Extraterrestrial Civilizations (8 page)

It became customary, therefore, to think of Mars as having moved farther along the evolutionary path than Earth; not only with respect to its planetary characteristics, but with respect to the life upon it. Similarly, Venus had not moved as far along the evolutionary path. Thus, the Swedish chemist Svante August Arrhenius (1859–1927) drew an eloquent picture in 1918 of Venus as a water-soaked jungle.

This sort of thinking was reflected in science fiction stories, which very often depicted Mars as occupied by an intelligent race with a long history that dwarfed that of Earthly human beings. The Martians were pictured as far advanced beyond us technologically, but often as decadent and weary of life—in their old age as a species.

On the other hand, many stories were written of a junglelike Venus, or one with a plantetary ocean—in either case filled with primitive life forms. In 1954, I myself published a novel,
Lucky Starr and the Oceans of Venus
, in which the planet was described as having a planetary ocean. But only two years later our thoughts about Venus were revolutionized.

After World War II, astronomers gained a large number of new and extraordinarily useful tools for the exploration of the worlds of
the Solar system. They could send out microwaves to the surfaces of distant planets, receive the reflections, and from the properties of those reflections deduce the nature of the surface even if they could not see them optically. They could receive radio waves sent out by the planets themselves. They could send out rocket-powered probes that could skim by the planet or even land on their surfaces and send back useful data (as in the case of the mapping of Mercury’s surface by
Mariner 10
).

In 1956, the American astronomer Robert S. Richardson analyzed radar reflections from Venus’s surface beneath the cloud layer and found it was rotating, very slowly, in the wrong direction—clockwise.

In that same year, a team of astronomers under Cornell H. Mayer received radio waves from Venus and were astonished to find that the intensity of those waves was equivalent to what would be expected from an object far hotter than Venus was thought to be. If this were so, there could be no planetary ocean on Venus; indeed no liquid water of any kind (and there went my poor novel when it was only two years old).

On December 14, 1962, an American Venus probe,
Mariner 2
, passed close by Venus’s position in space, monitored its radio-wave emission, and confirmed the earlier report. On June 12, 1967, a Soviet Venus probe,
Venera 4
, entered Venus’s atmosphere and sent back confirming data while descending for an hour and a half.
Venera 5
and
6
, landing on Venus’s surface on May 16 and 17, 1969, put the matter beyond all doubt.

Venus has an extraordinarily dense atmosphere, about 95 times as dense as Earth’s. Venus’s atmosphere, what’s more, is 95 percent carbon dioxide, the molecules of which have a mass of 44. (Carbon dioxide had been detected in Venus’s atmosphere by more ordinary methods as long before as 1932.)

It is natural enough for a planet to have an atmosphere containing carbon dioxide. Our own atmosphere has a small quantity of carbon dioxide (0.03 percent) and that small quantity is essential to the growth of plant life.

The photosynthesis of green plants uses the energy of the Sun to combine carbon dioxide molecules with water molecules to form the components of plant tissue—sugar, starch, cellulose, fats, proteins, and
so on. In the process, though, free oxygen is formed in excess and is discharged into the atmosphere.

It is generally thought, in fact, that at some time in the distant past, the Earth’s atmosphere was far richer in carbon dioxide than it is now, and that free oxygen was absent. (We’ll get back to this matter later in the book.) Earth’s early atmosphere, then, was somewhat like Venus’s present one, but less dense; and it is only the action of photosynthesis that gradually removed the carbon dioxide and replaced it with oxygen.

From the fact that Venus’s atmosphere is so rich in carbon dioxide and so poor in oxygen (none has been detected), we can deduce at once that photosynthesis in its Earthly form is absent from the planet or, at the very least, has not been established for long.

This would seem to indicate that there are no green plants of any consequence on the planet, and therefore no animal life (which depends ultimately on plants for food), and therefore no intelligence.

It might be argued that photosynthesis is not essential to life and, indeed, it isn’t. On Earth there are forms of life that neither use photosynthesis nor depend on other forms of life that use photosynthesis. These forms of life are all at the bacterial level, however, and there is no indication that now or ever has any form of life beyond the bacterial existed on Earth without need, direct or indirect, of photosynthesis.

It might also be argued that Earth need not form a rule in this respect. Suppose a form of life got its energy from the Sun and made use of carbon dioxide, but somehow stored the oxygen instead of emitting it into the atmosphere. In due course of time, it made use of the oxygen for the purpose of combining it with carbon atoms and restoring carbon dioxide to the atmosphere. In that way, you could have photosynthesis while retaining a carbon dioxide atmosphere.

This is not beyond the bounds of possibility, but—

Carbon dioxide has the property of absorbing infrared radiation. It allows the high-energy visible light of the Sun to pass through and strike the surface of a planet, but then absorbs the low-energy (and invisible) infrared radiation the planet reemits to space at night. This is called the greenhouse effect because the glass of a greenhouse does the same thing.

By retaining the infrared radiation of the planet, the carbon dioxide in the atmosphere raises the temperature of the planet, as the
glass’s retention of infrared radiation raises the temperature inside a greenhouse. Because of the very high content of carbon dioxide in Venus’s atmosphere, the surface temperature of the planet is far higher than we would expect it to be from its distance from the Sun alone, especially since ordinarily we would expect its clouds to shield it from much of the Sun’s heat. Venus is the victim of a runaway greenhouse effect.

The result is that Venus’s surface temperature is about 480° G (900° F), considerably higher than Mercury’s surface temperature. Mercury may be closer to the Sun, but it doesn’t have a heat-conserving atmosphere.

The surface temperature of Venus is far above the boiling point of water and is, indeed, hot enough to melt lead easily. There can be no liquid water anywhere on the planet. What water it has must exist as vapor in the clouds, and there is evidence that the liquid droplets in the clouds are, to a considerable extent, the extremely corrosive substance sulfuric acid.

It takes a vivid imagination indeed to conceive of life on such a planet, and Venus must be crossed off as a possible abode for extraterrestrial intelligence.

As for Mars, that from the beginning seemed to have a much better chance for life. Its rotation, its axial tip, its ice caps all seemed hopeful. Its presumed great age gave it, it would seem, a particularly good chance at advanced life.

About 1830, astronomers began to make serious attempts to map Mars. The first map produced was by a German astronomer, Wilhelm Beer (1797–1850). Others followed, but success was not remarkable. It was hard to see details through two atmospheres, those of Earth and of Mars, from a distance of hundreds of millions of kilometers. Each astronomer who tried to map Mars seemed to end up with a map that was completely unlike the ones produced by his predecessors.

All agreed, however, that there seemed to be light areas and dark areas, and the notion grew that the light areas represented land surface and the dark areas water surface.

A particularly good chance for observation came in 1877 when Mars and Earth happened to be in those parts of their orbits that brought them as closely together as they ever got to be. And by then, of course, astronomers had better telescopes than they ever had before.

One observer with an excellent telescope was the Italian astronomer Giovanni Virginio Schiaparelli (1835–1910). During his observations in 1877, he drew a map of Mars that, once again, looked altogether different from anything that had been drawn before. With his map, though, things settled down. Finally, he saw what there really was to see, or so it seemed; for later astronomers over the next 100 years saw generally what he had seen in the way of a pattern of light and dark areas.

By that time, though, Maxwell and Boltzmann had come out with their kinetic theory of gases, and it didn’t seem that a body with the mass and gravitational field of Mars ought to have large, open bodies of water. Even at Mars’s low temperature, water vapor must have found it too easy to escape, if the atmosphere were thinner than Earth’s. The suspicion grew, therefore, that Mars must be water poor. It had its ice caps, to be sure, and it might have its marshy and boggy regions—but open seas and oceans seemed unlikely.

What, then, were the dark areas?

They might be areas of vegetation, growing in the boggy regions, while the light areas were sandy desert. It was interesting that when it was summer in a particular hemisphere, and the ice cap shrank as it presumably melted, the darkened areas became more extensive as though the melting ice irrigated the soil and allowed vegetation to spread.

Many people began to take it for granted that Mars was the abode of life.

In the course of his observations of Mars in 1877, moreover, Schiaparelli noticed there were rather thin dark lines present on Mars, each of which connected two larger dark areas. These had been noticed back in 1869 by another Italian astronomer, Pietro Angelo Secchi (1818–1878). Secchi had called them channels, a natural name for a long thin body of water connecting two larger bodies. Schiaparelli used the same term. Both Secchi and Schiaparelli naturally used the Italian word for channels, which is
canali
.

Schiaparelli’s
canali
were longer and thinner than those Secchi had reported seeing, and they were more numerous. Schiaparelli saw about forty of them and included them on his map, giving them the names of rivers in ancient history and mythology.

Schiaparelli’s map and his
canali
were greeted with great interest and enthusiasm. Nobody besides Schiaparelli had seen the
canali
in the course of the 1877 observations, but afterward astronomers started looking for them in particular and some reported seeing them.

What’s more, the word
canali
was translated into the English word
canals
. That was important. A channel is any narrow waterway, and is usually a naturally formed body of water. A canal, however, is a narrow, artificial waterway constructed (on Earth) by human beings. As soon as Englishmen and Americans began calling the
canali
canals instead of channels, they began automatically to think of them as being artificial and therefore as having been built by intelligent beings.

At once there came to be enormous new interest in Mars. It was the first time (so it seemed) that scientific evidence had been advanced that strongly favored the existence of extraterrestrial intelligence.

The picture created was of a planet that was older than Earth and that was slowly losing its water because of the weakness of its gravitational field. The intelligent Martians, with a longer history than ours and with a more advanced technology, faced death by desiccation.

Heroically, they strove to keep the planet alive. They built huge canals to transport needed water from the last planetary reservoir, the ice caps. It was a very dramatic picture of an ancient race of beings, perhaps a dying species, who refused to give up and who kept their world alive by resolution and hard work. For nearly a century, this view remained popular with many people, and even with a few astronomers.

There were astronomers who added to Schiaparelli’s reports. The American astronomer William Henry Pickering (1858–1938) reported round dark spots where canals crossed, and these were called oases. Flammarion, who was a great believer in extraterrestrial life, as I said before, was particularly enthusiastic about the canals. In 1892, he published a large book called
The Planet Mars
, in which he argued in
favor of a canal-building civilization.

By far the most influential astronomer who supported the notion of a Martian civilization was the American Percival Lowell (1855–1916). He was a member of an aristocratic Boston family and he used his wealth to build a private observatory in Arizona, where the mile-high dry desert air and the remoteness from city lights made the visibility excellent. The Lowell Observatory was opened in 1894.

For fifteen years, Lowell avidly studied Mars, taking thousands of photographs of it. He saw many more canals than Schiaparelli ever did, and he drew detailed pictures that eventually included over five hundred canals. He plotted the oases at which they met, recorded the fashion in which the individual lines of particular canals seemed to double at times, and studied the seasonal changes of light and dark that seemed to mark the ebb and flow of agriculture. He was completely convinced of the existence of an advanced civilization on Mars.

Nor was Lowell bothered by the fact that other astronomers couldn’t see the canals as well as he. Lowell pointed out that no one had better seeing conditions than he had in Arizona, that his telescope was an excellent one, and that his eyes were equally excellent.

In 1894, he published his first book on the subject,
Mars
. It was well written, clear enough for the general public, and it supported the notion of an ancient, slowly drying Mars; of a race of advanced engineers keeping the planet alive with gigantic irrigation projects; of canals marked out and made visible from Earth by the bands of vegetation on both borders.

Lowell’s views were even more extreme in later books he published—
Mars and Its Canals
in 1906 and
Mars as the Abode of Life
in 1908. The general public found the whole thing exciting, for the thought of a nearby planet populated by an intelligence advanced beyond that of human beings was dramatic.