Answer: Mariner 10
In the early 1970s, NASA & # 39; s spacecraft Mariner 10 entered the record books for two different achievements. It was the first spacecraft to use interplanetary gravity fields as a kind of gravitational slingshot. It was also the first space mission to visit two planets. Launched in late 1973, Mariner 10 first flew to Venus and then turned to use Mercury using Venus' gravity to alter its trajectory.
Mariner 10 made observations of the surface, atmosphere and other physical features of Venus and Mercury. Mariner 10's contributions to our understanding of the two planets include mapping 45% of Mercury's surface and providing evidence of rotating clouds and weak magnetic fields on Venus.