore an eight-dimensional search space.

“Although there is a long way to go in the search for extraterrestrial intelligence, telescopes such as the MWA will continue to push the limits—we have to keep looking.”

The MWA is a precursor for the instrument that comes next, the Square Kilometre Array (SKA), a 1.7 billion Euro observatory with telescopes in Western Australia and South Africa. To continue the Douglas Adams references, think of the MWA as the city-sized Deep Thought and the SKA as its successor: the Earth.

A time-lapse sequence of more than 1,000 images captured at the Murchison Radio-astronomy Observatory in Mid West WA. Tile 107, or “the Outlier” as it is known, is one of 256 tiles of this Square Kilometre Array precursor instrument located 1.5km from the core of the telescope. Lighting the tile and the ancient landscape is the Moon. Credit: Pete Wheeler / ICRAR

“Due to the increased sensitivity, the SKA low-frequency telescope to be built in Western Australia will be capable of detecting Earth-like radio signals from relatively nearby planetary systems,” said Professor Tingay.

“With the SKA, we’ll be able to survey billions of star systems, seeking technosignatures in an astronomical ocean of other worlds.”

The MWA is located at the Murchison Radio-astronomy Observatory, a remote and radio quiet astronomical facility established and maintained by CSIRO—Australia’s national science agency. The SKA will be built at the same location but will be 50 times more sensitive and will be able to undertake much deeper SETI experiments.

Reference: ‘”A SETI Survey of the Vela Region using the Murchison Widefield Array: Orders of Magnitude Expansion in Search Space” by C. D. Tremblay and S. J. Tingay, 8 September 2020, Publications of the Astronomical Society of Australia (PASA).
DOI: 10.1017/pasa.2020.27


A consortium of partner institutions from seven countries (Australia, USA, India, New Zealand, Canada, Japan, and China) financed the development, construction, commissioning, and operations of the Murchison Widefield Array radio telescope. The consortium is led by Curtin University.

We acknowledge the Wajarri Yamatji as the traditional owners of the Murchison Radio-astronomy Observatory site.

We acknowledge the Pawsey Supercomputing Centre which is supported by the Western Australian and Australian Governments.

SETI: Everything you need to know about how we're listening in for aliens

In 1960, astronomer Frank Drake pointed the Green Bank Observatory’s giant radio telescope at two Sun-like stars for 150 hours hoping to find a hint of alien life.

Drake’s search was unsuccessful but it prompted humanity’s ongoing quest to observe the cosmos in an effort to answer a massive existential question: are we alone in the universe?

More than 60 years later, Drake’s method is still at play, although slightly more finessed. The astronomer’s initial quest to find alien life led to the foundation of the SETI (Search for ExtraTerrestrial Intelligence), a series of interrelated programs looking for intelligent life beyond our solar system, mostly by trying to eavesdrop on their radio signals.

But a recent injection of cash — and some new unconventional detection methods — have brought new life to SETI and brought us closer than ever to finding out just how lonely the cosmos are, or hopefully aren’t.

As SETI researchers lend their ears to the cosmos, Inverse breaks down the history of the institute, their methods to search for aliens, and their ongoing quest to answer humanity’s burning questions.

Radio signals

But scientists aren't just looking for signs of extraterrestrial life — they're also listening for them.

For more than two decades, SETI, the Search for Extraterrestrial Intelligence Institute, has conducted research to understand the origins of life in the universe, and to detect and analyze evidence of life emanating from places other than Earth. This effort includes investigations of microbial life within our solar system, such as on the surface of Mars or under the icy crust of Jupiter's moon Europa. SETI scientists are also monitoring the universe for signals in light or radio wavelengths that originate far away and could be signs of technologically advanced alien life, SETI explains on its website.

At SETI, astronomers use the Allen Telescope Array (ATA) of 42 radio antennas to "listen" for signals over a range of radio frequencies, tuned to "hear" the regions around 20,000 red dwarf stars (a broad term describing stars smaller than our sun and in a certain spectral range) that are closest to Earth, Seth Shostak, a senior astronomer at the SETI Institute, told Live Science.

Investigating red dwarf stars for life-supporting worlds is a relatively recent development at SETI. In the past, stars that were more like our own sun — a yellow dwarf — were thought to be the most likely candidates to host planets harboring life. But over the last few decades, astronomers have determined that many red dwarf stars host planets that could be at the right distance from the star to be habitable, according to Shostak.

"That's something we didn't know when we started," he said.

And SETI radio-signal monitoring is accelerating, as telescopes become more sensitive and technological developments increase the number of radio channels and locations in the sky that can be studied at once, Shostak explained.

"Until now, the total number of star systems that have been looked at carefully over a wide range of the radio dial is measured in the thousands. In the next 20 years, with new technology, you could increase that number to maybe a million," he said. [4 Places Where Alien Life May Lurk in the Solar System]

Astronomers Unable to Explain Latest Mysterious Radio Burst

The search for extraterrestrial life has lately been focused on fast radio bursts (FRBs), short but incredibly powerful spikes in radio signals coming from beyond our own galaxy. While some scientists have optimistically pointed to these as proof of advanced alien civilizations , there are plenty of naturally-occurring astrophysical phenomena which could just as easily create such spikes.

These radio bursts clearly stand out against baseline background noise.

However, a recently-discovered FRB seems to defy the explanations astrophysicists typically assign to such anomalous signals. In a new pre-publication study on, an international body of astronomers searched for the usual follow-up signals across radio, optical, X-ray, gamma-ray, and neutrino emission bands. None were found.

The signal was picked up by radio telescopes at the Parkes Observatory in Australia.

The study’s main author, Emily Petroff from the Netherlands Institute for Radio Astronomy, told Gizmodo that this latest radio burst is a complete anomaly . Astronomers all over the world ran various tests to determine what its origin might be, Petroff says, but none of those tests was conclusive:

We spent a lot of time with a lot of telescopes to find anything associated with it. We got new wavelength windows we’ve never gotten before. We looked for high-energy gamma rays and neutrinos…we ruled out some source classes but no detection is a little unhelpful. We’re still trying to figure out where this one came from. It’s not very often in science that you get to work on something that’s so brand new and so unknown that you get to answer the fundamental questions.

This particular radio burst, named FRB 150215, passed through an incredibly dense region of the Milky Way on its way to Earth, possibly beaming through a tiny gap between stars and other bodies along the way.

Such bursts typically only last a few milliseconds.

While some might say this is a sign that the signal was beamed intentionally towards us by an advanced race of aliens, Petroff has been insisting through her Twitter account that she does not believe the radio burst has an alien origin. In all likelihood, there is a perfectly natural explanation for the radio signal such as a gamma ray burst or exploding star, but our telescopes likely missed it just prior to detecting the burst. Still, discovering how to identify and trace the origins of these signals might some day lead to that one lucky discovery which changes everything – or crush our hopes and make us realize just how alone we are.

The 21 cm Line

In a neutral hydrogen atom, an electron orbits a proton. Both these particles have a magnetic dipole moment ascribed to their spin, whose interaction results in a slight increase in energy when the spins are parallel, and a decrease when antiparallel. The spins can only have parallel and anti-parallel orientation because the angular momentum in quantum mechanics is discrete.

The 21 cm line

The configuration in which the spins are anti-parallel has lower energy. When the electron ‘flips’ and makes its spin anti-parallel to that of proton, energy is released in the form of an electromagnetic wave. From Planck’s law, the wavelength associated with this energy is about 21 cm. This is known as the 21 cm spectral line or the hydrogen line and is observed in radio astronomy.

By calculating the Doppler shifts from this line, we can determine the relative speed of each arm of the galaxy. The rotation curve of our galaxy has been calculated using the 21 cm hydrogen line. It is then possible to use the plot of the rotation curve and the velocity to determine the distance to a certain point within the galaxy. The 21 cm line is widely used in cosmology to study the early universe.

Image: NRAO

Technosignatures and the Search for Extraterrestrial Intelligence

The word “SETI” pretty much brings to mind the search for radio signals come from distant planets, the movie “Contact,” Jill Tarter, Frank Drake and perhaps the SETI Institute, where the effort lives and breathes.

But there was a time when SETI — the Search for Extraterrestrial Intelligence — was a significantly broader concept, that brought in other ways to look for intelligent life beyond Earth.

In the late 1950s and early 1960s — a time of great interest in UFO s, flying saucers and the like — scientists not only came up with the idea of searching for distant intelligent life via unnatural radio signals, but also by looking for signs of unexpectedly elevated heat signatures and for optical anomalies in the night sky.

The history of this search has seen many sharp turns, with radio SETI at one time embraced by NASA , subsequently de-funded because of congressional opposition, and then developed into a privately and philanthropically funded project of rigor and breadth at the SETI Institute. The other modes of SETI went pretty much underground and SETI became synonymous with radio searches for ET life.

But this history may be about to take another sharp turn as some in Congress and NASA have become increasingly interested in what are now called “technosignatures,” potentially detectable signatures and signals of the presence of distant advanced civilizations. Technosignatures are a subset of the larger and far more mature search for biosignatures — evidence of microbial or other primitive life that might exist on some of the billions of exoplanets we now know exist.

And as a sign of this renewed interest, a technosignatures conference was scheduled by NASA at the request of Congress (and especially retiring Republican Rep. Lamar Smith of Texas.) The conference took place in Houston late last month, and it was most interesting in terms of the new and increasingly sophisticated ideas being explored by scientists involved with broad-based SETI .

“There has been no SETI conference this big and this good in a very long time,” said Jason Wright, an astrophysicist and professor at Pennsylvania State University and chair of the conference’s science organizing committee. “We’re trying to rebuild the larger SETI community, and this was a good start.”

During the three day meeting in Houston, scientists and interested private and philanthropic reps. heard talks that ranged from the trials and possibilities of traditional radio SETI to quasi philosophical discussions about what potentially detectable planetary transformations and by-products might be signs of an advanced civilization. (An agenda and videos of the talks are here.)

The subjects ranged from surveying the sky for potential millisecond infrared emissions from distant planets that could be purposeful signals, to how the presence of certain unnatural, pollutant chemicals in an exoplanet atmosphere that could be a sign of civilization. From the search for thermal signatures coming from megacities or other by-products of technological activity, to the possible presence of “megastructures” built to collect a star’s energy by highly evolved beings.

All but the near infrared SETI are for the distant future — or perhaps are on the science fiction side — but astronomy and the search for distant life do tend to move forward slowly. Theory and inference most often coming well before observation and detection.

So thinking about the basic questions about what scientists might be looking for, Wright said, is an essential part of the process.

Indeed, it is precisely what Michael New, Deputy Associate Administrator for Research within NASA’s Science Mission Directorate, told the conference.

He said that he, NASA and Congress wanted the broad sweep of ideas and research out there regarding technosignatures, from the current state of the field to potential near-term findings, and known limitations and possibilities.

“The time is really ripe scientifically for revisiting the ideas of technosignatures and how to search for them,” he said.

He offered the promise of NASA help (admittedly depending to some extent on what Congress and the administration decide) for research into new surveys, new technologies, data-mining algorithms, theories and modelling to advance the hunt for technosignatures.

Among the several dozen scientists who discussed potential signals to search for were the astronomer Jill Tarter, former director of the Center for SETI Research, Planetary Science Institute astrobiologist David Grinspoon and University of Rochester astrophysicist Adam Frank. They all looked at the big picture, what artifacts in atmospheres, on surfaces and perhaps in space that advanced civilizations would likely produce by dint of their being “advanced.”

All spoke of the harvesting of energy to perform work as a defining feature of a technological planet, with that “work” describing transportation, construction, manufacturing and more.

Beings that have reached the high level of, in Frank’s words, exo-civilization produce heat, pollutants, changes to their planets and surroundings in the process of doing that work. And so a detection of highly unusual atmospheric, thermal, surface and orbital conditions could be a signal.

One example mentioned by several speakers is the family of chemical chloroflourohydrocarbons ( CFC s,) which are used as commercial refrigerants, propellants and solvents.

These CFC s are a hazardous and unnatural pollutant on Earth because they destroy the ozone layer, and they could be doing something similar on an exoplanet. And as described in the conference, the James Webb Space Telescope — once it’s launch and working — could most likely detect such an atmospheric compound if it’s in high concentration and the project was given sufficient telescope time.

A similar single finding described by Tarter that could be revolutionary is the radioactive isotope tritium, which is a by-product of the nuclear fusion process. It has a short half-life and so any distant discovery would point to a recent use of nuclear energy (as long as it’s not associated with a recent supernova event, which can also produce tritium.)

But there many other less precise ideas put forward.

Glints on the surface of planets could be the product of technology, as might be weather on an exoplanet that has been extremely well stabilized, modified planetary orbits and chemical disequilibriums in the atmosphere based on the by-products of life and work. (These disequilibriums are a well-established feature of biosignature research, but Frank presented the idea of a technosphere which would process energy and create by-products at a greater level than its supporting biosphere.)

Another unlikely but most interesting example of a possible technosignature put forward by Tarter and Grinspoon involved the seven planets of the Trappist-1 solar system, all tidally locked and so lit on only one side. She said that they could potentially be found to be remarkably similar in their basic structure, alignment and dynamics. As Tarter suggested, this could be a sign of highly advanced solar engineering.

Grinspoon seconded that notion about Trappist-1, but in a somewhat different context.

He has worked a great deal on the question of today’s anthroprocene era — when humans actively change the planet — and he expanded on his thinking about Earth into the galaxies.

Grinspoon said that he had just come back from Japan, where he had visited Hiroshima and its atomic bomb sites, and came away with doubts that we were the “intelligent” civilization we often describe ourselves in SETI terms. A civilization that may well self destruct — a fate he sees as potentially common throughout the cosmos — might be considered “proto-intelligent,” but not smart enough to keep the civilization going over a long time.

Projecting that into the cosmos, Grinspoon argued that there may well be many such doomed civilizations, and then perhaps a far smaller number of those civilizations that make it through the biological-technological bottleneck that we seem to be facing in the centuries ahead.

These civilizations, which he calls semi-immortal, would develop inherently sustainable methods of continuing, including modifying major climate cycles, developing highly sophisticated radars and other tools for mitigating risks, terraforming nearby planets, and even finding ways to evolve the planet as its place in the habitable zone of its host star becomes threatened by the brightening or dulling of that star.

The trick to trying to find such truly evolved civilizations, he said, would be to look for technosignatures that reflect anomalous stability and not rampant growth. In the larger sense, these civilizations would have integrated themselves into the functioning of the planet, just as oxygen, first primitive and then complex life integrated themselves into the essential systems of Earth.

And returning to the technological civilizations that don’t survive, they could produce physical artifacts that now permeate the galaxy.

While the conference focused on technosignature theory, models, and distant possibilities, news was also shared about two concrete developments involving research today.

The first involved the radio telescope array in South Africa now called MeerKAT, a prototype of sorts that will eventually become the gigantic Square Kilometer Array.

Breakthrough Listen, the global initiative to seek signs of intelligent life in the universe, would soon announce the commencement of a major new program with the MeerKAT telescope, in partnership with the South African Radio Astronomy Observatory ( SARAO ).

Breakthrough Listen’s MeerKAT survey will examine a million individual stars – 1,000 times the number of targets in any previous search – in the quietest part of the radio spectrum, monitoring for signs of extraterrestrial technology. With the addition of MeerKAT’s observations to its existing surveys, Listen will operate 24 hours a day, seven days a week, in parallel with other surveys.

This clearly has the possibility of greatly expanded the amount of SETI listening being done. The SETI Institute, with its radio astronomy array in northern California and various partners, have been listening for almost 60 years, without detecting a signal from our galaxy.

That might seem like a disappointing intimation that nothing or nobody else is out there, but not if you listen to Tarter explain how much listening has actually been done. Almost ten years ago, she calculated that if the Milky Way galaxy and everything in it was an ocean, then SETI would have listened to a cup full of water from that ocean. Jason Wright and his students did an updated calculation recently, and now the radio listening amounts to a small swimming pool within that enormous ocean.

The other news came from Shelley Wright of the University of California, San Diego, who has been working on an optical SETI instrument for the Lick Observatory.

The Near-Infrared Optical SETI ( NIROSETI ) instrument she and her colleagues have developed is the first instrument of its kind designed to search for signals from extraterrestrials at near-Infrared wavelengths. The near-infrared regime is an excellenr spectral region to search for signals from extraterrestrials, since it offers a unique window for interstellar communication.

The NIROSETI instrument utilizes two near-infrared photodiodes to be able to detect artificial, very fast (nanosecond) pulses of infrared radiation.

The NIROSETI instrument, which is mounted on the Nickel telescope at Lick Observatory, splits the incoming near-infrared light onto two channels, and then checks for coincident events, which indicate signals that are identified by both detectors simultaneously.

Wright of Penn State was especially impressed by the project, which he said can look at much of the sky at once and was put together with on very limited budget.

Wright, who teaches a course on SETI at Penn State and is a co-author of a recent paper trying to formalize SETI terminology, said his own take-away from the conference is that it may well represent an important and positive moment in the history of technosignatures.

“Without NASA support, the whole field has lacked the normal structure by which astronomy advances,” he said. “No teaching of the subject, no standard terms, no textbook to formalize findings and understandings.

“The Seti Institiute carried us through the dark times, and they did that outside of normal, formal structures. The Institute remains essential, but hopefully that reflex identification will start to change.”

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Science: Radio Astronomy

There is no question that Carl Sagan’s book, Contact, was influenced by space exploration and the technological breakthroughs that were being made during the time in which he was writing this novel. Sagan used radio astronomy in his early career to make one of his most notable discoveries. Using the plant Venus’s radio emissions, Sagan was able to find the cause of these radio emissions was due to the extreme conditions of the planet’s atmosphere. Sagan also writes about the use of the radio telescope in order to make contact with extraterrestrial life in his book, Contact. However, none of this would have been possible without the discovery and the main contributors to the field of radio astronomy.

Before the early 1930s, not much was known about radio waves. The only studies or research performed was in the 1890s when scientist tried to detect radio waves from the Sun. The results were inconclusive due to primitive equipment. From then on radio waves were thought to only exist on Earth or were undetectable in the solar system. In 1932, a man named Karl Janksy proposed an idea that was thought to be ridiculous at the time by the rest of the world. While working as a radio engineer assigned to detect the source of radio static or noise that would block wave transmission for the Bell Telephone Laboratories Janksy discovered an interesting cause for the communication static. He explained that this static was caused by waves that were being emitted beyond the solar system, more commonly known as extraterrestrial radio waves.

Most astronomers of the time paid no attention to Janksy’s discovery. Nevertheless, one man, Grote Reber, believed in Janksy’s work. Lisa Yount’s Modern Astronomy: Expanding the Universe recalls Reber’s account of the findings as, “a fundamental and very important discovery” (Yount, 2006). The year of 1937 was eventful for Reber. With help from friends and family Reber was able to manufacture the first radio telescope in his backyard. Weighing approximately two tons with a parabola shaped iron mirror measuring nine meters in diameter, the telescope was capable of transforming the electric signals into electric signals. The electric signals produced were then recorded on paper. Reber was able to confirm the radiation from the Milky Way that Janksy had first discovered.

After committing his work to radio waves and radio telescopes, Reber produced the first radio maps of the sky in the early 1940s and found the center of the Milky Way was the source of some of the strongest signals. In 1944 Reber finally published a complete radio map of the sky after working for three years in hopes of worldwide recognition. Sadly, the world’s engagement in World War II masked his hopes of obtaining the world’s recognition. Luckily, one of his articles caught the eye of Jan Oort, the director of the Netherlands’ Leiden Observatory. Oort believed that the fixed lines of the electromagnetic spectrum created by specific wavelengths of radio waves could be moved from their present position by the Doppler effect. This would allow astronomers to “measure the distance and movement of objects that did not give off light such as gas clouds themselves” (Yount, 2006).

One of Oort’s students predicted that, “atoms of hydrogen… would give off radio waves 21 centimeters (about 8 in.) long” (Yount, 2006). After this prediction was proved to be correct in 1951, these hydrogen emissions were used to prove that the Milky Way galaxy was indeed a spiral like shape. Contrary to popular belief, radio telescopes do not actually carry sound, but instead radio waves are processed and have the possibility of being converted into images on a computer or TV screen.

Without the brilliant and courageous scientists, our ideas of modern space and time would be greatly altered. The use of radio astronomy has led to amazing discoveries in the past few decades. Pulsars, quasars, and many events that occur in space are just a few of these discoveries.

The study of space is a very difficult yet intriguing field. The beauty of this unknown is slowly catching the eyes of many astronomers like Carl Sagan. Sagan worked diligently in an attempt to show the world the marvels of the universe. This is especially evident in his writings. He not only wrote about the things discussed in this novel, but also spent his life researching them.

The book, Contact, is believed to give an insight into some of Sagan’s personal ideas about various realms of space and science. A book review published by Jeff Clark in 1985 reads, “the ideas are stimulating, and Contact makes for entertaining reading” (Clark, 1985). This was always a goal of Sagan, to inform the world of the entertaining and awe inspiring aspects that our universe has to offer. The sciences and scientists that contributed to the ideas of contained in the book deal with whether or not further research in some fields like extraterrestrial life should be continued. Carl Sagan was a brilliant scientist, idealist, and author that forever altered the world of astronomy and other aspects of science through his devotion to research and his works of literature.

Listed below are a few more relevant links including one to a TV series that Sagan helped write:

Works Cited

Clark, Jeff. “Contact.” Library Journal 110.20 (1985): 128. Academic Search Premier. Web. 1 July 2014.

Dominik, M., and J. C. Zarnecki. “The Detection of Extra-terrestrial Life and the Consequences for Science and Society.” Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 369.1936 (2011): 499-507. Highwire Press Royal Society. Web. 28 June 2014. <

Elbers, Astrid. “The Establishment of the New Field of Radio Astronomy in the Post-War Netherlands: A Search for Allies and Funding.” Centaurus 54.4 (2012): 265-85. Web. 26 June 2014.

Jones, Barry O. Dictionary of World Biography. Melbourne, VIC: Information Australia, 1994. Print.

Lindley, David. “The Birth of Wormholes.” Focus 15 (2005). American Physical Society. Web. 30 June 2014. <

Overbye, Dennis. “Please Call Earth. We Still Haven’t Found You.” The New York Times 2 Mar. 2008: WK4. ProQuest Historical Newspapers. Web. 29 June 2014. <

Sagan, Carl. Contact: A Novel. New York: Simon and Schuster, 1985. Print.

Smith, Robert W. “Collaboration, Competition, and the Early History of Radio Astronomy.” Metascience (2014) 23 (2013). Ebscohost. Web. 28 June 2014.

Spangenburg, Ray, and Diane Moser. Carl Sagan: A Biography. Westport, CT: Greenwood Pub. Group, 2004. Print.

Terzian, Yervant, and Elizabeth M. Bilson. Carl Sagan’s Universe. Cambridge, U.K.: Cambridge UP, 1997. Print.

Yount, Lisa. Modern Astronomy: Expanding the Universe. New York: Chelsea House, 2006. Print.

Radio Astronomy Points to Extraterrestrial Life - HISTORY

I have Downloaded the SETI program at my home on 2 different computers, it's great. I was wondering and looking, if there is any SETI like program that lets you not only see the radio waves but hear it also ?

Not that I know of. And in fact, such a thing couldn't exist, because you can't actually "hear" radio waves. Radio waves are electromagnetic radiation (just like visible light, except with longer wavelengths). You can't hear them.

Despite the insistence of Hollywood, the media, and your everyday experience with your radio, there's nothing about radio waves that makes them equivalent to sound. What happens with your radio is that the radio station's transmitter is encoding information in the radio signal (modulating it in either frequency or amplitude) that gets decoded by your radio so that it knows what sounds to make. There's no reason to believe that the ET's would be doing the same thing. And, even if they were, we'd have no idea how to decode it to figure out what the sounds are supposed to be.

If you were to try turn the SETI signal into sound using the same method as a radio, it would just sound like noise—probably even if there was a real signal from aliens.

This page was last updated June 27, 2015.

About the Author

Christopher Springob

Chris studies the large scale structure of the universe using the peculiar velocities of galaxies. He got his PhD from Cornell in 2005, and is now a Research Assistant Professor at the University of Western Australia.

Drake Equation Tutorial

In November 2006, I was a participant in a panel discussion Defining the Drake Equation at the Windycon Science Fiction Convention. My co-panelists were Seth Shostak of the SETI (Search for Extraterrestrial Intelligence) Institute Bill Higgins, a physicist at Fermi National Accelerator Laboratory (Fermilab) and Bill Thomasson. You can see a picture of our panel at MidAmerican Fan Photo Archive Windycon 33 Saturday Panels. I have decided to turn the preparation that I did for that panel, and notes taken during the panel discussion, into a tutorial on the Drake Equation.

Drake Equation History

The year is 1960 and Frank Drake of the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia undertakes the first attempt to find extraterrestrial civilizations. Dubbed Project Ozma, for a period of 6 hours a day for four months the NRAO radio telescope listens for radio signals of intelligent origin. None are found.

Within a year a meeting is hosted in Green Bank to explore the issue of extraterrestrial intelligence. Frank Drake needed to come up with an agenda for the meeting in order to provide some structure to the discussion. To serve as an agenda, he devises the Drake Equation. Sometimes known as the Sagan-Drake Equation in the past, the meeting was attended by approximately a dozen interested parties.

Drake Equation Overview

The Drake Equation is an attempt to encapsulate all the variables that would be relevant to establishing the number of intelligent civilizations that existed in the Milky Way galaxy and which were broadcasting radio signals at this particular point in time. The Drake Equation is composed of seven terms. The first six are used to compute the rate at which intelligent civilizations are being created and the final term identifies how long each lasts on average as a broadcasting civilization. It is worth stressing that the Drake Equation applies only to intelligent civilizations in the Milky Way galaxy. It does not apply to civilizations in other galaxies because they are too distant to be able to detect their radio signals.

The Drake Equation is:
N = R * fp * ne * fl * fi * fc * L

N = The number of broadcasting civilizations.
R = Average rate of formation of suitable stars (stars/year) in the Milky Way galaxy
fp = Fraction of stars that form planets
ne = Average number of habitable planets per star
fl = Fraction of habitable planets (ne) where life emerges
fi = Fraction of habitable planets with life where intelligent evolves
fc = Fraction of planets with intelligent life capable of interstellar communication
L = Years a civilization remains detectable

According to the Wikipedia entry for the Drake Equation, the following values were those used in the original formulation of the Drake Equation:
R = 10
fp = 0.5
ne = 2.0
fl = 1.0
fi = 0.01
fc = 0.01
L = 10000

Plugging Drake's original numbers into the Drake Equation produces a value of 10 for the number of broadcasting civilizations in our galaxy. Now lets go through each of the terms in detail.

R - The rate of formation of Suitable Stars in the Milky Way Galaxy

Estimates for the number of stars in the Milky Way vary from a low of 100 billion to a high of 400 billion. Estimates for the age of the Milky Way also vary from a low of 800 million years to a high of 13 billion years. If we go with the lowest star count and the oldest age for the galaxy, the average rate of star formation works out to 7.7 new stars per year. If we go with the highest star count and the youngest age for the galaxy, the average rate of star formation becomes 500 new stars per year.

An important caveat to the above values is that the rate of star formation in the galaxy is not constant over time. In the galaxy's younger days, stars were being formed at a much higher rate. Today, estimates for the overall star formation rate range from 5 to 20.

Another caveat is that not all stars are created equal. For example, very massive stars are not considered suitable. Some versions of the Drake Equation use the R term for the overall rate of star formation and then add a second term to estimate the fraction of these stars that are like our own Sun. A suitable star would be one that has a reasonably long life (approximately 10 billion years for our Sun which is now in midlife) and sized so that the fusion process that powers the star produces the right amount of energy to sufficiently warm the planets but not turn them into toast. Estimates are that the rate of formation of Sun sized stars is on the order of 1 per year.

Fp - The Fraction of Stars with Planets

At the time the Drake Equation was created, the only planets that were known were those of our own solar system. Since that time approximately 200 extrasolar planets have been discovered.

When the Drake Equation was created, it was thought that planets would only be found in single star systems. It was believed that gravitational disruptions in multiple star systems would prevent planets from forming. This hypothesis removed approximately 50 percent of the stars from consideration. It has now been shown theoretically that these multiple star systems can have planets. For example, if a planet is in orbit around a star that is X units of distance away, then the planet's orbit can be stable if the companion star is more than 5X units away. Alternatively, if two stars are X units away from one another, then a planet that orbits these stars from a distance of more than 5X units should have a stable orbit.

So what fraction of stars have planets? Estimates range from a low of 5% to a high of 90%. If you use a value of 0.1 you are saying that you believe that 1 in 10 stars will have planets. Alternatively if you use a value of 1.0 you are saying that every single star will have planets.

Ne - The Average Number of Habitable Planets per Star

In his original equation, Drake optimistically assigned a value of 2 to this parameter meaning that there are on average two Earth-like planets per star for those stars with planets. Factors that must be considered in arriving at a value for this parameter are the chemical composition of the solar nebula from which the planets were created (the presence of sufficient quantities of the necessary elements) and the idea of a star's habitable zone (the range of orbital distances within which liquid water can exist)

Something else to consider is that our idea of habitable may be too restrictive. Does life require an Earth-like planet? This is a question of life as we know it versus life as we don't know it. However, from a biochemical standpoint, it is hard for us to imagine life that does not require liquid water.

Choosing a value of 1.0 for this parameter means that you think that every star with planets will have one habitable planet. A value of 0.5 means that there will be one habitable planet for every two stars with planets.

Fl - The Fraction of Habitable Planets Where Life Emerges

This parameter is something of a wildcard in that we only have one example of life. It is difficult for us to say how easy or hard it is for life to start given suitable environmental conditions. One interesting point to consider is this:

  • the Earth is approximately 4.5 billion years old
  • the period of heavy bombardment during which the planets were pummeled by debris left over from the birth of the solar system ended about 3.8 billion years ago
  • the oldest known sedimentary rocks and deposits, found in northwestern Australia, are estimated to be 3.5 - 3.8 billion years old
  • the oldest known fossil evidence of life is of cyanobacteria found in these deposits dated at 3.5 billion years old.

The implication of this is that life got started rather quickly on Earth. The big unknown is just how common are the conditions which resulted in life. This is one reason why the search for evidence of past life on Mars is so important. Finding or not finding evidence of past and/or present life on Mars will help us to better answer the question of the likelihood of life elsewhere in the galaxy and universe.

Choosing a value of 0.01 for this parameter means that you think that life develops on only 1 of every 100 habitable planets whereas a value of 1.0 means that life develops on every habitable planet.

Fi - The Fraction of Planets With Life Where Intelligence Life Evolves

Given that life evolves on a planet, how likely is it that intelligent life will appear? This is another big unknown. Of all the millions of species that have ever existed on Earth, only one has evolved the level of intelligence necessary to develop technology.

Further, while very simple life appeared very quickly on Earth, complex life took far longer to develop. Given that there is not a parameter to distinguish microscopic life (which lacks the complexity to develop intelligence) from the development of complex macroscopic life, this aspect must be taken into account in the context of this parameter.

Whereas Drake believed that life would develop on every planet that had habitable conditions, he estimated that intelligent life would emerge on only 1 of every 100 of these planets

Choosing a value of 0.001 for this parameter means that you think that intelligent life will appear on only 1 of every 1000 planets with life. A value of 1.0 means that the development of intelligent life is a certainty on those planets where life develops

Fc - The Fraction of Intelligent Civilizations with Interstellar Communication

So what if aliens have no equivalent of a Maxwell or a Morse or a Marconi or an Edison? They may be smart enough to construct towns and transportation but do they ever invent radio? Drake was of the opinion that 1 out of every 100 civilizations would discover radio. What do you think?

A value of 1.0 means that every civilization develops radio and a value of 0.001 means that only one in a thousand civilizations develop radio.

L - The Number of Years an Intelligent Civilization Remains Detectable

The L parameter turns the equation from a rate into a number. It is also a number for which there is no real basis for the assignment of a value. We are the only intelligent civilization we know of and we do not know how long we will remain detectable. A conservative estimate for this value would be 50 years based on our own experience to date. Drake felt that 10,000 years was a good guess.

N - The Answer is the Number of Detectable Civilizations at this Time

And the answer is N - the number of intelligent civilizations that are broadcasting their presence to the Universe.

Experiment with the Drake Equation

To facilitate your own experimentation with the Drake Equation, I have created an OpenOffice Calc spreadsheet and a Microsoft Excel spreadsheet. If you do not have OpenOffice, I strongly encourage you to get it. OpenOffice is the free, open source alternative to Microsoft Office. You can learn more at the OpenOffice web site

In the spreadsheet you will find that I have inserted my own values for the seven parameters. Following is an explanation for the values I used.

R = 2 which is double the estimated rate of formation of Sun-like stars but well below the maximum estimate of 20 new stars per year in the galaxy.

fp = 0.45 which is 1/2 the high estimate of 90% of these stars having planets.

ne = 0.50 because I do not believe that every star that has planets will have habitable planets. Recall that Drake assigned a number of 2 for this parameter. My optimistic estimate is that for every two stars with planets, there will be one habitable planet.

fl = 0.2 with no sound basis, I decided that life will emerge on only 1 in 5 habitable planets.

fi = 0.05 again guessing that intelligent life will develop on only 5 out of every 100 planets with life.

fc = 0.5 because I am optimistic that if there is intelligent life, there is at least a 50-50 chance that they will develop the technology necessary for interstellar communication.

L = 500 because I am not as optimistic as Frank Drake about the number of years for which an intelligent civilization will be broadcasting its presence by way of radio transmissions.

I was very much surprised to see that the combination of values that I used yielded a result of 1.13 currently broadcasting civilizations. That makes us the one. Going back and changing only the L parameter to Drake's value of 10,000 yields 22.5 broadcasting civilizations. If we were to assume that the Milky Way is a cylinder with a radius of 50,000 light years and a thickness of 1,000 light years, then there would be one broadcasting civilization for every 349 billion cubic light years of space.

Now consider this. Let's make the following assumptions:

  • the radius of the Milky Way is 50,000 light years
  • there are currently 22.5 broadcasting civilizations
  • all civilizations lie on the galactic equator in a 2 dimensional distribution

Given these assumptions, this means that on average each of these civilizations are separated by a distance of just over 21,000 light years. That means that any civilization that began broadcasting less than 21,000 years ago, like us for example, would not yet be detectable.


The Drake Equation must be one of the swaggiest (SWAG being the acronym for Scientific Wild-A** Guess) equations ever created because of the uncertainty associated with its parameters. The Drake Equation does do a great job of identifying and categorizing the relevant parameters. It also accomplishes the task of providing structure to the ongoing debate about the search for extraterrestrial intelligence and the likelihood of its existence. The large degree of uncertainty associated with so many of its parameters does tell us one important thing: that we have a lot more to learn.

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