The moon, when we got there, turned out to be a dead place from which the living earth looked wonderful. Mars, when our robots got there, seemed disconcertingly like the moon, without the compensating view: none of the primitive plants suspected by scientists; no imperial canals like those of Edgar Rice Burroughs’ Barsoom stories. Just dust.
The original architects of the space age saw Mars as the obvious next destination beyond the moon, a challenge which would require fleets of spacecraft and, later, research stations, settlements, even colonies far from the earth. There were many practical and (above all) political reasons why this dream was not to be-but the disconcerting deadness of Mars itself certainly played its part, and so did the glorious sight of the earth rising over the limb of the moon. When the most wonderful thing in the solar system is the thing you already live on, why emigrate?
Barren as it looked at first sight, though, Mars continued to fascinate scientists, and they built up an increasingly complex picture. The impression of a moon-like surface provided by the first probes in the 1960s gave way, in the 1970s, to a planet with a more intriguing history. A picture of Mars emerged in which the planet had once been active and exciting: its atmosphere thicker and warmer, its surface cut by rivers and scoured by floods, and life a distinct possibility. But this period was brief and long, long ago. Mars was now the mummified husk of this vibrant child.
The idea that there was a bygone Mars more interesting than today’s slowly rekindled the dream of human exploration. It suggested that there were secrets to be found beneath the dust, and that these scientific subtleties might be the sort of thing which would only ever be decipherable by people there, on the ground. The capabilities of even the most sophisticated robotic rover, enthusiasts pointed out, remain trivial compared to what a well-trained field geologist can do. Mars as a human adventure could thus be tied to the idea of Mars as an engrossing scientific subject. Long term, there was even the extraordinary dream of restoring the wet warmth of the early Mars-“terraforming” the planet so that once again it could be made suitable for life.
By the early 1990s, this view of Mars exploration had become one of the few topics which both believers in…