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Lost World: Images of Mars Before the Space Age

Clive Davenhall
28 January 2013

These notes are an abstract of the talk Lost World: Images of Mars Before the Space Age presented to the Astronomical Society of Edinburgh on 7 December 2012 and some suggestions for further reading.

Abstract

The modern understanding of Mars is the result of forty-odd years of exploration by robotic spacecraft. However, before the space-age the planet had a long history of observation by Earth-bound astronomers, dating back to 1609-10 when Galileo Galilei first applied the telescope to astronomy. Mars is the only body, apart from the Moon, on which surface features were definitively identified and mapped prior to the space-age. Further, the planet appeared both like and unlike the Earth, offering suggestive similarities and tantalising differences. It is unsurprising then, that it played an important role in the development of ideas about planetary evolution, the debate over extra-terrestrial life and in the development of the genre of science fiction.

By the middle of the nineteenth century Mars was understood as a world basically similar to the Earth. Indeed it seemed the most Earth-like of the planets and the most likely to be inhabited. The Martian disk is mostly orange with smudges of grey/green markings (mostly in the south). Though the details change with time, the basic features are permanent. The orange regions were thought to be continents and the grey/green areas to be seas. In addition there were white spots at the pole which waxed and waned with the Martian year, implying seasons similar to the terrestrial ones. The planet seemed to have a substantial atmosphere which supported occasional clouds.

1877 saw a favourable perihelic opposition that was well-observed. Notably, Giovanni Schiaparelli, a Professor of Astronomy at Milan, published a map, more detailed than any produced hitherto, which showed unusual linear features that he called in Italian canali. This word can be applied to both natural and artificial waterways, but it was mistranslated into English as 'canal', suggesting an artificial origin. Initially only Schiaparelli saw the canals, but after several years they were also reported by other observers. The 1992 perihelic opposition was awaited with interest.

The 1892 opposition ushered in the infamous 'canal craze' which lasted for a couple of decades, in part due to the forceful advocacy of Percival Lowell and Camille Flammarion. The canals were understood as a giant civil engineering project undertaken by an ancient and advanced Martian civilisation to irrigate their increasingly desert planet. These ideas, however far-fetched, were widely popularised and discussed, featuring in numerous books and countless newspaper and magazine articles, and even in advertisements.

The existence, let alone any artificial origin, of the canals was always controversial amongst astronomers, but they fell from favour completely after about 1910. For the rest of the twentieth century astronomers saw Mars as an increasingly inhospitable, desert world. However, the popular image of the planet remained firmly rooted in turn of the century, Lowellian ideas, which continued to feature in newspaper and magazine articles and contributed to the development of the nascent genre of science fiction.

In the event even the astronomer's inhospitable Mars proved to be overly optimistic. The first successful fly-by, by the US Mariner 4 in 1964, returned just 21 grainy, low-resolution black-and-white photographs, but they transformed our understanding of the planet, showing a barren, cratered landscape more reminiscent of the Moon. The probe also estimated the surface atmospheric pressure to be only a hundredth of the terrestrial value. Subsequent probes have, of course, swung the pendulum back somewhat, revealing a fascinating world with active geologic processes and perhaps a warmer, wetter past. Nonetheless the old Mars was gone forever.

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