Ash: "You still don't understand what you're dealing with, do you? …. Perfect organism. Its structural perfection is matched only by its hostility."
Lambert: "You admire it."
Ash: "I admire its purity. A survivor... unclouded by conscience, remorse, or delusions of morality."
One of the first (fictive) depictions of Martians was published in the book "Un habitant de la planète Mars" in 1865, based on the assumed similarities of Earth and Mars. This Martian creature, evolved in an environment resembling Earth, was very similar to humans, different only in minor details like body proportions and skin colour.
Apart of science-fiction authors, also astronomers had for a long time tried to imagine the physical appearance of the supposed Martians based on what was known about Mars. Amateur astronomer Percival Lowell argued that due the smaller mass of the planet, the gravity was much weaker and therefore the body and physical strength of Martians should appear significantly greater if compared to a human.
"Now apply this principle to a possible inhabitant of Mars, and suppose him to be constructed three times as large as a human being in every dimension......The cross-section of his muscles would be nine times as great...... Now consider the work he might be able to do. His muscles, having length, breadth, and thickness, would all be twenty-seven times as strong as we, and could accomplish twenty-seven times as much."
Lowell 1895 "Mars"
A quite different approach was adopted by the British journalist Herbert George Wells (1866-1946), trained in biology.
Fig.1. A Martian feeding on his prey, an illustration for the novel "War of the Worlds" (1898) by artist Henrique Alvim Corrêa (1876-1910), image in public domain. Wells Martians were quite different if compared to the image of a wise and peaceful race of Martians imagined by early astronomers.
Wells Martians were the results of evolution in an unearthly environment. The planet Mars was believed to be older than Earth, due his position in the outer parts of the solar system. Slowly cooling and loosing his interior heat, Mars was now a cold and dry desert. The Martians evolved from a race maybe resembling humans, but to survive on the dying planet, they had lost their ineffective alimentary tract and were now able to process directly the blood of their victims. Their intellect had grown enormously; the body degenerated in the low gravity field.
Fig.2. Illustration by William R. Leigh for the article "The Things That Live on Mars" by H.G. Wells (Cosmopolitan Magazin, March 1908). After the success of his novel, Wells imagined an entire (now again a more peaceful) ecosystem for Mars. In the cold atmosphere the Martians evolved feathers and in the low gravity field of Mars wings are quite useful, an idea already proposed by the astronomer Flammarion, image in public domain.
The civilization on Mars and the advanced Martians collapsed with the deaths of two of its most prominent advocates. After Schiaparelli (died in 1910) and Lowell (died in 1916), interest for Mars quickly eroded. Experiments had shown that the human mind tends to connect single points to form lines on images with low resolution, also improved telescopes and a Mars approaching Earth (due the orbits of the two planets this is the case every 15-17 years) revealed that there were no canals or similar features on Mars. However the still observable changes on the Martian surface intrigued astronomers. Some of them, despite rejecting a Martian civilization, still imagined a primitive ecosystem dominated by a sparse vegetation, creeping over the planetary surface. Life on Mars remained - even if a remote - possibility.
July 14, 1965 the U.S. space probe Mariner 4 returned 21 images of the Martian surface, showing nothing than large craters. The surface of Mars resembled the surface of the lifeless Moon and the well preserved craters proved that there was no - and hadn't been for million of years - change, erosion, water and vegetation on Mars.
Fig.3. The Mariner and Viking missions provided a new view on Mars, compared to the earth-based observations of the 19th/early 20th century, image by NASA 1980; in public domain.
But like life on earth, also the idea of a life-bearing Mars was hard to eradicate. Astro- or Exobiology (the study of life in the universe) emerged as a serious scientific field in the decade 1950-1960, supported by the theories of Aleksander Oparin, J.B.S. Haldane and the experiments by Stanley Miller and Harold Urey in 1953. As it was realized that the components of life could form in an atmosphere consisting of carbon dioxide, nitrogen, methane and water, and all these chemical components can be found on Mars, it was in theory possible that Mars was - in the past or present - alive.
The two U.S. Viking space probes arrived at the planet in 1976, Viking 1 landed in Chryse Planitia and Viking 2 in Utopia Planitia. Both Viking landers were equipped with various instruments and experiments to identify life forms or their products in the Martian soil. In the "Pyrolytic Release" and "Labeled Release" experiments possible microorganisms in the samples should adsorb radioactive carbon, in the "Gas Exchange" experiment the chemical reactions of a moist sample were monitored and finally detectors should search for organic molecules in the Martian soil. At the landing site of Viking 1 the experiments showed positive results, maybe even too positive. The release of oxygen from the soil samples was 200 times higher then expected for biological activity and happened even if the sample was heated as high as 500°C (930°F), a temperature high enough to destroy organic molecules and therefore any life as we know it. The chemical detectors found also no signs of organic molecules in the samples - even less than in samples from the moon ! (contaminated by comets). However the results of Viking 2 were more intriguing, as the reactions here were weaker, inside the limits of a hypothetical low biological activity.
Even if the results were disappointing, there was still hope, as the Viking mission could only demonstrate that life on the recent surface of Mars - a dry, cold landscape sterilized by strong ultraviolet-radiation - was virtually impossible. But the orbiters of the Viking mission also revealed that in the past Mars was very different.
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HOTAKAINEN, M. (2008): Mars - From Myth and Mystery to Recent Discoveries. Springer, New York: 253
NOLAN, K. (2008): Mars - A Cosmic Stepping Stone - Uncovering Humanity's Cosmic Context. Copernicus Books - Springer Media: 379