Some years ago Hollywood brought out a movie titled When Worlds Collide. It concerned an astronomer who discovered a new planet headed on a collision course for Earth. With a little help from his friends he succeeded in building a spaceship to save a remnant of humanity after the world’s destruction.

His ship got away and landed on a strange planet. The sun came out, and the people from Earth saw green fields, forest glades, and other pleasing prospects. Despite the disaster to Earth, the future of the human race was assured.

This movie—one of the last of its type made before the Space Age—expressed a hope that people have long cherished: The hope of finding new lands, new places for settlement. From the time of Columbus through the closing years of the last century this hope could find fulfillment within the limits of our own planet. In this century it has been one of the major reasons for interest in space travel.

Closely associated with this is the hope that other civilizations will be found in space, or at least other life. If we cannot visit them, perhaps we can communicate with them or invite them to visit. These ideas lie behind much current work in the field of exobiology, the search for life in space. Even eighty years ago there were proposals to create huge triangles and other geometric diagrams in the Sahara and the Siberian pine forests—any large and unused stretch of land—in hopes that the Martians would see and give us a sign in turn.

People don’t want to be alone. They don’t want to feel as if they are cosmic strangers without a neighbor to talk to. That is why, in a time of increasingly tight budgets for space exploration, the United States still was willing to spend $1 billion on the Viking program. Amid increasing astronomical evidence that the only life-bearing planet of the solar system is Earth, Viking’s Mars landers and life-detecting instruments represented virtually our last hope of finding other life near to us in space.

In the earlier years of this century, astronomers were quite willing to accept the likelihood of life on Mars. As our knowledge advanced, scientists’ views concerning the probability of life on Mars went from “quite likely” to “perhaps” to “we can’t really say no” to “most likely, no,” where it is today. If science can’t give people what they want to believe, quite a few people are willing to believe anyway. In recent years there has been increasing popular interest in the subject of visitors from outer space.

There is something of a minor industry in this country catering to those who would like to believe that somewhere, someone has come to visit. Perhaps the leading worker in this industry is Erich von Daniken. His method is simple. Anything in archaeology that looks even a little odd is evidence that Somebody once dropped by.

For instance, there is his discussion of Easter Island. He notes that the Polynesians called it “the eye that looks toward heaven,” and describes the strange stone statues scattered there. Then he says, “Aha!” and you can guess the rest.

But in Polynesian lore “heaven” is the place whence the ancestors came and has nothing to do with the sky. Easter Island is the island closest to South America. We have good reasons today (ever since Thor Heyerdahl’s voyage on the raft Kon-Tiki) to believe that the Polynesians originally came from South America by raft. So Easter Island was most likely a religious and cultural center. Boatloads of people would come there over long stretches of ocean to help build new monuments.

When it comes to the Pyramids, von Daniken has a field day. Egyptology has been a science at least since Champollion deciphered the Rosetta Stone in 1799. In the British Museum there are samples of the heavy rope and the architects’ plans used in construction. But von Daniken blithely goes ahead and writes of visitors levitating the huge blocks into place.

The theme of visitors from space actually is quite a recent one in world literature. Probably the first work written on this topic was H. G. Wells’ The War of the Worlds, in 1895. We know what gave rise to these first stories; it was the modern era in the study of Mars, which began in the 1860s and reached a peak of popular attention after 1877. In that year Giovanni Schiaparelli observed Mars and announced that he had seen canali. In Italian the word means channels or grooves, but to most other people the word was interpreted as the canals of Mars. Schiaparelli eventually turned his attention to other matters, including fathering a line of descendants one of whom was the famous arbiter of fashion. But his reports fired the imagination of a wealthy American, Percival Lowell (of the Boston Lowells), who built himself an observatory in the pine-forested mountains and clear air of Flagstaff, Arizona.

Lowell’s books Mars as the Abode of Life and Mars and Its Canals were published around the turn of the century. He described the canals as true engineering works built by a race of advanced beings facing a water shortage. The canals, he speculated, served to carry water from the polar caps. His writings fired the imagination of Edgar Rice Burroughs, who in turn inspired a whole generation of science-fiction writers, including Ray Bradbury and Robert Heinlein.

As the century progressed, other astronomers studied Mars. Some of the best observations were made high in the Pyrenees of France at the Pic du Midi observatory, where the seeing is always magnifique. The best observers, working in the best conditions, could not see canals. They saw instead an irregular patchwork of fine detail, which under slightly poorer conditions tended to blur into lines and curves.

By the 1950s, few professional astronomers gave much credence to the Lowellian view of a Mars transformed by inhabitants facing their own limits to growth. Still, nothing conclusive had been found to rule this out. In any case to the public Mars still was very much not only colored red but colored by the works of half a hundred science-fiction writers following the Lowellian tradition.

That was the situation on July 14, 1965. On that day, the Mariner IV spacecraft flew past Mars and returned twenty-two crude pictures. The pictures showed craters like those of the moon, an obviously lifeless body. Newspapers wrote of the “moonfaced Mars,” and public belief in life on Mars suffered an abrupt blow. This affected public interest in the space program: If Mars indeed was not a new Earth, then shouldn’t we spend the money on this Earth instead? In the weeks after that July 14, Lyndon Johnson committed the nation to war in Vietnam, Watts exploded in riots, and the space program was never the same again.

Some scientists still held out hope. Carl Sagan of Cornell University asked the interesting question, “Is there life on Earth?” He pointed out that there were many thousands of weather-satellite photos of Earth, each showing more detail than the best of Mariner IV’s photos. Of these, only one or two showed evidence of the works of humans. This evidence, moreover, could be interpreted only if you knew beforehand exactly what you were looking at.

In 1969, Mariners VI and VII flew past Mars taking detailed photos of the south polar cap—and more craters. In 1971 Mariner IX became the first spacecraft to orbit the planet. It showed an entirely new Mars which we had completely missed on the earlier space missions. The satellite’s photographs revealed immense volcanic piles, vaster than any on Earth; the largest known mountain in the solar system, Olympus Mons, 75,000 feet high; gargantuan rift valleys, ten times wider and longer than the Grand Canyon and four times as deep, and curious features resembling streambeds.

Mariner IX showed a Mars that still could hold out hope for life. Not of princesses in crystal palaces awaiting their husbands’ return from the canal works, no. But apparently there once had been water there, and there once had been a thicker atmosphere. In 1976 even better photos from the Viking orbiter showed conclusively that there had been extensive flows of water on Mars. So perhaps there are spores, or creatures resembling bacteria, which yet might be found. The Viking landers failed to find evidence for life which could not also be interpreted in terms of chemical activity on the Martian surface. Still, Viking may not have been looking in the right places or with the right experiments, and hope for life will continue to spring eternal.

It is quite a change. In the 1890s there was wide interest in signaling somehow to the presumed Martian cities. Today the best we hope for is to find a spore or a bacterium which may stir to life in the life-detecting instruments of spacecraft such as Viking. But so compelling is the hope of life in space, so cherished is the dream, that even this discovery would be regarded as a milestone of the times.

If Mars is now to be regarded as something less than an abode of life, what of other planets? Venus was once regarded as a candidate. For over two centuries it has been known that Venus is perpetually shrouded in cloud. The clouds hide the surface below, affording considerable opportunity for speculation about hidden civilizations.

Venus is closer to the sun and receives more solar energy but its clouds reflect much of this away; so it was possible for a long time to believe that the surface would be no hotter than the Earth. In addition, Venus is nearly the same size as Earth; so there were those ready to regard it as a sister planet. A younger sister, perhaps, with dinosaurs in steamy swamps and pterodactyls in the sky.

The first solid new data to be obtained on Venus in this century demolished this picture. This data came from the first radio observations of Venus, made about 1956. By observing Venus with radio telescopes, it became possible to look below the clouds. These observations showed a hot Venus, at least 600°F. This was confirmed by the spacecraft Mariner II in 1962, which measured 800°.

As the 1960s went on, new data came in. Venus’ atmosphere was found to be some one hundred times thicker than that of Earth. Consequently, the surface pressure would be similar to the ocean a half-mile or more down. Still, all was not lost. A trace of water vapor was discovered above the clouds, and some scientists suggested that there could be life floating high in the cooler regions of the atmosphere. This hope was dashed when it was discovered that the atmosphere contains sulfuric acid.

The picture of Venus emerging from all this is a picture of one of the more unpleasant places in the solar system. The atmosphere of Venus is, indeed, very much like the traditional picture of Hell—hot, stiflingly thick, sulfurous, gloomy under thick reddish clouds.

In the solar system the search for life increasingly focuses on places which our spacecraft haven’t visited yet, or about which we still know very little. One of these places is Jupiter. Jupiter’s atmosphere contains hydrogen, methane, ammonia, and water. The planet also has lightning and very turbulent weather, with vast energies playing amid the atmosphere of a world over three hundred times the mass of Earth. Ever since the work of Stanley Miller in 1953, we have known that these are potentially fruitful conditions wherein life may arise.

Miller prepared a mixture of those simple chemical substances and subjected it for a week to electric flashes. When he analyzed the mixture he found it had turned brown. The brown was from amino acids, the building blocks of proteins. Other investigators have since gone further. They have tested other forms of energy; shock waves appear to give particularly good results. They have changed their mixtures, heating and cooling them in various ways. These experiments have caused some of the amino acids to link up to form microspheres, small spheres resembling cells. All this has not yet produced life in a test tube but nevertheless represents important steps which nature may have followed on the road to the first cell.

Conditions on Jupiter may resemble a Miller experiment on a planet-wide scale. But further discoveries have shown that there are strong vertical winds blowing in the Jovian atmosphere. These would tend to carry any interesting molecules which form down into the lower regions of the atmosphere. Here, temperatures are high enough to destroy them, to break them up into the water, ammonia, and hydrogen from which they were formed. And from this, Jupiter looks like very much less than what Isaac Asimov hoped it would be when he wrote: “If there are seas on Jupiter, think of the fishing.”

In all this, there is a common theme. Life on another planet is anticipated on the basis of the first highly incomplete data to be obtained from the planet. As more detailed data come in, the possibilities first shrink, then begin to vanish. And we are left here on Earth, apparently more and more alone in space. This could almost be a new scientific law: The probability of finding life on another planet is inverse to the amount of data we have on that planet.

Currently there is one more place in the solar system where it is said that life may exist. It’s on a satellite of Saturn, Titan, 3600 miles in diameter. In 1944 the astronomer Gerard Kuiper found that Titan has an atmosphere containing methane. More recently, Donald Hunten has found that the atmosphere is nearly as thick as that of Earth. He has found it contains a good deal of hydrogen and probably nitrogen as well. These gases quite likely trap heat and raise the surface temperature to the point where Miller-type chemical reactions can proceed. Indeed, there appears to be a reddish color to the disk of Titan, seen through a telescope. This may be the color of clouds or of the surface; it may be due to the presence of complex organic molecules or even of (who knows?) life.

That is where things stand today. In 1977 and 1978, NASA will launch two spacecraft to Saturn with a prime objective of examining Titan at close quarters. If past history is any guide, the first look at these bodies will raise more questions than it will answer. The most anyone hopes for on Titan are very simple life-forms. No one is writing of Titanian cities and of princely battles over ownership of Saturn’s rings.

As hope for life elsewhere in the solar system shrinks, interest in civilizations around other stars continues to grow. Here, few people doubt that if we could send spacecraft out to search, we would indeed in time find at least the spores and bacteria which are so avidly sought on Mars. The emphasis instead is on bigger game—advanced technical civilizations, ready and willing to communicate with us.

The world of the galaxies appears to be a friendly, congenial place for life. The astrophysicists Fred Hoyle and Freeman Dyson have shown that the processes whereby the chemical elements are formed involve a number of fortuitous coincidences which, acting together, provide this congeniality. Among the results of these coincidences is the fact that it is relatively easy to form carbon, on which life depends. And where there is life, there may in time be civilization. How many civilizations are there out there? There have been heated debates on this question with more than one scientific conference seeking an answer since about 1960. One formula for calculating the number of civilizations in space is: Multiply the number of stars formed per year, over the lifetime of the galaxy, by (1) the fraction of such stars with planets, by (2) the fraction of such planets suitably located for life to develop, by (3) the fraction of such cases in which life actually develops, by (4) the fraction of such planets on which intelligent life develops, by (5) the fraction of cases of intelligent life for which the intelligence gives rise to a technical civilization, by (6) the lifetime in years of such technical civilizations.

In this formula the factors near the beginning are items of which we do know something, but as we near the end we find that we know less and less. For instance there are about 200 billion stars in the galaxy. They have formed over some 10 billion years, the age of the galaxy. About half of these stars are in double star systems. Double star systems are very unfavorable places for planets to form because the presence of a second star will usually disrupt the quiet, even conditions needed for planets to evolve. But nearly all single stars are believed to have planets.

It seems reasonable to believe that stars similar to the sun, at least, will often enough have one or more life-bearing planets. And then things begin to get sticky.

If there is life, what is the chance of it being intelligent? It is difficult to see how there can be intelligence except in multicellular organisms. From the chauvinism of our multicellular point of view, we are prone to see the ancestral one-celled organisms as mere way stations along evolution’s road to the glory that is you and I. But from the viewpoint of a one-celled creature, it may be that we and our multicellular friends are just evolution’s newest creation. Life seems to have arisen on Earth some four billion years ago. For over 80 percent of the time since then, until about 600 million years ago, the most complex organisms were blue-green algae and other one-celled plants and animals.

The one-celled stage of life appears to be extraordinarily stable. For generation after generation, over billions of years, these cells grow and divide, grow and divide, grow and divide. The step up to multicellularity, with specialized organs and (most importantly) a brain, appears very difficult. By this measure, a trilobite or a primitive marine worm is far closer biologically to you and me than it is to the blue-green algae.

Did this advance to multicellularity occur relatively late on this planet? Or relatively early? Does a comparable advance occur on most planets with life? We will not truly know until we have had the chance to do detailed studies upon a dozen or so planets which not only have life but also a well-preserved fossil record. If multicellularity arises, then perhaps a few hundred million years will bring about the dawn of intelligence.

The intelligence may be like that of whales or dolphins. They lack hands and live in the water and will never develop a technical civilization. It is far from obvious that the highest and most successful forms of life must be intelligent. Life on Earth has been so successful even without intelligence, and intelligence has arisen so late in the world’s history, that it could quite easily never have arisen at all. Perhaps the human race would merely be a species of smart monkeys, except for the challenges of the Ice Ages. And how many planets will experience similar upheavals in the weather? It may be that most planets experience more moderate, even climates than we have known in the Ice Ages of the past million years. On such planets life might never face the challenges which could lead to the dawn of intelligence. On planets whose climates become only slightly more erratic, on the other hand, most higher life might be wiped out as were the dinosaurs.

If civilization can arise partly through billions of years of evolution, partly through good luck, how long will it last? A culture like that of ancient China or Egypt may exist continuously for thousands of years. But such a culture could never be detected from space, lacking radio signals or similar indications of technical prowess. From the cosmic point of view, television transmission is a surer indication of civilization than is the Parthenon. We know of only one such culture, our own. We have been sending out radio signals for only a few decades.

So how many civilizations are there? The answer is little better than guesswork, but there may be quite a few million in our galaxy.

How can we communicate with them?

The first actual attempt to receive signals from them was made in the spring of 1960. This was Project Ozma. The scientists involved studied two nearby stars, Tau Ceti and Epsilon Eridani, and found nothing. We know now that Epsilon Eridani is a double star, which may mean that there are no planets there at all.

More recently Soviet astronomers using better equipment studied twelve nearby stars. They found nothing. While few such organized searches have been conducted (radio telescopes are too valuable not to be used for astronomical problems for which answers can fairly easily be found), it’s a safe bet that quite a few informal searches have been carried out. It’s easy to imagine that late at night, when the astronomer has finished his observing and still has some time, he turns to the night assistant and says, “Let’s have a look at Eta Cassiopeiae.” It is likely that if anyone does detect radio signals from a planet of another star, it will be in this way, known as “bootleg research.”

The signals most easily detected would be radio beacons purposely set up and beamed toward the sun. As our radio telescopes improve, it becomes possible to study not merely nearby individual stars, but nearby galaxies or great star clusters in our own galaxy. The entire Andromeda galaxy, the nearest large galaxy to the Milky Way, can be observed all at one time by our largest radio telescopes. If just one planet in that entire immense array—just one civilization—has built a beacon and pointed it at the Milky Way, we might soon detect it.

So far no one has found anything of the sort. (Perhaps the Andromedans’ space budget has been cut, reducing the strength of their beacon just below the detection threshold of our equipment.) But we have already tried to make our presence known in this way.

The world’s largest radio telescope is at Arecibo, Puerto Rico; it is 1000 feet in diameter, built into a hollow surrounded by low hills. It could send and receive messages with an instrument of equal size located anywhere in the galaxy. Moreover, it was recently rebuilt to make it even more sensitive. When the improved Arecibo instrument was ready for use, one of the first things it did was to send a powerful beam, a radio signal, toward the Hercules globular cluster. This cluster, known to astronomers as M-3, contains thousands of stars and is located some 13,000 light years from us. If there is anyone there to listen, perhaps we will get a message back—in 26,000 years or so.

It may be that radio communication is not the way to go. Perhaps most of the cosmic civilizations are millions of years in advance of us, using communication methods incomprehensible to us. They may talk only among themselves. As Carl Sagan observed in his book, The Cosmic Connection (Dell Books, 1975):

We are like the inhabitants of an isolated valley in New Guinea who communicate with societies in neighboring valleys by runner and drum. When asked how a very advanced society will communicate, they might guess by an extremely rapid runner or by an improbably large drum. . . . And yet, all the while, a vast international cable and radio traffic passes over them, around them, and through them. . . . We will listen for the interstellar drums, but we will miss the interstellar cables.

If this is true, there is nothing to do but to wait and see what advancing science may bring. Eighty years ago, at the height of belief in the Martian engineers, it was thought we might communicate with them by creating geometric diagrams in the Sahara, or perhaps by setting off a great charge of photographers’ flash powder. Eighty years from now our current ideas may seem similarly quaint.

Is there life in space? Within the solar system, which we can reach and are now beginning to explore, the answer may be: Nothing but spores and bacteria. Perhaps the answer is: Nothing. Beyond our region of space the answer may yet be: Civilizations and cultures of greatness and magnificence untold. But we have not yet learned to detect them or to communicate with them.

As this has become apparent there has been a reaction against many of the more utopian hopes associated with space flight. Less than fifteen years ago John Kennedy could commit the nation to explore “this new ocean,” with widespread hope that we were entering a new Age of Discovery. Today it is fashionable to believe that our problems can find solution only on the earth and there is nothing in space which can aid us in any way.

This is not so. If we cannot find planets fit for us to live on, or if Mars is not up to our fondest hopes—very well. We can take our own life into space. We can build colonies in space, as pleasant as we want and productive enough to markedly improve humanity’s future prospects. And, we can begin to do this anytime we please.