Mariner 10 was launched on November 3, 1973. The ultimate goal of this mission was to be the first spacecraft to reach Mercury. However, in order to reach Mercury Mariner 10 had to fly by Venus in 1974 for a gravity assist. Mariner thus became the first spacecraft to visit two planets. The probe passed only 5760 km from Venus; during its short time close to Venus Mariner 10 cameras photographed the Venusian atmosphere in ultraviolet light. These photographs helped scientists to determine that Venus' atmosphere rotates much faster than the solid body underneath: the atmosphere rotates about the rest of the planet in only four days.
