Country: USA
Mission: Venus & Mercury Flyby
Launched: November 3, 1973
Launch Vehicle: Atlas-Centaur 34
Spacecraft Mass: 502.9 kg
Arrival:
Mariner 10 was the first mission to use the gravitational attraction of one planet to reach another. On November 3, 1973, Mariner 10 was launched toward Venus, reaching the Venusian atmosphere on February 5, 1974. Some 4,000 photos of Venus revealed a nearly round planet enveloped in smooth cloud layers. Venus exhibited a slow rotational period of 243 days and had only 0.05 percent of Earth's magnetic field.
After the Venus flyby, Mariner's trajectory was bent in toward the Sun to accelerate and fling it out of Venus's gravitational field and onward to Mercury. Mariner 10 reached Mercury on March 29, 1974, passing over the planet at just 705 kilometers (438 miles) above the surface. Photographs revealed an intensely cratered, Moon-like surface and a faint atmosphere of mostly helium. After the flyby, Mariner entered solar orbit, flying by Mercury again on September 20-23, 1974, and photographing the sunlit side of the planet and the south polar region.
