The FT Of London Has An Excellent Article On Finding ET

Science: Transmission mission

By Clive Cookson

Published: December 23 2010 23:34 | Last updated: December 23 2010 23:34

Anybody out there: the plaque Nasa sent into space in the 1970s, comprising encoded date about humans, Earth and our solar system (behind); and how aliens might respond (for a decryption, see below)

You might expect Frank Drake to feel he has wasted his professional life on the search for extraterrestrial intelligence (Seti). Fifty years after he put Seti in motion, pointing the Green Bank radio telescope in West Virginia at two nearby stars to listen for signals from an alien civilisation, we are still waiting to detect even the faintest squeak that cannot be explained by natural processes.

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Yet Professor Drake, today an elder statesman of astronomy, feels far from a failure. He is proud to have helped to build up Seti from a flaky fringe activity into a serious scientific endeavour – which he is confident will sooner or later hear from ET.

“It is only a matter of time,” he says. And when the time comes the discovery will make more impact on humanity than any other in the history of science, he adds: “This will certainly enrich our lives like nothing else could.”

Even astronomers who are far less optimistic than Prof Drake about the prospects of hearing from ET believe an expanded Seti is worthwhile because the pay-off – from sheer intellectual satisfaction to the prospect of practical advice from a more advanced civilisation – would be so great. And the costs of listening in are far lower than exploring space by voyaging out from Earth.

“It would be crazy to give up now after spending 50 years tuning up for a really effective search,” says Paul Davies, a cosmology professor at Arizona State University, who thinks the prospects of success are low.

Two factors are providing extra impetus as the search begins its second half-century. One is technological: new radio telescopes will give astronomers a better chance of picking up that elusive extraterrestrial radio signal. Increasing computing power improves the prospect of picking out any alien signal from the radio “noise” generated by myriad natural and man-made sources. “The speed of the search is doubling every 18 months,” says Seth Shostak, senior astronomer at the Seti Institute in California.

ALIEN MESSAGES DECODED

Communication decoded (anticlockwise from top left): an alien rendering of the atomic spectrum shown on the Nasa plaque; a depiction of radio waves travelling through space; the species’ genes hybridised with those of others; what the species looks like; the alien’s planetary system; commonly reported Ufo shapes; a star circled by the species’ spacecraft; and, in Morse code, an ominous message: ‘Resistance is futile’

The other factor is scientific. Life must presumably start on a planet orbiting a star that keeps it in the “Goldilocks zone” – not too hot and not too cold – just like the Earth and the Sun. Until 1995 there was no scientific proof that any planets existed beyond our solar system, though theories of star formation suggested they would be plentiful. In the past 15 years, however, astronomers have been discovering extrasolar planets at an accelerating pace.

More than 500 planets are already known, and planet-spotting telescopes such as Nasa’s Kepler space observatory are expected to add hundreds more, including many whose size and position with respect to their parent star make them potentially habitable. They will be targets for Seti, which has until recently had to listen in to stars without knowing whether they had orbiting planets.

As things stand, we cannot be sure that even the simplest micro-organisms exist beyond Earth. But growing evidence suggests that life is widely distributed through our Milky Way galaxy. This comes not only from the knowledge that extrasolar planets are widespread but also from the discovery that molecular building blocks of biology, such as amino acids, are abundant in interstellar dust.

SIGNALS FROM SPACE

The intergalactic rules: if ET calls, should Earth call back?

To beam or not to beam? The question is whether to make the search for extraterrestrial intelligence a two-way process by deliberately transmitting messages from Earth as well as listening for incoming signals.

Some scientists warn that it could be suicidal to draw attention to ourselves. They worry about the risk of attracting predatory aliens.

For example, Stephen Hawking, the Cambridge university cosmologist, made a plea this year for terrestrial radio silence in a Discovery Channel documentary.

“Advanced aliens would perhaps become nomads, looking to conquer and colonise whatever planets they can reach,” he cautioned.

Others dismiss such fears as absurd. “The danger is minuscule,” says Professor Paul Davies of Arizona State University. “Fear of the unknown is understandable but if we always wait until there are no demons lurking we would never do any science and never explore our world.”

Intelligent aliens would know already that there was life on Earth from our oxygen-rich atmosphere – and probably by directly imaging our planet – even if they did not pick up the undirected radio leakage from human radar, broadcasting and telecommunications.

Some radio-astronomers, such as Russia’s Alexander Zaitsev, have sent out deliberate messages to any extraterrestrial civilisations that happen to be listening. These are short descriptions of Earth and its inhabitants, written in a simple mathematical code – essentially electronic versions of the famous plaque that Nasa sent into interstellar space on the Pioneer 10 probe in the 1970s.

The pressure to transmit will intensify if planet-hunting observatories discover a world whose atmosphere shows signs of biological activity, says Tim O’Brien, head of Britain’s Jodrell Bank radio telescope: “I’m sure there will be a lot of people sending signals to it, even if we don’t know it has intelligent life.”

Actually receiving a signal from an extraterrestrial civilisation would transform the situation. Of course, humanity’s response would depend on the content of the message – whether it was directed specifically at us or at any intelligent civilisation that happened to pick it up, and whether its tone was friendly, neutral or hostile.

The UN recognises recommendations about Seti (Search for Extra-Terrestrial Intelligence) formulated by the International Academy of Astronautics, a professional body for space exploration. The current IAA declaration of principles states: “No transmission in response to a signal or other evidence of extraterrestrial intelligence should be sent until appropriate international consultations have taken place.”

But Prof Davies, who chairs the IAA Seti post-detection taskforce, admits: “Unfortunately history gives me very little confidence in the efficacy of ‘international consultations’.”

In reality, if we received a signal, the media frenzy would probably generate a plethora of terrestrial responses with varying degrees of official sanction – which might be just what was needed to give ET an accurate sense of the diversity of human opinions.

While the laws of organic chemistry suggest that simple life must have started on many planets, science still has little to say about the likelihood of a technologically advanced civilisation eventually evolving from primitive precursors such as single-cell microbes – a process that took more than 3bn years on Earth.

In the 1960s, Prof Drake formulated his famous Drake equation to estimate the number of intelligent civilisations from which we might receive a signal. This equation has seven factors: the number of stars in our galaxy; the proportion of stars with planets; the proportion of planets that are habitable; the proportion of habitable planets on which life starts; the proportion of planets on which simple life evolves into advanced civilisation; the proportion of civilisations that communicate over interstellar distances; and the average lifetime of a communicating civilisation.

The number of stars in our galaxy is about 400bn – and if we look beyond the Milky Way to the whole universe the stellar count is 300,000bn-bn, according to the latest estimate from US astronomers this month. There must be many umpteen billions of planets, but the other factors in the Drake equation remain speculative.

Prof Drake, who works at the Seti Institute, estimates that the answer to his own equation is that there are 10,000 potentially contactable civilisations out there. Many astronomers, including supporters of Seti, would come up with a much lower number.

“Although simple life will arise widely through the galaxy, I think it takes a very special arrangement of star, planet and Moon to provide the long-term stability for complex and then intelligent life to evolve,” says Ian Morison of Manchester university’s Jodrell Bank observatory.

Earth has been an extraordinarily benign biological environment for several reasons, besides its favourable distance from the Sun. Our large Moon stabilises the globe’s rotational axis, providing equable temperatures that oscillate very little over time. An unusually thin crust permits plate tectonics, a geochemical mixing process that has helped maintain an atmosphere favourable to biology. Our solar system contains few interplanetary bodies large enough to hit Earth and put an end to life.

. . .

How might we detect an extraterrestrial civilisation when we know absolutely nothing about it? Most scientists believe it will have to be done at a distance because interstellar travel costs so much in time and energy. They discount the claims of ufologists and alien abduction enthusiasts that extraterrestrials are among us now, though Prof Davies says we should not rule out completely the possibility that they have visited Earth at some point within the past few hundred million years. Aliens might even have left behind some sign to be detected or activated by a future terrestrial civilisation – anything from a watermark in the DNA of living creatures to an artefact on an asteroid or the moon, as in 2001: A Space Odyssey.

When Seti started, the obvious method of long-distance detection was by radio – and radio telescopes still dominate the search, looking either for “here we are” signals deliberately beamed by aliens or for radiowaves leaking inadvertently, like the television and radar transmissions that have been travelling out from Earth for about 70 years.

Many radio telescopes have been used for Seti, and a dozen are taking part in a co-ordinated worldwide search (called Project Dorothy to mark the 50th anniversary of the original search, which Prof Drake named Project Ozma, in homage to a princess from the Oz novels by L. Frank Baum). While publicly funded observatories must devote most of their resources to less speculative astronomy projects, the Allen Telescope Array in California has been designed specially for Seti. Its first phase, comprising 42 receiver dishes funded by a $25m donation from Microsoft co-founder Paul Allen, started operating in 2007.

But Prof Drake concedes radio may be a less desirable search medium than 50 years ago. Earth itself has become a quieter radio object as more efficient, less powerful systems replace previous sources of radio leakage. For example 20th-century terrestrial television transmitters, which sent a megawatt of radio energy into space, are disappearing as low-power digital, cable and satellite TV take over. “Very soon our Earth will be­come undetectable,” says Prof Drake.

While he remains enthusiastically involved in radio searches, he is also among the astronomers developing “optical Seti” as an alternative. This aims to detect bursts of laser light carrying signals from an alien civilisation. Such a civilisation could use a laser similar to technology already available on Earth to send a directed flash so intense that for a billionth of a second it far outshines its parent star. Several optical Seti projects are under way, using adapted telescopes to scour the sky for unexpected bursts of light with data content.

“We have to use ourselves and our technologies as a model for an extraterrestrial civilisation,” Prof Drake says. But of course more advanced civilisations may communicate via exotic particles and forces that are literally beyond our current comprehension.

Prof Davies, whose sceptical book about Seti, The Eerie Silence, was published this year, says scientists should not be afraid to draw inspiration from science fiction. He favours supplementing the communications-based searches with a much broader look for signs of super-advanced life through the universe. For example, almost any large scientific database – from pictures of the lunar surface to the human genome – could be scoured with special searchware to look for “suspicious patterns” that might have been inserted by alien intelligence.

Another “new Seti” approach is to look for distant signs of stellar engineering. An energy-hungry supercivilisation might, for instance, build a “Dyson sphere” around a star to trap and use its output of light and heat. This swarm of particles or satellites (named after the futurist Freeman Dyson) would alter the star’s normal radiation spectrum sufficiently for astronomers to identify the change from the other side of the galaxy.

“These ideas are very long shots,” says Prof Davies, “but are they longer shots than traditional Seti?”

However, Prof Drake is content to pursue the search through radio and optical communications. At the age of 80, the father of Seti is not confident that extraterrestrial intelligence will be found in his lifetime. “Our best calculations tell us that, even with our present very powerful equipment, the discovery is probably decades away,” he says. “On the other hand we could with very good luck chance upon a signal tomorrow.”