Mars Exploration: Surface
& Orbital Reconnaissance

Introduction: Is There Life On Mars? continued

rate, which was not finally resolved until about 1967 at 243 Earth days (Dyce:1970 p.156). In the meantime figures for the rotation period would vary from one to 225 Earth days, the implications of which for life were quite different at either end of this range: the lower end being the most favourable. Nevertheless, the discovery in 1932 of Carbon dioxide in the atmosphere later led to the suggestion by Rupert Wildt (1940) of a greenhouse effect raising surface temperatures to above 100 degrees Centigrade: significantly, above the temperature that would permit liquid water on the planet. Mayer and colleagues in 1956, using radio techniques, would raise this figure to 600 Kelvin (327oC). The Whipple-Menzel ocean theory of that time began to look very unlikely.

As for Mars, in 1924 William Coblentz and others unexpectedly found that temperatures could rise above freezing, so suggesting that vegetation may in fact survive there. Further independent work, however, indicated otherwise. Walter Adams and Charles E. St. John in 1925 found water vapour and oxygen to exist there in very small amounts: this lack of water also implied extreme desert conditions. Nevertheless, this result did not seem to dent the belief in vegetation on Mars. It has been suggested that this was due to the greater weight that astronomers gave to visual/photographic methods over physical methods, and which appeared to offer more favourable evidence for water and oxygen.

Despite these observations there were alternative visions of Venus and Mars. In 1918 Svante Arrhenius (1859-1927) in his Destinies of the Stars, for example, envisaged a Venus replete with swamps and lush vegetation. At the planet's poles where temperatures were perhaps as low as 10oC he expected organisms to be more advanced: in the distant future the highest forms of life in the Solar System may reside on Venus. Charles Greeley Abbot (1872-1973), director of the Smithsonian Astrophysical Observatory, was even bolder. In 1920 he claimed that Venus was the most likely abode for extra-terrestrial intelligence in our Solar System. The planet he believed possessed large regions of cloud cover, which without doubt consisted in water vapour, whilst its temperatures were almost identical to Earth's. In spite of observational evidence to the contrary, Abbot reiterated this view in his 1926 book The Earth and the Stars. The Venus portrayed in David Lasser's book The Conquest of Space (1932) is similar to that found in Arrhenius. It is a young world, at an evolutionary stage resembling that of the Earth about six to ten million years ago. Its atmosphere is hot and dense and its surface humid: should plant and animal life exist there its complexity would conceivably compare with that of Earth's Palaeozoic era, although in form be very different. Mars by contrast, whilst understood to be the only non-terrestrial planet to "definitely" contain oxygen and water vapour, is regarded as only barely meeting the conditions for life of a terrestrial kind. Nevertheless, Lasser states that "Mars can support life, and that with proper equipment at their disposal it could support men (p.251)."* In 1949 science writer Willy Ley also wrote a book entitled, The Conquest of Space, in which he states that Mars’ polar caps were in fact composed of water-ice, "The carbon-dioxide theory" allegedly having been proved flawed since, contrary to the behaviour of dry-ice, “we could see them [the poles] melt."** Thus, "there is water on Mars." He continues: "we are justified in believing in life on Mars – hardy plant life" because the "colour changes" on Mars he considers to be most logically and simply explained by vegetation: the Tibetan landscape is believed to offer a "good idea of what to expect," essentially, a desert, bleak, empty, bare and with no mountains. (For more details click here)

*(Later, in his book The Exploration of Space (1951), Clarke spoke similarly of Venus, believing that humans would probably require no more than a supply of oxygen to survive there.)
**(We now know that Mars' polar caps comprise both carbon-dioxide and water-ice, the former sublimating or evaporating from ice to vapour during the Martian summer whilst leaving the water-ice behind: during the Martian winter this carbon dioxide vapour returns to the poles either as snow or condenses on the surface as frost gradually increasing the size of the polar cap once again.)

Importantly, in the time between the publication of Lasser's book The Conquest of Space in 1931 and the publication of Ley’s book in 1949, a crucial turnaround had occurred in the world of planetary science. Specifically, Jeans's tidal hypothesis implying the extreme rarity of planetary systems had fallen, in part due to its inability to adequately address issues raised in 1935 by Henry Norris Russell