Mariner 10

Mission Profile

Mariner 10 was NASA's first dual-planet mission, launched on 3 November 1973 aboard an Atlas SLV-3D Centaur to conduct flybys of both Venus and Mercury — the first spacecraft to reach the innermost planet. Using Venus's gravity to reach Mercury — the first use of a gravity assist maneuver for an interplanetary mission — Mariner 10 flew past Mercury three times in 1974-75, imaging 45% of the surface and discovering a weak but structured magnetic field, a tenuous atmosphere, and a heavily cratered terrain. The discovery of Mercury's magnetic field was unexpected for such a small, slowly-rotating planet and remained unexplained until MESSENGER's later measurements revealed the planet's large iron core. Mariner 10 remains the only spacecraft to use a gravity assist to reach another planet in the inner solar system, pioneering the trajectory planning used by countless subsequent missions.