Visions (and Revisions) of Mars

The invention of the telescope in the 17th century provided scientists with unprecedented, and ever-clearer, views of Mars. Much remained hazy, however, leaving observers plenty of room in which to exercise their imaginations. The result was a tantalizing vision of an oddly Earth-like Mars, a planet inhabited by "little green men" who built canals and plotted invasions-in short, a vision of a Mars too strange to be true.

Christiaan Huygens, a Dutch astronomer, sparked this vision in 1659 with a sketch of Mars based on his observations; the drawing showed shifting areas of light and dark, which to Huygens indicated the presence of vegetation that changed with the seasons. A century later, the American astronomer Frederic William Herschel observed dark areas of Mars, which he concluded were oceans, and shifting patterns of lighter areas, which he believed were "clouds and vapors." The "inhabitants" of Mars, he speculated in 1774, "probably enjoy a situation similar to our own."

Images of Mars, 1659-2004

Images of Mars, 1659-2004

In 1877, Italian astronomer Giovanni Schiaparelli reported seeing straight lines on the surface of Mars. He named them canali — "channels" in Italian. In other countries, however, the word was mistranslated as "canals," or waterways constructed by an advanced civilization. Schiaparelli drew maps of these canali. Other enthusiastic astronomers claimed the canali ended in large dark spots they called "oases." The notion of a wet Mars gained force in 1894, when telescope observations of Mars revealed polar ice caps that grew in winter and shrank in summer. Many astronomers interpreted these seasonal changes as evidence of a climate suitable for farming. Most, however, were not convinced. In his 1907 book, Is Mars Habitable? Alfred Russel Wallace argued (correctly, it turned out) that Mars was a frozen desert. Wallace predicted that the ice caps were more likely frozen carbon dioxide than water. (On that front, he was only half right: Scientists today suspect that Mars's ice caps may be a mixture of frozen carbon dioxide and frozen water.)

In 1908, the American astronomer Percival Lowell argued that Schiaparelli's canali were actual canals dug by intelligent Martians to transport water from the polar ice caps for irrigation. From his observatory in Arizona, Lowell mapped hundreds of supposed canals. Lowell's many articles and books, including Mars as the Abode of Life in 1908, did much to popularize the idea of a race of intelligent Martian farmers. (Lowell also saw "canals" on the surface of Venus, an observation that no other astronomer could duplicate. Recently, a team of ophthalmologists concluded that in fact Lowell had made the aperture of his telescope so small that he'd effectively turned it into a mirror: the Venusian "canals" were actually the reflected shadows of the blood vessels in the back of his eyeball.)

Debunking Lowell's theories, Alfred Russel Wallace countered that only "a race of madmen" would build open canals to carry water on Mars because the planet was so cold and airless that any liquid water would instantly evaporate. Nonetheless, by the 1920s, influenced by Lowell's active imagination, some popular illustrations of Mars included light and dark spots labeled "Vegetation," "Marshes," "Snow Clad Mountains," and "Hurricanes Dispersing the Mists." Some people argued that the canal-like lines many observers thought they saw on Mars were actually huge pictures drawn on the Martian surface to attract our attention "for the purpose of interplanetary communication."


Unfortunately for scientists, if not for science fiction fans, these theories attracted much interest among the general public. Mars hysteria peaked in 1938, when Orson Welles produced a radio adaptation of H. G. Wells's book "War of the Worlds," which describes a Martian invasion of Earth. Broadcasting the fictional story in the form of live news reports, Welles created widespread panic among gullible listeners. By the 1950s, men from Mars had become a staple of B movies. In the 1953 film "Invaders from Mars," for instance, a young boy sees a flying saucer land in his backyard. Big, green Martian zombies, controlled by a tentacled, disembodied head in a glass bubble, emerge from the spaceship to take over the town. Evidently these Martians had mastered interplanetary travel but had nothing better to do with their time than pester their neighbors.

Science eventually overtook science fiction. The first close-up pictures of the Martian surface, sent back by Mariner IV in 1965, revealed a cratered, moonlike wasteland. In 1972, however, NASA's Mariner IX photographed huge volcanoes and giant canyons that, if Earth was any model, appeared to have been cut by former waterways — a sign, perhaps, that water may indeed have been abundant on Mars at some time in the past. In 1976, two Viking orbiters made detailed maps of Mars, and two Viking landers set down on the planet. The landers tested the Martian soil for signs of life. They didn't find any, but they did send back dramatic photographs of the Martian surface.

The best large-scale images of Mars to date come from NASA's Mars Global Surveyor, which has been orbiting the planet since the year 2000, and the European Space Agency's Mars Express orbiter, which arrived in December 2003. Their photographs are at least 50 times more detailed than the earlier Viking photographs. Scientists are still sifting through this trove of data. So far, they have found evidence of surprisingly recent volcanic activity and, most exciting, of what appear to be water-carved canyons and gullies. And the two NASA rovers, Spirit and Opportunity, which are currently roaming the Martian surface on opposite sides of the planet, are providing scientists on Earth with a steady stream of data — leaving less room for the imagination, perhaps, but prompting a new vision of Mars no less exciting for its basis in fact.