The Channels of Mars
The Surface of Mars
In my youth it was a popular assumption that the “canals” on the planet Mars had been constructed by intelligent beings. Our other near planetary neighbor, Venus, was perpetually covered in clouds and these were assumed to be Earth-like clouds obscuring a surface that could well be exotic in its fauna and flora. The shattering of any such beliefs by the space investigations during the last twenty years marks one of the greatest advances in astronomical knowledge in recent times. Venus, although closely similar to Earth in size and density, has been revealed as a most inhospitable planet, the searing heat on the surface and the poisonous constituents of its clouds making any form of biological evolution out of the question.
The American and Soviet spacecraft had already established this about Venus at the time when the American Viking spacecraft were dispatched to Mars in the summer of 1975. During the long journey until the spacecraft landed in July and September 1976 there was eager anticipation that the biological sampling of the surface would reveal some form of life, however primitive, on the surface of the planet. That hope has not materialized in any positive or decisive manner, but any consequent disappointment has been counteracted by the acquisition of information about the nature of Mars. The two books under review deal with that subject through the analysis of the astonishing high-definition photographs of the planetary surface transmitted to Earth by the series of Mariner and Viking spacecraft after the first successes with Mariner 4 in 1965.
When this spacecraft successfully flew by the planet at a distance of a little under 10,000 kilometers on July 15, 1965, a new and revolutionary era of the exploration of Mars commenced. Until that time our sole knowledge of the planet came from earth-bound observations. Even before the invention of the telescope the observation of the motion of Mars across the sky by Tycho Brahe had presented a problem that seemed insoluble by the Copernican hypothesis that the Earth and the planets moved in circular orbits around the Sun. The motion of Mars against the background of the stars was irregular—for short periods it appeared to reverse its direction of motion with respect to the stellar background. It was this feature that led Kepler to conclude after laboring for ten years that Mars could not be moving in a circular orbit but that the orbit of Mars and the other planets must be elliptical with the Sun at one of the foci of the ellipse. Kepler’s great work, in which he enumerated the first two laws of planetary motion, was published in 1609; almost simultaneously Galileo was viewing Mars for the first time through his small telescope.
It is unlikely that Galileo could see any particular features of the planet, and another half century elapsed before Huyghens made drawings which showed polar caps and some markings of the surface. Another century passed and at the time when William Herschel discovered the …