Mariner 10 - USA Mercury/Venus Flyby - 526 kg - (November 3, 1973 - March 24, 1975) flew past Venus for a gravity assist to the planet Mercury. Mariner 10 was the first dual planet mission. Mariner 10 was the first spacecraft to have an imaging system. It recorded circulation in the Venusian atmosphere and showed the temperature of the cloud tops to be -23°C. Mariner 10 flew past Mercury 3 times on March 29, 1974, September 21, 1974, and March 16, 1975. These three encounters produced over 10,000 pictures with 57% planet coverage. It recorded surface temperatures ranging from 187°C to -183°C on the day and night sides. A weak magnetic field was detected but it failed to detect an atmosphere. Mariner 10 is now in a solar orbit.