WHO, GAZING AT THE STAR-lit sky, has not wondered whether there is anyone “out there?” From the philosophers and theologians of the past to the scientists and science fiction writers of today, this question has not ceased firing imaginations, feeding speculations, and fueling debates; it has now become a legitimate object for the scientific enterprise.
More than 2,000 years ago, the Roman poet and philosopher Lucretius reasoned that ours cannot be the only inhabited world. “Confess you must,” he wrote in his De Rerum Natura, “that other worlds exist in other regions of the sky, and different tribes of men, kinds of wild beasts.” For agreeing with Lucretius, the Dominican friar Giordano Bruno paid with his life in 1600, burned at the stake on a Roman piazza, by order of the Inquisition.
Extraterrestrial civilizations made a dramatic entrance into science in 1877 when the Italian astronomer Giovanni Schiaparelli proposed that the lines detected on the surface of planet Mars by his colleague Angelo Secchi were artificial waterways. Intrigued by this notion, a wealthy American astronomer, Percival Lowell, built a special observatory in Flagstaff, Arizona, for the sole purpose of studying Mars. He mapped many of the alleged canals and conjectured how the Martians had dug them to irrigate the surface of the barren planet with water tapped from the poles. This idea, in turn, caught the imagination of the British writer Herbert George Wells, who had the Martians invade Earth in his War of the Worlds (1898), which was adapted for radio 40 years later by the American movie director and actor Orson Welles, causing widespread panic when the piece was first broadcast on Halloween eve, 30 October 1938. Mars is still very much in the news today, but no longer as the site of an extraterrestrial civilization, whether friendly or menacing. The Martian waterways indeed exist, but they have been dry for more than three billion years, and they were dug by nature, not by little green men. Whether their banks ever bore life has become a question of burning interest.
Exactly 23 years after the 1938 panic, on Halloween eve 1961, a small group of distinguished scientists, among them the American chemist Melvin Calvin who had just been awarded the Nobel prize in chemistry for his work on photosynthesis, and the charismatic American scientist and television personality Carl Sagan, met at the National Radio Astronomy Observatory, in Green Bank, West Virginia, at the invitation of a young American astronomer, Frank Drake. The purpose of the meeting was to discuss ways of detecting radio signals that might be sent by some extraterrestrial civilization. Remarkably, this outlandish—in both senses of the word—project eventually led to an undertaking of considerable magnitude, supported by the National Aeronautics and Space Administration (NASA) under the acronym SETI (Search for ExtraTerrestrial Intelligence). When a parallel project was started in the Soviet Union by the astrophysicist Iosif Shklovsky, the two superpowers entered into a major international cooperation at a time when glasnost was still far off in the future. Today, NASA no longer supports the SETI project, but the search continues with private support, under the direction of astronomer Jill Tarter.
Not all space exploration enthusiasts were ambitious or optimistic enough to look for extraterrestrial intelligence; many would have been quite content with evidence of extraterrestrial life. At present, efforts in this direction are so diverse and important as to have spawned a new discipline variously termed exobiology, bioastronomy, or astrobiology, with its own institutes, meetings, and publications.
In this connection, something of a climax was reached on 7 August 1996, when a special, televised press conference, introduced by President Clinton himself, was convened in Washington by NASA administrator Daniel Goldin, to announce to the world that evidence of past life on Mars had been detected by a team of American investigators led by NASA geologist David McKay. No expensive mission had brought this startling news to Earth, but rather a chance missile, a 1.8-kilogram piece of rock discovered in Antarctica, in December 1984, by Roberta Score and six other American explorers and identified as most likely originating from Mars. Dislodged from the surface of that planet some 16 million years ago by an impacting object, the meteorite, now famous under its classification number ALH 84001, had, after a long sojourn in space, wandered close enough to be caught by Earth’s gravitational pull, ending up in Antarctica, where it remained buried in the ice for some 13,000 years until it was dug out, carefully put in a sterile wrap, and transported to the United States for analysis. As I shall mention later, the ALH 84001 evidence has failed to convince a majority of experts. But the enthusiasm for life on Mars and other extraterrestrial sites remains unabated. If we were asked to accept bets as this book is written, what odds would we offer for the existence of life elsewhere in the universe?
First, we must decide what we mean by “life.” I shall stick here to my definition of Chapter 1, based on the properties of life as we know it, not, of course, necessarily in the form of animals, plants, or even bacteria present on Earth, but built with the same kind of chemistry under the same kind of cellular constraints. One often reads of possible forms of life constructed with molecular components other than proteins, nucleic acids, and other typical biological constituents, or even made of different atoms, for example, with carbon replaced by silicon, its closest kin in the table of elements. There is at present no valid basis for such speculations. In any event, if we are to identify life by chemical or fossil traces, we must perforce draw our criteria from what we know of life as it is.
With this definition in mind, what do we know or suspect of the existence, past or present, of life outside Earth? Let us look at our own solar system first.
Our two nearest neighbors, Venus, which is closer to the Sun than Earth, and Mars, which is further away from it, occupy the outer edges of what is sometimes called the habitable zone. Of the two, Venus, with a surface temperature close to 500° C, is definitely too hot nowadays to harbor life. It may possibly have been habitable in the early days after its formation. But the question is essentially academic. No doubt, we shall never know.
Mars, on the other hand, with an average surface temperature of −53° C, is too cold to harbor life, at least on its surface. It has a thin atmosphere, made mostly of carbon dioxide, part of which freezes every winter to cover the poles with a white cap, formerly believed to be made of water ice but now identified as what we know as dry ice, the stuff spewed by fire extinguishers. There is abundant water on Mars, however; it exists as permanent ice underneath the North polar cap of dry ice and in the soil in the form of permafrost, such as is found in some parts of Siberia, for example. It is generally agreed that liquid water must be present in some areas below the permafrost blanket. Should molecular hydrogen be available, bacteria similar to some forms present in Earth rocks could possibly exist there. How deep in the Martian crust one would have to dig to find them is, however, unclear.
There is strong evidence that Mars enjoyed a milder climate at a younger age, some four billion years ago. This is indicated by the “canals” mentioned above, which show unmistakable signs of having been carved into the planet’s surface by some running liquid, most likely water.1 This fact suggests that living organisms may have been present on the Martian surface at that time. There is thus an enormous interest in looking for signs of present or past life on the red planet.
The first attempt in this direction was made in the summer of 1976, when two beautifully designed, robotized laboratories landed safely on the surface of Mars, launched from the Viking orbiter spaceships. The robots successfully carried out three kinds of chemical tests on samples of Martian soil. At first, the results they sent out to Earth seemed indicative of life. But they proved to be “false positives,” due to nonbiological mechanisms, after a fourth test, performed by a highly sensitive technique, revealed no trace of organic carbon.
Enthusiasm for the search for life on Mars was seriously dampened by the negative results of the Viking mission, until the ALH 84001 meteorite dramatically reawakened interest in this quest. In this case, all the resources of modern technology could be applied to the rock, allowing highly sophisticated tests. A number of chemical analyses yielded results that, singly, could be considered only suggestive, each being explicable by nonliving mechanisms, but, together, were viewed by the investigators as strongly indicative of past life. What appeared to be the clinching argument was the morphological detection of small grains taken to be the fossilized remains of “nanobacteria” (from the Greek nanos, midget, which has become a prefix meaning one-billionth, as in nanometer). Upon critical examination, this evidence turned out to be the weakest of all, as the size of the alleged Martian organisms (some 25 nanometers) is at least one order of magnitude smaller than that of any known bacterium and, in fact, is such that it could not possibly house the strict minimum needed for autonomous Earth life. The matter is still being debated, but most experts are skeptical, agreeing with the American microfossil specialist William Schopf, who, at the 1996 press conference, quoted Carl Sagan as having said: “extraordinary claims require extraordinary evidence,” clearly implying that this requirement had not been met.2
Whatever the issue, ALH 84001 has had the merit of stimulating new projects. Unfortunately, next to the successful launching of two spacecrafts in 1996, Global Surveyor and Mars Pathfinder, two catastrophic failures have seriously compromised the program elaborated by NASA. On 23 September 1999, the Mars Climate Orbiter, instead of being put in orbit around the planet, was sent crashing to the planet’s surface by a command erroneously calculated in American units while the equipment was programmed in metric units. Cost of this mistake no high-school kid would have made: 125 million dollars. Less than three months later, the Mars Polar Lander, worth 165 million dollars, lost all contact with Earth after a poorly programmed, overly rough landing. These disasters have slowed down implementation of the program but without causing it to be abandoned. Several missions are planned for the next few years, including at least one in which highly sophisticated, robotized equipment will dig material one meter below the Martian crust and subject it to a number of critical analyses capable of revealing traces of biological substances, such as proteins. On the other hand, the project to send a manned mission has been indefinitely postponed. In this project, a spacecraft had been planned to carry a fully equipped laboratory in which the crew would perform fairly complicated experiments and choose the materials they were to take back to Earth for further analysis.
There is also interest in some celestial objects too distant from the Sun to be sufficently heated by radiation but deriving enough heat from internal sources, such as tidal friction or volcanic activity, to be able to contain liquid water and, therefore, to harbor life. Especially promising are the Jupiter moon Europa, which appears to be covered by ice, most likely surmounting a liquid ocean, and the Saturn moon Titan, which is believed to possess seas of liquid methane and other hydrocarbons, below which there could be water.
The example of Titan illustrates one of the difficulties in ascertaining the existence of extraterrestrial life. The mere presence of organic carbon compounds is not enough proof. We saw in Chapter 3 that organic molecules, including such typical biological constituents as amino acids, are found in many extraterrestrial sites, where their formation is almost certainly due to nonbiological chemical processes. The problem was also encountered with the ALH 84001 meteorite, which was found to contain traces of materials known as PAHs (polycyclic aromatic hydrocarbons). This clue was not considered demonstrative by the critics, because similar substances have been identified in comets and meteorites.
There is another difficulty. Should authentic evidence of life ever be discovered on Mars or on another component of the solar system, the finding would obviously be of tremendous interest, but it would not provide a definitive answer to our main question. The problem would remain whether life actually arose locally or came from Earth, carried by some meteorite. The alternative possibilities that Earth life came from the extraterrestrial site or that both terrestrial and extraterrestrial life came from some third source also must be considered. Given the distances involved, such possibilities cannot be ruled out.
Our Sun is but one among some 100 billion stars, arranged in a large, disk-shaped swarm with a diameter of about 100,000 light years, or one billion billion kilometers (light, travelling at 300,000 kilometers per second, would take 100,000 years to cross the disk). When viewed through the plane of the disk, on a clear summer night, this huge cluster of stars appears as a white trail in the sky, the Milky Way, or Galaxy (galaxias, from gala, milk, is the name the ancient Greeks gave to the Milky Way).
According to modern theories, stars arise through the gravitational collapse of swirling clouds of gas and dust. In this process, the cloud flattens into what is called a protoplanetary disk, the heart of which condenses by gravitation into the central star, which heats up tremendously and becomes an active generator of nuclear energy, while the peripheral parts fragment into separately condensing bodies, the planets. Depending on the size of the initial cloud, the star becomes anything between a dwarf and a giant, with significantly different histories. About one-third of the Galaxy’s stars have sizes sufficiently comparable to that of the Sun to allow the hypothesis that they have a similar history. If all this is correct, there must be, in our galaxy, billions of solar systems, of which a significant fraction may include a planet with Earthlike properties.
Fortunately, this hypothesis is theoretically accessible to verification, because the Galaxy is in constant evolution, with stars continually being born and dying. Thus solar systems in various stages of their histories should be there to be observed, given sufficiently sensitive techniques. Recent advances are beginning to allow this in practice. Clear evidence of the existence of protoplanetary disks has been found around several nearby forming stars. From present results, it is estimated that between one-quarter and one-half of the young stars in our galaxy have disks around them.
Planets cannot usually be observed directly in the glare of the star, but their presence can be ascertained indirectly by a method that detects the periodic wobbling of the star caused by the gravitational pull of the orbiting companion. There are two problems with this technique. First, it does not readily allow the distinction between a true planet and a “brown dwarf,” which is a smaller, companion star that forms by a different mechanism. The second difficulty is that only objects sufficiently large and near their sun to cause a measurable degree of wobbling can be identified in this manner. Our own planet, for example, could not on its own betray its presence in this way; its pull on the Sun is too weak.
The first circumstellar object to be detected by this method, later identified as a brown dwarf, was discovered in 1989 around a star catalogued under the number HD 114762. Since then, more than 50 companions, of which many are considered true planets, have been located around nearby stars. There is also hope, supported by recent observations, that further technical progress will allow direct visualization of the companion.
We are still far from detecting an actual Earthlike planet capable of bearing life. But present results are important in that they indicate that planet formation is a frequent concomitant of star formation. The theoretical surmise that a large number of stars in our galaxy may be surrounded by planets is thereby comforted, making the presence of an Earthlike planet around a significant subset of stars very likely on probabilistic grounds. An earlier estimate that the Galaxy may contain as many as one million planets with a history comparable to that of Earth thus appears plausible. Note, however, that this opinion is far from being unanimously shared.
What proportion of the habitable planets of our galaxy, assuming some exist, actually bear life? It is not likely that this question will ever be answered in concrete terms, as only a minuscule portion of the Galaxy is accessible to direct exploration, even with the most advanced means of space travel conceivable. Only incoming radiation can inform us, and even that information is flawed, since radiation does not travel instantaneously. The news we receive is bound to be stale by up to many tens of millennia, depending on the distance separating us from its source. In addition, for radiation to tell us something about the presence of life, some life-specific signal would be needed. As we have seen, spectral evidence of the presence of organic molecules does not suffice for this purpose. A possibility that has been evoked is to rely on the detection of molecular oxygen (or of oxygen-derived ozone). This would indeed be a strong indication of life, but in an advanced form. Remember that it took Earth life close to two billion years before it started raising the oxygen content of the atmosphere. In any case, whatever the signal adopted, the technical problems of detecting an almost imperceptible emission close to a star’s enormously stronger brilliance appear today as totally insurmountable.
This is no reason to be discouraged, however. As pointed out in the early chapters of this book, there are strong reasons to believe that life arose through highly deterministic chemical processes that were bound to take place under the prevailing; physical-chemical conditions. We now find that our galaxy probably contains many solar systems, of which a number may include an Earthlike planet on which life-generating conditions could be duplicated. There is thus a significant probability that life may be abundant in our galaxy. If this is true, there could possibly be a life-bearing planet near enough in our neighborhood to allow its detection, perhaps not with present-day technologies, but with those of the future. How many times in history has the impossible of today become the reality of tomorrow! Finding life elsewhere would be such a tremendous discovery that a substantial effort to enable it deserves to be made.
Until the early part of the twentieth century, we knew of only our galaxy. To be true, some fuzzy objects, called nebulae for this reason, had been detected in addition to stars. But only in the 1920s were nebulae clearly identified as galaxies by the American astronomer Edwin Hubble, using a newly built, giant telescope at the Mount Wilson observatory, in California. Hubble made an even more important discovery, known as the “red shift” Basically, what he found was that the characteristic wavelength of a given type of radiation received on Earth is shifted to an increasingly higher value the more distant its source. He interpreted this finding in terms of a phenomenon first studied for sound waves by the Austrian physicist Christian Doppler, and later extended to light waves by the French physicist Hippolyte Fizeau.
In the domain of sound, the Doppler effect is familiar to all of us. When a hooting car or train moves toward us, the pitch of the sound goes up progressively (shorter wavelength), to subsequently fall (longer wavelength) once the vehicle has passed us. This is understandable. The waves are compressed as their source approaches us and expanded as the source moves away from us. The Doppler effect thus gives information on the direction (by its sign) and on the speed (by its magnitude) of a moving source of sound. Transposed to the light emitted by a star or galaxy, the Doppler (Fizeau) effect provides the same type of information. It allowed Hubble to conclude that the stars and galaxies move away from us (shift to higher wavelengths), which has become the central piece of evidence supporting the concept of an expanding universe that started from an original Big Bang. In addition, Hubble made the cardinal observation that the velocity with which stars move away from us is directly proportional to their distance from us. On the strength of this relationship, now known as Hubble’s law, he was able to infer from the red shift of the nebulae that they were much further away from us than the stars of our galaxy, thus identifying them as distinct galaxies. These monumental achievements have been commemorated in the satellite-borne Hubble Space Telescope, which is now scanning the skies far above any interference by Earth’s atmosphere. It will be remembered that this splendid piece of equipment was almost ruined by a flaw, a distortion of its mirror, which was corrected by one of the most delicate space missions ever undertaken.
Today, more than 100 billion galaxies are known to exist. The nearest ones, the Magellanic Clouds, are between 150,000 aand 200,000 light years away from us, near the edge of our own galaxy. The most distant galaxies are almost 15 billion light years away from us, making their existence known to us by information emitted at the dawn of the universe. Thus from the nearest to the most distant galaxies, we receive a cut through time spanning almost the entire history of the universe. This is a tremendous boon to astronomers and cosmologists. But it is of little help to exobiologists.
If evidence of life is hardly likely to be detectable in our own galaxy, except in our immediate neighborhood, the search for life elsewhere is obviously hopeless. All we can say is that if other galaxies are like our own, they too may be teeming with life. Multiplying the estimate of one million life-bearing planets in our galaxy (see above) by the number of galaxies (on the order of 100 billion), we arrive at the conclusion that there may be as many as 1017 (one followed by seventeen zeros) foci of life in the universe. Even allowing a margin of error of many orders of magnitude, we are still left with a respectable number of planets able to give rise to life as we know it. Unless the astronomers’ estimate and my own are completely off the mark, life is widespread throughout the universe.
Put in simple terms, the probability of extraterrestrial intelligence is equal to the probability of extraterrestrial life, multiplied by the probability of life’s evolving into mind. Knowing only of one form of life, which happens to be intelligent, we obviously lack the information for such a computation. All we have to go by are “guestimates,” based on available knowledge, plausible surmise, and critical assessment, but unavoidably imprecise and exposed to personal bias. It was argued in Chapter 12 that the emergence of human intelligence by vertical evolution, although dependent on a large number of chance occurrences, was nevertheless subject to such stringent constraints as to make its probability much higher than is generally maintained. Even if this view is correct, there remains the question of how many life-bearing planets would provide the conditions allowing this evolution to take place. In a recent book,3 two American scientists, geologist Peter Ward and astronomer Donald Brownlee, have defended the view that the number of conditions that had to be met simultaneously for higher animals, let alone humans, to arise on our planet is so high as to make it very unlikely that such an event could ever take place elsewhere. Their conclusion, it should be noted, concerns only animal life. “We believe,” they write, “that life in the form of microbes or their equivalents is very common in the universe, perhaps more common than even Drake and Sagan envisioned.”4
In principle, intelligence should be easier to detect than mere life, especially if it is manifested by the kind of technological civilization humankind has developed. Imagine an alien scanning our part of the world. The creature would have no difficulty recognizing strange signs on our blue planet, glowing at night with myriad artificial lights and, especially, ceaselessly throbbing with countless electromagnetic waves covering a wide gamut of wavelengths. At least there would be no difficulty provided the alien were close enough. From a faraway planet or spaceship, only the glare of the Sun would be detectable, totally obliterating the evidence of our existence. Should we wish to advertise our presence “cosmos- wide,” we could not just rely on letting ourselves be discovered. We would have to send a message beamed out on a carefully selected wavelength and framed in such a way as to alert any observer’s attention to the fact that something unusual is going on. This is what Frank Drake and Carl Sagan actually tried to do in the early 1970s, creating a strong protest on the part of the British astronomer Martin Ryle, who considered it reckless to thus betray our existence to hostile aliens who might use the information to launch an attack on us. Realizing that many years, if not centuries or millennia, might be required for their message to be received and answered, the defenders of the SETI project also bet on the chance that some alien civilization might want to get in touch with us in the same way.
What made these projects feasible was the development of radio- astronomy, a discipline that explores the skies by collecting invisible radio waves instead of light waves. One of the pioneers of this new technology was Martin Ryle, the scientist whose hostility to cosmic radio signalling was alluded to earlier. In Chapter 3, mention was already made of how the spectral analysis of incoming radiation, mostly in the centimetric wavelength region, has allowed the detection of a number of organic molecules and radicals in outer space. This type of radiation is also used for other purposes. It has, for example, allowed the discovery of pulsars (pulsating stars) and distant galaxies, whose light is too faint to be detectable with light telescopes.
Not that the signals are easily detectable; their power is so weak that only supersensitive instruments can record them. In a recent book, the British astrophysicist Martin Rees5 recounts that visitors to Ryle’s laboratory in Cambridge, England, were invited to pick up a tiny slip of paper on which was written: “In picking this up you have expended more energy than has been received by all the world’s radio telescopes since they were built.” In the words of Drake,6 “all the energy collected in the history of radio astronomy barely equals the energy released when a few snowflakes fall on the ground.” And he adds: “that’s the energy released when they hit the ground, mind you; the energy lost as they melt is much greater.”
Only the magic of modern amplifiers, combined with huge receiving surfaces, has made the detection of such weak signals possible. The most sophisticated such facility exists in Arecibo, in the northern hills of Puerto Rico. It boasts a shiny aluminum, bowl-shaped reflecting dish, 300 meters wide, with a collecting area of 80,000 square meters, capable of covering millions of channels at the same time. A new facility, already in an advanced stage of planning, will group 500 to 1,000 separate, small dishes over an area of one hectare (10,000 square meters) at some site in California. This “One Hectare Telescope” (lhT), which should be much more effective and cheaper than the Arecibo telescope, is expected to serve as a prototype for the “Square Kilometer Array” (SKA), of 100 times larger surface area.
In spite of all this technical wizardry, the SETI project remains an enormous gamble, as it does not just depend on the probability of extraterrestrial intelligence; it requires several other conditions. First, if it takes extraterrestrial life as long as it has taken terrestrial life to evolve intelligent beings, i.e., almost four billion years, all biospheres younger than that age at the time the signal is to be sent to be receivable on Earth today are excluded, as they cannot yet have reached the intelligent stage. A second condition is that the extraterrestrials should have attained a degree of technical development at least as advanced as ours and, in addition, should actually want to communicate with aliens such as us. That they have not yet done so has been quoted by a humorist as the best proof of the existence of intelligent extraterrestrials. A final important factor is the likely duration of an extraterrestrial civilization, which limits the time during which signals can be sent. Should they last only a few million years—the time allowed our civilization by some futur- ologists—the window of opportunity for our receiving a signal becomes very small. In spite of these uncertainties, the SETI project is still vigorously pursued, no longer supported by NASA but by private donations.
Scientific vocabulary has recently been enriched with a new word, “terraforming,” which refers to the transformation of a planet in such a way that it becomes habitable. With Mars, for example, a first step would consist of warming the planet with “supergreenhouse gases,” so that the carbon dioxide polar caps are sublimated into atmospheric carbon dioxide, which would subsequently help maintain a mild climate by its own greenhouse effect. Plants would then be introduced to generate the oxygen that, after an estimated 100,000 years, would allow our descendants to settle on the red planet.
This may sound like “superscience fiction.” But the prospect of humankind progressively colonizing space has been entertained by a number of scientists and has even been taken seriously enough to alert “space ecologists” concerned about the protection of planetary environments. This preoccupation became a practical problem when the project to send a man to the moon began to take shape. Elaborate precautions were taken to minimize the danger of contaminating the moon with Earth germs as well as the reverse risk of bringing moon germs back to Earth. The exploration of Mars, which, unlike the moon is viewed as a possible abode of life, is raising even greater worries. In particular, if manned missions should land on Mars and spend some time there, contamination of the planet will be almost unavoidable, since astronauts can hardly be made germ-free. Fortunately, local conditions are such that the risk of a lasting implantation of human-carried Earth germs seems remote.
Given that we can imagine colonizing space, the possibility exists that extraterrestrials may have the same idea. Perhaps, if their degree of technological development is greater than ours, they could already have started implementing it. The invasion of Earth by extraterrestrials, which, starting with H. G. Wells’s War of the Worlds, has inspired many works of fiction, is not pure fantasy; it is a possibility. The fact that it has not yet happened has even been used as an argument against the existence of extraterrestrial intelligence (the opposite argument has also been made in jest, see above). It is said that the Italian-American physicist Enrico Fermi, one of the prime builders of the atomic bomb, who was a firm believer in extraterrestrial intelligence, used to go around asking: “If they exist, why are they not here already?” To this question, often referred to as the “Fermi paradox,” the Hungarian-born American physicist Leo Szilard, a colleague of Fermi’s in the Manhattan project, famous for his wit, allegedly answered: “They are among us, but they call themselves Hungarians.”
What to Szilard was a joke and to science fiction writers and movie makers has proved an inexhaustible source of imaginary drama, has been perceived as a true and often frightening reality by millions of people, ever since a pilot, Kenneth Arnold, flying his own plane near Mount Rainier on 24 June 1947, “saw” nine “flying saucers” cruising in his vicinity. The news made a sensation and was soon followed by other sightings of UFOs (Unidentified Flying Objects), some seen landing in a blaze of light and disgorging strange occupants. The buildup became so intense as to prompt the United States Air Force to commission an in-depth study of the question by a distinguished physicist, Edward Condon. As summarized by the American mathematician and professional “debunker” Martin Gardner, the 1,000-page “Condon report” concluded that “there are no UFOs that can’t be explained as hoaxes, hallucinations, or honest misidentifications of such natural objects as meteors, Venus, huge balloons, conventional aircraft, reentering satellites, and atmospheric illusions.”7 Needless to say, confirmed “ufologists” and their believers are not convinced.