While the Soviets were busy with Venus, United States scientists were conducting a series offlybys of the planet Mars. Mariner 4 was launched in November 1964 and yielded a total of 22 photographs that revealed a heavily cratered terrain. Mariners 6 and 7 produced 201 photos, including the first close-up views of a Martian polar cap.
The most successful of the early Mars missions was Mariner 9, which entered orbit around the Red Planet on 3 November 1971, and spent the next 349 days photographing the surface. The probe's two video cameras returned more than 7,000 images and obtained fascinating close-up views of the planet's two moons, Phobos and Deimos.
Both Venus and Mercury were the targets of Mariner 10, launched 3 November 1973. Its cameras, equipped with ultraviolet filters, took photos of the layered cloud tops of Venus and revealed a complex global circulation pattern. Then the probe flew on to Mercury, where it captured more than 10,000 close-up photos of the Moon-like surface and discovered the planet's magnetic field.