Mariner 10

Mariner 10 was the last spacecraft of the Mariner program, launched on November 3, 1973; this was an unmanned space mission (Mariners 11 and 12 were redesignated as Voyager 1 and Voyager 2). Mariner 10 was launched ~2 years after Mariner 9 and its mission was to explore Mercury and Venus. Mariner 10 made use of a "gravitational slingshot", using Venus to bend its flight path. Using a near-ultraviolet filter, it produced photographs of the Venusian chevron clouds[?] and performed other atmospheric studies. On March 29 and September 21, 1974, and March 16, 1975; Mariner 10 passed by Mercury and was able to map 40-45% of the planet. No spacecraft has since returned to Mercury.