by Ben Miller
To try and get a handle on how far away the source was, the team measured the dispersion of the pulses. Dispersion, as you probably know, occurs when higher frequency waves travel faster through a medium than lower frequency ones. The classic example is of white light dispersing into all the colors of the rainbow as it passes through a glass prism. Interstellar space may not be full of glass, but it is far from empty. In fact, the spiral arms of our galaxy sit in a sort of gas of free electrons. Just as glass slows down low-frequency red light more than it does higher-frequency blue light, this “gas” of free electrons slows lower-frequency radio waves more than the higher-frequency ones. Send a pulse through interstellar space, and after a while, thanks to dispersion, the lower-frequency parts of the pulse will start to lag behind the higher-frequency parts. In the case of Bell Burnell’s mystery object, by the time the pulses reached Earth there was a noticeable delay.
By measuring this time delay between the highest and lowest frequencies in the signal, and then using a simple model for the number of free electrons that the pulse had passed through, the team was able to work out how far away the source was. Their calculations placed it well outside the solar system but well within the galaxy, at a distance from Earth of roughly 200 light-years.14
Next, they pondered what the setup of this alien civilization might be. What if the signal was coming from an Earthlike planet which was in orbit around a Sun? What could they test? If the aliens were in orbit, surely their signal ought to be in orbit, too. If it was, sometimes it should be moving away from Bell Burnell’s radio telescope, and sometimes it should be moving toward it. That movement should produce an effect; in fact it’s a commonplace one called the Doppler Effect.
There’s a classic example of the Doppler Effect in the change in pitch of a passing train’s horn. The train horn is producing one note. As it approaches, the sound of that note is pitched up. As it passes, the sound is pitched down. Put in more general terms, when the source of a wave signal is moving relative to a detector, it changes the frequency of that signal.
Was there a Doppler Effect in the signal? To the team’s surprise, there was. Yet it wasn’t due to the motion of the alien signal around some alien Sun. You see, Bell Burnell’s telescope was itself in orbit, around our own Sun. The Doppler Effect that the team measured in the signal turned out to be due to the relative motion of the telescope to the source. As Bell Burnell herself wryly puts it, the team had simply managed to prove that the Earth revolves around the Sun. Reassuring, but of itself not much of a breakthrough.
They did make some progress. Once they had isolated this small Doppler Effect, they could see that the pulses in the signal were extraordinarily regular, with the gap between them varying by less than one part in ten million. That meant that whatever was producing them had a lot of mass, and therefore a lot of energy. If it was aliens, they really meant business. Someone had built themselves a very powerful transmitter indeed.
THE THIRD EYE
Feeling more and more certain that the signal they had found was not the result of some random man-made interference or faulty wiring, and increasingly sure that its source was something massive and extremely compact that was situated well within the galaxy but beyond the nearest stars, Jocelyn Bell Burnell and her team decided to bite the bullet. They would go and ask a rival telescope if they could see it, too.
Keeping it in the family, Hewish approached his colleague Paul Scott and his research student Robin Collins, who were operating a radio telescope at the same frequency. They calculated that the signal should show up in the second telescope just twenty minutes after it appeared in Bell Burnell’s. As soon as the signal appeared in Bell Burnell’s telescope, the team moved over to the second chart recorder. Twenty minutes went by with no signal. Hewish and Scott wandered off down the hall, with Bell Burnell tagging behind, discussing what could possibly cause the signal to appear in the one telescope and not the other. Suddenly, there was a shout from the lab. Robin Collins had hung back, waiting, and there the signal was, pulsing away. They had miscalculated the delay by five minutes. The source was real.
On December 21, 1967, Anthony Hewish and the head of the group, Martin Ryle, held a meeting at the Mullard to discuss what to do about the object they half-jokingly called LGM, as an abbreviation for Little Green Men. If it really was a pulse from an alien civilization, then those aliens were a contrary lot. For a start, the radio frequency of the pulse, 80MHz, seemed an unlikely choice; although perfect for quasars, it happens to be a very noisy frequency.
If Bell Burnell’s Little Green Man was signaling to Earth, or other Earthlike planets, surely he would tune his signal to sit in the microwave window? Instead he had chosen a part of the spectrum where it would most likely get absorbed by gas and dust. Why send a signal at a frequency where it was less likely to be picked up?
Nevertheless, there the signal was, and if science teaches us anything it is to be humble in the face of the facts. If this really was an alien radio signal, who should they tell first? An astrophysical journal, or the Prime Minister?
Bell Burnell returned home for supper decidedly disgruntled. She had spent two precious years of her life wiring up a state-of-the-art radio telescope, ready to search for quasars. Instead, her experiment had been hijacked by a bunch of numbskull aliens. She only had six months of grant money left, and the window for her to finish her PhD and secure some sort of academic career was rapidly closing. As she put it herself, “I was furious. For some reason, some silly lot of green men had decided to use my frequency and my aerial to signal to Earth.”
IN THE BLEAK MIDWINTER
That evening, Bell Burnell returned to the lab, determined to get back on track. A backlog of 2,500ft of chart paper had built up and was begging for analysis. Just before 10.00 p.m., when the lab was due to shut, she was looking at a section that belonged to the constellation of Cassiopeia when she thought she spotted some more “scruff.”
Hurriedly, she laid out all the other bits of chart paper she could find that corresponded to Cassiopeia. There the “scruff” was again. The timing couldn’t be more acute. The next day she was going back home to Ireland for Christmas to announce her engagement. Calculating that the patch of sky she wanted would be in the telescope at around two o’clock in the morning, she decided on no sleep till Belfast, and headed over to the observatory.
This being the dead of winter, the equipment was cold and temperamental, but Bell Burnell “breathed on it and swore at it, and I got it to work at full power for five minutes. It was the right five minutes and at the right setting. In came a stream of pulses, this time at intervals of one-and-a-quarter seconds, not one-and-a-third.”
That settled it. There was no fault with the equipment, no man-made interference; there was something out there in the stars. And it couldn’t be Little Green Men. After all, what were the chances that there would be two lots of Little Green Men on opposite sides of the universe, both signaling at an obscure frequency to our little blue planet? Unlikely as it seemed, somewhere out there in the galaxy were massive, compact objects that produced pulses of radio waves. Jocelyn Bell Burnell had discovered the pulsar.
JOURNEY TO THE STARS
That might seem an anticlimax—we are hunting for aliens after all—but to my mind it’s glorious. Null results might be the bane of pseudoscience, but they are a boon to science. No matter how much we want aliens to be out there, we have to go by the evidence. If SETI ever does pick up an alien radio signal, we can guarantee it will be subjected to the same kind of scrutiny that Bell Burnell’s pulsar was, and that is a very good thing indeed. As the late Oliver Sacks put it: “Every act of perception is to some degree an act of creation, and every act of memory is to some degree an act of imagination.” When it comes to things we dearly want to believe, we have to be on our guard.
A pulsar is like an enormous lighthouse: a fast-spinning, highly magnetized ball mostly made up of densely packed material rich in neutrons, radiating a beam of electr
omagnetic radiation into space. They are the highly compressed corpses of large stars, formed after they have run out of fuel and exploded as supernovae. Each is unique, with its own distinctive type of radiation and pulse rate. Since Jocelyn Bell Burnell discovered them, we have found pulsars which spin so fast there are millisecond gaps between pulses. We have found still others whose “beam” is made of x-rays, and others where it is visible light.
As we know, when NASA launched the Voyager 1 probe, etched on to the casing of the Golden Record was a map showing the position of the Earth relative to its fourteen closest pulsars, with the pulse period of each pulsar coded in binary.15 If ever an alien intelligence intercepts it and comes to pay us a visit, Bell Burnell’s pulsar will be one of the landmarks that guides them here.
CHAPTER THREE
PLANETS
In which the author searches for Earthlike planets, learns about the Wow! Signal, and takes a stroll around Vienna with the UN Ambassador for the Human Race.
There is something oddly futuristic about the United Nations. Though the squat Arrivals building of its Vienna offices bears more than a passing resemblance to my low-rise 1970s primary school, the enormous courtyard I step out into is unfeasibly impressive. Everything about the place should seem dated: the mountains of grey concrete; the jet fountains that strafe an enormous shallow circular pool; the towering Cold War-style flagpoles; but instead the overall effect is of vertiginous progress. The trappings may all be mid-twentieth century, but the very existence of a super league of sovereign nations, united in the common interest of mankind, still seems like pure science fiction.
And it’s this unique position in the world of human affairs that interests me today, because it’s been widely reported in the British press that thanks to the recent discoveries of Earthlike planets by the Kepler Space Telescope—and the possibility that they might harbor intelligent life that we can make radio contact with—the UN is appointing a spokesperson for the human race. This “Ambassador for Earth” has been named by no less a newspaper than the UK’s Sunday Times as one Dr. Mazlan Othman of the United Nations Office for Outer Space Affairs (UNOOSA), and I have an appointment to meet her for lunch.
Yet as I mount the stairs to Dr. Othman’s office, the strong scientific imperative for my visit suddenly evaporates. This is the opposite of “l’esprit d’escalier,” a phrase nonexistent in French but which we English take to mean the inspiration which strikes as soon as an encounter is over and we are heading down the stairs on our way home. The more floors I climb, the drier my mouth gets and the sweatier my brow becomes, until all confidence in my mission has completely drained away.
In the world of extraterrestrial intelligence, this discomfort is commonplace, and is known simply as “the giggle factor.” For some reason, when talking about the very real, scientifically sound possibility of communicating with aliens, everyone gets the urge to laugh. And here, where national flags flutter at the tops of impossibly tall flagpoles, and where international diplomats negotiate the gravest of choices while pursuing the loftiest of ambitions, what on Earth do I think I’m doing asking the UN’s head space executive about flying saucers?
It doesn’t help that Dr. Othman has an extremely impressive CV. Malaysian by birth and an astrophysicist by training, in the early noughties she spearheaded the Malaysian space program, ANGKASA, and built a space observatory on the island of Langkawi, launched a remote-sensing satellite, RazakSAT, in the world’s first near-equatorial Low Earth Orbit, and oversaw the launch of the first Malaysian astronaut to the International Space Station in 2007. Since then, she has served as the Director of UNOOSA, and was appointed Deputy Director-General of the United Nations Vienna Office in 2009.
I needn’t have worried. Once I have sweated and spluttered my way past her secretary in a manner even Hugh Grant would think was exaggerating, Dr. Othman greets me warmly, blaming the layout of the UN rather than my terrible sense of direction, and is disarmingly relaxed and informal. She leads me through to her office, a bright and breezy affair with a spectacular view across the Danube toward the Old City. Her desk sits in the far corner, half obscured by a jungle of luscious potted plants and, to my right, a sideboard displays glittering scale models of satellites and space stations.
We sit, and I do my best to try and convince her that I am not a crazy person, that I know my stuff about science, and that, while I think the evidence for UFOs is feeble, I am very interested in the possibility that there is intelligent, communicable life on other planets. I state my belief that biology is as universal as chemistry and physics, and that the recent discoveries of the Kepler Space Telescope have shown us plenty of places where that biology might get a chance to do its thing. In short, I do everything I can to try and reassure her that I am an emotionally well-balanced, scientifically literate individual with a passion for astrobiology. And, in doing so, I am fairly sure that I come across as a crazy person.
When I finally pause for breath, I see that the Director of the United Nations Office for Outer Space Affairs has a twinkle in her eye. “Come on,” she says. “Say it. You want to talk about aliens.”
TWINKLE TWINKLE LITTLE PULSAR
Strange as it now seems, as little as twenty years ago we still had no hard evidence that planets existed outside our own solar system. As an undergraduate student in the late eighties, I remember feeling very excited by reports that a planet had been discovered orbiting Gamma Cephei, a binary star some forty-five light-years away in the northern constellation of Cepheus.1 This seemed almost too good to be true. One of the most iconic moments of the first Star Wars movie had been Luke Skywalker looking out from his home planet, Tatooine, at two setting suns. Could it be that this new planet, like Tatooine, was a lawless desert world, blasted by the heat of two stars, where humanoid beings farmed moisture in underground dwellings? What else had George Lucas got right? Is it really possible to dodge a blast from a laser gun?
Sadly, though the first reports of this first planet were published in 1988, the year I began my PhD, they were then retracted in 1992, the year I turned professional as a comedian.2 I only hope there was no connection. If there was, I needn’t have worried, because that same year Aleksander Wolszczan and Dale Frail, working at the Arecibo Observatory in Puerto Rico, found the first bona fide planet in the constellation of Virgo. In fact, they found two, orbiting at roughly half the distance that the Earth orbits the Sun. Only they weren’t orbiting a star. They were orbiting a pulsar.
That, obviously, was not what we were expecting at all, and I doubt that Frank Drake was straining at the leash to point a radio telescope at PSR B1257+12 to try and pick up a message. For a start, it’s a thousand light-years away, so the conversation would be a little stilted. And, secondly, pulsars are awesome things, but for life as we know it, being blasted by x-rays is always going to have its drawbacks.
Then finally, in 1995, we discovered 51 Pegasi b, the first planet orbiting a Sun-like star. That wasn’t quite what we were expecting either. Fifty light-years away in the constellation of Pegasus, it was half the mass of Jupiter, but extremely close to its home star, taking only 4.2 days to complete an orbit. How had it gotten so close? After all, in our own solar system it’s small rocky planets like Mercury, Venus, Earth, and Mars that sit close to the Sun. Gas giants like Jupiter and Saturn roam much farther out, and medium-sized icy stuff like Uranus and Neptune sit out in the boondocks. Could it be possible that, in some solar systems, planets didn’t stay put?
Once someone had found something that was definitely a planet, the floodgates opened. Radio astronomers every- where tried to get in on the act, and all manner of planets turned up. Many of them, like 51 Pegasi b, were so-called “Hot Jupiters”: large gas planets tucked up close to their home stars. Others were so-called “Hot Neptunes”: medium-sized planets that had also migrated into tight orbits. Still others were truly monstrous creations patrolling at unfeasibly large distances.3 What we didn’t find was anything like the Earth.
Which is to say we found nothing Earth-sized that was an Earth-type distance from a Sun-like star. One of the things we think makes Earth such a good home for life is the fact that most of it is covered in water. In fact, astronomers define something called the habitable zone, which means the range of orbits where the temperature of an orbiting planet is going to be neither so hot that water simply vaporizes (such as on Mercury and Venus) nor so cold that it freezes (such as on Mars). In the official jargon, we couldn’t find any Earth-sized planets in the habitable zone of their home star. Could it be that, far from being mediocre, the Earth was incredibly special?
Formally, this became known as the Rare Earth Hypothesis. Microbial life might be common, the argument went, but intelligent life is rare because planets like the Earth are rare. After all, many things conspire to make the Earth ideal for life. Firstly, it’s a good size. Much smaller, and its gravity would be too weak to hold on to an atmosphere, and without a decent atmosphere there would be no greenhouse effect to keep the surface warm. This, of course, is the problem with Mars, which has only been able to hold on to the thinnest of atmospheres.
Secondly, it’s volcanic. As we shall shortly see, one of the most promising hypotheses for how life got started depends on volcanic springs, and, in any case, the gases released and consumed by the rock cycle play a vital role in maintaining a life-friendly carbon dioxide–rich atmosphere. Not only that, but plate tectonics also ensures that heavier elements like metals get recycled into the oceans and atmosphere, providing lots of esoteric chemistry that life can make use of.
Thirdly, the Earth has a strong magnetic field. Not only is that handy if you are trying to find your way around, but it means that we are protected from the hail of damaging radiation known as the solar wind. Fourthly, it has a large Moon, which not only slows its rotation, giving milder weather, but keeps the Earth’s axis pointing in the same direction. Without a Moon, the Earth’s spin axis might flip, wreaking climatic havoc. And, finally, it has Jupiter as a cosmic vacuum cleaner to protect it from comets.4