First mission to explore two planets in a single mission

On 29/03/1974, NASA’s Mariner 10 spacecraft achieved a major milestone by becoming the first spacecraft to visit two planets during a single mission. This accomplishment was realized when the probe completed its first flyby of Mercury, following an earlier encounter with Venus on 05/02/1974. Mariner 10 was launched on 03/11/1973 with a trajectory designed to take advantage of gravitational forces for navigation. After its Venus flyby, the spacecraft used the planet’s gravity to alter its path toward Mercury, marking the first use of a gravity-assist maneuver in interplanetary exploration. This approach allowed the spacecraft to reach Mercury with reduced fuel consumption, setting a precedent for future missions. During the Mercury flyby on 29 March 1974, Mariner 10 transmitted the first close-up images of the planet’s surface. The data revealed a heavily cratered terrain, similar to the Moon, along with large geological features such as the Caloris Basin. The mission also detected Mercury’s magnetic field and provided measurements of its surface temperature and thin exosphere. By successfully exploring both Venus and Mercury, Mariner 10 demonstrated the feasibility of multi-planet missions using carefully planned trajectories. The spacecraft would go on to perform additional flybys of Mercury in September 1974 and March 1975, further expanding scientific knowledge of the planet.