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The Search For Life In The Universe
by David Little (
Production Assistant
Henry Buhl, Jr. Planetarium and Observatory
Carnegie Science Center
One Allegheny Avenue
Pittsburgh, PA 15212-5850

Editor's Note: This is the script for a planetarium show which premiered at the Carnegie Science Center, Pittsburgh PA, in January 1999.

[Opening Sequence/Introduction]

Are we alone in the Universe?

Could it be, that in the immensity of space, human beings represent the ONLY intelligent life; perhaps the only form of life at all? Or is it possible that other creatures; other intelligent beings; even other civilizations, populate the Universe around us?

What if we are NOT alone?
What would these other beings be like?
Would they be as curious about our existence as we are about theirs?
Have they the desire or ability to reach out to us across the void of space?
Do they have the technology to send signals over the vast distances that separate the stars?
What messages would these signals carry, and would we be able to understand them?
And how might we answer?

Once these questions were only to be found in science fiction, and were not considered to be worth the time of thoughtful scientists. Today, however, they are the subject of serious investigation. For the first time in our history, we now have both the will and the technology to attempt to find the answers. Today, we are engaged in one of the greatest quests of all time...


(Title sequence)

[Ancient Curiosity -- Pop Culture/Media]

As a species, our fascination with worlds beyond our own is not new.

Human beings have speculated about the existence of extraterrestrial life - literally life “beyond Earth” - for thousands of years. Our natural curiosity leads us to investigate the Universe, and in so doing, we are led to question our place among the seemingly infinite stars of the night sky. Through the centuries we have tried to make sense of it all. As our knowledge and technology advanced, our struggle for understanding was reflected in our handiwork.

All around the surface of our planet, there exist symbols, structures and buildings that seem to evoke the otherworldly. In recent times, many people have tried to unlock the meaning of these ancient and long abandoned places.

Many have claimed that these works were contact points, designed to call out to visitors from other worlds. Others have even claimed that the works themselves could only have been accomplished with the assistance of alien technology. And yet, all the evidence we have suggests, not the work of extraterrestrial intelligence, but the work of terrestrial minds.

As we look to the skies, we have also been intrigued by the strange phenomena we sometimes see there. Especially in modern times, when the average person is no longer as familiar with the night sky as our ancestors were, hundreds of people report sightings in the sky that they cannot explain.

Such sightings are usually referred to as unidentified flying objects, or UFOs. In fact, about 90% of all such reports have actually been explained. Sometimes, the source of wonder is actually a very “earthy” item - such as an aircraft or weather balloon.

Sometimes the culprit is most definitely of celestial origin - such as Venus, meteors, aurorae or even the Moon. Sometimes what is seen are in fact spacecraft - our spacecraft - such as the space shuttle or space station MIR, or robotic craft like the new Iridium satellites that can create brilliant “flares” in the night sky.

And sometimes, perhaps more often than we’d like to admit, the source of our puzzlement is actually a very clever individual who has set out to create an extraterrestrial hoax.

In spite of the overwhelming lack of evidence that extraterrestrials have been among us, the notion of alien visitations has taken hold in our popular culture. The last century, and the last fifty years in particular, have seen an amazing number of books, magazines, movies and more that have portrayed contact between humanity and other citizens of the Cosmos.

There is no denying that this vast amount of extraterrestrial science fiction owes its existence to our powerful interest in the question, “are we alone?”. It is this same curiosity that has driven the search for life in the Universe from the realm of the mysterious to the realm of the scientific.

[Diversity of Life/Rise of Life]

At times it seems dizzying to contemplate the wide range of possibilities that human beings have been able to imagine when representing alien life forms.

And yet, in reality, our best creativity pales in contrast to the actual hand of nature. For as strange and exotic as the products of human imagination may seem, we need only to look under a rock, or turn over a leaf, to reveal the true diversity of life that already exists on our own small planet.

The complex web of earthbound life spans millions of varieties of creatures. It stretches from the microbes that inhabit a puddle of water, to the birds that soar through the atmosphere. It includes the beetles that thrive in the driest deserts; the wide range of creatures that call the ocean depths home; and of course, Homo Sapiens - humankind. If such diversity exists on our home world, where all life shares a common origin and most of its genetic code, then what incredible diversity might we find on new worlds whose environment and history is far different from our own?

Understanding the rise of life on our own planet is a key first step in trying to comprehend the possible nature of life on other worlds. And yet, piecing together the puzzle of the origins of life on Earth is a task on which we have only just begun to make progress. Though the problem is immensely complex, there are a few major points that have already become clear to us.

The most important requirement for life as we know it is the presence of liquid water. This is the one substance that can serve as a universal solvent - that is, it can dissolve and transport minerals and nutrients from both the ground and from the atmosphere and can allow the mixing of these materials. No other substance can perform this function that is integral to the appearance and continuation of life as we know it. Therefore, within even our limited understanding, it seems that liquid water is essential to the formation of life.

As human beings, we are watery creatures that inhabit a watery world. With over two-thirds of our planet engulfed in liquid water, we may be tempted to conclude that this all important material is easily found on other planets as well. But a quick survey of the other planets in our own Solar System shows us that this would be too hasty a judgment. Among the nine planets that orbit the Sun, only Earth has the moderate temperatures that allow water to flow freely. Other planets are either too hot or too cold to allow water to exist in a liquid state.

It seems then, that Earth exists within a unique position in the Solar System, located neither too close nor too far from the Sun. This location, where temperatures are consistently warm enough for liquid water, is known as the habitable zone. For our Sun, the habitable zone ranges from just outside the orbit of Venus to just inside the orbit of Mars. For life to exist on worlds orbiting other stars they must also be located at the correct distance from their star to sustain liquid water.

The consequences of failing to meet this condition can be seen in the hellish environment of Venus, where temperatures soar to 900 degrees farenheight... and on the frigid, dry flood plains of Mars, where water has been relegated to subterranian permafrost and polar ice caps.

At first it may seem that this fact would limit each star to only one habitable zone, greatly restricting the chances for life to emerge. But recent evidence in our own Solar System shows that this may not be the case.

It is possible for liquid water temperatures to occur in more than one way. For example, recent studies of Europa, one of the giant moons of Jupiter, indicate that it may have an icy surface that covers a huge ocean of liquid water. This would seem impossible in a world more than five times farther from the Sun than Earth. The answer to the paradox lies in the fact that Europa receives a tremendous amount of heat from internal friction, resulting from its constant gravitational tug-of- war with immense Jupiter. This second heat source means that it need not rely solely on the Sun to raise the temperature of water to the melting point.

With other sources of energy available, there may be several habitable zones that exist for the planets or moons of any given star system. The fact that at least two such zones are found in our own Solar System is a very encouraging sign for those who seek life among the other stars.

While liquid water is essential to the formation of life as we know it , it is not the only ingredient needed. All of the life forms with which we are familiar require not only water, but the element carbon. Carbon readily bonds with other elements such as hydrogen, nitrogen and oxygen to create a wide range of compounds. These carbon compounds are the building blocks of life on Earth, and presumably throughout the rest of the Universe as well.

It was the presence of carbon and other essential building blocks of life, in an environment containing large quantities of liquid water, that set the stage for the formation of primitive life on planet Earth. Experiments conducted in the early 1950s by Stanley Miller at the University of Chicago showed the potential for complex combinations of essential elements of life to form, if exposed to electrical charges and mixtures of gases that simulate the lightning and atmosphere of the early Earth. Such experiments are far from conclusive, and they certainly do not reveal the crucial steps in the evolution of carbon-based compounds to living organisms.

However, they do allow us to speculate that where similar environments exist, similar chemistry would occur. Wherever liquid water and carbon compounds are found, there is the potential for life.

And it is this fundamental belief of science- that the laws of nature must work in the same way throughout the Universe - that makes it possible to believe that other forms of life may exist among the stars. The fact that other beings could exist is a stunning revelation, but it tells us nothing about the evolution of those beings. Here on Earth, it took several billion years, and a winding path with many detours along the way, to move from the simplest forms of life to intelligent beings. It is hard to imagine how incredibly different the history of evolution must be on other worlds. And with such different histories, it may well be that intelligent beings on other planets would be more different from us than we are from a spider, or a bird, or a dinosaur! There is no way to be sure what kinds of creatures a search for life in the Universe will uncover.

[History of the Scientific Search]

As little as 50 years ago, almost any credible individual would have said that human beings were alone in the cosmos. It seemed obvious that we were the only intelligent life to be found. As we’ve seen, the idea of life among the stars existed for thousands of years, but until recently it did not have large popular support. Recent polls, however, show that about 80% of the public believe that we are not alone among the stars. And an overwhelming portion of the scientific community believes this as well. Some scientists are taking steps to study the possibility.

In the past, such work might have earned you the scorn of your colleagues, and at some points in history it could not only have ruined your career, but actually put your life in danger! The reason is that even though the idea of life beyond Earth goes back at least to the ancient Egyptians, more recently, it was a popular notion that the Earth was the most important body in the Universe. All other heavenly bodies were believed to revolve around Earth. This notion, which held sway for some 1500 years, was used as justification for the belief that humans must hold the central position in the cosmos, and therefore must be the most important form of life.

In the mid-sixteenth century, this popular notion was challenged by the Sun-centered Universe proposed by Copernicus. Over the next century and a half, the work of Galileo, Kepler, Newton and others provide the explanations and the evidence to help create our understanding of the Universe today. In the eighteenth and nineteenth centuries the work of chemists and of biologists, like Darwin, allowed us to begin to understand the nature of life and the place of human beings within the development of life on Earth.

In the last century, scientists from many fields have worked to refine and advance these ideas. After nearly two millennia of seeing ourselves as the center of the Universe, Earth has been “demoted”. Science has now painted for us a new picture: one in which human beings are one form of life among many that have evolved on just one planet, orbiting just one star, in just one galaxy in an immense Universe. While this new picture is certainly humbling, it also makes us aware, once again, of the possibility of other intelligent life in the cosmos.

It was this new world-view, that allowed scientists to begin to turn their attention to other life among the stars. It was within this context that the first serious studies of how to detect other life began. It was also within this framework that humans made the first attempts to reach out to other possible beings.

In late 1959, an article written by two physicists, Giuseppe Cocconi and Philip Morrison, argued that because of the great distances between stars, the only practical method of communication between extra-terrestrial civilizations would be by means of electromagnetic radiation.

Electromagnetic radiation is a broad term. This type of radiation consists of a large number of different forms collectively known as the electromagnetic spectrum, or EMS.

The EMS includes a wide variety of radiation such as the x-rays used to find broken bones, the light that you see with your eyes and the heat you feel from a fire. It also includes the radio and TV signals that come into your home for information and entertainment, and the microwaves you use to make popcorn. All of these types of radiation have the benefit of traveling through space at the fastest possible rate - the speed of light.

This speed, over 186,000 miles per second, is faster than any spacecraft could ever travel. In addition, it is far easier to broadcast radiation than to build large ships and head out on incredibly long voyages. For these reasons, the electromagnetic spectrum seemed a natural means of making contact with extraterrestrials. Cocconi and Morrison argued that our technology had reached a level where detecting signals from the electromagnetic spectrum was now possible.

The first serious scientific attempt to detect extraterrestrial life was made by the radio astronomer Frank Drake in 1960. Drake and others came to the conclusion that among all possible radiation swirling through the Universe, signals in the radio range would be the easiest to send and detect. This conclusion was based in part on the realization that there was a naturally quiet band in the Universe located in the radio range. This area is bounded by strong radio emissions by hydrogen and hydroxyl ions. These ions, or charged particles of matter, together would form water. For this reason, this relatively quiet spot has been poetically dubbed the “water hole”. Drake and other astronomers independently came to believe that any intelligent beings interested in making contact would recognize the significance of this radio frequency and broadcast their messages in this range.

Using this logic, Drake listened-in on two nearby, Sun-like stars. The results were negative, but science and technology had finally been brought to bear on this age-old mystery.

Drake took the scientific investigation of extraterrestrials a step further the following year, when he proposed an equation to calculate the number of intelligent and communicating civilizations in the galaxy. Known ever since as "the Drake equation", the formula is not so much a problem to be solved as a guide to understanding the issues in the search for life in the Universe. It says:

N=R* x fp x ne x fl x fi x fc x L (visual!)

N, the number of observable civilizations in our galaxy can be found by multiplying some very specific factors.
R sub * (star) is the rate of star formation in the galaxy.
F sub p is the fraction of those stars that have planets.
N sub e is the number of Earth-like planets in the average solar system.
F sub l is the fraction of those planets with life.
F sub i is the fraction of those planets with intelligent life.
F sub c is the fraction of those planets with intelligent life that becomes capable of communicating, and
L is the average lifetime of such a civilization.

Though we have gained a tremendous amount of information since Drake first proposed his equation, we are still only at the point of filling in about one half of the numbers in it. This may seem like little progress, but trying to solve the Drake equation has allowed human beings to grasp the complex issues involved in searching for life in the Universe.

While Drake and others pondered the possibilities of listening-in on alien communications, some astronomers were interested in doing the communicating themselves.

In the 1970s two sets of planetary probes were launched to study the outer planets of our own Solar System. It was realized that these four probes would eventually leave the Solar System entirely and wander out into interstellar space.Several individuals, including Carl Sagan, proposed that these spacecraft could be used as our interplanetary ambassadors.

Specifically, they suggested that some day these human-made machines might be picked up by other civilizations. They convinced NASA to fit the craft with messages from Earth.

The two Pioneer probes of the early 70’s carry plaques containing pictures of human beings. They also contain road maps, identifying the Sun and the planet Earth as their point of origin.

Two Voyager spacecraft were launched in the late 70’s and rewrote the book on our understanding of our own Solar System. They carry special records containing pictures, sounds, music and greetings from the people of Earth.

Today these four small craft are making their way into the void between the stars. Like cosmic messages in a bottle, they drift toward an unknown future, perhaps someday bringing word of Earth to another world.

At about the same time, astronomers convinced that we might hear the radio signals of distant worlds also used radio to send their own greeting. In 1974, a brief radio message was beamed into space. Originating in Arecibo, Puerto Rico at the giant 1000ft. radio telescope, the message was aimed at a star cluster called M13. The message will take 25,000 years to reach its target. This two-and-one-half minute message contained a string of 1,679 ones and zeroes. By color coding the zeroes as white squares and the ones as black squares we can create an optical representation of the message.

It contains the numbers one through ten, symbols for the common chemicals of life on Earth, the double helix of DNA, a picture of a human being, a sketch of the Solar System and a profile of the telescope itself. The information is written in the language of science and math, because no matter how different another life form may be from us, we believe that they would recognize these common ideas.

These first few tentative steps in the search for life in the Universe started us on the road to exploring the potential for contact with extraterrestrial life. But the concept remained on the fringe of the scientific community until very recently. In just the last decade and a half, a string of remarkable scientific discoveries have made the possibility of life beyond Earth seem a more credible idea than at any other time in our history.

In the mid-eighties, astronomers discovered the first evidence of disks of material circling other stars. The images of these “extrasolar disks” were taken with infra-red satellite technology and revealed numerous stars accompanied by orbiting debris. Could these be planetary systems in formation?

In the 1990s the Hubble Space Telescope has taken this discovery a step further. With its powerful optical system, Hubble has revealed proto-planetary disks, or proplyds, deep in the stellar nurseries of large dust and gas clouds called nebulae. These stunning images have shown far more planetary formation than astronomers had imagined in 1961. With these powerful images as evidence, many astronomers believe that it is now safe to assume that nearly half of all stars that form in our galaxy will also develop a family of planets. This gives us one of the key numbers used in the Drake Equation.

While it’s fasinating to catch planetary systems in formation, it is even more amazing to find actual planets around other stars. While astronomers have assumed the presence of such planets for decades, it's only in the last few years that such bodies have actually been detected. Starting in 1995, astronomers around the world, using powerful telescopes and computing equipment, began to detect the telltale evidence of planets - subtle wobbles in the motion of nearby stars.

When two objects orbit one another, neither is at the center of the system. Instead they both orbit a common center of mass. In the Sun’s case, the mass of the Earth pulls it off its center by about 279 miles. From the nearest star, Proxima Centauri, which is 4.2 light-years, or 25 trillion miles away, this shift would be the same as looking at a coin, on edge, from about 46,000 miles away. This is an incredibly small amount of movement. But with extremely sensitive equipment, it can be detected.

Using this technique, astronomers are able to deduce the presence and nature of planets without being able to take actual images of them. To date, astronomers have been able to use careful detective work in locating over a dozen planets orbiting other stars.

Two of these new planets were discovered by the Allegheny Observatory in Pittsburgh, PA. Here, late 19th century technology has been revamped with late 20th century electronics in order to make the hidden planets of stars detectable by carefully monitoring the motion of the parent star through space. This work is a tremendous boost to those hoping to find evidence of alien life.

But the Drake Equation also makes us ask, "Are these newly discovered planets actually capable of supporting life as we know it?"

We know from the experience of our own Solar System that planetary evolution yields diversity among worlds just as biological evolution leads to different forms of life.

Orbiting our own Sun, we find rocky worlds like Mercury, Venus, Earth and Mars, all different in their features, temperatures and atmospheres.

The outer worlds of our system contain gas giants - Jupiter, Saturn, Uranus and Neptune - each maintaining its own mini-solar system of moons and debris. Are these newly discovered systems like our own?

So far, the vast majority of planets discovered have been of the gas giant variety. Many of these planetary behemoths have been found orbiting close to their parent stars, greatly limiting the chance of Earth-like worlds. In fact, only two of the worlds discovered appear to be in their star’s habitable zone. This could mean that the number of Earth-like planets in the Drake Equation would be terribly low, diminishing the chances of extraterrestrial contact. But , its far too early to make such a definitive prediction. Our techniques for finding new planets are still primitive, and they skewed toward the larger planets, which are easier to detect.

In order to resolve this dilemma, NASA has plans for a new space telescope system that will be devoted to the discovery and imaging of Earth-like worlds. In the next decade, this project and others may provide us with a better understanding of whether or not the Earth is a rare find among planets.

Other recent discoveries that have made headlines in the search for life in the Universe include the detection of the building blocks of life throughout the galaxy, in much larger quantities than had previously been thought to exist.

For example, the recent passes of Comets Hyakutake and Hale-Bopp lead to the detection of compounds such as methane and ammonia in their dusty tails. These chemicals were key to the formation of early life on Earth. In addition, recent studies have found large amounts of water molecules deep inside the gaseous nebulae that are the birthplaces of stars. Such a discovery leads us to conclude that the chances of water being present on at least one newly-formed planet in an emerging planetary system may be quite good.

Taken together, these discoveries have led astronomers to speculate that many of the chemicals required to form life - water and carbon compounds - can be found abundantly in the Universe. If this is so, then we are closer to solving another piece of the Drake equation. Perhaps the formation of life, at least at a simple level, is a very common occurrence in the Universe. If this is true, the chances for a large number of communicating civilizations again goes up.

Besides learning more about other planetary systems, we continue to learn things about life in our own backyard. In just the last few years our understanding of where and how life can form and sustain itself has been greatly expanded. On our own world, new highly resilient forms of life have been found around undersea volcanic vents. In this setting, at first thought too dangerous for life to survive, organisms seem to thrive in the intense heat and harsh chemical environment.

In 1996, NASA announced the discovery of an amazing Martian meteorite that crashed into Earth sometime in the past. Inside the rock were found what some scientists believed to be fossilized microbacteria. It was thought that these bacteria may have formed during an earlier period in Mars’ history. At that time, liquid water may have flowed on its surface and temperatures there may have been much warmer.

In the Sun’s earlier years the habitable zone would have stretched out beyond the red planet, making liquid water a reality, even if only for a brief time in the planet’s past. While this finding is currently the source of great debate and the evidence is slim, it has still served to have us think in much broader terms concerning the environments in which life might develop.


As we reach the dawn of the 21st century, it seems that evidence points ever more strongly toward the possibility that life may have arisen in other locations in our Universe. But if this is true, and if other intelligent civilizations may have developed from that life, what is being done today to seek out these beings?

The acronym SETI stands for the Search for Extra Terrestrial Intelligence. The term was coined in the 1960’s to describe the work of Drake and others using radio telescopes in the search for electromagnetic signals of possible alien origin. It is a growing science, and many schools and organizations have their own SETI programs.

One of the most prominent groups is called the SETI Institute. The group’s project Phoenix was originally funded by the U.S. government as the Targeted Search portion of NASA’s High Resolution Microwave Survey. The HRMS was terminated by Congress due to budget pressures in October 1993. The SETI Institute is currently a privately funded organization that continues this work, checking individual stars for possible radio signals.

At least a half dozen other major SETI projects are underway around the globe, from New England to Australia. Some of the most interesting projects allow for the participation of amateur enthusiasts.

For example, the SETI League is a grass roots organization that is made up of amateur radio astronomers and others from many walks of life, sharing the common belief that we are not alone. They spend their own time and resources to build radio telescopes for the purpose of listening to the stars.

Today the SETI League is taking steps to complete an all-sky survey. Their goal is to have at least 5000 small dishes, used as radio telescopes, to give a complete view of the sky so that an elusive signal, if it comes, will not be missed.

1999 sees the launch of the latest search for life in the Universe. The SETI@home project is the most recent in a long list of search projects based out of the University of California, Berkeley. This project is unique in that it puts the search in the hands of anyone with a computer and a connection to the Internet. By downloading a special screen saver program, computers around the world will be accessing radio signal data received by the Arecibo Radio Telescope. The hope is that by combining the computing power of literally millions of computers, the chance of detecting a signal from space, however slim, would be greatly multiplied.

Most of these projects cover only a small portion of the sky or only a small portion of the radio spectrum. They point their radio telescopes at the stars and listen for signals that indicate the activity of alien cultures.

The activity they are looking for could be the same type of stray radio signals that we ourselves have been sending into space for decades. For example, in 1936 the opening ceremonies for the Berlin Olympics were broadcast on the first TV signals strong enough to leave the Earth. Ever since that time we have been spewing signals into the cosmos. Our earliest transmissions have now travelled nearly 64 light years away, over 10,000 stars fall within this distance from Earth. If anyone is living around one of those stars, they already know of our existence if they are listening.

Interestingly, the signals that SETI programs listen for don’t really need to “say” anything - that is, they don’t have to carry information. Some researchers are hoping that another civilization might use beacons for navigation much as we do for ships on the ocean. A beacon is something that repeats and can be accurately tracked. SETI researchers over the years have conducted what are called "targeted searches" looking for such beacons.

This is accomplished by creating a list of candidate stars, much like our own Sun, and then surveying each of the stars individually looking for signs of intelligent life.

Over the past 35 years, dozens of such searches have been conducted, but none of them have yielded conclusive results. They have searched hundreds of stars for brief periods of time at limited frequencies. However, with more than 200 billion stars in our galaxy alone and billions of galaxies in the universe, the search will continue long before we have been able to make a meaningful dent in the number of possible sources.

Part of the problem is that while you are looking at one star, a signal from another star could go by the Earth unnoticed. To pick up all signals would require the ability to listen to the whole sky at once. Most of the current SETI projects are far from this goal. With one radio telescope, only about 1 millionth of the sky can be seen at a time.

It has been said that to find one signal could require that your scope be aimed exactly at the source, and if the signal is sporadic you would have to be aimed at it at just the right time to get the message. Under such circumstances your chances of success are the same as walking into the Library of Congress blindfolded and picking out exactly the book that you wanted.

If the odds are so great against success, why is anyone even looking at all?

Most SETI researchers point out that success, no matter how slim the chances may be, would have a profound impact on the human race; and they are quick to point out that if we do not look, then the chances of success are exactly zero.

Just as the ancient marineers set sail into uncharted waters in search of new land, we hope that the promise of contact with another civilization will broaden our horizons of scientific understanding.

The search for life in the Universe is as great a challenge as has ever faced humankind. Recent developments and discoveries in this field are what ignite our hope and push us on, but the goal is elusive.

Will ours be the generation that first sees the ships?
Will ours be the generation who first hears the signals?
Will ours be the generation to become ambassadors to the Universe?
Until the final answer comes, we watch...we listen...and we wait.

It has been said that, “we are made of starstuff”. The matter that was once a part of another star is now a part of you and me. The web that binds us to the stars may be the thread that keeps us longing to answer this riddle. The thrill is akin to seeking buried treasure...the question we ask is not if, but when? And while we wait for that first contact we stand face-to-face with the Universe, nightly pondering the existence of other beings on other worlds.

And as you sit beneath the vault of the heavens, imagine another creature standing beneath the stars of its own world, pondering the vastness of space and asking the question...”Are we alone in the Universe?”

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