Hello, is there anybody out there?

 

Hello, is there anybody out there?

 WHETHER we are alone in the universe is one of the oldest questions humans have pondered.

Drew Barrymore as Gertie says an alien goodbye in ET: The Extra-Terrestrial. Picture: AP Source: AP

 

Posted 03 August 2011, by Paul Davies, The Australian (News Limited), theaustralian.com.au

 

For most of history, it has belonged squarely in the provinces of religion and philosophy. In recent decades, however, scientists also have been attracted to the problem in increasing numbers. Fifty-one years ago, a young astronomer by the name of Frank Drake began sweeping the skies with a radio telescope in the hope of stumbling across a message from an alien civilisation. Thus began SETI — the Search for Extraterrestrial Intelligence — an ambitious enterprise to survey thousands of sunlike stars in our neighbourhood of the Milky Way galaxy for any signs of artificial radio traffic.

When SETI began in 1960, it was regarded as quixotic at best, crackpot at worst. “A quest of the most adverse odds,” was the way distinguished biologist George Simpson expressed it. The prevailing opinion among scientists was that life was the result of a chemical fluke so improbable it would be unlikely to have happened twice in the observable universe. “Life seems almost a miracle,” wrote Francis Crick, the co-discoverer of the structure of DNA. It was echoed by another Nobel prizewinning biologist, Jacques Monod, in a bleak assessment: “Man at last knows that he is alone in the unfeeling immensity of the universe, out of which he emerged only by chance.”

In one of the most astonishing shifts of scientific fashion, the consensus today is that the universe is teeming with life. Christian de Duve, the Belgian-born biologist and another Nobel prizewinner, has gone so far as to call life a “cosmic imperative”, believing it is “almost bound to happen” on any Earth-like planet. And where there is life, intelligence may eventually follow. In the 1990s, US space agency NASA created an astrobiology institute to co-ordinate the burgeoning program of research into the origin, distribution and evolution of life in the universe. Although wary of directly funding SETI, NASA nevertheless enthusiastically embraces it under the broader astrobiology umbrella.

Despite this sea change in thinking, there is still not a shred of evidence for any life beyond Earth, intelligent or otherwise. Instead of the hoped-for clamour of interstellar messages, there is only an eerie silence. Why, then, the upbeat assessments from so many scientists? Part of the reason is the spiralling number of planets being discovered orbiting other stars. Hundreds have been detected using modest ground-based telescopes, and still more from a customised satellite named Kepler. Planets are not imaged directly but inferred through the way they blot out light as they cross the face of the parent star or cause a detectable wobble in the star from the tug of gravity. Although Earth-like planets are harder to detect and remain elusive, estimates suggest that our galaxy alone may contain more than one billion. So there is plenty of real estate for life.

It is a fallacy, however, that habitable is the same as inhabited. To be sure, a planet should be reasonably like Earth to support life, at least life as we know it. But that is far from sufficient. The problem concerns the origin of life and the actual probability that it will emerge on a typical Earth-like planet. A century and a half ago, Charles Darwin explained how life has evolved across billions of years from simple microbes to the richness and complexity of the biosphere we see today. But he pointedly left out of his account how life got going in the first place. “One might as well speculate about the origin of matter,” he quipped.

Unfortunately, the science of biogenesis has progressed very little since. We still have no idea of the pathway that led from non-living chemicals to the first living cell. In fact, we may never have a blow-by-blow account of life’s origin; it happened so long ago that all traces must have been obliterated. But to answer the question about the prevalence of extraterrestrial life we merely need to know whether the transition from non-life to life is probable or improbable.

Carl Sagan, the charismatic American astronomer and ever the optimist, believed that life must arise easily because it started on Earth rather quickly. Our planet was born 4.5 billion years ago amid a disc of gas and dust swirling around the proto-sun. But for hundreds of millions of years it was pounded by giant asteroids, some big enough to boil the oceans in the aftermath of their impacts. Yet there is good evidence from Western Australia that by 3.5 billion years ago life was already well established.

Sadly, Sagan’s argument is flawed. Our planet will become uninhabitable in less than a billion years when the sun swells up as it starts to run out of fuel. Unless life had started quickly, intelligent beings like us may never have had time to evolve to ask questions like “Are we alone?” before biology got snuffed out. It is therefore impossible to argue, from a sample of one selected by our very existence, that life will always pop up readily on earthlike planets.

Some people pin their hopes for settling the matter on scientists making life in the lab. In 1952 the University of Chicago chemist Harold Urey persuaded a student, Stanley Miller, to try to recreate the conditions of the early Earth inside a flask. Miller sparked electricity through a mix of common gases and water, and found that his “primordial soup” could make the building blocks of proteins within a few days. For a while, Miller’s experiment looked like the first step on the road to life. Unfortunately subsequent steps have proved a lot harder, and most experiments in pre-biotic chemistry seem to lead to blind alleys. The fundamental problem is that even the simplest living cell is already so fiendishly complex it’s hard to imagine how it could have arisen simply from more of the same Miller-Urey processes.

It is worth contrasting Miller’s experiment with the work of a new breed of “synthetic biologists” such as Craig Venter, who helped sequence the human genome. Venter and his colleagues have succeeded in making novel microbes by inserting customised DNA into existing living cells. This work is often misrepresented as life created in the proverbial test tube, but it is very far from that. Rather, synthetic biology seeks merely to redesign existing life by modifying its genetic instructions, not to make life from scratch out of basic chemicals.

The latter prospect is a very long way off, and even were it to succeed, it would still fall short of proving that life arises readily.

It is one thing to make life in a laboratory with all sorts of fancy equipment operated by an intelligent designer, quite another for it to emerge spontaneously from a grubby sludge on the sea bed — or wherever it first began.

The popular belief that life starts easily in earthlike conditions would immediately be verified if we were to find a second sample of it. Many astrobiologists think Mars offers a possibility. The red planet has been a favourite abode for life since the astronomer Percival Lowell thought he had glimpsed canals on its surface and H.G. Wells wrote War of the Worlds in 1898. In the 1970s NASA decided to put the matter to the test by sending two spacecraft called Viking to land on the Martian surface, each equipped with experiments to sniff out microbes in the soil. The landers found a freeze-dried desert of highly oxidising dirt bathed in deadly ultra-violet radiation and protected by a very thin atmosphere.

In spite of the hostile conditions, one of the experiments gave a strikingly positive result. Designed by the organic chemist Gil Levin, it used an ingenious technique to detect if any bugs in the dirt were eating a nutrient broth, by looking for radioactively tagged carbon dioxide being given off as waste.

The experiment worked repeatedly at both landing sites, but returned null results when the dirt was strongly heated, as might be expected if Martian microbes were killed by the elevated temperature. To this day, Levin maintains that he found life on Mars, but most astrobiologists are sceptical, partly because the other Viking experiments were negative or ambiguous, and partly because one cannot rule out reactive soil chemistry mimicking the results.

Even if Mars is a dead planet today, it may not always have been so. Survey photographs from a series of high resolution orbiters show a dramatic landscape sculpted by liquid water. Rivers, flood plains, gullies, lakes and shorelines are conspicuous in the topography. On-the-ground analysis reveals water ice in the polar caps, and fluvial features in the rocks. Clearly, in the far past Mars was warmer and wetter than today, probably the result of massive greenhouse warming from an early thick atmosphere of carbon dioxide, now mostly leaked away into space. Hopes remain high that Mars once hosted life, though probably no more complex than bacteria.

In 1996 US president Bill Clinton electrified the world’s press when he stood on the White House lawn and announced that NASA had evidence of life on Mars in the form of a meteorite found in Antarctica, containing blobs that resemble tiny bacteria. From time to time, Mars takes a hit by an asteroid or comet with enough force to propel rocks into space. A fraction of this ejected debris eventually lands on Earth; Clinton’s meteorite was one of these rocks, purportedly containing fossilised microbes. However, after years of follow-up studies, the evidence for ancient life inside the meteorite is very tenuous.

Unless we get lucky and find clearer evidence in another meteorite, the best hope for detecting traces of life on Mars rests with a sample return mission. The plan is to send a spacecraft that will garner a rag-bag of rocks and convey them back to Earth for detailed analysis. Unfortunately this ambitious scheme has stalled for lack of funding and exaggerated concerns that the harvested rocks might harbour living microbes that could trigger a killer plague or some other calamity if exposed to Earth conditions.

Although the prospects for extant life on the Martian surface, if not quite zero, are nevertheless slim, it remains possible that deep underground pockets of microbes may still eke out a living in briny aquifers warmed by the planet’s internal heat. Sketchy evidence for seasonally varying gases exuding from the permafrost could point to methane-producing subsurface organisms like those in similar locations on Earth. In the longer term, a future manned expedition to Mars may offer the best hope for settling the issue.

Even if we did obtain irrefutable evidence for microbes on Mars, it would not of itself prove that life is a cosmic imperative, enjoying multiple origins. The problem concerns the traffic of Martian rocks to Earth, which has been going on throughout the history of the solar system. Cocooned inside a rock, protected from the harsh conditions of space and shielded from deadly radiation, a microbe could probably survive the journey between the two planets, even if it took millions of years. It is very likely that if life did get going on Mars billions of years ago when conditions were still favourable, then it will have spread to Earth in this manner. Indeed, it is possible that life on Earth started on Mars and came here inside Martian meteorites. And just as Mars may have seeded Earth with life, so Earth may have seeded Mars with life, because our planet too suffers impacts that fling rocks into space. The natural cross-contamination of Earth and Mars via traded rocks complicates the story of life’s origin. If we do find evidence for life on Mars, it may be the same as earth life and point to a single common origin.

The search for a second genesis of life may not require anything as expensive and challenging as a Mars expedition, however. No planet is more earthlike than Earth itself, so if life does start up readily in earthlike conditions, wouldn’t it have begun many times on Earth? Could there be traces of a second sample of life right here?

Biology textbooks claim that all life on Earth is descended from a common ancestral form.

Evidence cited includes many identical features in life’s basic machinery, such as the universal genetic code that implements the instructions contained in the four-letter alphabet of DNA. But while it is true that all life so far studied seems to be related, we cannot be sure that fundamentally different forms of life may yet be discovered.

The vast majority of terrestrial organisms are microbes, and we have only just scratched the surface of the microbial realm. You can’t tell by looking what makes a microbe tick — you have to study its biochemical innards. It is entirely possible that, intermingled with bacteria and other microbes that lie on the same tree of life as you and me, are some microbial life forms that are radically different — so different that they belong not just to another branch on the known tree of life, but to a separate tree altogether, with an independent origin. In other words, it would be life, but not as we know it.

The idea that Earth hosts more than one form of life, while highly speculative, has nevertheless gained some traction in recent years, and is often dubbed the “shadow biosphere”, or Life 2.0. Easiest to spot would be if Life 2.0 occupied a habitat beyond the reach of the hardiest organisms of known life. And known life boasts some pretty bizarre representatives. Microbes have been found living near deep ocean volcanic vents that thrive in temperatures above 120C. Others tolerate extremes of salt, acidity, alkalinity or radiation. Nevertheless, all these “extremophiles” are adaptations of known life. If microbes were found living at, say, 180C, these would stand out as candidates for Life 2.0.

Much harder would be if the shadow biosphere interpenetrated the familiar biosphere. In that case Life 2.0 microbes might be all around us, unidentified for what they are, and unresponsive to standard biochemical analysis. If we did find Life 2.0 here on Earth, it would greatly boost the search for life in the universe, because it would be unlikely that life would have started twice on one earthlike planet and not at all on all the others.

Meanwhile, we should expand our search for ET beyond looking for customised radio messages beamed at Earth. Any signature of alien technology would serve to answer the question of whether we are alone in the universe. One possibility is to look for radio or optical beacons. An advanced civilisation might build a beacon to sweep the Milky Way every few months or years, perhaps as a monument to its greatness, a means of attracting attention, or even as a warning.

A radio beacon would show up as a transient pulse, or series of pulses, repeated periodically. Bursts of radio waves from deep space have been detected, but without follow-up to see whether they are repeated, their origin remains unknown. We could also look for signs of large-scale astro-engineering. All technology has an impact on its environment; for example, global warming from human industry could be detected from light years away.

A very advanced alien community might have left an imprint, not just on its planetary environment, but on its astronomical neighbourhood too. Telltale signs could be artificial structures, the depletion of resources or the accumulation of waste, all of which might be detectable through changes in the light from the parent star.

An even more exciting, but yet more speculative possibility, is that one or more alien civilisations has spread beyond its home planet out into the galaxy, most likely through robotic probes or self-reproducing machines. It is conceivable our own corner or the galaxy has been visited, an idea popular among UFO enthusiasts and science fiction writers. When might this have happened?

At 4.6 billion years, our solar system is about a third of the age of the galaxy; stars and planets existed long before Earth formed. If intelligent life is indeed common, then there may be planets that hosted advanced civilisations billions of years ago. If one of these civilisations sent spacecraft to the solar system, there is no reason it would have been in the recent past. Most likely it was a very long time ago — say, 100 million years. That raises the fascinating question of what physical traces, if any, would survive for 100 million years, even if they were right here on Earth.

Three possibilities come to mind. Nuclear waste, perhaps from a nuclear-powered craft, if dumped on Earth or the moon would still be detectable 100 million years later in form of decay products. Large-scale mines or quarries, though buried beneath overlying rock strata, would show up in geological surveys. On the moon they might be visible from simple photographic surveys of the sort now being carried out by NASA’s Lunar Reconnaissance Orbiter. Most tantalising of all, products of alien biotechnology, such as tinkering with the genomes of terrestrial organisms or even the creation of a non-competing shadow biosphere of Life 2.0 organisms, could be found by microbiologists today. My favourite is the message in a bottle, created in the form of an engineered series of letters etched into microbial genomes, which might show up during routine gene sequencing research.

Although all these extreme ideas, entertaining though they may be, almost certainly represent a wild goose chase, they may nevertheless be pursued for very little money. For example, genomes are being sequenced anyway and it costs nothing to do a computer search for anything fishy. And cost is the dominating factor when doing highly speculative science. The jewel in the crown of mainstream SETI is a dedicated bank of smallish radio telescopes part-paid for by Paul Allen, the co-founder of Microsoft. Sadly, in spite of his $US31 million investment, the project lacks a partner to fund the $US2m ($1.86m) a year running costs, so the Allen Telescope Array has been hibernated to await better financial times.

SETI is undeniably a long-shot, but it is one worth undertaking. Looking for alien civilisations is really, in the words of its founder Frank Drake, a search for ourselves, who we are and how we fit into the great cosmic scheme of things. It is a subject that compels us to address the great questions of existence What is life? What is intelligence? Is the universe bio-friendly? What is the destiny of mankind? A society that is too mean-spirited to spare a minuscule fraction of its resources to reflect on its place in the cosmos is a society with an unpromising future.

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