Moons of Mars satellites, Earth had one and Jupiter had four (known at the time), that Mars by analogy must have two. Furthermore, as they had not yet been discovered, it was reasoned that they must be small and close to Mars. This would lead Swift to making a roughly accurate estimate of their orbital distances and revolution periods. In addition Swift could have been helped in his calculations by his friend, the mathematician John Arbuthnot. Voltaire's 1752 short story "Micromégas", about an alien visitor to Earth, also refers to two moons of Mars. Voltaire was presumably influenced by Swift. In recognition of
The Case for Mars Mars. The Mars Direct plan was originally detailed by Zubrin and David Baker in 1990. "The Case for Mars" is, according to Zubrin, a comprehensive condensation for laymen of many years' work and research. Chapters one and four deal with Mars Direct most completely. For Robert Zubrin, the attractiveness of Mars Direct does not rest on a single cost-effective mission. He envisions a series of regular Martian missions with the ultimate goal of colonization, which he details in the seventh through ninth chapters. As initial explorers leave hab-structures on the planet, subsequent missions become easier to undertake. Large subsurface, pressurized