Sixty years ago today, on October 30th, 1938, a deep, gravelly voice intoned a chilling message over the CBS radio network in the United States: "Ladies and gentlemen," it said, "I have a grave announcement to make. Incredible as it may seem, strange beings who landed in New Jersey tonight are the vanguard of an invading army from Mars." The broadcast went on to describe Martians as high as the tallest buildings exterminating helpless crowds with poison gas.
Pandemonium ensued. Thousands of listeners fled in panic into the streets or drove wildly for the open spaces. Police switchboards were jammed, and roads and churches became thronged with desperate people. Many claimed to have seen the Martians, and at least one person died from heart failure.
Of course it was all a great misunderstanding. The putative newscaster was in fact the actor Orson Welles, whose Mercury Theatre Company was presenting an over-realistic dramatisation of The War of the Worlds by H.G. Wells. Nowadays, however, in so far as we get excited about Mars at all, it is in the context of traffic in the opposite direction. Adventurous souls entertain ambitions that some day the planet may be colonised.
The first prerequisite, and indeed the hardest task, would be to raise the temperature. One way in which this might be achieved would be to build chemical factories on the planet that would pump greenhouse gases into its atmosphere to trap the solar heat. All the ingredients required are already present in the Martian rock; all that is necessary is to supply the energy needed to release them, possibly by means of nuclear reactors.
As the greenhouse effect took hold and the temperature of the planet gradually increased, the permafrost would melt, carbon dioxide, nitrogen and water vapour would seep from the Martian crust in ever increasing quantities, and eventually a hydrological cycle would become established. The colour of the sky would change from pink to blue, and after several hundred years, as the atmosphere gradually became thicker, the barometric pressure might have risen to 500 mb, about half that to which we are accustomed here on Earth.
The next step would be to provide oxygen. At first some could be liberated by artificial heat from the iron oxide in which Mars is rich, and then the process could be augmented by introducing primitive, perhaps genetically altered, forms of vegetation. Finally, perhaps 500 years from now, some honorary Martian citizen may be able to remove his or her space helmet out of doors for the first time: "O, brave new world, that has such people in't."