The Mariner 10 spacecraft was first launched into space by the Atlas Centaur in 1973. Its main purpose was to study the planets of Mercury and Venus.
Discoveries
During its two-year mission, it transmitted over 12,000 images of these two mysterious planets. In February of 1974 Mariner 10 discovered rotating clouds over the surface of Venus. While visiting Mercury the probe mapped out about half of the planet's surface, and discovered that it had an extremely thin atmosphere and a previously unknown magnetic field. Its mission ended in March 1975 and ever since then it has been orbiting the Sun, even though its electrical system has most likely been severely damages by solar radiation.
Important Firsts
Many important maneuvers occurred during its flight. The first was that NASA found out that it was possible to make giant corrections in the course of the spacecraft from Earth. Also, NASA used one planet's gravitational forces in order to propel the spacecraft toward another planet. Lastly, Mariner 10 used solar wind as a means of locomotion, the fuel level of the thrusters ran low so the scientists creatively used the probes solar panels as sails. All in all the mission was considered a complete success.