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Life Outside Earth Essays

Winston Churchill is best known as a wartime leader, one of the most influential politicians of the twentieth century, a clear-eyed historian and an eloquent orator. He was also passionate about science and technology.

Aged 22, while stationed with the British Army in India in 1896, he read Darwin's On the Origin of Species and a primer on physics. In the 1920s and 1930s, he wrote popular-science essays on topics such as evolution and cells in newspapers and magazines. In a 1931 article in The Strand Magazine entitled 'Fifty Years Hence'1, he described fusion power: “If the hydrogen atoms in a pound of water could be prevailed upon to combine together and form helium, they would suffice to drive a thousand-horsepower engine for a whole year.” His writing was likely to have been informed by conversations with his friend and later adviser, the physicist Frederick Lindemann.


Noah Baker finds out about Winston Churchill’s close relationship with science.

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During the Second World War, Churchill supported the development of radar and Britain's nuclear programme. He met regularly with scientists such as Bernard Lovell, the father of radio astronomy. An exchange about the use of statistics to fight German U-boats captures his attitude. Air Chief Marshal Arthur 'Bomber' Harris complained, “Are we fighting this war with weapons or slide rules?” Churchill replied, “Let's try the slide rule.”2

He was the first prime minister to employ a science adviser, hiring Lindemann in the early 1940s. The science-friendly environment that Churchill created in the United Kingdom through government funding of laboratories, telescopes and technology development spawned post-war discoveries and inventions in fields from molecular genetics to X-ray crystallography.

Despite all this, it was a great surprise last year, while I was on a visit to the US National Churchill Museum in Fulton, Missouri, when the director Timothy Riley thrust a typewritten essay by Churchill into my hands. In the 11-page article, 'Are We Alone in the Universe?', he muses presciently about the search for extraterrestrial life.

He penned the first draft, perhaps for London's News of the World Sunday newspaper, in 1939 — when Europe was on the brink of war. He revised it lightly in the late 1950s while staying in the south of France at the villa of his publisher, Emery Reves. For example, he changed the title from 'Are We Alone in Space?' to 'Are We Alone in the Universe?' to reflect changes in scientific understanding and terminology. Wendy Reves, the publisher's wife, passed the manuscript to the US National Churchill Museum archives in the 1980s.

Riley, who became director of the museum in May 2016, has just rediscovered it. To the best of Riley's knowledge, the essay remained in the Reves's private collection and has never been published or subjected to scientific or academic scrutiny. Imagine my thrill that I may be the first scientist to examine this essay.

Here I outline Churchill's thinking. At a time when a number of today's politicians shun science, I find it moving to recall a leader who engaged with it so profoundly.

Modern thinking

Churchill's reasoning mirrors many modern arguments in astrobiology. In essence, he builds on the framework of the 'Copernican Principle' — the idea that, given the vastness of the Universe, it is hard to believe that humans on Earth represent something unique. He starts by defining the most important characteristic of life — in his view, the ability to “breed and multiply”. After noting that some viruses can be crystallized, making them hard to categorize, he decides to concentrate on “comparatively highly-organised life”, presumably multicellular life.

His first point is that “all living things of the type we know require water”. Bodies and cells are largely composed of it, he notes. Other liquids cannot be ruled out but “nothing in our present knowledge entitles us to make such an assumption”. The presence of water in liquid form still guides our searches for extraterrestrial life: on Mars, on the moons of Saturn and Jupiter or on extrasolar planets (beyond our Solar System). As well as being essential for the emergence of life on Earth, water is abundant in the cosmos. This wonderfully universal solvent — almost every substance can dissolve in it — can transport such chemicals as phosphates into and out of cells.

Churchill then defines what is known today as the habitable zone — that narrow 'Goldilocks' region around a star that is neither too cold nor too hot, so that liquid water may exist on the surface of a rocky planet. He writes that life can survive only in regions “between a few degrees of frost and the boiling point of water”. He explains how Earth's temperature is fixed by its distance from the Sun. Churchill also considers the ability of a planet to retain its atmosphere, explaining that the hotter a gas is, the faster its molecules are moving and the more easily they can escape. Consequently, stronger gravity is necessary to trap gas on a planet in the long term.

Taking all these elements together, he concludes that Mars and Venus are the only places in the Solar System other than Earth that could harbour life. He eliminates the outer planets (too cold); Mercury (too hot on the sunny side and too cold on the other); and the Moon and asteroids (their gravities are too weak to trap atmospheres).

Churchill began his essay not long after the 1938 US broadcast of the radio drama The War of The Worlds (an adaptation of H. G. Wells's 1898 story) had generated 'Mars fever' in the media. Speculation over the existence of life on the red planet had been going on since the late nineteenth century. In 1877, Italian astronomer Giovanni Schiaparelli described seeing linear marks on Mars (canali; mistranslated as canals) that were thought to be constructed by some civilization. These turned out to be optical illusions but the idea of Martians stuck. Science-fiction stories abounded, culminating with Ray Bradbury's The Martian Chronicles (Doubleday, 1950), published in the United Kingdom as The Silver Locusts (Rupert Hart-Davis, 1951).

Cosmic outlook

Churchill's essay next assesses the probability that other stars host planets. He reasons that “the sun is merely one star in our galaxy, which contains several thousand millions of others”. Churchill assumes that planets are formed from the gas that is torn off a star when another star passes close to it — a model suggested by astrophysicist James Jeans in 1917, which has since been ruled out. He infers that, because such close encounters are rare, “our sun may be indeed exceptional, and possibly unique”.

Now Churchill shines. With the healthy scepticism of a scientist, he writes: “But this speculation depends upon the hypothesis that planets were formed in this way. Perhaps they were not. We know there are millions of double stars, and if they could be formed, why not planetary systems?”

Indeed, the present-day theory of planet formation — the build up of a rocky planet's core by the accretion of many small bodies — is very different from Jeans's. Churchill writes: “I am not sufficiently conceited to think that my sun is the only one with a family of planets.”

Thus, he concludes, a large fraction of extrasolar planets “will be the right size to keep on their surface water and possibly an atmosphere of some sort” and some will be “at the proper distance from their parent sun to maintain a suitable temperature”.

This was decades before the discoveries of thousands of extrasolar planets began in the 1990s, and years before astronomer Frank Drake presented his probabilistic argument for the rarity of communicating civilizations in the cosmos in 1961. Extrapolating data from the Kepler Space Observatory suggests that the Milky Way probably contains more than a billion Earth-size planets in the habitable zones of stars that are the size of the Sun or smaller3.

Reflecting on the enormous distances involved, Churchill concludes that we may never know whether such planets “house living creatures, or even plants”.

Bigger picture

Churchill sees great opportunity for exploration in the Solar System. “One day, possibly even in the not very distant future, it may be possible to travel to the moon, or even to Venus or Mars,” he writes. By contrast, he notes, interstellar travel and communication are intrinsically difficult. He points out that it would take light some five years to travel even to the nearest star and back, adding that the nearest large spiral galaxy to the Milky Way (Andromeda — one of the “spiral nebulae”, as he calls them) is more than several hundred thousand times as far away as the nearest stars.

The essay finishes eagerly: “with hundreds of thousands of nebulae, each containing thousands of millions of suns, the odds are enormous that there must be immense numbers which possess planets whose circumstances would not render life impossible.” Here Churchill shows that he was familiar with the findings of astronomer Edwin Hubble in the late 1920s and early 1930s, who discovered that there are many galaxies beyond the Milky Way (about 2 trillion, according to a recent estimate4).

Taking a bleaker turn that reflects his times, Churchill adds: “I, for one, am not so immensely impressed by the success we are making of our civilization here that I am prepared to think we are the only spot in this immense universe which contains living, thinking creatures, or that we are the highest type of mental and physical development which has ever appeared in the vast compass of space and time.”

Almost 80 years later, the question that obsessed Churchill is one of the hottest topics of scientific research. Searches for signs of subsurface life on Mars are ongoing. Simulations of Venus's climate hint that it may once have been habitable5. Astronomers believe that, in a few decades, we will discover some biological signatures of present or past life in the atmospheres of extrasolar planets, or at least be able to constrain its rarity6.

Timely find

Churchill's essay is testament to how he saw the fruits of science and technology as essential for society's development. When he helped to establish Churchill College at the University of Cambridge, UK, in 1958, he wrote7: “It is only by leading mankind in the discovery of new worlds of science and engineering that we shall hold our position and continue to earn our livelihood.”

Yet he was also concerned that without understanding the humanities, scientists might operate in a moral vacuum. “We need scientists in the world but not a world of scientists,” he said8. In order for science to be “the servant and not the master of man”, he felt that appropriate policies that drew on humanistic values must be in place. As he put it in a 1949 address to the Massachusetts Institute of Technology's convocation: “If, with all the resources of modern science, we find ourselves unable to avert world famine, we shall all be to blame.”

Churchill was a science enthusiast and advocate, but he also contemplated important scientific questions in the context of human values. Particularly given today's political landscape, elected leaders should heed Churchill's example: appoint permanent science advisers and make good use of them.

Kurt Hutton/Picture Post/Getty

Winston Churchill at his desk in 1939: a prolific writer, he covered scientific topics as diverse as evolution and fusion power.

NASA/JPL/Univ. Arizona

An image taken by the Mars Reconnaissance Orbiter of the Martian surface, where the search for water is ongoing.

“Churchill sees great opportunity for exploration in the Solar System.”

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Life beyond Earth

For years the pantheon of characters dreamed up by science fiction writers has both excited and alarmed us. Taking the myth out of science fiction and into the realms of respectable science is the relatively new interdisciplinary field of astrobiology.

By Karen Pearce

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What is life?

If we are going to look for life, we need to be able to define what it is that distinguishes living from non-living. Unfortunately for us, life defies simple definition.

There is no neat sentence that sums up what life is, no mathematical formula, no straightforward schematic. Instead we have resorted to describing life, with lists of characteristics that living things have. These familiar characteristics can be found in any biology text, and include cellular organisation, ability for growth and reproduction, heredity, metabolism, movement, and response to stimuli.

While all living organisms on Earth exhibit these characteristics, vexingly, so do some non-living entities. Fire can be said to metabolise, that is convert energy from one form to another, but fire is not alive. Crystals can reproduce, but they are not alive. Viruses are seemingly living when they take over the machinery of a host cell, but by themselves are not alive.

Although there are difficulties with the way we answer this most fundamental of questions, without some idea of what constitutes life, we will find it very difficult to go and look for it. So, while the clumsy definitions that we currently employ have a range of limitations, we do not have a great deal of choice but to use them in our search to see if we are the only creatures in the universe that exhibit this peculiar set of characteristics.

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Origins of life on Earth

In the search for life beyond Earth, it's also important that we have some understanding of how and where life on Earth originated. As we can be 100% certain that life has emerged once in the universe, discovering the origins of life on this planet has the potential to tell us a great deal about the occurrence of life on others.

There are a number of theories on how life began on Earth. It may have cooked up in a primordial soup of increasingly complex compounds on the Earth's surface 3.5 billion years ago. Alternatively, it could have originated many miles underground in the exceedingly hot and chemically volatile regions of the Earth's still forming crust. It may have even arrived from space, riding in on one of the vast number of meteorites that impacted the surface of the newly formed earth. We can not be sure.

The latter theory, widely known as panspermia, has for the most part been widely disregarded. Recently, in light of findings such as the discovery of amino acids in the Murchison meteorite, and evidence of microfossils in a meteorite of Martian origin, the theory has undergone a resurgence of popularity.

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Primordial Soup?

The primordial soup theory, while still popular, is losing some support in favour of the idea that life may have evolved deep in the Earth's crust.

Evolution of life on the surface of the relatively young Earth would have had a lot of obstacles to overcome, not least of which was frequent bombardment by meteorites and radiation. Although the subterranean environment would have provided shelter from bombardment, and allowed early life a reasonably uninterrupted chance to establish, the extreme conditions present there were thought to be too harsh for life to exist. Now, with the relatively recent discovery of a totally new order of life, known as Archaea, this belief is being reviewed.

Archaean microbes live in environments of extreme temperature, pressure, salinity and pH. Broadly termed extremophiles, the different groups have been given equally inventive names to describe their particular habitat. Thermophiles live in temperatures of 50-80°C, while hyperthermophiles have been found in the temperature range 80-115°C. On the other end of the scale are the psychrophiles, which live at temperatures of around -2°C. Halophiles live in very saline environments. Barophiles live in high pressure environments (up to 110 Mpa). Acidophiles live in conditions where pH ranges from 0.7-4, while alkalophiles can be found in pH ranges of 8-12.5.

The interest in these organisms, apart from the very novelty of their existence, is that the inhospitable conditions in which they thrive may be similar to what Earth was like 1 billion years or so after its formation. The discovery of extremeophiles lends a great deal of support to the theory that life may have emerged on Earth in the high pressure, high temperature, chemically volatile depths of the planet, and only emerged once things had settled down on the surface.

If this is the case, and life could have emerged in such unfriendly conditions on Earth, why couldn't the same be said for other planets that until now were thought not to be suitable for life?

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What's the chance of life beyond Earth?

"If science fiction authors and Star Trek writers can envision life as we don't know it ... then surely the Universe is equally creative." — Michael Lemonick

It was recently estimated that there are 70 thousand million million million observable stars in the universe, not to mention those that are beyond our detection. Given this, it is my personal belief is that we are not alone in the universe. There's no real science behind this belief, but to me the size and numbers involved seem to indicate that there is more than a fair chance that there is life, intelligent or otherwise, somewhere out there. Otherwise, it would be an incredible waste of space.

There are, of course, many people who are more scientific in their approach to determining the existence of life beyond earth than I am. One such person is Frank Drake. Currently Chairman of the Board of the SETI Institute, in 1961 he developed the now famous Drake equation, which for the first time attempted to quantify the probability of detecting life (in this case, intelligent life) beyond Earth.

The Drake equation basically states that the number of civilizations we could detect will depend on the rate at which stars like our sun form, then the fraction of these stars that form planets, then the number of these planets that are hospitable to life, then the number of these planets where life actually emerges, then the number of these planets were life evolves to develop intelligence, then the fraction of these planets where interstellar communication evolves and, finally, the time that communication is carried on for before these intelligent civilizations die out or stop trying. More succinctly, the equation looks like:

The Drake equation - N = R* Fp Ne Fl Fi Fc L


N the number of detectable civilizations

R* the rate at which Sun-like stars form

Fp the fraction of stars that form planets

Ne the number of planets per solar system hospitable to life

Fl the fraction of planets where life emerges

Fi the fraction of life bearing planets where intelligence evolves

Fc the fraction of such planets where the inhabitants develop interstellar communication

L the length of time such civilizations continue to communicate before they end

Not only does the Drake equation convert the question of the existence of extraterrestrial neighbours from one of metaphysics to hard science, but it gives those looking for life beyond Earth a place to start.

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What are we looking for?

It's accepted that life on Earth is highly unlikely to be representative of all life in the universe, but we have to start somewhere.

The most basic requirement of life on Earth is the presence of liquid water. Water is important to life because, in liquid form, it is an excellent medium for carrying chemical and biological compounds. It is also stable as a liquid over a wide temperature range, a temperature range that (conveniently) accommodates a wide range of biological processes. In identifying places where life may exist, astrobiologists are looking for signs of water, particularly in liquid form.

Astrobiologists are also looking for the right cosmic chemistry in their search for life. The presence of organic (carbon) compounds, while not conclusive, could be suggestive of life. Atmospheric concentrations of certain substances could also be indicative of living organisms. Oxygen and methane, for example, are both found in our atmosphere, but are both highly reactive molecules. Their individual presence suggests that molecules are being constantly produced to replenish the numbers in the atmosphere, and the source of this replenishment could be life.

Given that life did emerge and evolve on Earth, it seems a logical step to look for Earth-like planets as potential hosts for extraterrestrial life. These planets would be of a similar age and size to Earth, and orbit a similar distance from sun-like stars — far enough away from the star that any water present doesn't evaporate, but close enough that it doesn't freeze.

If there are highly evolved life forms out there we may even intercept signals from them. This search is the whole premise of the SETI program - the Search for Extraterrestrial Intelligence. Rather than looking for chemical and biological artefacts, SETI scientists are aiming to make contact with ETI through radio astronomy.

Of course, finding all of these things does not mean that we should not expect to find life forms (particularly evolved or higher life forms) that are in any way similar to life as we know it. The Earth's biota is the result of a set of unique conditions shaping the products of the natural life giving processes — the laws of chance dictate that finding a planet whose population has survived five great extinction events, not to mention geological, meteorological , physical, chemical and biological conditions that ensued as a result of each other, is exceedingly slim, and even if we did, the probability of life beyond Earth following exactly the same evolutionary pathway is too remote to contemplate.

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Where are we looking?

On Earth

Although it may seem an odd place to look for our extraterrestrial neighbours, there are a vast number of astrobiological projects taking place here on Earth. Apart from being easier to access and a whole lot cheaper to study than sites in deep space, the terrestrial laboratory that is our planet provides an array of fascinating opportunities for astrobiologists. Extremophile studies may help to unlock the origin of life on Earth, and so offer insights into life beyond it. Animal communication studies utilising information theory, which allows the complexity of a given signal to be measured, will hopefully allow us to identify the long awaited signal from space once it comes from random noise.

Other studies that are being undertaken involve examining materials from space that we find here on Earth. Over 22,000 meteorites have been discovered on Earth, including 28 of Martian origin. As mentioned earlier, studies of these meteorites have broadened our ideas about the beginnings of life, and about its distribution in the solar system and beyond.

These lines of enquiry are but a few of the many being examined on Earth in the search for life beyond it. NASA's astrobiology site gives details of many more.

In the Solar System


Mars has always been a favourite source of speculation when it comes to extraterrestrial life. Its proximity means that it is also a target for scientific expeditions. Since 1960 there have been 34 missions to Mars.

Of the successful ones (16 have failed), four have involved landing spacecraft on the surface of Mars. In 1971 the first Martian landing was accomplished by the Soviet Mars 3 mission. Although only broadcasting information for 20 seconds, landing a craft on another planet was a huge success. NASA followed with the successful deployment of two orbiter-lander pairs in 1976 — Viking 1 and Viking 2. The landers conducted experiments looking for signs of life, but found no conclusive proof at their landing sites. Most recently, the Carl Sagan Memorial Station lander and Sojourner rover of NASA's 1997 Pathfinder mission collected information suggesting that Mars was at one time warm and wet — conditions suitable for life.

Mars is again the destination du jour with three separate craft winging their way to the red planet. The European Space Agency (ESA) launched its Mars Express mission in June 2003, with the primary objective being the search for subsurface water. The Mars Express spacecraft is carrying the Beagle 2 lander which will perform exobiological and geochemical research after it lands on the Martian surface in December 2003. NASA's Mars Exploration Rover program is also looking for signs of water, and has two separate rovers on their way to Mars. Spirit, launched in June 2003, and Opportunity, launched in July 2003 are set to arrive at their destination in January 2004.

In addition to the missions landing on the surface of the red planet, there have been a number of orbiting spacecraft sent to try and unlock some of its mystery. At present the Japanese spacecraft Nozomi is on its way there. Although plagued with problems since its launch in 1998, it is hoped that Nozomi will make it to Mars where it will study the upper Martian atmosphere. A summary of all missions to Mars, past and present, is on the NASA website.


Europa is one of the four large "Galilean satellites" orbiting Jupiter. Although it is the smallest of these satellites, Europa is still the sixth largest satellite in the solar system, only slightly smaller than our own moon. Europa has a relatively smooth, icy surface under which there is good evidence for the presence of liquid or semi-liquid "oceans". As liquid water is one of the key signs of potential life beyond Earth, Europa has caused a great deal of excitement in astrobiological circles.

Pioneer 10 and 11, and Voyager spacecraft have flown by Jupiter, but Galileo has given us the most information about Europa. Galileo was launched in October 1989, and after arriving at Jupiter in July 1995, made 11 orbits of Jupiter and its moons over the two year period of its prime mission. In addition, a probe was sent plummeting through the Jovian atmosphere early in the mission, where it recorded 58 minutes of data before being destroyed by the harsh conditions it encountered. In 1997 after the prime mission was completed Galileo completed an additional 14 orbits, eight of which were around Europa.


Titan is Saturn's largest moon, and it is believed that the atmospheric composition (nitrogen, methane, ammonia and argon) and surface conditions might be similar to those that we would have found on Earth when life was first emerging.

Pioneer 11 made the first direct observations of Saturn in 1979, with the two Voyager spacecraft following in 1980-81. These spacecraft took photographs of Titan (although the hazy atmosphere of the moon obscured the surface) and obtained atmospheric pressure and composition readings.

The latest mission to head to Saturn is Cassini-Huygens, an international collaboration between NASA and the ESA. Scheduled to reach Saturn in the second half of 2004, the craft consists of the Cassini orbiter (NASA), and the Huygens probe (ESA). On arrival, the Huygens probe will be deployed to the surface of Titan, where it will relay information about what it finds to the Cassini orbiter. This part of the mission is expected to last for four hours. The Cassini orbiter will continue to orbit Saturn and its moons for another four years.

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Beyond the Solar System

Earth-like planets

Although more than 100 planets have been found orbiting stars outside of our solar system, they have all been more "Jupiter-like" than "Earth-like". At present, we do not have sensitive enough equipment to detect the presence of relatively tiny planets like Earth. A number of missions are being planned in an attempt to overcome these limitations such as NASA's Terrestrial Planet Finder which it is hoped will be implemented in 2006, and the ESA's Darwin mission, to be launched in 2014.

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Search for Extraterrestrial Intelligence (SETI)

Perhaps the most well known search for life beyond earth is the Search for Extraterrestrial Intelligence. Projects under the SETI banner are not just looking life beyond earth, but highly evolved, intelligent life.

The search is based on the premise that the intelligent civilizations will be either deliberately or inadvertently transmitting signals that we will be able to detect on earth. The largest program being undertaken at present is Project Phoenix. Starting in 1995 at the Parkes Radio Telescope in Australia, the program is now based at the world's largest single-dish radio telescope at Arecibo in Puerto Rico. It involves the systematic scrutiny of space in the vicinity of sun-like stars. To date approximately half of the target stars have been investigated with no success. However, there are still an awful lot of stars to go...

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... so the search continues

The search for life beyond earth is potentially one of the most exciting, illuminating and confronting pieces of science ever to be undertaken. Its success will change the face of science and life as we know it forever. The journey through space and time that this success could take us on has profound implications, but none more so I suspect, than the realisation that at the end of the day, there's no place like home. Maybe then we'll give our own planet the care and attention it deserves.

Tags: astronomy-space, planets-and-asteroids, the-universe, space-exploration, stars

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Published 25 September 2003

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Saturn's largest moon Titan is home to oceans of methane which, unlike water on Earth, is not an ideal environment to sustain life. (Source: NASA/JPL/Space Science Institute)

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