24 April 2008

The Search for Life on Mars: Part 1

Posted by Ryan Anderson

Pre-Space Age

The prospect of life on Mars has tantalized humans for centuries. We long to find some proof that we are not alone, that the universe is not as empty as it seems, and so we look to the most Earth-like planet in our solar system for signs of life. Early astronomers quickly noticed that Mars shares some properties with the Earth. In 1783, William Herschel discussed the similarities between the two planets:

The analogy between Mars and the earth is, perhaps, the greatest in the whole solar system. The diurnal motion is nearly the same; the obliquity of their respective ecliptics, on which the seasons depend, not very different; of all the superior planets the distance of Mars from the sun is by far the nearest alike to that of the Earth … If, then, we find that the globe we inhabit has its polar regions frozen and covered with mountains of ice and snow, that only partially melt when alternately exposed to the sun, I may well be permitted to surmise that the same causes may probably have the same effect on the globe of Mars … I have often noticed occasional changes of partial bright belts … and also once a darkish one, in a pretty high latitude … and these alterations we can hardly ascribe to any other cause than the variable disposition of clouds and vapors floating in the atmosphere of that planet. -William Herschel, 1783

The striking similarities between Mars and the Earth led some to speculate that the planets must be similar in other ways. Some went so far as to say that, since the planets are so alike, that it would be absurd to propose that there is not life on Mars!

Shall we recognize in Mars all that makes our own world well-fitted for our wants – land and water, mountain and valley, cloud and sunshine, rain and ice, and snow, rivers and lakes, ocean currents and wind currents, without believing further in the existence of those forms of life without which all of these things would be wasted? … it is yet to speculate ten-thousand times more rashly to assert … that Mars is a barren waste, either wholly untenanted by living creatures or inhabited by beings belonging to the lowest orders of animated existence. – Richard Proctor, 1870

Although Proctor’s logic is flawed, and many of the similarities that he cites were themselves based on speculation, arguments like the one above were very influential because they struck a chord with the fundamental desire to find worlds like our own and other forms of intelligent life.

As telescopic observations improved, many astronomers tried to map the bright and dark features that they saw on the Martian surface. The features were given romantic names such as “Margaritifer Sinus” (Pearl-bearing Bay), “Chryse” (an island rich in gold), and “Aromatum Promontorium” (the Cape of Fragrant Spices). With such evocative names, it is no wonder that Mars captured the imagination of astronomers and the public alike.

In the late 1870s, an Italian astronomer named Giovanni Schiaparelli began drawing maps of the martian surface with dark, linear features that he called “canali”. In Italian, this is a generic term for a “channel” that can apply to either natural or artificial waterways. When translated to English as “canals” the features were interpreted as evidence of planetary-scale engineering by intelligent life.

Percival Lowell in particular helped to promote this idea, drawing elaborate maps of the canals and speculating about their purpose. In his book Mars as the Abode of Life he described in detail the plight of a dying race of Martians whose once-lush planet was becoming a parched desert. The globe-spanning web of canals diverted water from the remaining reservoirs near the ice caps to the great equatorial cities.

Despite skepticism from many astronomers who pointed to evidence that Mars had a thin, waterless atmosphere and frigid surface temperatures, the evocative story of the Martian canals persisted. It was so fascinating and appealing that mere evidence would not sway people’s beliefs. Mars and its Martians found themselves firmly ingrained in the minds of the populace. In fact, many people began to regard it as well-known fact that Mars was inhabited. Astronomer and writer Camille Flammarion went ever farther and suggested that the Martians were wiser and more advanced than humans. Notice that, rather than interpreting the variations in the position of the canals drawn by different observers at different times as evidence that the canals are imaginary, he instead uses the observed “changes” as evidence that the Martians are very advanced:

[T]he present inhabitation of mars by a race superior to ours is very probable. The considerable variations observed in the network of waterways testify that this planet is the seat of an energetic vitality…[W]e may hope that, because the world of Mars is older than our own, mankind there will be more advanced and wiser. – Camille Flammarion, 1892

Not everyone was so optimistic. In The War of the Worlds, H.G. Wells described the Martians as highly intelligent, but jealous of Earth’s resources and bent on conquest:

No one would have believed in the last years of the ninteenth century that this world was being watched keenly and closely by intelligences greater than man’s and yet as mortal as his own … With infinite complacency men went to and fro over this globe about their little affairs, serene in their assurance of their empire over matter. … At most terrestrial men fancied there might be other men upon Mars, perhaps inferior to themselves and ready to welcome a missionary enterprise. Yet across the gulf of space, minds that are to our minds as ours are to those of the beasts that perish, intellects vast and cool and unsympathetic, regarded this earth with envious eyes, and slowly and surely drew their plans against us. – H.G. Wells, The War of the Worlds, 1898

Since The War of the Worlds, Mars has been a staple in popular culture. Marvin the Martian, the 1948 Looney Tunes character is familiar around the world. Some of the most famous science fiction stories, including this blog’s namesake: Ray Bradbury’s The Martian Chronicles (1950), and Robert Heinlein’s 1961 novel Stranger in a Strange Land, are based on the premise of civilizations on Mars.

Many scientists also thought that there may be life on Mars. Variations in the brightness and darkness on the planet with the seasons were even hypothesized to be due to changing vegetation. Well into the 20th century, scientists echoed the hopeful stories of life on Mars:

“On Mars, the crumbling remains of ancient civilizations may be found, mutely testifying to the one-time glory of a dying world.”

– P.E.Cleator, 1936, founder of British Interplanetary Society

Needless to say, hopes were high in 1964 when Mariner 4 was launched to Mars. It would be the first mission to another planet and would finally return up-close images from the Red Planet. It might even give Earthlings the first glimpse of Martian life.

The world was in for a surprise.