The Green Bank meeting did produce a consensus number, based on the not inconsiderable expertise of the participants: there are of the order of 10,000 civilisations present now in the Milky Way with whom we could communicate if we had enough radio telescopes and the will to conduct a systematic search. Interestingly, Philip Morrison, veteran of the Manhattan Project, felt that the lifetime of technological civilisations may be so short that this number could well be zero, although he observed that ‘… if we never search, the chance of success is zero’.
I had the privilege of meeting Frank Drake during the filming of Human Universe. In my view he is one of the greatest living astronomers. Frank collects and cultivates orchids, and by complete coincidence I arrived at his house when his Stanhopea orchid was flowering. These delicate and complex flowers bloom for only two days every year, and the chance of seeing one on a random visit is therefore small. Frank turned to me and said ‘well, so it is with SETI – we’ve learned that we must search over and over and over through the years, until we are in the right place at the right time to make the discovery’. There is ‘hope’ in its name, and there is nothing wrong at all with admitting a dash of hope.
Throughout the 1960s and 1970s, SETI projects both big and small continued to develop across the planet. Soviet scientists joined their American contemporaries in pointing radio receivers to the sky in the hope of detecting a signal in the noise. NASA considered funding Project Cyclops, a $10 billion super-array of 1500 dishes that could listen for signals originating up to 1000 light years from Earth. It never progressed beyond the planning stage, but the scale of the project demonstrates that SETI was considered to be a serious scientific endeavour. By the mid-1970s, various projects had come and gone but none had detected the faintest hint of a significant signal. This failure, combined with a lack of progress in pinning down any of the terms in the Drake Equation – it was not even certain that planets existed in large numbers beyond our solar system – made the search look increasingly futile. Not only was there a deafening silence, no one had much idea where to look or how hard to listen. NASA didn’t lose faith, however, and in 1973 Ohio University’s ten-year-old Big Ear telescope was optimised for a SETI survey and began taking data.
Four years later, on 18 August 1977, Jerry R. Ehman, then a volunteer at the Big Ear, received a knock on the door of his house. It was a Thursday morning and, as usual, standing at the door was a technician carrying reams of paper printouts. This was an age when a state-of-the-art hard disk could hold only a couple of megabytes, and every few days someone had to visit the telescope, print out the data and wipe the disks clean. Ehman put the three days’ worth of printed data onto his kitchen table and began searching. He was confronted with dozens of pages covered in hundreds of letters and numbers.
The list of numbers and letters depicts the strength of the signal hitting the telescope at different times. A space denotes low intensity, and higher intensities are registered as numbers from 0 to 9. For stronger signals still, letters between A and Z are used. Most of the data the ‘Big Ear’ recorded contained no letters; a stream of 1s and 2s signified sweeps across the general radio hiss of the sky. That morning, however, Ehman stumbled across something different. At approximately 10.16pm Eastern Standard Time on 15 August, a radio pulse of extreme intensity entered the antennae, recorded with the alphanumeric code 6EQUJ5. The signal lasted for 72 seconds, precisely the length of time a transmission of distant origin would register as the rotation of the Earth swept the telescope past the source. This is extremely important. If the signal had been caused by some kind of Earth-based interference, it would be highly unlikely to rise and fall in this manner, precisely and coincidently simulating the rotation of the Earth and the telescope’s field of view on the sky. The peak was marked by the letter U, the strongest signal ever recorded by the Big Ear, denoting an intensity over 30 times that of the background emission of the galaxy. Equally strangely, the signal had a wavelength of 21cm – the hydrogen line favoured by Morrison and Cocconi in their 1959 Nature paper. A smoking gun for extraterrestrial communication?
With a now-famous flourish, Ehman circled the six characters and scribbled ‘Wow!’ on the printout. He then continued as a research scientist should, and looked to see if it happened again. He flicked through page after page, but the event of 10.16pm on 15 August was a solitary blip in the background noise. This presented a problem, because it should have happened again. The Big Ear telescope scans each part of the sky twice, separated by 3 minutes, so there should have been a similar Wow! signal in the data 3 minutes afterwards. None was present. This doesn’t rule out an intelligent extraterrestrial origin; perhaps ET just turned the transmitter off a minute or so after it was first detected. Who knows?
The origin of the Wow! signal was narrowed down to a point in the sky in the direction of the constellation Sagittarius. Tau Sagittarii, a stable orange star twice the mass of our Sun and around 122 light years away, is the closest bright star to the source. Since August 1977 multiple attempts have been made to recover the signal using the world’s most sensitive radio telescopes. Many hours have been spent listening, but nothing unusual has ever been detected again. Today, over 35 years later, there is no satisfactory explanation, but no serious scientist, no matter how embedded in SETI, would claim it as definitive evidence of intelligent extraterrestrial communication. Scientific results have to be repeatable, and the observation has never been repeated. For the moment, the Wow! signal remains an interesting anomaly in an otherwise silent sky. It is the stuff of dreams; the faintest of whispers in a great silence.
* * *
PROBES ON TOUR
The Voyager probes have visited most of the outer planets on their way out of the solar system. Each visit has also used the planets’ gravitational pull to slingshot the probes on their journey.
* * *
THE GOLDEN VOYAGE
Two days after Jerry Ehman spotted the Wow! signal, the human race responded with a long-planned contribution to the interstellar conversation. In an explosive, serendipitous moment, the Voyager 2 spacecraft blasted into the sky above Space Launch Complex 41 at Kennedy Space Centre, followed two weeks later by its twin Voyager 1.
The Voyager missions were designed to take advantage of a rare planetary alignment to study the outer solar system gas giants Jupiter, Saturn, Uranus and Neptune. I remember the launch – I had collected a series of PG Tips tea cards called ‘The Race Into Space’, in which the Grand Tour mission was described as ‘the most ambitious unmanned space project known’. Using the newly proposed gravity assist, a spacecraft could accelerate around Jupiter, Saturn and Uranus to encounter Neptune only a decade from launch. The Voyagers delivered, I suspect, way beyond their designers’ wildest dreams, returning the first detailed pictures of the esoteric moons of Jupiter and Saturn, and in the case of Voyager 2, sweeping onwards to become the only spacecraft to date to visit Uranus and Neptune, where it photographed the distant ice moon Triton in the summer of 1989.
At the time of writing, on 8 July 2014, Voyager 1 is the most distant man-made object at over 127 astronomical units from Earth, so distant that radio waves take over 17 ½ hours to reach it. This puts Voyager 1 at the very edge of the solar system, on its way into interstellar space. The bus-sized spacecraft has enough electrical power to continue to communicate with its home world until around 2020, at which point it will fall silent. In 40,000 years it will drift within 1.6 light years of the red dwarf star Gliese 445 in the constellation of Camelopardalis. Voyager 2 will reach Sirius, the brightest star in the night sky, in 296,000 years.
The Voyagers are accompanied on their lonely flights out of our solar system by a dream – an unusually sentimental and hopeful afterthought to a scientific mission bolted to their sides almost 40 years ago.
The Voyager Golden Record is our message in a bottle. An old-fashioned phonograph record constructed of gold-plated copper floating through the universe, it contains what some would term a surreal mixture of
sound recordings, images and information. It was designed to provide an alien civilisation with information about who we are, what we know and what our planet is like. There are 116 images on the disc; the first 30 or so are scientific, illustrating our solar system, our home world, the structure of DNA, the anatomy of our bodies, our reproduction and our birth. Anatomy takes up more room than any other subject, perhaps reflecting our own fascination with what aliens might look like. In the most magnificently colloquial and futile gesture towards the aliens’ moral sensibilities, no nudity was allowed! I find it hard enough to imagine the inner workings of alien brains, but I cannot begin to fathom what it must be like inside the mind of a person who raised such an objection to the depiction of the human body. ‘How do these beings reproduce? Perhaps they use those ten dangly things on the ends of their arms? Disgusting!’
This is a present from a
small, distant world, a token
of our sounds, our science,
our images, our music,
our thoughts and our feelings.
We are attempting to
survive our time so we may
live into yours.
US President Jimmy Carter
The illustrations go on to detail our planet’s landscapes and the variety of life on Earth, before dedicating 50 images to our lives and the civilisation we’ve constructed – from the Great Wall of China to a supermarket. Finally, there are images of the scientific instruments we have used to explore the universe from microscopes to telescopes, including the Titan rocket that launched the Voyagers into space. Chosen by a committee chaired by Carl Sagan, the disc also contains music and sounds, including human greetings in 55 languages, recordings reflecting ‘the sounds of the Earth’, and the ultimate 1977 mix tape featuring 90 minutes of music from Beethoven to Chuck Berry. Sagan wanted the Beatles’ ‘Here comes the Sun’ on the disc, but EMI refused copyright permission for the universe. I like to imagine that Carl Sagan put the song on the record anyway in a great cosmic two-fingered salute to corporate Earth. That would have been pure Sagan – ‘You’re most welcome to go fetch it’.
The outside cover of the golden disc is more functional. As well as instructions on how to play back the images and sounds at precisely revolutions per minute for the audio, and how to build a record player, it also contains a map so that any extraterrestrial civilisation will be able to trace the record back to our planet. The map uses the position of 14 pulsars whose precise locations are marked relative to the Sun. The pulsars are identified by their fingerprints – each has a unique and unvarying rate of rotation. The most important piece of content on the cover is the key to unlock the information – a diagram illustrating the spin configurations of a hydrogen atom. The 21cm hydrogen emission line is a fundamental and universal property of nature, a Rosetta Stone that will allow an alien scientist to unlock the secrets of Earth. The disc also contains one last invisible source of information: electroplated onto the surface of the cover is an ultra-pure sample of uranium 238, an isotope with a half-life of 4.468 billion years. This is Voyager’s clock, a way for any civilisation to determine the age of the record, assuming that they aren’t creationists who disagree with radiometric dating. Perhaps these are the sorts of aliens that would also be offended by nudity.
* * *
THE 1977 PLAYLIST
Brandenburg Concerto No. 2 in F First Movement, Bach
‘Kinds of Flowers’ Court gamelan, Java
Percussion Senegal
Pygmy girls’ initiation song Zaire
‘Morning Star’ & ‘Devil Bird’ Aborigine songs, Australia
‘El Cascabel’ Mexico
‘Johnny B. Goode’ Chuck Berry
Men’s House Song New Guinea
‘Tsuru No Sugomori’ (‘Crane’s Nest’), Shakuhachi, Japan
‘Gavotte en rondeaux’ from the Partita No. 3, Bach
Queen of the Night aria, no. 14. The Magic Flute, Mozart
‘Tchakrulo’ Chorus, Georgian S.S.R.
Panpipes & Drum Peru
‘Melancholy Blues’ Louis Armstrong
Bagpipes Azerbaijan S.S.R.
Rite of Spring Stravinsky
The Well-Tempered Clavier Book 2, Bach
Fifth Symphony Beethoven
‘Izlel je Delyo Hagdutin’ Bulgaria
Night Chant Navajo Indians
‘The Fairie Round’ Holborne, Paueans, Galliards, Almains
and Other Short Aeirs
Panpipes Solomon Islands
Wedding Song Peru
‘Flowing Streams’ Ch’in, China
‘Jaat Kahan Ho’ Raga, India
‘Dark Was the Night’ Blind Willie Johnson
String Quartet No. 13 in B flat Beethoven
* * *
For all the thought and care that went into these discs, neither Voyager spacecraft is heading towards any particular star; these tiny craft constructed by human hands will almost certainly never be found. The vastness of space swallows travellers, and of course Voyager’s scientists and engineers knew this. That, however, is not the point; the act of launching these gilded emissaries into space expresses something important. It’s my childhood science fiction dream of living in a Star Wars galaxy filled with life and possibilities. It is a desire to reach out to others, to attempt contact even when the chances are vanishingly small; a wish not to be alone. The golden discs are futile and yet filled with hope; the hope that we may one day know the boundaries of our loneliness and lay to rest the unsettling internal noise that accompanies the enduring silence.
Friends of space, how are you all? Have you eaten yet?
Come visit us if you have time.
Margaret Sook Ching, Voyager Golden Record
ALIEN WORLDS
Let us now return to Frank Drake’s equation and use it as intended, as a framework to address in a systematic manner the question of our solitude. Recall that the equation consists of a series of terms which, when multiplied together, give an estimate of the number of currently contactable civilisations in the Milky Way galaxy. At the 1961 Green Bank meeting only the first term – the rate of star formation in the Milky Way – was known with any precision. Over half a century later, we can do much better. The next term in the equation is the fraction of stars in the Milky Way that have planets orbiting around them – most definitely a prerequisite for an intelligent civilisation to emerge. It’s true that the civilisation may not have remained confined to its home world, and we will discuss this possibility later on. But it must be true that for life to emerge and evolve to the point where it can build spacecraft, a planet of some sort is required.
This space we declare to be infinite …
In it are an infinity of worlds of the same kind as our own.
Giordano Bruno, 1584
The existence of alien worlds has been speculated about for many centuries. Ever since Copernicus began the process of demoting our solar system from its preferred place in the cosmos, it has been natural to assume that at least some of the stars in the sky must have planetary systems. Yet despite this seemingly common-sense conclusion, reached by virtually every right-thinking astronomer from Giordano Bruno onwards, the existence of other planets remained nothing more than an educated guess well into my lifetime. The vast distances between the stars and the limitations of technology locked us inside our own solar system with no way of seeing beyond. Throughout the nineteenth century a number of astronomers claimed to have detected distant planets, but all these observations proved to be flawed.
Today the picture couldn’t be more different; the night sky is known to be awash with worlds. One of the more enticing of the known solar systems is located around a slightly smaller, cooler version of our Sun called Kepler-62. About 1200 light years from Earth in the constellation of Lyra, the system has been widely studied because it has at least five planets. Two of them, Kepler 62-e and Kepler 62-f, are particularly interesting because they are Earth-like in both size and distance from the star. Bathed i
n Kepler-62-shine, these worlds may, if they have the right atmospheric conditions, support oceans of liquid water on their surfaces. We will discuss the significance of this in the context of life later on.
An intrinsically improbable
event may become highly
probable if the number of events
is very great … [I]t is probable
that a good many of the billions
of planets in the Milky Way
support intelligent forms of life.
To me this conclusion is
of great philosophical interest.
I believe that science has
reached the point where it is
necessary to take into account
the action of intelligent beings,
in addition to the classical
laws of physics.
Otto Struve
Human Universe Page 8